Journal of Petrology Advance Access originally published online on March 18, 2005
Journal of Petrology 2005 46(7):1443-1487; doi:10.1093/petrology/egi022
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Tertiary Ultrapotassic Volcanism in Serbia: Constraints on Petrogenesis and Mantle Source Characteristics
1,2,*1
1 FACULTY OF MINING AND GEOLOGY, UNIVERSITY OF BELGRADE, DJU
INA 7, 11000 BELGRADE, SERBIA & MONTENEGRO
2 INSTITUTE OF GEOLOGICAL SCIENCES, UNIVERSITY OF MAINZ, BECHERWEG 21, 55099 MAINZ, GERMANY
3 GEOFORSCHUNGSZENTRUM POTSDAM, TELEGRAFENBERG, D-14473 POTSDAM, GERMANY
4 SCHOOL OF EARTH SCIENCES, BIRKBECK COLLEGE, MALET STREET, LONDON WC1E 7HX, UK
RECEIVED OCTOBER 10, 2003; ACCEPTED FEBRUARY 7, 2005
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
The Serbian province of Tertiary ultrapotassic volcanism is related to a post-collisional tectonic regime that followed the closure of the Tethyan Vardar Ocean by Late Cretaceous subduction beneath the southern European continental margin. Rocks of this province form two ultrapotassic groups; one with affinities to lamproites, which is concentrated mostly in the central parts of the Vardar ophiolitic suture zone, and the other with affinities to kamafugites, which crops out in volcanoes restricted to the western part of Serbia. The lamproitic group is characterized by a wide range of 87Sr/86Sri (0·70735–0·71299) and 143Nd/144Ndi (0·51251–0·51216), whereas the kamafugitic group is isotopically more homogeneous with a limited range of 87Sr/86Sri (0·70599–0·70674) and 143Nd/144Ndi (0·51263–0·51256). The Pb isotope compositions of both groups are very similar (206Pb/204Pb 18·58–18·83, 207Pb/204Pb 15·62–15·70 and 208Pb/204Pb 38·74–38·99), falling within the pelagic sediment field and resembling Mesozoic flysch sediments from the Vardar suture zone. The Sr and Nd isotopic signatures of the primitive lamproitic rocks correlate with rare earth element fractionation and enrichment of most high field strength elements (HFSE), and can be explained by melting of a heterogeneous mantle source consisting of metasomatic veins with phlogopite, clinopyroxene and F-apatite that are out of isotopic equilibrium with the peridotite wall-rock. Decompression melting, with varying contributions from depleted peridotite and ultramafic veins to the final melt, accounts for consistent HFSE enrichment and isotopic variations in the lamproitic group. Conversely, the most primitive kamafugitic rocks show relatively uniform Sr and Nd isotopic compositions and trace element patterns, and small but regular variations of HFSE, indicating variable degrees of partial melting of a relatively homogeneously metasomatized mantle source. Geochemical modelling supports a role for phlogopite, apatite and Ti-oxide in the source of the kamafugitic rocks. The presence of two contrasting ultrapotassic suites in a restricted geographical area is attributable to the complex geodynamic situation involving recent collision of a number of microcontinents with contrasting histories and metasomatic imprints in their mantle lithosphere. The geochemistry of the Serbian ultrapotassic rocks suggests that the enrichment events that modified the source of both lamproitic and kamafugitic groups were related to Mesozoic subduction events. The postcollisional environment of the northern Balkan region with many extensional episodes is consistent at regional and local levels with the occurrence of ultrapotassic rocks, providing a straightforward relationship between geodynamics and volcanism.
KEY WORDS: kamafugite; lamproite; Mediterranean; Serbia; mantle metasomatism; veined mantle; petrogenesis
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Ultrapotassic volcanism within the Mediterranean region is spatially and temporally associated with the Late Cretaceous–Cenozoic convergence of Africa–Arabia with Eurasia that resulted in the progressive closure of ocean basins, and ultimately in the collision of the Alpine orogen with the southern passive continental margin of Europe (Wilson & Bianchini, 1999
). Ultrapotassic rocks of Tertiary–Quaternary age occur in numerous localities, but have been most thoroughly investigated in Italy (Venturelli et al., 1984b; Peccerillo, 1985, 1990, 1995, 1998; Conticelli & Peccerillo, 1992; Conticelli et al., 1992, 2002; Conticelli, 1998) and in southeastern Spain (Venturelli et al., 1984a, 1988, 1991; Benito et al., 1999; Turner et al., 1999). The Tertiary province described and discussed in this paper occurs in the central Balkan Peninsula and is the third large ultrapotassic province to be described from the Mediterranean region (Prelevi
et al., 2001a, 2001b, 2002a, 2002b, 2003).
Ultrapotassic volcanic rocks have some of the most extreme Sr, Nd and Pb isotopic compositions of any mantle-derived magmas. Lamproites are of special interest as they may represent extreme examples of partial melting of mixed enriched and depleted mantle source rocks. Many intracontinental mantle-derived magmatic rocks may be less extreme blends of these or similar end-members (Wilson & Downes, 1991; Foley, 1992a; Anderson, 1995) The incompatible element concentrations and Sr, Nd and Pb isotope systematics of the most primitive Mediterranean ultrapotassic rocks demonstrate that their mantle sources were enriched by metasomatic agents. Extensive investigations of the extremely diverse Italian ultrapotassic rocks (Rogers et al., 1985; Peccerillo, 1992, 1995, 1999, 2003; Conticelli et al., 2002) have indicated roles for shallow-level interaction of mantle-derived magmas with the subducting slab, the overlying mantle wedge and the continental crust in their genesis. There is a general consensus that the geochemistry and isotope characteristics of the most enriched Mediterranean ultrapotassic rocks are due to a crustal signature acquired by the mantle source (Vollmer, 1976, 1989, 1991; Ellam et al., 1989). The location, nature and ultimate origin of this metasomatic reservoir is, however, a matter of debate (Nelson et al., 1986; Vollmer, 1989; Nelson, 1992; Bell, 2002; Gasperini et al., 2002; Murphy et al., 2002; Bell et al., 2003). Three groups of models have been proposed to explain Mediterranean ultrapotassic volcanism, mostly based on the example of the Italian rocks: (1) the multistage mantle evolution model explains the ultrapotassic rocks as melts of the sub-continental lithospheric mantle previously metasomatized by subducted upper continental crust (Peccerillo, 1999, 2003); (2) the single-stage mantle evolution model explains the generation of the Tertiary ultrapotassic and potassic magmatism as caused by a mantle plume head with a diameter approaching 1000 km centred under Italy (Vollmer, 1976; Bell, 2002; Bell et al., 2003), whereby the crustal signature is incorporated in the deep-mantle plume source; a similar deep-mantle source for the crustal component in lamproites has been put forward recently for Gaussberg, Antarctica, and also for Spanish lamproites (Murphy et al., 2002); (3) the slab-window model proposes that some melts are derived directly from mantle plumes, whereas the rest of the magmatism represents mixtures of plume material and subducted upper crustal components (Gasperini et al., 2002).
The issue of asthenospheric or lithospheric mantle sources and the age of the crustal component can be addressed by studying cogenetic ultrapotassic rocks of similar age emplaced within different lithospheric terrane blocks. If considerable differences in isotopic and trace element characteristics exist among the primitive rock types, the magmas are more likely to reflect derivation from a lithospheric source.
In this study we present mineral chemistry, major and trace element and Sr–Nd–Pb isotope data for samples from the newly delineated Serbian ultrapotassic province, which contains rocks of both lamproitic and kamafugitic affinity, as in Italy. The Serbian ultrapotassic province has the potential for better location and definition of the nature of the mantle source than for other Mediterranean ultrapotassic rock provinces. Its major advantage is the spatial distribution of ultrapotassic volcanism across several lithospheric terrane blocks of different provenance (the western blocks are of Gondwana affinity, whereas the eastern blocks are derived from Eurasia). Additionally, the magmatism is post-collisional, intra-continental and postdates the last subduction events by at least 30 Myr (Karamata et al., 1997a, 1997b, 1999). We argue that the Serbian ultrapotassic magmatism is derived from the lithospheric mantle, and demonstrate that the primary ultrapotassic melts result from partial melting of at least two distinct lithospheric mantle sources.
|
GEOLOGICAL BACKGROUND AND DISTRIBUTION OF MAGMATISM IN THE SERBIAN ULTRAPOTASSIC PROVINCE |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
The Balkan Peninsula reflects the complexity of the tectonic evolution of the Mediterranean region. Its central axis comprises several geotectonic units, some of which may be regarded as microcontinents (Fig. 1, inset): (1) the East Serbian composite terrane (or Carpatho-Balkanides; lower Palaeozoic units merged before the Upper Permian) and the Serbo-Macedonian composite terrane (a crystalline terrane that formed the late Mesozoic southern European continental margin), which are fragments of Eurasia to the east; (2) the Vardar ophiolitic suture zone, which is the main suture zone of the Balkan Peninsula; (3) the Jadar Block (an exotic terrane thought to be derived from further west); (4) the Drina–Ivanjica terrane (a microcontinent); (5) the Dinaride ophiolite belt terrane, the suture of a Middle Triassic–Late Jurassic marginal sea of Gondwana; (6) the External Dinarides. All these units merged at the end of the Mesozoic.
|
The Tertiary history of basaltic and ultrapotassic magmatism in Serbia comprises three magmatic episodes, a first episode of Paleocene or Eocene alkaline basalts with sodic character, and two later (Oligocene or Miocene and Pliocene) episodes dominated by high-K calc-alkaline, shoshonitic and ultrapotassic magmatism (Cvetkovi
et al., 2004a). The sodic Paleocene–Eocene alkaline basalts are confined to the eastern tectonic units (Serbo-Macedonian and East Serbian composite terranes) where they form a trend broadly parallel to the terrane boundary (Fig. 1). Geochemically, the Paleocene–Eocene alkaline basalts show a clear ocean island basalt (OIB)-like Nd–Sr isotopic affinity (Cvetkovi et al., 2004a), resembling rocks from other intracontinental European alkaline provinces such as the Massif Central and the Rhenish Massif in Germany (Wilson & Patterson, 2001). This magmatism generally postdates Late Cretaceous subduction-related volcanism of the Timok area, for which high-precision U–Pb age determinations have yielded ages from 86 to 70 Ma (von Quadt et al., 2003); that is, they are at least 10 Myr older than the Palaeogene alkaline rocks. The alkaline basalts have been interpreted as being erupted during short relaxational phases between predominantly compressional conditions (Cvetkovi et al., 2004a).
The Oligocene–Miocene and Pliocene rocks are dominated by high-K calc-alkaline, shoshonitic and ultrapotassic types. The Oligocene–Miocene volcanic episode started after a hiatus of at least 15 Myr (Fig. 2), indicating a distinct geodynamic trigger. Available radiometric ages (Cvetkovi et al., 2004a) indicate the onset of ultrapotassic volcanism around 30 Ma in the northern part of the province along the WNW–ESE-trending Zvornik line (Fig. 2). The volcanism migrated southward over the next 20 Myr, during which plugs and flows of ultrapotassic rocks were emplaced within the SW part of Serbian Dinaride ophiolite belt. The Pliocene volcanic period is documented by K–Ar ages of 6·6 Ma and 3·9 Ma and these are most probably related to Macedonian magmatism to the south (Terzi & Sve
njikova, 1991; Altherr et al., 2004). In Serbia, these rocks occur to the south of the Scutari–Pe line (Fig. 1), which is believed to be the northernmost limit of the influence of Aegean collapse (Kissel et al., 1995). In terms of their mineralogy and geochemistry, the youngest volcanics are mostly of ultrapotassic character and cannot be distinguished from the older ultrapotassic rocks from the Vardar ophiolitic suture zone.
|
|
ANALYTICAL METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Minerals were analysed on a CAMECA SX 100 microprobe at the GeoForschungsZentrum Potsdam using PAP correction procedures. Counting times for all elements were 20 s for the peak position and 10 s for the background on each side of the peak. Operating conditions were 15 kV and 20 nA, and well-defined natural minerals were used as standards.
Whole-rock major elements and Cr, Ni, V, Co, Cu, Zn, Ba, Rb, Ga, Sr, Pb, Y, Zr and Nb [also U, Th, La, Ce and Nd in samples not analysed by inductively coupled plasma mass spectrometry (ICP-MS)] were determined by X-ray fluorescence (XRF) spectrometry on fused discs at the University of Greifswald using a sequential wavelength-dispersive Philips PW2404 X-ray spectrometer equipped with a single goniometer-based measuring channel, covering the complete measuring range. Details of the accuracy and analyses of international standards using this method have been reported by Prelevi et al. (2004a).
Concentrations of rare earth elements (REE), Li, Sc, Cs, Hf, Th and U were measured by ICP-MS at the University of Bristol using standard operating conditions on a VG PlasmaQuad PQ2 Turbo-plus ICP-MS system with a Meinhard Nebulizer. Details of the accuracy and analyses of international standards using this method are given in Electronic Appendix 1, which may be downloaded from the Journal of Petrology web site at http://www.petrology.oupjournals.org.
Whole-rock Sr and Nd isotopic compositions were determined at the GeoForschungsZentrum Potsdam following procedures described by Romer et al. (2001). Unleached sample powders were dissolved with 52% HF for 4 days at 160°C on a hot plate; digested samples were dried and taken up in 6N HCl overnight. Sr and Nd were separated and purified using cation-exchange chromatography. 87Sr/86Sr and 143Nd/144Nd were analysed on a VG 54-30 Sector and a Finnigan MAT262 multi-collector mass spectrometer, respectively, operated in dynamic mode. Ratios were normalized to 86Sr/88Sr = 0·1194 and 146Nd/144Nd = 0·7219, respectively. Multiple measurements of NBS 987 Sr reference material and La Jolla Nd reference material gave 0·710277 ± 0·000009 (n = 4) and 0·511860 ± 0·000007 (n = 4), respectively. Analytical uncertainties are 2
mean. 87Sr/86Sri and 143Nd/144Ndi were calculated for known K–Ar ages, using 87Rb = 1·42 x 10–11 years–1 and 147Sm = 6·54 x 10–12 years–1.
Pb from unleached whole-rock sample powders was separated using anion exchange resin Bio Rad AG1-X8 (100–200 mesh) in 0·5 ml Teflon columns by HCl–HBr ion exchange chemistry using procedures described by Romer et al. (2001, and references therein). Pb was purified by a second pass over the column. Pb was loaded together with H3PO4 and silica gel, on single Re filaments. The isotopic composition of Pb was determined at 1200–1250°C on a Finnigan MAT262 multicollector mass spectrometer using static multicollection. Instrumental fractionation was corrected with 0·1% per a.m.u. as determined from repeated measurement of lead reference material NBS 981. Accuracy and precision of reported Pb ratios is better than 0·1% at the 2 level.
|
CLASSIFICATION AND PETROLOGY OF SERBIAN ULTRAPOTASSIC ROCKS |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
All the studied rocks are ultrapotassic, following the criteria of Foley et al. (1987)
, with K2O >3%, MgO >3% and K2O/Na2O >2, except for samples where analcimization of leucite has caused drastic reduction of the K2O/Na2O ratio. Two principal groups of Serbian Tertiary ultrapotassic rocks are recognized: (1) a group with lamproitic affinity (LAG); (2) a group with kamafugitic affinity (KAG). The term ‘affinity’ is used to signify similarity to one of the generally recognized ultrapotassic rock groups lamproites, kamafugites and Roman province type rocks (Foley et al., 1987). It indicates probable similarities in the source characteristics of rocks with a given affinity despite considerable petrographic dissimilarities, both within the Serbian rock groups, and between some of the Serbian rocks and the ultrapotassic type rocks. Representative photomicrographs of the Serbian ultrapotassic rocks are given in Fig. 3, and detailed petrographic descriptions and further microphotographs are reported in Electronic Appendices 2 and 3, respectively, which may be downloaded from the Journal of Petrology web site at http://www.petrology.oupjournals.org.
|
The two Serbian ultrapotassic suites are restricted to specific geotectonic units (Fig. 1). The LAG rocks are concentrated within the central axis of the Balkans, within the Vardar ophiolitic suture zone and Jadar block terranes, with only one exception (Bogovina, situated in the East Serbian composite terrane), whereas the KAG rocks occur exclusively in the western terranes (Dinaridic ophiolite belt terrane and Drina–Ivanjica terrane).
The LAG comprises a variety of petrographically defined rock types, forming two subgroups: (1) primitive (plagioclase-free) and (2) evolved (plagioclase-bearing) LAG rocks, on the basis of the presence or absence of plagioclase in the groundmass and/or as a xenocryst, Cr and Ni content, and mineral chemistry. The primitive LAG rocks are lamproites, whereas the evolved LAG rocks cannot be considered as lamproites in the normal sense because of the presence of plagioclase (Foley et al., 1987; Mitchell & Bergman, 1991). Evolved LAG rocks exhibit different degrees of differentiation and the variable, but common, presence of felsic xenoliths and xenocrysts. They may occur in composite intrusions in which decimetre-sized shoshonitic and latitic margins surround phenocryst-rich metre-sized dacitic interiors. The mafic parts of the composite dykes mineralogically and geochemically resemble rocks from nearby minette and lamproite dykes. According to Prelevi et al. (2004a) these mafic parts represent a wide spectrum of hybrid ultrapotassic and potassic magmas, generated by mixing of lamproitic mantle-derived magmas (primitive LAG) with magmas of silicic composition. These composite intrusions emphasize the role of magma-mixing in the evolution of Serbian LAG volcanism. Moreover, throughout the province, evolved LAG rocks host resorbed and reacted quartz, plagioclase, sanidine, biotite and salitic clinopyroxene, as well as partially digested cumulate nodules of two types: olivine–phlogopite + clinopyroxene + chromite (Type 1) and salitic-Cpx–biotite–plagioclase (Type 2) (Electronic Appendix 3-m, o-Type 1 and p-Type 2). Partial melting of quartz xenocrysts, crystallization of clinopyroxene coronas and resorption of plagioclase xenocrysts are almost ubiquitous (Electronic Appendix 3-n, q and r).
The KAG rocks mostly form 100–1000 m size volcanic flows. Although their exact petrographic name should, in most cases, be analcimite, we term them ugandites (olivine leucitites), leucite basanites and ankaratrites (Fig. 3d–f; Electronic Appendix 3-h, i, j, k and l), as the analcime originates by transformation of previously existing primary leucite (Prelevi et al., 2004b). Leucite occurs only in the freshest lavas at Koritnik. KAG rocks are not kamafugites sensu stricto because they lack characteristic kamafugitic minerals such as melilite and kalsilite (Woolley et al., 1996; Le Maitre, 2002). The common occurrence of ugandite, leucite basanite and ankaratrite is, however, reminiscent of the alkaline mafic volcanics of the Toro–Ankole volcanic province, where kamafugites were originally described (Holmes & Harwood, 1937). Thus, we refer to the ‘kamafugitic affinity’ of the Serbian suite to emphasize the resemblance to kamafugites, although still using IUGS terminology (Woolley et al., 1996; Le Maitre, 2002).
|
MINERAL CHEMISTRY |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Below is a brief summary of the mineralogy and mineral chemistry of Serbian ultrapotassic rocks. Detailed descriptions are included in Electronic Appendix 4. Also, representative mineral composition data are reported in Electronic Appendix 5, and more comprehensive electron microprobe analyses are included in two supplementary datasets. All these files can be downloaded from the Journal of Petrology web site at http://www.petrology.oupjournals.org. Mineral abbreviations are after Kretz (1983)
.
In the LAG rocks, phenocrysts of high-Mg olivine (Fo mostly 90–93; Fig. 4a), with a modal abundance of 10–15 vol. %, usually host Mg-chromite inclusions with high Cr-number [atomic Cr/(Cr + Al)] as high as 0·94 and Fe3+-number (Fe3+/
Fe) of 0–0·40 (Fig. 5). The most extreme composition with Cr-number up to 0·99 and Fe3+-number = 0 occurs in samples from Arandjelovac. Mica phenocrysts from primitive LAG samples show lamproitic core–rim compositional trends (Mitchell & Bergman, 1991). Cores have Mg-number 90–80, Al2O3 11·7–14·0 wt %, and Cr2O3 up to 2·15 wt %, whereas rims and poikilitic groundmass crystals have TiO2 up to 10 wt %, high FeOT (around 11 wt %) and BaO (up to 3 wt %), low Al2O3 (around 10 wt %) and MgO (around 17 wt %). The core compositions of the evolved LAG phlogopites resemble phlogopite cores in the primitive LAG rocks, but their core–rim trend is towards higher Al contents, resembling calc-alkaline lamprophyres and Roman province lavas (Mitchell & Bergman, 1991) (Fig. 6a). Clinopyroxene encompasses phenocrysts and megacrysts, glomeroporphyritic clusters, accumulations of acicular quench crystals, groundmass crystals and also xenocrysts of sieve-structured green salite, usually mantled by diopside, that originated from Type 2 cumulate nodules (Fig. 3b; Electronic Appendix 3c, d, e, f, m, n, o, p, q). Microphenocrysts, phenocrysts and megacrysts (0·5–10 mm) in primitive LAG rocks usually have Mg-number around 90, Al is <0·025 Al atoms per formula unit (Fig. 6c), insufficient to compensate for the deficiency of Si in the tetrahedral site. Line analyses across zoned Cpx grains (Fig. 4c) illustrate normal zoning trends, sometimes repetitive, with restricted zones of lower Mg composition with Mg-number down to 85, TiO2 up to 1·5 wt % and Cr2O3 abundances <0·1 wt %, but without variation of Al2O3 content (Fig. 4c). In contrast, Cpx phenocrysts and microphenocrysts from evolved LAG samples are commonly intensely zoned (Fig. 4e): cores have similar compositions to phenocrysts from the LAG, and show more than one episode of gradual evolution towards lower Mg-number (down to 75), higher Al2O3 (up to 3 wt %) and TiO2 (up to 2·5 wt %), disrupted by narrow zones of the primitive, core-like compositions. The behaviour of both Ti and Al with Si is conspicuously antipathetic (Fig. 4e), in contrast to Cpx from primitive LAG rocks where only Ti varies (Fig. 4c). Green salitic clinopyroxene (En30–36Fs11–20Wo45–47, up to 7% Al2O3) forms single crystals usually mantled by clinopyroxene of composition similar to the acicular clinopyroxenes (Fig. 4f). It is resorbed, sieved and embayed to different extents.
|
|
|
In primitive lamproitic rocks, the groundmass commonly contains Fe-rich alkali feldspar (up to 3% FeOT), sanidine (sometimes hyalophane with up to 23 vol. % celsian), and leucite (universally pseudomorphed by analcime). Plagioclase occurs only in the groundmass of evolved LAG rocks (Ab40–44An40–45Or10–15) together with low-Fe sanidine and leucite pseudomorphed by analcime. Moreover, primitive LAG rocks contain rare rutile, ilmenite and Ti-magnetite; in some samples these minerals coexist.
In the rocks with kamafugitic affinity, olivine, consistently less magnesian than in LAG rocks (Fo 88–89), appears as phenocrysts, with a modal abundance of 5–15 vol. % (Fig. 4b). It hosts Mg-chromites with significantly lower Cr-number than spinels from LAG rocks, with values not exceeding 0·81, and having higher Fe3+ and slightly higher TiO2 contents (Fig. 5b). Phlogopite is not a phenocryst phase in the KAG rocks, but appears as large millimetre-sized poikilitic laths enclosing earlier minerals in ugandites, interstitially in the groundmass of leucite basanites, and also in vesicle fillings and rare centimetre-sized amoeboid pegmatitic segregations in ankaratrites (Fig. 3d and e; Electronic Appendix 3h, i and j). The large poikilitic phlogopites in ugandites have uniform compositions with high Mg-number in the range of 88–84, low Al2O3 contents down to 7 wt %, high TiO2 up to 7 wt % and variable BaO and high F contents of 2–3 wt % and up to 6 wt %, respectively (Electronic Appendix 5). The interstitial tiny phlogopitic plates in leucite basanites always have lower Mg-number in the range 70–75, higher Al2O3 contents (up to 15 wt %) and similar TiO2 and F contents, but are enriched in BaO (up to 6 wt %). The most exotic compositions with Mg-number around 75, Al2O3 15 wt %, high TiO2 (up to 10 wt %), low SiO2 (down to 33 wt %), but high BaO (up to 12 wt %) are found in phlogopites from ankaratrites (Fig. 6b). Clinopyroxene in KAG rocks occurs as phenocrysts. Core compositions have Mg-number 82–88, Al2O3 is mostly >2%, and TiO2 2–3%, and trend towards rims with Mg-number 80–70, and higher Al2O3 and TiO2 contents (Fig. 4d). In contrast to clinopyroxenes from the lamproitic group, KAG clinopyroxenes contain sufficient Al to balance silica deficiencies in the tetrahedral site and have higher Ti content for the same Mg-number. Clinopyroxenes from ugandite and leucite basanite occupy distinct areas on a plot of Al vs Ti (Fig. 6d).
The presence of both leucite and nepheline in the groundmass is a common feature of rocks with kamafugitic affinity. In ugandite, leucite is mostly pseudomorphed by analcime, and only in ugandites from the Koritnik volcano has fresh leucite been found. Nepheline varies in modal abundance and composition between lithologies. In ugandites, it is least abundant and has the highest proportion of kalsilite component (
38 mol %), whereas the kalsilite component decreases with increasing nepheline abundance in other KAG rocks. Minor phases in the groundmass are Ti-magnetite with 30–60 mol % ulvöspinel, hyalophane in ugandites (Or53·4Cn34·6Ab8·6An3·4), and plagioclase in leucite basanites.
|
GEOCHEMICAL CHARACTERISTICS |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Major and trace element compositions of Serbian ultrapotassic rocks are listed in Tables 1–3. Sr and Nd isotopic analyses of selected samples are given in Table 4, and Pb isotope data in Table 5. In the discussion, we include previously published Sr and Nd isotope data (Cvetkovi
et al., 2004a) for samples from the same localities.
|
|
|
|
|
Major and compatible trace elements
Primitive LAG samples are slightly silica-undersaturated to -saturated, with SiO2 in the range of 43–52 wt %, Mg-number up to 80 [100Mg/(Mg + 0·85FeT)], Al2O3 contents 10–13 wt % and Cr and Ni up to 1200 and 550 ppm, respectively (Fig. 7a, b and d). TiO2 is around 1 wt % in most primitive lamproitic samples, although a few display higher contents (>2 wt %). With respect to major elements, the majority of the primitive lamproitic rocks resemble lamproites from Spain (Venturelli et al., 1984a
, 1988; Benito et al., 1999; Turner et al., 1999) and Italy (Venturelli et al., 1984; Conticelli & Peccerillo, 1992; Conticelli et al., 1992, 2002; Peccerillo, 1995). They mostly plot in the lamproite field on the classification diagrams of Foley et al. (1987) (Fig. 7c, e and f), although in some diagrams they plot largely in the Roman province field (Fig. 7c). Evolved LAG rocks have higher SiO2 contents, mostly around 55%, but up to 62 wt %. Mg-number is <70, mostly around 65, Al2O3 ranges from 11 to 15 wt % and Cr and Ni are less than 500 and 250 ppm, respectively. Their TiO2 contents are mostly <1 wt %. They mainly plot in the Roman province field, resembling the potassium series (KS), transitional rocks (TRANS) and high-potassium series (HKS) rocks of the Italian province (Conticelli & Peccerillo, 1992; Peccerillo, 1995, 2003; Conticelli et al., 2002).
|
In contrast to the highly variable LAG rocks, ugandites and leucite basanites of the kamafugitic group are remarkably uniform in composition. They are silica-undersaturated, commonly showing normative feldspathoid contents up to 30%. SiO2 contents are in the range 42–46 wt %, Mg-number 66–73 (mostly >70), and Cr and Ni up to 550 and 300 ppm, respectively. CaO contents are elevated but never exceed 12 wt %, whereas alumina contents range from 10 to 14 wt %. There is no significant correlation of either SiO2 or Al2O3 content with Mg-number or Cr content, indicating that fractionation of mafic minerals is not the major cause of the SiO2 and Al2O3 variations (Fig. 7a and b). Compared with ugandites and leucite basanites, ankaratrites have lower Mg-number (down to 58–68), and considerably lower Cr and Ni contents, below 200 and 150 ppm, respectively. These samples also show ubiquitously higher CaO contents, up to 14 wt %. The alkalis are disturbed in most rocks with kamafugitic affinity as a result of analcimization of leucite. This is most intense in ankaratrites, which show a decrease of K2O content down to 0·05% and K2O/Na2O ratio to 0·03. Analcimization has not occurred in the Koritnik samples, whose K2O content of 5·3% indicates the original K2O content of the other KAG rocks.
High volatile contents (loss on ignition; LOI) are characteristic of most of the Serbian ultrapotassic rocks. This is due to a combination of the high modal abundance of phlogopite and two major alteration processes: analcimization of leucite and iddingsitization of olivine. In some melanocratic varieties of LAG, phlogopite makes more than 30 vol. % of the rocks, and olivine is almost universally iddingsitized (Electronic Appendix 3-g). The influence of analcimization on LOI values is best illustrated by the analcime-bearing KAG samples from Nova Varo, Trijebine and Dru
etii: these have LOI values that are substantially higher (4·8–7·2 wt %) than in the analcime-free samples from Koritnik (1·8–2·3 wt %).
Incompatible trace elements
Incompatible trace element variations are summarized in Fig. 8. Primitive mantle normalized patterns for the primitive LAG rocks from the Vardar ophiolitic suture zone are similar but abundances vary widely. They exhibit extreme enrichment in large ion lithophile elements (LILE; Cs, Rb, Ba, Th and U), in the range of 300–1000 times primitive mantle for most samples. The level of enrichment is highest for Cs (>5000 times primitive mantle), Th and U, giving rise to troughs in the patterns at Rb and Ba. Primitive lamproitic rocks display characteristic Pb peaks (Fig. 8a and b) and Sr and P troughs of variable intensity. They are depleted in high field strength elements (HFSE), with Nb and Ti troughs and high LILE/HFSE ratios, resembling other Italian and Spanish Mediterranean-type lamproites (Fig. 8a). Ba, P and Sr troughs correlate with the level of general enrichment of incompatible elements (including REE, see also below), disappearing in the samples from Arandjelovac, which are most HFSE depleted. The patterns for the samples from Bogovina (in the East Serbian composite terrane) are slightly different from other LAG rocks in that the Ti, Nb and Ba troughs are much less pronounced (Fig. 8b). The evolved LAG rocks show similar incompatible element patterns but with slightly higher levels of enrichment. La/Yb ratios of primitive LAG rocks range from 20 to 60 but are mostly around 40 (Fig. 9a and b). The extent of REE fractionation for all primitive LAG rocks, except Bogovina, and their level of enrichment correlate with Nb, Zr, Hf and TiO2, with the most depleted samples coming from the Arandjelovac dyke (Fig. 9a). The most enriched samples display a Eu trough, which passes into a slight positive anomaly in the Arandjelovac samples (Fig. 9a). The rocks from Bogovina do not show a Eu anomaly and also display considerable depletion in heavy REE (HREE), with LuN below 10 times chondrite (Fig. 9b). Evolved LAG rocks show a large range of REE enrichment and are fractionated to different extents (Fig. 9c). They also show different intensities of Eu anomaly.
|
|
Incompatible elements in KAG rocks are generally similar to those in LAG rocks, but with less pronounced LILE enrichment and LILE/HFSE fractionation (Fig. 8c). Troughs at K and Rb are apparent in analcime-bearing samples (Fig. 8c), and are extremely large in the ankaratrites (Fig. 8d), but absent in non-analcimized samples. All KAG samples have Nb and Ti troughs and a Pb peak, but all these anomalies are much less pronounced than in the LAG rocks. The incompatible element patterns are broadly similar to those of Italian kamafugitic rocks, but not those from East African. Light REE (LREE) concentrations in KAG rocks are high (up to 500 times chondrite), and overall pattern shapes are steeply and consistently fractionated with only a slight Eu anomaly (Fig. 9d). Concentrations of HREE are low, but mostly slightly above 10 times chondrite.
Radiogenic isotopes
LAG rocks vary widely in 87Sr/86Sri (0·70735–0·71299) and 143Nd/144Ndi (0·51251–0·51216) (Fig. 10). Primitive lamproitic samples plot in the enriched quadrant, clearly trending towards the space usually occupied by upper crustal rocks. Evolved LAG rocks are dispersed in the same space, with a few samples showing less radiogenic Sr and more radiogenic Nd isotopic values. In contrast to the wide variation of 87Sr/86Sr and 143Nd/144Nd, the LAG rocks display only slight variations in 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios (Fig. 11). They plot above the northern hemisphere reference line (NHRL) on 206Pb/204Pb vs 207Pb/204Pb and 208Pb/204Pb diagrams (Fig. 11) and fall within the pelagic sediment field of Ben Othman et al. (1989).
|
|
The radiogenic isotopic signatures of Serbian LAG rocks with a large range of Sr and Nd isotopic values and a restricted variation of Pb isotopes highlight a strong similarity to other Mediterranean ultrapotassic provinces (Nelson et al., 1986
; Conticelli et al., 2002). They are more enriched in radiogenic Sr and depleted in radiogenic Nd than any known basaltic volcanics or/and mantle xenoliths in the region, including those from Macedonia and the Pannonian basin (Fig. 10). Although primitive LAG samples have higher Nd and lower Sr isotopic ratios than Italian and Spanish lamproites, Pb isotope systematics are almost identical to Italian and Spanish samples. It is interesting to note that primitive Serbian LAG samples lie on an extension of the Sr–Nd isotopic trend exhibited by lamproitic rocks from Spain, Tibet and Italy.
KAG rocks display considerably less variable Sr and Nd isotopic ratios than LAG rocks. The ugandites and leucite basanites have relatively uniform Nd and Pb isotopic compositions, whereas Sr isotope ratios vary within the range 0·70599–0·70655 with analcimized samples having the highest values (Fig. 10). Prelevi et al. (2004b) interpreted decoupling of Sr and Nd isotopes to be a result of analcimization. The ankaratrites are enriched in radiogenic Sr, but depleted in radiogenic Nd, possibly indicating that assimilation–fractional crystallization (AFC) processes could have operated during their evolution. Compared with the isotopic composition of alkaline volcanic rocks from the broad surrounding areas, the data for KAG rocks most closely resemble samples from Monte Vulture carbonatites and melilitic rocks as well as xenoliths that they host (Downes et al., 2002). The Pb isotope compositions of KAG rocks overlap almost completely with those of the LAG rocks, and also cluster within the pelagic sediment field. In contrast to Sr isotopes, the lack of considerable differences in Pb isotope values between analcimized and non-analcimized rocks suggests that Pb isotopes reflect primary compositions inherited from the mantle and are not affected by low-pressure processes.
As the Pb isotope compositions of both suites resemble those of pelagic sediments (Ben Othman et al., 1989), we also analysed Mesozoic flysch sediments from the Vardar ophiolitic suture zone (sample AV01; Table 5), which give very similar results. The flysch sediments are part of the overstep sequence above the ophiolitic mélange and are primarily derived from the continental margin, sometimes as completely preserved turbidites. They represent a plausible crustal end-member reflecting the average composition of local upper-crustal sediments that may have been involved in the origin of Serbian LAG rocks.
Finally, no correlation of Pb isotope data is seen that could indicate that the type of binary mixing between HIMU and DM reservoirs invoked for Italian volcanic rocks [Aeolian Islands, Etna–Iblean province and Vesuvius (Gasperini et al., 2002)] may be relevant for Serbian ultrapotassic rocks.
The impact of analcimization on the geochemistry of Serbian ultrapotassic rocks
Analcimization of leucite of the Serbian ultrapotassic rocks is very intense: fresh leucite survives only in ugandites from the Koritnik lava flows as well as in rare leucite inclusions in Cpx. Analcimization has had a great impact on the geochemistry of the rocks, but affects only a restricted number of chemical parameters. Analcimization causes changes in the K2O/Na2O ratio, fractionation of LILE, the 87Sr/86Sr enrichment and the increase in the whole-rock 
18O values (Prelevi et al., 2004b).
Leucite is a major reservoir of Rb and K but not for Ba (DRb up to 7·8 but DBa around 0·04; Foley & Jenner, 2004), and these elements are lost during alteration because they cannot be incorporated into analcime. This is confirmed by the absence of relative depletion of Rb and K in leucite-bearing Koritnik rocks (Fig. 8c). Moreover, extreme enrichment of Cs in some analcime-bearing samples (up to 900 ppm) is unusual, and may be related to analcimization (Prelevi et al., 2004b). Similar selective enrichment of Cs in hydrothermal analcimes has been reported in Yellowstone Park (Keith et al., 1983), and it is explained by the zeolitic behaviour of the analcime and its high sorption potential for Cs and also for Sr (Redkin & Hemley, 2000). Analcimization is also recognized by an increase in whole-rock 18O values of around 3
, which correlates with the level of whole-rock hydration (Prelevi et al., 2004b). Finally, the 87Sr/86Sr enrichment at nearly constant 143Nd/144Nd exhibited by some KAG rocks also results from analcimization of leucite. All samples with higher 87Sr/86Sr are from the Nova Varo lava flows, where 87Sr/86Sr values correlate with the modal analcime abundance, LOI of whole rocks and the whole-rock 18O values. The leucite-bearing rocks of Koritnik have lower 87Sr/86Sr, LOI and 18O values.
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Low-pressure processes
The two Serbian ultrapotassic suites are characterized by contrasting styles of low-pressure magmatic evolution. The LAG magmas erupted within a region (Fig. 1; Veliki Majdan, Bora
-Kotlenik, Kopaonik) that produced mainly dacitic, andesitic and basaltic extrusions of high-K calc-alkaline affinity in Oligocene–Miocene times (Cvetkovi et al., 2000, 2004a). It is likely that the different magma types used the same conduits, providing much potential for magmatic interaction. In contrast, KAG rocks occur exclusively in the western tectonic units, where no contemporaneous magmatism of other types has been detected.
The large range of isotopic variation correlates in some cases positively, but in others negatively, with indices of differentiation (Mg-number, SiO2), indicating that fractional crystallization alone cannot account for the variation in major element composition of the LAG rocks (Figure 12a and b). Several lines of evidence, including the occurrence of composite intrusives, and the common presence of resorbed felsic xenocrysts and xenoliths (see Electronic Appendix 3m, n, o, p, q and r), indicate that mixing between primitive LAG melts and contemporaneous high-K calc-alkaline felsic and intermediate magmas is an important process in the petrogenesis of the evolved LAG magmas. Petrography, mineral chemistry and bulk-rock geochemistry at Veliki Majdan (Prelevi et al., 2004a) and Rudnik (Prelevi et al., 2001a) provide evidence that the lamprophyric and shoshonitic volcanics of the composite intrusives formed by hybridization between dacitic and primitive LAG magmas. The hybridization patterns in these composite intrusions imply a significant role for such hybridization processes throughout the region. Whereas clinopyroxenes and phlogopites from primitive lamproitic rocks clearly follow typical lamproite compositional trends (alumina deficiency), the evolved LAG rocks show an opposite trend towards higher Al contents (Fig. 6a and c) from similar core compositions. The differences may be attributed to late-stage changes in Al2O3 content from similar parental lamproite magmas. Similar trends have been recognized at Torre Alfina in Italy, where low-Al clinopyroxenes from the least contaminated samples are typical of lamproites, but more contaminated rocks trend towards the Al-enriched field typical for the Roman province clinopyroxenes (Conticelli, 1998). Comparable variation occurs in phlogopites from LAG rocks (Fig. 6a). In the Veliki Majdan composite intrusions, similar variation in phlogopites has been attributed to hybridization of lamproite melt with peraluminous granitic magma (Prelevi et al., 2004a). Furthermore, Type 2 cumulate nodules and resorbed xenocrysts originating by disaggregation of these nodules are common in the evolved LAG rocks. These are peraluminous and consist of assemblages of calc-alkaline character, defining similar trends of increasing Al, Ca and Na content to those seen during hybridization of lamproite and dacite magmas. These xenoliths may be interpreted as high-pressure cumulates of near-liquidus phases associated with hybridization of lamproitic melts and calc-alkaline basalts (Prelevi et al., 2001b).
|
The scattered Sr–Nd–Pb isotope compositions (Fig. 12) preclude a single straightforward model for the evolution of all the LAG magmas. If we look only at the Nd–Sr isotopes (Fig. 10), contamination of primitive lamproitic rocks by felsic magmas resembling Serbian Si-rich (granitic) rocks results in a Nd–Sr isotope signature that does not resemble that usually expected for crustal contamination processes; the samples would be shifted into the mantle array from the position of uncontaminated (mantle-derived) LAG rocks, because of the radiogenic Sr and unradiogenic Nd isotope signature of the LAG rocks. Figure 12a and b shows that many evolved LAG rocks plot along the trend line delineated by the primitive rocks, but appear to be contaminated to varying degrees. The Veliki Majdan volcanics define a trend of decreasing 87Sr/86Sr and increasing 143Nd/144Nd with increasing SiO2, subparallel to that of some of the evolved LAG rocks (Fig. 12a and b). This further confirms that contamination, most probably involving mixing of primitive LAG melts with Si-rich melts, may be a significant process during the evolution of the LAG magmas. Figure 12 demonstrates that such hybridization has had a significant impact on the geochemistry of the primitive LAG rocks, affecting not only major elements, but also Nd–Sr isotopes and HFSE ratios (Fig. 12c). In Figure 12d, both primitive and evolved LAG rocks have rather constant 206Pb/204Pb ratios (
18·7 ± 0·1) showing a trend between primitive LAG rocks and the Si-rich volcanics with unradiogenic 87Sr/86Sr (0·705) and 206Pb/204Pb isotope values between depleted mid-ocean ridge basalt (MORB) mantle (DMM) and HIMU-like mantle signatures. The major obstacle to a more quantitative assessment of the evolution of Serbian LAG rocks is the incompleteness of the isotope dataset for coeval magmatic rocks that represent potential contaminants. The mineral chemistry and whole-rock compositions (lower Mg-number, Cr and Ni contents) of the ankaratrites indicate that they are more evolved than the other KAG rocks. They contain lower modal Ol and Cpx contents, and have evolved Cpx compositions and high-Ba phlogopites. Fractionation of olivine from either ugandites or leucite basanites would result in near-constant SiO2 contents, decreasing MgO, Ni and Cr contents, and a slight increase in CaO, Al2O3 and P2O5, as found in ankaratrites. The low silica contents and similar incompatible element ratios (e.g. Zr/Nb and La/Yb) to other KAG rocks suggest that no interaction with LAG melts could be involved in the evolution of the ankaratrites. The relative increase in 87Sr/86Sr and decrease in 143Nd/144Nd of the evolved KAG relative to the primitive KAG (Fig. 12a and b) suggests instead the involvement of an AFC process. The nearly constant Pb isotope compositions are explained by the high Pb abundances and the dominance of a crustal Pb isotope signal in the mantle source of the magmas (see below). Although their major element compositions do not allow significant contamination with crustal materials, their Sr and Nd isotopic systematics require a minor effect of a crustal component. Alternatively, the more radiogenic Sr and unradiogenic Nd composition of the ankaratrites might indicate a locally more radiogenic mantle source than for the rest of the KAG localities.
The case for distinct mantle sources for the two ultrapotassic suites
Differences in oxidation state of the mantle sources
Oxygen fugacity is recognized as an important parameter in the origin of ultrapotassic magmas, controlling the speciation of C–O–H volatile components in the melt at high pressures and temperatures (Foley, 1985; Foley et al., 1986). Oxygen fugacity can exert a strong influence on the mineral assemblage in the mantle source (Foley, 1989, 1992a, 1992b), as well as on melt compositions by controlling the level of silica saturation (Eggler, 1974, 1983). However, the redox state of ultrapotassic rocks varies, with evidence in some cases for highly oxidized conditions (Carmichael et al., 1996; Righter & Rosas-Elguera, 2001), whereas in other cases reduced conditions apply (Foley, 1985). Experimental studies of the influence of oxygen fugacity on the composition of Mg-chromites in ultrapotassic rocks show that fO2 is strongly reflected in the ferric-number (atomic Fe3+/Fe) and Cr-number [Cr/(Cr + Al)] of spinel (Foley, 1985). Lamproite spinel compositions show considerable variation of ferric-number value, the most reduced resembling Cr-rich, Fe3+-poor compositions similar to spinel inclusions in diamonds (Barnes & Roeder, 2001).
Mg-chromites from the LAG and KAG samples indicate substantial differences in fO2 in their parental melts. The ferric-number of early Cr-spinel inclusions in olivine phenocrysts is considerably lower in LAG rocks than KAG rocks (Fig. 5c). Moreover, the spinels show contrasting evolutionary trends (Fig. 5a): the trend of LAG spinels indicates dominance of the trivalent substitution Cr 
Fe3+ on the Cr-number, emphasizing the significance of increasing fO2 in the melt during ascent. The general trend recognized between spinels from different localities also occurs in line analyses across large grains (Fig. 5a) showing that the most primitive spinels are the most reduced. Such trends may be accounted for by oxidation of melts during emplacement caused by dissociation of water (Sato, 1978) driven by diffusion of H2, which is more than a thousand times faster than water, and nearly a million times faster than oxygen (Wendlandt, 1991). This kind of ‘auto-oxidation’ can produce oxidation of lamproitic magmas by dissociation of only 0·1 wt % H2O (Foley et al., 1986).
Spinels from the KAG rocks have higher Fe3+/Fe ratios (Fig. 5c) and noticeably lower Cr-number. They display an evolutionary trend (Fig. 5a) resulting from equilibration of spinel with olivine, clinopyroxene and other Al-bearing minerals. This may indicate a longer residence time of the KAG melts in low-pressure magma chambers.
The oxygen fugacity of the Serbian ultrapotassic rocks was estimated using the spinel–olivine Fe–Mg exchange oxybarometer (Ballhaus et al., 1991) for spinel inclusions and their host olivine phenocrysts (olivine analysed <20 µm from the spinel inclusions). Temperatures were calculated by means of the olivine–chromite geothermometers of Ballhaus et al. (1991) and Poustovetov & Roeder (2001), assuming the pressure to be 20 kbar. For LAG rocks, we also estimated oxygen fugacity from coexisting Ti-magnetite and ilmenite using QUILF software (Andersen et al., 1993); a summary of estimates is shown in Fig. 13. All results confirm substantial differences between the LAG and KAG groups, but there is a discrepancy between the results for the LAG obtained with different oxybarometers. Coexisting ilmenite and Ti-magnetite pairs from the LAG rocks consistently indicate oxygen fugacities in the range of the quartz–fayalite–magnetite (QFM) to magnetite–wüstite (MW) buffer (around QFM –3 log units fO2; Fig. 13), whereas the spinel–olivine Fe–Mg exchange oxybarometer gives more variable values for fO2 for the same rocks. The discrepancy may be accounted for by post-entrapment equilibration of Cr-spinel with the melt and silicate minerals (Kamenetsky et al., 2001) following crystallization of Fe–Ti oxides that still record low fO2. Alternatively, the olivine–spinel oxybarometer may be less accurate for lamproites as a result of compositional differences from those used in calibration of the method. The fO2 for LAG rocks estimated from coexisting Ti–Fe oxides is in excellent agreement with the empirical spinel oxybarometer developed for lamproites (Foley, 1985), which predicts equilibration at the MW buffer for the LAG. The spinel–olivine pairs from the KAG rocks are equilibrated at consistently more oxidized conditions of nickel–nickel oxide (NNO) +1 to 2 (Fig. 13).
|
Differences in fertility of the sources
Olivines and their Mg-chromite inclusions may be used as proxies for the mantle-source characteristics of the Serbian ultrapotassic rocks. The idiomorphic tabular shape and homogeneous chemical composition of olivines from primitive LAG rocks indicate that they represent equilibrium phenocrysts (Fig. 3b; Electronic Appendix 3e and f). They have Fo contents up to 93 (Fig. 4a), and host chromite inclusions with Cr-number around 90. Such highly magnesian olivines are known from komatiites (Arndt et al., 1977
) and mantle xenoliths (Gaul et al., 2000), but are known to host such high Cr-spinels only in boninites (Arai, 1994; Falloon & Danyushevsky, 2000; Barnes & Roeder, 2001; Kamenetsky et al., 2002) and lamproites (Kuehner et al., 1981; Jaques et al., 1984; Venturelli et al., 1984a, 1984b; Thy et al., 1987; Mitchell & Bergman, 1991). Their presence is in apparent conflict with the relatively high SiO2 content and LILE-enriched character of the host magma from which they crystallized, but only if taken to indicate large degrees of melting of a lherzolitic mantle source, which would result in high MgO in the melt and depletion of the LILE. Such extensive melting would require temperatures above 1500°C, which should be further indicated by whole-rock Ni contents >500 ppm, and Cr2O3 in olivine >0·2% (Arndt et al., 1977; Campbell et al., 1979; Murck & Campbell, 1986; Campbell, 2001). The primitive LAG rocks have lower whole-rock Ni contents (highest value 480 ppm, average 390 ppm), and Cr2O3 contents in olivine lower than 0·15% (maximum 0·14%, average 0·12%), which may reflect considerably lower temperature melting. This clearly suggests that a normal peridotite mantle source and/or high-temperature melting are not appropriate for the primitive LAG olivines and Cr-spinels, whereas they do indicate that refractory, depleted peridotite forms one component of the mantle source, as for boninites (Cameron et al., 1983; Arai, 1994; Barnes & Roeder, 2001; Kamenetsky et al., 2002). Similarities in high MgO and SiO2 and low CaO, Al2O3 and Na2O have been interpreted previously as evidence for a strongly depleted mantle source for boninites and silica-rich lamproites of Mediterranean type (Foley & Venturelli, 1989). Furthermore, low-Al spinels together with low Al2O3 contents in the bulk rocks are typical for both lamproites and boninites; their spinel compositions overlap with those of spinel inclusions in diamonds, and are the most Cr-enriched compositions found in nature. The olivine–spinel pairs from primitive LAG rocks plot in the most refractory part of the olivine–spinel mantle array diagram (Arai, 1994; Fig. 5b) together with mineral pairs from boninites and arc-related high-Mg, high-Si magmas. This accords with the recent study of ultramafic xenoliths hosted by East Serbian Palaeogene basanites (Cvetkovi et al., 2004b), which shows that the lithospheric mantle beneath Serbia is more refractory than normal European lithosphere.
We may further extend the parallels between lamproites and boninites considering the similarities in models for their origin. In addition to depleted peridotitic mantle, a second, fluid or melt component must be involved in the origin of both rock types, which has considerably higher levels of incompatible elements in the case of lamproites. The additional hydrous component causes reduction of the solidus temperature. According to current interpretations, lamproites are the melting products of refractory mantle intersected by phlogopite- and clinopyroxene-bearing veins, the so-called vein + wall-rock melting model (Foley, 1992a; Mitchell, 1995). This model was prompted by the failure of experimental studies to locate multiphase saturation in peridotite minerals on the liquidi of ultrapotassic rocks, which should be found for purely peridotitic sources. According to the vein + wall-rock model, vein assemblages consisting principally of non-peridotitic, but ultramafic mineralogy, melt at lower temperatures than the surrounding peridotite, and the alkaline melt produced infiltrates and dissolves the peridotite. Accordingly, the second, ‘fluxing’ component may correspond to the content of the vein, with the presence of hydrous minerals.
The KAG olivine–spinel pairs are less refractory, more scattered, and mostly plot away from the mantle array (Fig. 5b), consistent with derivation from a less refractory mantle source. The large differences in the Cr-number of spinels from the KAG and LAG result from differences in both Cr and Al contents, whereas the Ti contents of the spinels from both groups are similar. These differences indicate that the KAG source is less refractory.
The source characteristics of Serbian ultrapotassic rocks and partial melting processes
To minimize the blurring effects of low-pressure processes on geochemical trends inherited from the mantle source, we restrict our attention to samples screened to have high Cr (>400 ppm) and Ni (>200 ppm) contents and the absence of felsic or crustally derived xenoliths and xenocrysts. In the case of the LAG rocks, this chemical screen is almost equivalent to our subclassification into primitive and evolved rocks; all primitive LAG rocks are included with the single exception of rocks from Klinovac. Although the Klinovac samples do not pass our chemical filter, we have included them in the discussion of mantle source characteristics because they are the most primitive samples from the southern part of the ultrapotassic province. For the KAG rocks, most of the ugandites and leucite basanites pass the chemical filter, whereas the ankaratrites are more evolved and were omitted.
The trace element characteristics and isotopic compositions of the screened samples are in agreement with the interpretations, based on mineral chemistry, that the two Serbian ultrapotassic suites (KAG and LAG) were derived from distinct mantle sources. No combination of fractionation of observed phenocryst phases, coupled with assimilation effects, can relate the observed groups geochemically. This is illustrated by the Nd–Sr isotope compositions of the screened samples: LAG rocks span a wide range of Nd–Sr isotopic ratios, whereas the KAG rocks have very restricted compositions. The 206Pb/204Pb vs 143Nd/144Nd diagram (Fig. 14a) clearly highlights the two different groups: the LAG rocks with less radiogenic Nd isotope compositions define a trend towards a mid-ocean ridge basalt-like (DMM) composition (with the exception of one Bogovina sample), whereas the KAG rocks display very little change in Nd–Pb isotopic values. The variations in Ba/Nb, Th/Nb and La/Yb vs 143Nd/144Nd (Fig. 14b–d) all efficiently discriminate between the two Serbian ultrapotassic groups.
|
The crustal signature in the mantle source
The geochemistry and isotope characteristics of Tertiary Mediterranean ultrapotassic igneous rocks are frequently explained as being due to a crustal signature acquired by the mantle source through subduction of continental materials (Nelson et al., 1986
; Ellam et al., 1989; Peccerillo, 1992). Likewise, numerous geochemical features of the Serbian ultrapotassic rocks might be interpreted to indicate a role for subduction-related processes in their petrogenesis. Arguments include relatively low Ti and Nb concentrations, high Cs concentrations, high Cs/Rb and Pb/Ce, and the presence of a trough at Eu.
Pb isotopes are one of the most sensitive indices of contamination of the mantle by sediments (Ben Othman et al., 1989), because of the huge contrast of Pb abundance between sediments and the mantle. An extremely small addition of sediment will significantly affect the mantle Pb isotope ratios and the source will assume the isotopic characteristics of the sediments. The Serbian ultrapotassic rocks show a relatively limited range of 206Pb/204Pb with radiogenic and slightly variable 207Pb/204Pb. These characteristics may be readily explained by mixing of sources, but not by closed-system decay of U. A radiogenic 207Pb/204Pb signature requires the existence of a long-term variation in U/Pb, which would give rise to a large variation in 206Pb/204Pb (Nelson et al., 1986). A single-stage extraction process with the metasomatic imprint originating from a depleted mantle source cannot explain the radiogenic 207Pb/204Pb together with relatively unradiogenic 206Pb/204Pb. The major argument against such a scenario is that the ancient isotopic signature demonstrated by the high 207Pb/204Pb values demands proportionally higher values of 206Pb/204Pb. On the other hand, Nelson et al. (1986) suggested that the metasomatic component that enriched the mantle source of the Spanish lamproites already had high 207Pb/204Pb, radiogenic Sr and unradiogenic Nd.
The strong similarity between the Pb isotope signature of Mesozoic flysch sediments and the screened Serbian ultrapotassic rocks is a strong argument for the influence of subducted sedimentary material. This crustal isotopic signature would have been introduced via Mesozoic subduction and stored in the form of metasomatic minerals in the mantle source. The different Sr and Nd isotope compositions of the two groups are interpreted below as depending upon the type of crustal material involved, and on the nature of the melting process. The involvement of Mesozoic flysch sediments explains mantle domains with high Rb/Sr, U/Pb and Th/Pb that have not yet evolved Sr and Pb isotopic ratios that differ considerably from those of the sediments.
The mantle source of the LAG rocks
The chemically screened LAG rocks show considerable isotopic variations that correlate with incompatible trace elements and their ratios (Fig. 14b–d). Given the high Sr, Nd and Pb concentrations, we may consider these isotopic compositions as representative of near primary mantle-derived melts. This variable isotopic composition of the primary melts indicates mixing between distinct mantle components in their source. Moreover, the coupling of isotopic and trace element ratios and abundances exhibited by the primitive LAG rocks is characteristic of mixing in the mantle (Nelson et al., 1986). The mineralogy and geochemistry of primitive LAG rocks indicates the involvement of at least two mantle end-members: the first is a highly refractory harzburgitic mantle source indicated by the extreme compositions of olivines and Cr-spinels. It is in accordance with the recent study of ultramafic xenoliths hosted by East Serbian Palaeogene basanites (Cvetkovi et al., 2004b), which indicates highly refractory lithospheric mantle underneath Serbia. Isotopically this component should have a signature similar to the depleted MORB mantle (DMM) of Zindler & Hart (1986). The second component should be responsible for the extreme enrichment in K2O and LILE and other incompatible elements such as TiO2 and HFSE, and is probably hydrous. It incorporates the crustal isotopic signature, probably stored in minerals such as phlogopite, amphibole, apatite and clinopyroxene (see below). Samples with radiogenic Sr and Pb and unradiogenic Nd isotope signatures resemble Serbian flysch sediments; this component we refer to as ‘Serbian enriched mantle’ (SEM; Fig. 15a and b). Samples with low 87Sr/86Sr and high 143Nd/144Nd ratios generally have the lowest 206Pb/204Pb (Fig. 15a and b, inset) suggesting involvement of a DMM component (Zindler & Hart, 1986) in their petrogenesis. Although the LAG trend suggests some affinity with the KAG mantle source in the Sr–Nd isotope covariation diagram (Fig. 10), similar trends do not occur on diagrams of 143Nd/144Nd or 87Sr/86Sr vs 206Pb/204Pb (Figs 14a, 15a and b). This further indicates that the two Serbian ultrapotassic suites do not have a common mantle end-member (Fig. 14).
|
Figure 15a and b illustrates a range of mixing curves in 87Sr/86Sri and 143Nd/144Ndi vs 206Pb/204Pbi plots for the Serbian ultrapotassic rocks between the two mantle end-members (DMM and SEM). The end-members used in the modelling in Fig. 15 are given in the figure caption. Hyperbolae of different curvature are the result of different Sr/Pb and Nd/Pb elemental ratios between DMM and SEM. The mixing trends for isotopic ratios will be nearly linear if the contributing components have similar elemental ratios (SEMSr/Pb:DMMSr/Pb and SEMNd/Pb: DMMNd/Pb
1:1). This is possible if, for instance, the enriched mantle component geochemically resembles the metasomatized lithospheric upper mantle of McDonough (1990), with similarly high Sr/Pb and Nd/Pb ratios to DMM. The strongly hyperbolic mixing trend defined by the primitive-LAG rocks, however, indicates contrasting geochemical parameters, with the ratios SEMSr/Pb:DMMSr/Pb and SEMNd/Pb:DMMNd/Pb close to 1:10 and 1:8, respectively. A quantitative evaluation of the contribution of the end-members in the final hybrid depends on the absolute element abundances; that is, whether they are represented by mixing of melts or solids. When we modelled mixing between solid end-members, the samples from Arandjelovac with least radiogenic Sr and Pb, and the most radiogenic Nd isotopic compositions required a source mixing with >95% of DMM in the final melt (not shown), which is geochemicaly unreasonable. Our preferred interpretation of the mixing curves is that they represent mixing of melts, when the proportions of DMM-derived melt (MORB-like) in the final hybrid would be <85% (Fig. 15), because of the higher concentrations of elements involved relative to solid end-members. The behaviour of some of the incompatible elements and their ratios also consistently illustrates the same mixing proportions, with the most enriched end-member showing the highest La/Yb ratios and Nb abundances (Fig. 15c and d). Moreover, the mineral chemistry of the primitive LAG rocks also varies in keeping with the proposed model: the most refractory composition of Cr-spinels [Cr-number = atomic Cr/(Cr + Al) up to 0·95] and lowest TiO2 content in Cpx occurs in the samples showing the highest degree of hybridization (Arandjelovac).
This type of mixing of melts in the mantle environment is consistent with the vein + wall-rock melting model of Mitchell & Bergman (1991) and Foley (1992a), and is in agreement with experimental data, which suggest a low-pressure origin for Si-rich lamproites (Foley, 1993). Vein material may not be in isotopic equilibrium with the surrounding peridotite. The complex mechanism of melt–solid interaction during the melting process is largely unconstrained and only few theoretical and experimental studies have been carried out (Meen et al., 1989; Foley, 1992a; Foley et al., 1999). The alkaline melts produced during the vein melting (in this case derived from the SEM) infiltrate, dissolve and trigger the melting of the depleted peridotite wall-rock. The isotopic effects of melting of exotic veins should be dramatic: the extremely radiogenic Sr and unradiogenic Nd that is characteristic of the lamproites is derived from the vein assemblage. Dissolution of the wall-rock preferentially adds a more refractory component to the melt, resulting in a spectrum of isotopic compositions. The isotopic composition of the melt will be strongly controlled by that of the vein, and only when a large amount of the wall-rock material is involved will it be displaced towards the depleted mantle composition (Meen et al., 1989). This is particularly apparent in the case of the primitive Serbian LAG rocks, which show a wide range of Sr and Nd isotopic compositions (Fig. 15) but very restricted variation in Pb isotopes. The Pb isotopic composition is dominated by the vein-derived end-member, which has a considerably higher Pb concentration than the wall-rocks. The mixing values obtained for primitive LAG rocks indicate that a considerable contribution of melt derived from the wall-rock (85%) was involved in the petrogenesis of the Arandjelovac samples, which is confirmed by the low HFSE abundances, approaching those of MORB-like melts. This apparently disagrees with typical explanations of the petrogenesis of potassic lavas as being generated by small degrees of melting of metasomatized mantle sources.
The Bogovina lamproite, the only LAG locality outside the Vardar ophiolitic suture zone, is an exception. In many of the variation diagrams (Fig. 15a–d), the Bogovina samples plot away from the main trends. Although the Bogovina samples show similar patterns in mantle-normalized trace element variation diagrams to those of other primitive LAG rocks (Fig. 8b and c), they show less pronounced Ti and Nb troughs and no Eu trough. Bogovina also shows the crustal Pb signature, but it is deflected slightly towards HIMU (Figs 11b, d and 15a–d). We can speculate that the mantle source of the Bogovina samples experienced multiple metasomatic episodes: first, the major subduction-related metasomatic event of Mesozoic age experienced by other Serbian localities, and a second, later event, explained by percolation of melts related to the Palaeocene–Eocene alkaline basaltic magmatic episode. This younger event would cause the deflection of the isotopic signature towards HIMU and enrichment in TiO2, Nb and Eu. Multiple mantle metasomatic episodes in the East Serbian lithospheric mantle have been reported recently from mantle xenoliths near Bogovina (Cvetkovi et al., 2004b). It is concluded that the mantle beneath this part of the Balkans records multiple metasomatic imprint via introduction of subduction-related and alkaline mafic melts. However, the existence of only one occurrence of ultrapotassic volcanism in the East Serbian composite terrane is not sufficient to fully evaluate the cause of chemical differences between this and the other volcanics.
The mantle source of the KAG rocks
Ugandites have the lowest SiO2 and Al2O3 contents and contain leucite; nepheline is less abundant than leucite but has an exceptionally high kalsilite component (up to 40 vol. % kalsilite component). The leucite basanites with higher SiO2 and Al2O3 contents contain plagioclase and K-poor nepheline (<15 vol. % kalsilite component) that is almost equal in abundance to leucite. This modal variation reflects the original potassium abundance, which is, however, strongly altered by the analcimization of the most KAG rocks. The compositional and mineralogical variations of the KAG rocks may be attributed to different degrees of partial melting of a relatively uniformly enriched mantle source. The variable HFSE enrichment and LREE/HREE fractionation combined with the limited isotopic variability of the screened KAG rocks (Fig. 14) implies a source that is homogeneous relative to the scale of melting. A relatively uniform enrichment of the KAG mantle source suggests that the metasomatizing agent probably equilibrated with the host peridotite. The lowest degree of melting may explain the ugandites, with higher degrees for leucite basanites. The differences in clinopyroxene chemistry (slope of Al vs Ti) in ugandites and leucite basanites (Fig. 6d) cannot be due to fractionation from common magmas because these clinopyroxenes have similar Mg-number and therefore represent the same degree of differentiation. These differences in Cpx chemistry are better explained by their rocks representing different degrees of melting.
Several geochemical parameters (Ti–Nb, Eu troughs and Pb spikes on normalized trace element variation diagrams) indicate that the KAG source also experienced crustally derived metasomatic imprint. Most notably, Pb isotope systematics indicate a crustal Pb signature, similar to the signature demonstrated by the LAG rocks. However, the KAG samples are characterized by less radiogenic Sr and more radiogenic Nd isotope ratios, which may be explained in two ways. First, the Sr and Nd systematics may indicate metasomatism by a metasomatic agent hosting a different crustal component from that affecting the LAG mantle source. If the metasomatic agent that enriched the KAG mantle source had high Sr and Nd concentrations (which is to be expected), the final isotopic signal should be dominated by the isotopic values of the metasomatic fluid or melt, because of the low abundance of these elements in the mantle. In that case, the KAG rocks should have inherited an isotopic signature of the subducted crustal component. Comparison with the isotope compositions of sediments usually considered to be involved in subduction processes suggests that the most reasonable candidates are oceanic biogenic sediments, including calcareous and siliceous sediments with a significant clay fraction (Ben Othman et al., 1989). Alternatively, the composition of the metasomatic agent that metasomatized the KAG mantle may isotopically resemble that which enriched the LAG source. However, this scenario would require that the KAG source was already metasomatized during an earlier episode that gave rise to an isotopic signature between DM and HIMU-like mantle reservoirs. The ultimate Sr–Nd isotopic signature results from binary mixing, whereas much intense overprinting of the previous isotopic signature would be shown by the Pb isotopes because of the high Pb concentration in the metasomatic agent bearing the crustal component. There are no closer constraints on the isotopic composition of the mantle below the Dinaride part of the Balkans, and we can only speculate about the presence of such a mantle component.
Constraints on the mineralogy of the mantle sources
Mineralogy of the source of the KAG rocks
Given the ultrapotassic character of the KAG rocks, phlogopite and K-richterite are reasonable candidates for K-bearing hydrous phases in the mantle source. Ugandites are interpreted as being produced by the smallest percent of partial melting and have higher K2O/Na2O ratios, more abundant modal leucite and higher kalsilite component in nepheline (up to 40 vol. %) than leucite basanites, implying a greater contribution from a high-K phase in the initial melts. This may be used to discriminate between the two potential mantle K-phases.
Experiments in natural lherzolitic systems (Konzett & Ulmer, 1999) demonstrate that K-richterite is stable between 5·5 and 6·0 GPa at 800°C and between 6·0 and 6·5 GPa at 1100°C but not at lower pressures, restricting it to the coldest regions of subcontinental lithosphere (heat flow <40 mW/m2). Melts of K-richterite-bearing peridotite are expected to be silica rich because K-richterite, itself a relatively Si-rich mineral, is eliminated soon after the solidus is crossed (Foley et al., 1999; Konzett & Ulmer, 1999). The generally low SiO2 contents and negative correlation between SiO2 and K2O/Na2O of the KAG rocks suggest that phlogopite, instead of K-richterite, is the K-bearing phase in the mantle source.
We have used the inverse method proposed for estimation of major melting parameters by Treuil & Joron (1975), and improved by Cebria & Lopez Ruiz (1996) and Class & Goldstein (1997), to constrain the mineralogy of the KAG source. This method can be used for the least differentiated samples from a cogenetic suite of rocks, which may be safely considered as representing primitive liquids (i.e. Mg-number 
70; high Ni and Cr) derived from a homogeneous mantle source. Use of the method requires that the melting of a relatively homogeneous mantle source should be the dominant process, and not mixing between various batches of mafic mantle melts derived from chemically different sources. Screened KAG samples (ugandites and leucite basanites) entirely meet these criteria, because they demonstrate consistency in the behaviour of trace elements, which, together with rather uniform Nd–Sr–Pb isotope compositions, reflects homogeneity of the mantle source during the melting process.
During the course of melting, partitioning of a trace element between a melt and the solid residue depends on the mineral phases present. Hence, the bulk solid–melt partition coefficient for various elements is a function of the uptake of the elements in the residual mineralogy. In an element–element diagram (e.g. Nd vs Zr or Nd vs Nb; Fig. 16a and b), the intercept of a linear regression between two elements of the same incompatibility should be zero, and its slope unity, whereas a difference in incompatibility should result in an increase of the intercept on the axis of the more compatible element, and a change of the slope. In an element–element ratio diagram (e.g. Nd vs Nd/Zr, Nd/Nb or Nd/P; Fig. 16c), the intercept of a linear regression between two elements of the same incompatibility should be unity, and its slope zero, whereas a difference in incompatibility should result in a decrease of the intercept and an increase of the slope. The most incompatible element with respect to the residual mineralogy (and not to a normal peridotitic mantle) has a positive intercept in all element–element diagrams (Fig 16a and b) and positive slope in all element–element ratio diagrams (Fig. 16c). The relative degree of incompatibility of other elements may be estimated by comparing their intercepts in element–element diagrams and their slopes in element ratio diagrams plotted against the most incompatible element (Fig. 16d) as has been proposed by Cebria & Lopez Ruiz (1996).
|
and 
denote concentration of element j at low and high degrees of partial melting (lowest and highest Nd concentrations, respectively). The extent of element incompatibility is quantified through its enrichment ratio (E), which is estimated as its relation with the index element, in our case Nd, according to the equation 
(a and b). The estimation of E values for all elements that were using in the evaluation is given in Electronic Appendix 6. (d) Relative degree of incompatibility of trace elements relative to the KAG mantle source mineralogy; the diagram plots the intercepts on element–element diagrams, A(n), and their slopes on ratio–element diagrams plotted against Nd, B(n); A(n) and B(n) are calculated from concentrations normalized relative to the highest concentration of each element. (e) Magma source mineralogy of the KAG rocks. The enrichment ratio (E) pattern for the KAG rocks uses estimated E values from Electronic Appendix 6. Partition coefficients used are presented in Electronic Appendix 7. We also recalculated E values for garnet lherzolite and spinel lherzolite sources with the composition shown in the diagram. The best-fit enrichment ratio pattern for the KAG rocks using a non-modal melting model is a garnet-bearing phlogopite peridotite with 0·5% Cpx, 0·4% Ap, 2·6% Grnt, 17·7% Phl and 0·2% Rut (0·1:0·1:0·14:60·8:0·1). The continuous black line denotes the same modal composition recalculated without apatite.An investigation of plots involving La, Nd, Ce, Pr, Eu, Dy, Yb, Lu, Sc, Nb, Zr, Ti, P, Sr, Th and Ba shows that Nd, Sm and Eu have the most incompatible behaviour relative to the mantle source of the KAG rocks (Fig. 16d). Estimating the relative degree of incompatibility of other elements, comparing their intercepts in element–element diagrams and their slopes in element ratio diagrams plotted against the most incompatible element (in this case Nd) (Fig. 16d) shows that Nd, Sm, Eu and Zr demonstrate similar behaviour, and that incompatibility decreases in the order of Pr, Dy, Th, Ce, Sr, La, Ti, Nb, Sc, Yb, Lu, P and Ba (Fig. 16d). This unusual order of incompatibility results from an atypical residual mineralogy (see also below). The concentration of Nd is highest in the ugandites, confirming that they are produced by the lowest degree of partial melting. Furthermore, we use Nd as an index for the degree of partial melting. Hence, its highest (
) and lowest (
) concentrations have been produced by the lowest (Flow) and highest (Fhigh) melting degrees, respectively. As has been shown by Maaløe (1994), Cebria & Lopez Ruiz (1996) and Maaløe & Pedersen (2003) for highly incompatible elements, we can approximate the relation 
, which enables us to estimate the relative range of the degree of melting for the KAG rocks (Fhigh/Flow = 2·21). Four major generalizations can be made from this modelling (Fig. 16d): (1) Ba is highly compatible, suggesting the presence of residual phlogopite in the mantle source; (2) the similar compatibility of Nb and Ti and their decoupling from Zr indicates the buffering effect of a Ti-oxide in the source; (3) the high compatibility of P suggests a role for residual apatite; (4) the high compatibility of Yb, Lu and Sc indicates the presence of residual garnet.
To put more quantitative constraints on the presence of residual phases, we further evaluated the mineralogy of the KAG source using the extent of element incompatibility quantified by their enrichment ratios (E). For a particular element j, E is estimated by its relation with the index element, in our case Nd (Fig. 16a and b), according to 
. Hence, E depends on concentrations of the element j for the lowest and highest melting degrees, reflecting the bulk partition coefficient during melting. The most incompatible elements have the highest E values. It is important to note that E values are independent of the chemical composition of the source and rely only on the residual mineralogy and degree of melting. A plot of estimated E values for the KAG rocks gives a highly uneven pattern using the common elemental sequence (Fig. 16e).
The enrichment ratio pattern of the KAG rocks confirms the major constraints on the mineralogy of the source made above, with negative anomalies for Ba, P, Ti and HREE reflecting the presence of residual phlogopite, apatite, Ti-oxide and garnet. Further, we modelled a best-fit enrichment ratio pattern for melting of this hypothetical source. The best-fit curve for non-modal batch melting (Shaw, 1970) for different mineral proportions was calculated for garnet-bearing phlogopite peridotite with 0·5% Cpx, 0·4% Ap, 2·6% Grnt, 17·7% Phl and 0·2% Rut, and contributions to the melt are calculated as 0·1 Cpx, 0·1 Ap, 0·14 Grnt, 60·8 Phl and 0·1 Rut (Fig. 16e; see caption for details of modelling and partition coefficients used). The relative amounts of olivine and orthopyroxene are not constrained because of their low partition coefficients. This modelling corresponds to an increase from 4·5 to 11% partial melting from ugandite to leucite basanites.
In this model, about 2% garnet is needed to reproduce the low enrichment ratio for HREE. The presence of garnet in the source may be also recognized by Dy/YbN and Tb/YbN ratios, which are usually 2·5–1·1 and 1·8, respectively, in liquids derived from the garnet-bearing mantle with Dy/YbN and Tb/YbN close to unity. Dy/YbN and Tb/YbN ratios for the KAG rocks are >1·4 and >1·9, respectively.
The presence of apatite is crucial for a good match to the trace element pattern of the KAG rocks. It is indicated by the compatible character of phosphorus (Fig. 16d) and the presence of a negative anomaly (Fig. 16e). Residual apatite may explain the unusual compatible behaviour of La, Th, U and Sr in the KAG rocks. Our best-fit modelled source composition without apatite (Fig. 16e) clearly illustrates the necessity for apatite. Experiments on partitioning between apatite and melt (Watson & Green, 1981) suggest D values for DLa–DSm–DDy–DLu to be as low as 3–5–4–2 for basaltic systems. The partition coefficients we used are measured from spinel lherzolites from Yemen (Chazot et al., 1996) representing hydrous lithospheric mantle peridotite. This study gives much higher partition coefficient values for LREE than HREE.
The decoupling of Nb and Zr is also well modelled, suggesting the presence of a Ti-oxide mineral in the source (Fig. 16a and b). Using available experimental partition coefficients for rutile (Foley et al., 2000), its amount in the source ought to be around 0·2%. Various Ti-oxides are found in the mantle xenoliths including rutile, armalcolite and ilmenite (Harte, 1987; Nixon, 1987; Ionov et al., 1999; Moine et al., 2001; Kalfoun et al., 2002). The hypothesis of a residual Ti-phase during partial melting of the KAG source is, however, apparently inconsistent with high saturation levels of TiO2 in low-silica melts (Green & Pearson, 1987; Ryerson & Watson, 1987). Green & Pearson (1987) concluded that at 1000°C the saturation level of TiO2 is 2·0 wt % at pressures of 20–30 kbar for melts of basaltic composition. Most KAG rocks have TiO2 concentrations below 2%. A combination of high H2O contents and thus low temperature, high fO2, and high alkali and CO2 contents all may still assist in suppressing the saturation level (Meen et al., 1989). Finally, if phlogopite serves as a major host of Ti and Nb, then there might not be a need for a Ti-rich phase in the source of KAG rocks. For this case we estimate 
at around 0·5. However, this is unlikely, despite the high Nb contents reported for phlogopites from mantle xenoliths (Ionov & Hofmann, 1995), as DNb for phlogopite (Foley et al., 1996; Schmidt et al., 1999; Green et al., 2000) is about an order of magnitude lower (around 0·07).
Mineralogy of the source of the LAG rocks
The geochemical variations, particularly Sr–Nd–Pb isotopes, shown by the LAG rocks cannot result from different degrees of partial melting of a relatively heterogeneous source, and require mixing of distinct melts in the mantle. We interpret coupling of the variable isotopic signatures with REE fractionation and HFSE enrichment of the primitive LAG rocks as being produced by vein + wall-rock melting. The LAG rocks are not suitable for the type of trace element modelling carried out for the KAG because they are produced from mixed mantle sources with large differences in mineralogy and chemical composition. This is in accordance with the guideline that if the source composition of the lavas differs by more that 3%, estimation of major melting parameters using this method yields inaccurate results (Maaløe & Pedersen, 2003).
However, following a similar line of reasoning as for the KAG rocks we can broadly ascertain the mineralogy of the source using trace element behaviour, but without putting quantitative constraints on the melting degree and source mineralogy. Zr has the most incompatible behaviour in the LAG rocks; it shows the widest compositional range and is most enriched in the samples with the highest K2O abundances that isotopically resemble flysch sediments. Therefore, it may serve as an index for vein + wall-rock melting. Figure 17 illustrates slight differences between the Vardar ophiolitic suture zone samples and the samples from Bogovina, situated in the East Serbian composite terrane. A small compositional gap between these groups also exists in Zr concentration.
|
Most element–element ratio diagrams (Fig. 17) show linear correlations; only Nb and La show broadly flat patterns. A question arises about the significance of the correlation: whether the residual mineralogy, considered responsible for linear variations in element–element ratio diagrams for the KAG rocks, may also play a role for the LAG rocks. Two interpretations may be proposed for this distribution: (1) it may be consistent with binary mixing of melts derived from distinct sources (according to isotopes, we recognized two potential end-members); (2) the mixing may be accompanied by partial retention of some minerals involved in the melting process, in which case considerable deflection towards lower Zr/Ci should occur. The second case can be viable only if the thermal stability of some minerals from the vein is high enough to allow their persistence until the highest degrees of vein + wall-rock melting. It has been proposed (Foley, 1992a
) that the presence of residual phases from the vein during vein + wall-rock melting is allowed through the prolonged stability of some non-peridotitic solid solution minerals that have high-temperature end-members, such as phlogopite, amphibole or apatite, because the melting occurs at temperatures lower than their solidus. In the case of primitive LAG rocks, the main candidates are F-rich phlogopite and F-rich apatite (see below).
The high K/Na ratio of LAG rocks indicates that phlogopite rather than K-richterite is the principal potassium mineral in the source (Foley et al., 1999). Given the low estimated oxygen fugacity of the source region of LAG rocks (around FMQ –3 log units fO2), low H2O/F and CO2/CH4 ratios may be expected. Therefore, the source may contain high-F, low-Al phlogopite that will give rise to perpotassic melts (with K/Al >1) during melting (Foley, 1989). Melting of such phlogopite in a vein should not contribute greatly to the Al content, but would still account for high K and LILE, as well as volatile enrichment. Moreover, its high thermal stability allows it to remain residual.
The LAG rocks, excluding the Bogovina samples, show a linear correlation between Zr and Zr/Ba (Fig. 17a), which is clearly different from the binary mixing relationship shown. This deflection from the mixing hyperbola may be explained by phlogopite remaining residual even at the highest degree of vein melting. The buffering effect of phlogopite may also explain the depleted character of the rocks from Arandjelovac, which are still ultrapotassic. However, the rocks from Bogovina are extremely Ba enriched (around 3000 ppm), which may be an effect of a Ba-enriched accessory phase in the mantle that was completely eliminated at the onset of melting. Alternatively, we cannot exclude hydrothermal alteration as a possible reason for such Ba enrichment.
Similarly, the variation of P2O5 and La (Fig. 17b and c) also deviates from the hyperbolic mixing line, indicating the buffering effect of apatite for the primary LAG melts produced by the lowest extent of vein + wall-rock melting. A greater buffering effect is to be expected for F-apatite as a result of its higher thermal stability than OH-apatite, offering a reasonable explanation for the otherwise paradoxical enrichment of P2O5 in the most depleted samples. Relatively constant Zr/Nb ratios for the whole LAG suite argue for the depletion of Nb not being controlled by a residual mineral in the source (Fig. 17d), implying that the Ti–Nb depletion is a feature of the metasomatic agent. Finally, the distribution of HREE and Sc (Fig. 17e and f) is consistent with the interpretation that residual garnet is present at Bogovina, whereas the LAG rocks from the Vardar ophiolitic suture zone are derived from the spinel-lherzolite facies.
Geodynamic significance and concluding remarks
The geodynamic history of the Balkans from the middle Mesozoic to the present consists of crustal shortening and convergence between the African and European plates, comprising periods of subduction, collision and extension (Karamata et al., 1999; Dimitrijevi, 2001). The closure of the Vardar branch of Tethys was completed by the end of the Late Cretaceous, resulting in at least two ophiolitic belts of Mesozoic age that make up the dominant features of Balkan geology: the Vardar ophiolitic zone and Dinaride–Hellenide ophiolite belt. The closure of two oceanic areas was accompanied by the subduction of oceanic and perhaps some continental crust. It is generally accepted that the Late Cretaceous–Paleocene volcanic rocks of subduction affinity of the Timok magmatic complex (Fig. 1) resulted from northeastward subduction of the Vardar oceanic plate (Karamata & Djordjevi, 1980; Cioflica et al., 1995, 1996). Conversely, such volcanism has not been detected on the Dinaride side. These subduction episodes may have had a major role in the enrichment of the lithospheric mantle of terranes that merged during the collision.
Given the resemblance between the Serbian ultrapotassic volcanics and the much more voluminous Italian ultrapotassic and potassic volcanism, it is interesting to consider what these two spatially adjacent and partly contemporaneous provinces have in common. In Italy, the relationship between the geophysically well-characterized subduction zone environment and a mantle plume postulated by some workers (e.g. Bell, 2002; Bell et al., 2003) is unclear. The magmatism of the Balkan area postdates the latest subduction events by around 30 Myr (Karamata et al., 1997a, 1997b, 1999), eliminating the possibility that the volcanism is directly related to subduction. Furthermore, there is no evidence to relate this volcanism to mantle plume activity like that which has been proposed by Bell (2002) and Bell et al. (2003) to be active under the Tyrrhenian Sea. The alternative explanation proposed for the Italian volcanism related to plume channelling through a subducting slab window (Gasperini et al., 2002) seems also implausible for the Serbian volcanism.
In active rifting zones above a contemporaneous mantle plume, large-scale uplifting of the whole area should be expected, which is not observed in the Balkans. Beginning in the Oligocene, the northern Balkans were characterized by a blocky structure, which was clearly related to major extensional tectonic episodes in the surroundings: Dinaride collapse, Pannonian Basin collapse and Aegean collapse. Both spatially and temporally, the Serbian ultrapotassic volcanism is linked with extensional tectonics, providing a straightforward relationship between geodynamics and volcanism. Our geochemical data also provide further evidence against a plume relationship: the presence of residual phlogopite and apatite in the source strongly suggests a lithospheric origin for the parental magmas. It has been shown that phlogopite is not stable under the thermal conditions of a mantle plume (Class & Goldstein, 1997). Finally, none of the isotopic compositions of the Serbian ultrapotassic volcanics show any affinity with the mantle component HIMU, unlike those of some Italian volcanoes (Fig. 11).
There is general agreement (Marovi et al., 1998, 1999, 2000, 2001, 2002) that Tertiary tectonic activity in this part of the Balkan Peninsula resulted from three competing factors: (1) isostatic reaction and collapse of the Dinaride orogen; (2) NW movement of the Adriatic plate and collision with the Dinaride orogen; (3) extensional processes related to the opening of the Pannonian and Aegean basins. The interplay of these factors resulted in extensional and compressional episodes in the northern Balkan Peninsula from Oligocene to Pliocene times (Fig. 2) accompanied by voluminous intermediate to acid magmatism and associated basaltic volcanism (Cvetkovi et al., 2004a). The onset of ultrapotassic volcanism at around 30 Ma (Fig. 2) is coincident with the activation of new fractures oriented WNW–ESE and west–east (e.g. the Zvornik and Sava lines), instead of former old NNW–SSE to north–south faults or terrane boundaries. This resulted in simultaneous magmatic activity at Bogovina, Rudnik, Ozrem, Boljkovac, Mionica and Veliki Majdan, transecting the main axis of the Balkan Peninsula including the Vardar ophiolitic suture zone, the Jadar Block and the East Serbian composite terrane. This is a very pronounced feature of Serbian ultrapotassic volcanism, emphasizing the connection between the timing of magmatism and changes in the regional stress field. These magmas indicate a post-collisional, relaxational stress regime, which is an optimal geodynamic setting for generating ultrapotassic melts (Mitchell & Bergman, 1991; Vaughan, 1996; Vaughan & Scarrow, 2003). In spite of later displacements of the tectonic units in Miocene times (Balla, 1986), the linearity of the oldest ultrapotassic volcanics does not seem to be accidental. Ultrapotassic volcanism could be regarded as the starting point of an isostatic reaction and the collapse of the Dinarides that provided the necessary conditions for Late Paleogene–Early Neogene magmatism. The distribution of ultrapotassic volcanism resembles the extent of the Oligocene–Early Miocene Dinaride–Kraishtide lacustrine province of Marovi et al. (1998, 1999) or Krsti (2001), which is interpreted as a result of a wide dextral wrench corridor that occurred along the axis of the collapsing Dinaride orogen. Figure 18 illustrates the geodynamic situation during Serbian ultrapotassic volcanism as being triggered mostly by the collapse of the Dinaride orogen. The Vardar ophiolitic suture zone is shown as a simple rootless suture unit (Dinter, 1998), although some consider it to have originally consisted of different domains or lithospheric blocks (Karamata et al., 1999). Rough approximations of crustal and lithospheric thickness are based on estimates for recent continental crust in former Yugoslavia (Aljinovi, 1987). The extensional episode with its surface expression in the pull-apart basins and lacustrine provinces (Djurdjevi, 1992; Obradovi et al., 1994) corresponds at both regional and local levels to the ultrapotassic magmatism. The younger magmatic ages (around 22 Ma) were partly contemporaneous with the westward displacement and clockwise rotation of the Tisza–Alcapa domain (Balla, 1986; Csontos et al., 1992; Csontos, 1995) that resulted in the Middle Miocene extension and collapse in the Pannonian Basin. Finally, the youngest tectonic movements related to rotation of the external Albano-Hellenides along the the Scutari–Pe line, initiated by the Late Miocene–Pliocene extension of the Aegean Basin (Kissel et al., 1995; Marovi et al., 1998), gave rise to the youngest ultrapotassic volcanism at around 5 Ma.
|
The spatial distribution and geochemical features of the two Serbian ultrapotassic suites are discontinuous even within the same magmatic cycle. This may reflect the different lithospheric blocks on which they occur. If this is correct, the spatial separation of the two ultrapotassic suites, regardless of age, implies their derivation from different lithospheric mantle domains. This idea, although not fully constrained, is supported by the general geology of the area. The Balkans are composed of a number of micro-terranes, of different age, origin and provenance. The Pan-African affinity of the Dinaride basement (Ili
et al., in preparation), together with previous geotectonic interpretations, implies different provenance for the two terranes (Dinarides and Vardar) in which the two ultrapotassic magmatic suites occur. However, there is a complete lack of deep seismic data on the structure of the Vardar ophiolitic suture zone to allow further constraint on the structure and composition of the lower crust and mantle.
The close isotopic resemblance of the Serbian ultrapotassic rocks to Mesozoic flysch sediments from the central Serbian suture zone lends support to the interpretation that the enrichment of their mantle sources is probably related to Mesozoic subduction. The occurrence of a crustal signature in the source of the ultrapotassic magmas from all the lithospheric segments suggests that the mantle below the Dinarides was also affected by subduction. During subsequent convective thinning of the lithospheric mantle and advection in the region of the thermal boundary layer, these enriched lithospheric domains were exposed to the hot asthenosphere, giving rise to melting. Our results suggest zonation of metasomatic assemblages in the lithospheric upper mantle. For the central and eastern Serbian units, a phlogopite-bearing refractory spinel lherzolite (Central Serbia) and garnet lherzolite (easternmost LAG rocks) source with phlogopite and apatite situated in veins is most probable. The spatial distribution of the LAG magmatism is along a NW–SE-trending line striking roughly parallel to the Zvornik line (Fig. 1); this lineament probably represents a fundamental fracture zone that allowed migration of melts from metasomatized lithosphere domains. The western terranes host the KAG volcanics, which appear to be derived from homogeneously metasomatized phlogopite + apatite + Ti-oxide + garnet-bearing mantle peridotite. These volcanics may be regarded as counterparts of the Italian low-silica ‘leucite-bearing’ rocks (Conticelli et al., 2002), suggesting a common geodynamic history of their sources (Dinarides and Apennines) and a similar pre-eruptive mantle metasomatic event.
|
SUPPLEMENTARY DATA |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Supplementary data for this paper are available at Journal of Petrology online.
|
ACKNOWLEDGEMENTS |
|---|
D.P. is greatly indebted to the late Milivoje Jovanovi
for his close collaboration and guidance during the fieldwork. The authors are very grateful to O. Appelt and D. Rhede for assistance with the microprobe analyses. Professor Dr. Mahmut Tarkian and Barbara Cornelisen from Mineralogisch–Petrographisches Institut Hamburg provided access to the microprobe for D.P., making possible very helpful early reconnaissance study. We thank Sandro Conticelli, Nick Rodgers and an anonymous reviewer for very constructive and helpful reviews that extensively improved the paper. Finally, during thorough editorial handling, Marjorie Wilson substantially improved the presentation of our arguments in the manuscript. This research has been supported by the Deutsche Forschungsgemeinschaft (DFG) within the project Fo 181-15. We also acknowledge the support of the European Community Access to Research Infrastructure action of the Improving Human Potential Programme, contract HPRICT-199900008 awarded to Professor B. J. Wood (EU Geochemical Facility, University of Bristol).
* Corresponding author. Present address: Johannes Gutenberg - Universitaet, Institut fuer Geowissenschaften, FB 22, Mineralogie, Becherweg 21, 55099 Mainz, Germany. Telephone: (49)(0)6131 39 24763. Fax: (49) (0)6131 39 23070. E-mail: prelevic{at}uni-mainz.de
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONGEOLOGICAL BACKGROUND AND...ANALYTICAL METHODSCLASSIFICATION AND PETROLOGY OF...MINERAL CHEMISTRYGEOCHEMICAL CHARACTERISTICSDISCUSSIONSUPPLEMENTARY DATAREFERENCES |
|---|
Aljinovi
, B. (1987). On certain characteristics of the Mohorovicic discontinuity in the region of Yugoslavia. Acta Geologica 55, 13–18.Altherr, R., Meyer, H.-P., Holl, A., Volker, F., Alibert, C., McCulloch, M. T. & Majer, V. (2004). Geochemical and Sr–Nd–Pb isotopic characteristics of Late Cenozoic leucite lamproites from the East European Alpine belt (Macedonia and Yugoslavia). Contributions to Mineralogy and Petrology 147, 58–73.[CrossRef][Web of Science]
Andersen, D. J. & Lindsley, D. H. (1988). Internally consistent solution models for Fe–Mg–Mn–Ti oxides; Fe–Ti oxides. American Mineralogist 73, 714–726.[Abstract]
Andersen, D. J., Lindsley, D. H. & Davidson, P. M. (1993). QUILF; a Pascal program to assess equilibria among Fe–Mg–Mn–Ti oxides, pyroxenes, olivine and quartz. Computers and Geosciences 19, 1333–1350.
Anderson, D. L. (1995). Lithosphere, asthenosphere and perisphere. Reviews of Geophysics 33, 125–149.[CrossRef][Web of Science]
Arai, S. (1994). Compositional variation of olivine–chromian spinel in Mg-rich magmas as a guide to their residual spinel peridotites. Journal of Volcanology and Geothermal Research 59, 279–293.[CrossRef][Web of Science]
Araujo, A. L. N., Carlson, R. W., Gaspar, J. C. & Bizzi, L. A. (2001). Petrology of kamafugites and kimberlites from the Alto Paranaíba Alkaline Province, Minas Gerais, Brazil. Contributions to Mineralogy and Petrology 142, 163–177.[Web of Science]
Arndt, N. T., Naldrett, A. J. & Pyke, D. R. (1977). Komatiitic and iron-rich tholeiitic lavas of Munro Township, Northeast Ontario. Journal of Petrology 18, 319–369.
Balla, Z. (1986). Palaeotectonic reconstruction of the central Alpine–Mediterranean belt for the Neogene. In: Tectonics of the Eurasian Fold Belts. Amsterdam: Elsevier, pp. 213–243.
Ballhaus, C., Berry, R. F. & Green, D. H. (1991). High pressure experimental calibration of the olivine–orthopyroxene–spinel oxygen geobarometer; implications for the oxidation state of the upper mantle. Contributions to Mineralogy and Petrology 107, 27–40.[CrossRef][Web of Science]
Barnes, S. J. & Roeder, P. L. (2001). The range of spinel compositions in terrestrial mafic and ultramafic rocks. Journal of Petrology 42, 2279–2302.
Bell, K. (2002). The isotope geochemistry of the mantle below Italy. EUROCARB Workshop, Italy, 7–10 June 2002, Chieti; Abstracts, pp. 16–18.
Bell, K., Castorina, F., Rosatelli, G. & Stoppa, F. (2003). Large scale, mantle plume activity below Italy: isotopic evidence and volcanic consequences. European Geosciences Union, General Assembly 2003, Nice. CD with abstracts. European Geophysical Society.
Benito, R., López-Ruiz, J., Cebriá, J. M., Hertogen, J., Doblas, M., Oyarzun, R. & Demaiffe, D. (1999). Sr and O isotope constraints on source and crustal contamination in the high-K calc-alkaline and shoshonitic Neogene volcanic rocks of SE Spain. Lithos 46, 773–802.[CrossRef][Web of Science]
Ben Othman, D., White, W. M. & Patchett, J. (1989). The geochemistry of marine sediments, island arc magma genesis, and crust–mantle recycling. Earth and Planetary Science Letters 94, 1–21.[CrossRef][Web of Science]
Cameron, W. E., McCulloch, M. T. & Walker, D. A. (1983). Boninite petrogenesis; chemical and Nd–Sr isotopic constraints. Earth and Planetary Science Letters 65, 75–89.[CrossRef][Web of Science]
Campbell, I. H. (2001). Identification of ancient mantle plumes. In: Ernst, R. & Buchan, K. L. (eds) Mantle Plumes; their Identification through Time. Geological Society of America, Special Papers 352, 5–21.
Campbell, I. H., Naldrett, A. J. & Roeder, P. L. (1979). Nickel activity in silicate liquids; some preliminary results. Canadian Mineralogist 17, 495–505.
Carlson, R. W., Esperanca, S. & Svisero, D. P. (1996). Chemical and Os isotopic study of Cretaceous potassic rocks from southern Brazil. Contributions to Mineralogy and Petrology 125, 393–405.[CrossRef][Web of Science]
Carmichael, I. S. E., Lange, R. A. & Luhr, J. F. (1996). Quaternary minettes and associated volcanic rocks of Mascota, western Mexico; a consequence of plate extension above a subduction modified mantle wedge. Contributions to Mineralogy and Petrology 124, 302–333.[CrossRef][Web of Science]
Cebria, J. M. & Lopez Ruiz, J. (1996). A refined method for trace element modelling of nonmodal batch partial melting processes; the Cenozoic continental volcanism of Calatrava, central Spain. Geochimica et Cosmochimica Acta 60, 1355–1366.[CrossRef][Web of Science]
Cebria, J. M. & Wilson, M. (1995). Cenozoic mafic magmatism in Western/Central Europe: a common European Asthenospheric Reservoir? Terra Abstracts, EUG, 8, 162.
Chauvel, C., Hofmann, A. W. & Vidal, P. (1992). HIMU-EM; the French Polynesian connection. Earth and Planetary Science Letters 110, 99–119.[CrossRef][Web of Science]
Chazot, G., Menzies, M. A. & Harte, B. (1996). Determination of partition coefficients between apatite, clinopyroxene, amphibole and melt in natural spinel lherzolites from Yemen; implications for wet melting of the lithospheric mantle. Geochimica et Cosmochimica Acta 60, 423–437.[CrossRef][Web of Science]
Cioflica, G., Jude, R., Lupulescu, M. & Palaseanu, M. (1995). Late Cretaceous–Eocene arc magmatism in the western part of the South Carpathians, Romania. Geological Society of Greece, Special Publication, Proceedings of XV Congress of the CBGA 4/2, 495–500.
Cioflica, G., Jude, R., Lupulescu, M. & Ducea, M. (1996). Lower crustal origin of the late Cretaceous–Eocene arc magmatism in the western part of the South Carpathians, Romania. In: Kneevi-Djordjevi, V. & Krsti, B. (eds) Terranes of Serbia. Belgrade: Faculty of Mining and Geology, University of Belgrade, pp. 103–107.
Class, C. & Goldstein, S. L. (1997). Plume–lithosphere interactions in the ocean basins; constraints from the source mineralogy. Earth and Planetary Science Letters 150, 245–260.[CrossRef][Web of Science]
Conticelli, S. (1998). The effect of crustal contamination on ultrapotassic magmas with lamproitic affinity: mineralogical, geochemical and isotope data from the Torre Alfina lavas and xenoliths, Central Italy. Chemical Geology 149, 51–81.[CrossRef][Web of Science]
Conticelli, S. & Peccerillo, A. (1992). Petrology and geochemistry of potassic and ultrapotassic volcanism in central Italy: petrogenesis and inferences on the evolution of the mantle sources. Lithos 28, 221–240.[CrossRef][Web of Science]
Conticelli, S., Manetti, P. & Menichetti, S. (1992). Mineralogy, geochemistry and Sr-isotopes in orendites from South Tuscany, Italy; constraints on their genesis and evolution. European Journal of Mineralogy 4, 1359–1375.
Conticelli, S., D'Antonio, M., Pinarelli, L. & Civetta, L. (2002). Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr–Nd–Pb isotope data from Roman Province and Southern Tuscany. Mineralogy and Petrology 74, 189–222.[CrossRef][Web of Science]
Csontos, L. (1995). Tertiary tectonic evolution of the Intra-Carpathian area: a review. Acta Vulcanologica 7, 1–15.
Csontos, L., Nagymarosy, A., Horvath, A. & Kovacs, M. (1992). Tertiary evolution of the Intra-Carpathian area: a model. Tectonophysics 208, 221–241.[CrossRef][Web of Science]
Cvetkovi, V., Kneevi, V. & Pécskay, Z. (2000). Tertiary igneous formations of the Dinarides, Vardar zone and adjacent regions: from recognition to petrogenetic implications. In: Karamata, S. & Jankovi, S. (eds) Geology and Metallogeny of the Dinarides and the Vardar Zone. Banja Luka-Srpsko Sarajevo: Academy of Sciences and Arts of the Republic of Srpska, pp. 245–253.
Cvetkovi, V., Prelevi, D., Downes, H., Jovanovi, M., Vaselli, O. & Pécskay, Z. (2004a). Origin and geodynamic significance of Tertiary post-collisional basaltic magmatism in Serbia (Central Balkan Peninsula). Lithos 73, 161–186.[CrossRef][Web of Science]
Cvetkovi, V., Downes, H., Prelevi, D., Jovanovi, M. & Lazarov, M. (2004b). Characteristics of the lithospheric mantle beneath East Serbia inferred from ultramafic xenoliths in Paleogene basanites. Contributions to Mineralogy and Petrology 148, 335–357.[CrossRef][Web of Science]
Di Battistini, G., Montanini, A., Vernia, L., Bargossi, G. M. & Castorina, F. (1998). Petrology and geochemistry of ultrapotassic rocks from the Montefiascone Volcanic Complex (Central Italy): magmatic evolution and petrogenesis. Lithos 43, 169–195.[CrossRef][Web of Science]
Di Battistini, G., Montanini, A., Vernia, L., Venturelli, G. & Tonarini, S. (2001). Petrology of melilite-bearing rocks from the Montefiascone Volcanic Complex (Roman Magmatic Province): new insights into the ultrapotassic volcanism of Central Italy. Lithos 59, 1–24.[CrossRef][Web of Science]
Dimitrijevi, M. D. (2001). Dinarides and the Vardar Zone: a short review of the geology. Acta Vulcanologica 13, 1–8.
Dinter, D. A. (1998). Late Cenozoic extension of the Alpine collisional orogen, northeastern Greece: origin of the north Aegean basin. Geological Society of America Bulletin 110, 1208–1230.
Djurdjevi, J. (1992). Sedimentology of the Neogene lake basins, on the example of the Pranjani basin. M.Sc. thesis, University of Belgrade, 193 pp.
Downes, H., Kostoula, T., Jones, A. P., Beard, A. D., Thirlwall, M. F. & Bodinier, J. L. (2002). Geochemistry and Sr–Nd isotopic compositions of mantle xenoliths from the Monte Vulture carbonatite–melilitite volcano, central southern Italy. Contributions to Mineralogy and Petrology 144, 78–92.[Web of Science]
Eggler, D. H. (1974). Effect of CO2 on the melting of peridotite. Carnegie Institution of Washington, Yearbook 73, 215–224.
Eggler, D. H. (1983). Upper mantle oxidation state: evidence from olivine–orthopyroxene–ilmenite assemblages. Geophysical Research Letters 10, 365–368.[Web of Science]
Ellam, R., Hawkesworth, C., Menzies, M. & Rogers, N. (1989). The volcanism of southern Italy: role of subduction and the relationship between potassic and sodic alkaline volcanism. Journal of Geophysical Research 94, 4589–4601.
Falloon, T. J. & Danyushevsky, L. V. (2000). Melting of refractory mantle at 1·5, 2 and 2·5 GPa under anhydrous and H2O-undersaturated conditions: implications for the petrogenesis of high-Ca boninites and the influence of subduction components on mantle melting. Journal of Petrology 41, 257–283.
Foley, S. F. (1985). The oxidation state of lamproitic magmas. Tschermaks Mineralogische und Petrographische Mitteilungen 34, 217–238.[CrossRef][Web of Science]
Foley, S. F. (1989). Experimental constraints of phlogopite chemistry in lamproites; 1, The effect of water activity and oxygen fugacity. European Journal of Mineralogy 1, 411–426.
Foley, S. F. (1992a). Vein-plus-wall-rock melting mechanisms in the lithosphere and the origin of potassic alkaline magmas. Lithos 28, 435–453.[CrossRef][Web of Science]
Foley, S. F. (1992b). Petrological characterization of the source components of potassic magmas: geochemical and experimental constraints. Lithos 28, 187–204.[CrossRef][Web of Science]
Foley, S. F. (1993). An experimental study of olivine lamproite—first results from the diamond stability field. Geochimica et Cosmochimica Acta 57, 483–489.[CrossRef][Web of Science]
Foley, S. F. & Jenner, G. A. (2004). Trace element partitioning in lamproitic magmas—the Gaussberg olivine leucitite. Lithos 75, 19–38.[CrossRef][Web of Science]
Foley, S. F. & Venturelli, G. (1989). High K2O rocks with high MgO, high SiO2 affinities. In: Crawford, A. J. (ed.) Boninites and Related Rocks. London: Unwin Hyman, pp. 72–88.
Foley, S. F., Taylor, W. R. & Green, D. H. (1986). The role of fluorine and oxygen fugacity in the genesis of the ultrapotassic rocks. Contributions to Mineralogy and Petrology 94, 183–192.[CrossRef][Web of Science]
Foley, S. F., Venturelli, G., Green, D. H. & Toscani, L. (1987). The ultrapotassic rocks: characteristics, classification and constraints for petrogenetic models. Earth-Science Reviews 24, 81–134.
Foley, S. F., Jackson, S. E., Fryer, B. J., Greenough, J. D. & Jenner, G. A. (1996). Trace element partition coefficients for clinopyroxene and phlogopite in an alkaline lamprophyre from Newfoundland by LAM-ICP-MS. Geochimica et Cosmochimica Acta 60, 629–638.[CrossRef][Web of Science]
Foley, S. F., Musselwhite, D. S. & van der Laan, S. R. (1999). Melt compositions from ultramafic vein assemblages in the lithospheric mantle; a comparison of cratonic and non-cratonic settings. In: Gurney, J. J., Gurney, J. L., Pascoe, M. D. & Richardson, S. H. (eds) The J. B. Dawson Volume; Proceedings of the VIIth International Kimberlite Conference; Volume 1. Cape Town: Red Roof Design, pp. 238–246.
Foley, S. F., Barth, M. G. & Jenner, G. A. (2000). Rutile/melt partition coefficients for trace elements and an assessment of the influence of rutile on the trace element characteristics of subduction zone magmas. Geochimica et Cosmochimica Acta 64, 933–938.[CrossRef][Web of Science]
Fraser, K., Hawkesworth, C., Erlank, A., Mitchell, R. & Scott-Smith, B. (1985). Sr, Nd and Pb isotope and minor element geochemistry of lamproites and kimberlites. Earth and Planetary Science Letters 76, 57–70.[CrossRef][Web of Science]
Gasperini, D., Blichert-Toft, J., Bosch, D., Moro, A. D., Macera, P. & Albarède, F. (2002). Upwelling of deep mantle material through a plate window: evidence from the geochemistry of Italian basaltic volcanics. Journal of Geophysical Research 107, 2367.[CrossRef]
Gaul, O. F., Griffin, W. L., O'Reilly, S. Y. & Pearson, N. J. (2000). Mapping olivine composition in the lithospheric mantle. Earth and Planetary Science Letters 182, 223–235.[CrossRef][Web of Science]
Green, T. H. & Pearson, N. J. (1987). An experimental study of Nb and Ta partitioning between Ti-rich minerals and silicate liquids at high pressure and temperature. Geochimica et Cosmochimica Acta 51, 55–62.[CrossRef][Web of Science]
Green, T. H., Blundy, J. D., Adam, J. & Yaxley, G. M. (2000). SIMS determination of trace element partition coefficients between garnet, clinopyroxene and hydrous basaltic liquids at 2–7·5 GPa and 1080–1200°C. In: Austrheim, H. & Griffin, W. L. (eds) Element Partitioning in Geochemistry and Petrology; Special Volume in Honour of Brenda B. Jensen. Amsterdam: Elsevier, pp. 165–187.
Harangi, S. (2001). Neogene magmatism in the Alpine–Pannonian Transition Zone—a model for melt generation in a complex geodynamic setting. Acta Vulcanologica 13, 25–39.
Hart, S. R. (1984). A large-scale isotope anomaly in the Southern Hemisphere mantle. Science 309, 753–757.
Hart, S. R., Hauri, E. H., Oschmann, L. A. & Whitehead, J. A. (1992). Mantle plumes and entrainment; isotopic evidence. Science 256, 517–520.
Harte, B. (1987). Metasomatic events recorded in mantle xenoliths; an overview. In: Nixon, P. H. (ed.) Mantle Xenoliths. Chichester: John Wiley, pp. 625–640.
Hoch, M., Rehkamper, M. & Tobschall, H. J. (2001). Sr, Nd, Pb and O isotopes of minettes from Schirmacher Oasis, East Antarctica: a case of mantle metasomatism involving subducted continental material. Journal of Petrology 42, 1387–1400.
Holmes, A. & Harwood, H. F. (1937). The Volcanic Area of Bufumbira. Part II: The Petrology of the Volcanic Field of Bufumbira, South-West Uganda. Geological Survey of Uganda Memoir.
Ili, A., Neubauer, F. & Handler, R. (2005). Late Paleozoic–Mesozoic tectonics of Dinarides revisited: implications from 40Ar/39Ar dating of detrital white micas. Geology (in press).
Ionov, D. A. & Hofmann, A. W. (1995). Nb–Ta-rich mantle amphiboles and micas; implications for subduction-related metasomatic trace element fractionations. Earth and Planetary Science Letters 131, 341–356.[CrossRef][Web of Science]
Ionov, D. A., Grégoire, M. & Prikhodko, V. S. (1999). Feldspar–Ti-oxide metasomatism in off-cratonic continental and oceanic upper mantle. Earth and Planetary Science Letters 165, 37–44.[CrossRef][Web of Science]
Jaques, A. L., Lewis, J. D., Smith, C. B., Gregory, G. P., Ferguson, J., Chappell, B. W. & McCulloch, M. T. (1984). The diamond-bearing ultrapotassic (lamproitic) rocks of the West Kimberley region, Western Australia. In: Kornprobst, J. (ed.) Proceedings of the 3rd International Kimberlite Conference. Amsterdam: Elsevier, pp. 225–254.
Kalfoun, F., Ionov, D. & Merlet, C. (2002). HFSE residence and Nb/Ta ratios in metasomatised, rutile-bearing mantle peridotites. Earth and Planetary Science Letters 199, 49–65.[CrossRef][Web of Science]
Kamenetsky, V. S., Crawford, A. J. & Meffre, S. (2001). Factors controlling chemistry of magmatic spinel: an empirical study of associated olivine, Cr-spinel and melt inclusions from primitive rocks. Journal of Petrology 42, 655–671.
Kamenetsky, V. S., Sobolev, A. V., Eggins, S. M., Crawford, A. J. & Arculus, R. J. (2002). Olivine-enriched melt inclusions in chromites from low-Ca boninites, Cape Vogel, Papua New Guinea; evidence for ultramafic primary magma, refractory mantle source and enriched components. In: Hauri, E. H., Kent, A. J. R. & Arndt, N. (eds) Melt Inclusions at the Millennium; Toward a Deeper Understanding of Magmatic Processes. Amsterdam: Elsevier, pp. 287–303.
Karamata, S. & Djordjevi, P. (1980). Origin of the Upper Cretaceous and Tertiary magmas in the Eastern part of Yugoslavia. Bulletin de l'Académie des Serbe des Sciences et des Arts, Classe des Sciences Mathématiques et Naturelles, Sciences Naturelles LXXII, 99–108.
Karamata, S. & Krsti, B. (1996). Terranes of Serbia and neighboring areas. In: Kneevi-Djordjevi, V. & Krsti, B. (eds) Terranes of Serbia. Belgrade: Faculty of Mining and Geology, University of Belgrade, pp. 25–40.
Karamata, S., Steiger, R., Djordjevi, P. & Knezevi, V. (1990). New data on the origin of granitic rocks from western Serbia. Bulletin de l'Académie des Serbe des Sciences et des Arts, Classe des Sciences Mathématiques et Naturelles, Sciences Naturelles 32, 1–9.
Karamata, S., Kneevi, V., Pécskay, Z. & Djordjevi, M. (1997a). Magmatism and metallogeny of the Ridanj–Krepoljin belt (eastern Serbia) and their correlation with northern and eastern analogues. Mineralium Deposita 32, 452–458.[CrossRef][Web of Science]
Karamata, S., Krsti, B., Dimitrijevi, D. M., Dimitrijevi, M. N., Kneevi, V., Stojanov, R. & Filipovi, I. (1997b). Terranes between the Moesian Plate and the Adriatic Sea. In: IGCP Project No. 276; Paleozoic Geodynamic Domains and their Alpidic Evolution in the Tethys. Athens: Laboratoire de Géologie de l'Université, pp. 429–477.
Karamata, S., Dimitrijevi, N. M. & Dimitrijevi, D. M. (1999). Oceanic realms in the central part of the Balkan Peninsula during the Mesozoic. Slovak Geological Magazine 5, 173–177.
Keith, T. E. C., Thompson, J. M. & Mays, R. E. (1983). Selective concentration of cesium in analcime during hydrothermal alteration, Yellowstone National Park, Wyoming. Geochimica et Cosmochimica Acta 47, 795–804.[CrossRef][Web of Science]
Kissel, C., Speranza, F. & Milievi, V. (1995). Paleomagnetism of external southern and central Dinarides and northern Albanides: implications for the Cenozoic activity of the Scutari–Pec transverse zone. Journal of Geophysical Research 100, 14999–15007.[CrossRef]
Konzett, J. & Ulmer, P. (1999). The stability of hydrous potassic phases in lherzolitic mantle—an experimental study to 9·5 GPa in simplified and natural bulk compositions. Journal of Petrology 40, 629–652.[CrossRef][Web of Science]
Kretz, R. (1983). Symbols for rock-forming minerals. American Mineralogist 68, 277–279.[Abstract]
Krsti, N. (2001). Timing of the Neogene geotectonic events in the Carpatho-Balkanidic and Dinaridic Alps with adjoining regions. PANCARDI 2001, Sopron, Abstracts, p. 25.
Kuehner, S., Edgar, A. & Arima, M. (1981). Petrogenesis of the ultrapotassic rocks from the Leucite Hills, Wyoming. Amererican Mineralogist 66, 663–677.
Le Maitre, R. W. (ed.) (2002). Igneous Rocks: a Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge: Cambridge University Press, 236 pp.
Maaløe, S. (1994). Estimation of the degree of partial melting using concentration ratios. Geochimica et Cosmochimica Acta 58, 2519–2525.[CrossRef][Web of Science]
Maaløe, S. & Pedersen, R. B. (2003). Two methods for estimating the degree of melting and trace element concentrations in the sources of primary magmas. Chemical Geology 193, 155–166.[CrossRef][Web of Science]
Marovi, M., Djokovi, I. & Tolji, M. (1998). Genesis of the neotectonic structures of Serbia. Annales Géologiques de la Peninsule Balkanique LXII, 25–47.
Marovi, M., Krsti, N., Stani, S., Cvetkovi, V. & Petrovi, M. (1999). The evolution of Neogene sedimentation provinces of Central Balkan Peninsula. Bulletin of Geoinstitute 36, 25–94.
Marovi, M., Djokovi, I., Pei, L., Tolji, M. & Gerzina, N. (2000). The genesis and geodynamics of Cenozoic sedimentation provinces of the central Balkan Peninsula. Geotectonics 34, 415–427.
Marovi, M., Mihailovi, D., Djokovi, I., Gerzina, N. & Tolji, M. (2001). Wrench tectonic of the Paleogene–Lower Miocene basins of Serbia between the central part of the Vardar Zone and the Moesian Plate. PANCARDI 2001, Sopron, Abstracts, p. 28.
Marovi, M., Djokovi, I., Pei, L., Radovanovi, S., Tolji, M. & Gerzina, N. (2002). Neotectonics and seismicity of the southern margin of the Pannonian Basin in Serbia. EGU Stephan Mueller Special Publication Series 3, 1–19.
McDonough, W. (1990). Constraints on the composition of the continental lithospheric mantle. Earth and Planetary Science Letters 101, 1–18.[CrossRef][Web of Science]
McDonough, W. F. & Sun, S. S. (1995). The composition of the Earth. In: McDonough, W. F., Arndt, N. T. & Shirey, S. (eds) Chemical Evolution of the Mantle. Chemical Geology. Amsterdam: Elsevier, pp. 223–253.
Meen, J. K., Ayers, J. C. & Fregeau, E. J. (1989). A model of mantle metasomatism by carbonated alkaline melts; trace-element and isotopic compositions of mantle source regions of carbonatite and other continental igneous rocks. In: Bell, K. (ed.) Carbonatites; Genesis and Evolution. London: Unwin Hyman, pp. 464–499.
Miller, C., Schuster, R., Klötzli, U., Frank, W. & Purtscheller, F. (1999). Post-collisional potassic and ultrapotassic magmatism in SW Tibet: geochemical and Sr–Nd–Pb–O isotopic constraints for mantle source characteristics and petrogenesis. Journal of Petrology 40, 1399–1424.[CrossRef][Web of Science]
Mitchell, R. H. (1995). Melting experiments on a sanidine phlogopite lamproite at 4–7 GPa and their bearing on the sources of lamproitic magmas. Journal of Petrology 36, 1455–1474.
Mitchell, R. H. & Bergman, S. C. (1991). Petrology of Lamproites. New York: Plenum.
Mitchell, R. H., Platt, R. G. & Downey, M. (1987). Petrology of lamproites from Smoky Butte, Montana. Journal of Petrology 28, 645–677.
Moine, B. N., Grégoire, M., O'Reilly, S. Y., Sheppard, S. M. F. & Cottin, J. Y. (2001). High field strength element fractionation in the upper mantle: evidence from amphibole-rich composite mantle xenoliths from the Kerguelen Islands (Indian Ocean). Journal of Petrology 42, 2145–2167.
Murck, B. W. & Campbell, I. H. (1986). The effects of temperature, oxygen fugacity and melt composition on the behaviour of chromium in basic and ultrabasic melts. Geochimica et Cosmochimica Acta 50, 1871–1887.[CrossRef][Web of Science]
Murphy, D. T., Collerson, K. D. & Kamber, B. S. (2002). Lamproites from Gaussberg, Antarctica: possible transition zone melts of Archaean subducted sediments. Journal of Petrology 43, 981–1001.
Nelson, D. R. (1992). Isotopic characteristics of potassic rocks; evidence for the involvement of subducted sediments in magma genesis. Lithos 28, 403–420.[CrossRef][Web of Science]
Nelson, D. R., McCulloch, M. T. & Sun, S. S. (1986). The origins of ultrapotassic rocks as inferred from Sr, Nd and Pb isotopes. Geochimica et Cosmochimica Acta 50, 231–245.[CrossRef][Web of Science]
Nixon, P. H. (1987). Mantle Xenoliths. Chichester: John Wiley.
Obradovi, J., Djurdjevi, C. J., Vasi, N. & Grubin, N. (1994). Facies and characteristics of some Neogene lacustrine sediments in Serbia. Sedimentary Facies and Palaeogeography 14, 12–27.
Peccerillo, A. (1985). Roman comagmatic province (central Italy); evidence for subduction-related magma genesis. Geology (Boulder) 13, 103–106.
Peccerillo, A. (1990). On the origin of the Italian potassic magmas—comments. Chemical Geology 85, 183–196.[CrossRef][Web of Science]
Peccerillo, A. (1992). Potassic and ultrapotassic rocks: compositional characteristics, petrogenesis and geologic significance. Episodes—Journal of International Geoscience 15, 243–251.
Peccerillo, A. (1995). Mafic calc-alkaline to ultrapotassic magmas in central–southern Italy; constraints on evolutionary processes and implications for source composition and conditions of magma generation. In: Proceedings of the Symposium on the Physics and the Chemistry of the Upper Mantle. Rio de Janeiro: Academia Brasileira de Ciencias, pp. 171–189.
Peccerillo, A. (1998). Relationships between ultrapotassic and carbonate-rich volcanic rocks in central Italy: petrogenetic and geodynamic implications. Lithos 43, 267–279.[CrossRef][Web of Science]
Peccerillo, A. (1999). Multiple mantle metasomatism in central–southern Italy: geochemical effects, timing and geodynamic implications. Geology 27, 315–318.
Peccerillo, A. (2003). Plio-Quaternary magmatism in Italy. Episodes—Jornal of International Geoscience 26, 222–226.
Perini, G. & Conticelli, S. (2002). Crystallization conditions of leucite-bearing magmas and their implications on the magmatological evolution of ultrapotassic magmas: the Vico Volcano, Central Italy. Mineralogy and Petrology 74, 253–276.[CrossRef][Web of Science]
Poustovetov, A. A. & Roeder, P. L. (2001). The distribution of Cr between basaltic melt and chromian spinel as an oxygen geobarometer. Canadian Mineralogist, 39, pp. 309–317.[CrossRef][Web of Science]
Prelevi, D., Cvetkovi, V. & Foley, S. F. (2001a). Composite igneous intrusions from Serbia: two case studies of interaction between lamprophyric and granitoid magmas. Acta Vulcanologica 13, 145–157.
Prelevi, D., Cvetkovi, V., Foley, S. F., Jovanovi, M. & Melzer, S. (2001b). Tertiary ultrapotassic–potassic rocks from Serbia, Yugoslavia. Acta Vulcanologica 13, 101–115.
Prelevi, D., Foley, S. F. & Cvetkovi, V. (2002a). A Serbian ultrapotassic province reminiscent of central–southern Italy. In: EUROCARB Workshop, Italy, 7–10 June 2002, Chieti; Abstracts, pp. 23–25.
Prelevi, D., Foley, S. F. & Cvetkovi, V. (2002b). Petrology, geochemistry and geodynamic significance of the Serbian ultrapotassic igneous province. Berichte der Deutschen Mineralogischen Gesellschaft, Beihefte zum European Journal of Mineralogy 14, 133.
Prelevi, D., Foley, S. F., Romer, R. & Cvetkovi, V. (2003). Serbian Tertiary ultrapotassic province—petrology, geochemistry and geodynamic significance. In: Proceedings of the 8th International Kimberlite Conference, Victoria, BC, 22–27 June 2003, FLA_0165.
Prelevi, D., Foley, S. F., Cvetkovi, V. & Romer, R. L. (2004a). Origin of minette by mixing of lamproite and dacite magmas in Veliki Majdan, Serbia. Journal of Petrology 45, 759–792.
Prelevi, D., Foley, S. F., Cvetkovi, V. & Romer, R. L. (2004b). The analcime problem and its impact on the geochemistry of ultrapotassic rocks from Serbia. Mineralogical Magazine 68, 621–636.
Redkin, A. F. & Hemley, J. J. (2000). Experimental Cs and Sr sorption on analcime in rock-buffered systems at 250–300°C and Psat and the thermodynamic evaluation of mineral solubilities and phase relations. European Journal of Mineralogy 12, 999–1014.
Righter, K. & Rosas-Elguera, J. (2001). Alkaline lavas in the volcanic front of the Western Mexican Volcanic Belt: geology and petrology of the Ayutla and Tapalpa volcanic fields. Journal of Petrology 42, 2333–2361.
Rogers, N. W., Hawkesworth, C. J., Parker, R. J. & Marsh, J. S. (1985). The geochemistry of potassic lavas from Vulsini, central Italy and implications for mantle enrichment processes beneath the Roman region. Contributions to Mineralogy and Petrology 90, 244–257.[CrossRef][Web of Science]
Romer, R. L., Foerster, H. J. & Breitkreuz, C. (2001). Intracontinental extensional magmatism with a subduction fingerprint; the Late Carboniferous Halle volcanic complex (Germany). Contributions to Mineralogy and Petrology 141, 201–221.[Web of Science]
Ryerson, F. J. & Watson, E. B. (1987). Rutile saturation in magmas; implications for Ti–Nb–Ta depletion in island-arc basalts. Earth and Planetary Science Letters 86, 225–239.[CrossRef][Web of Science]
Sato, M. (1978). Oxygen fugacity of basaltic magmas and the role of gas-forming elements. Geophysical Research Letters 5, 447–449.[Web of Science]
Schmidt, K. H., Bottazzi, P., Vannucci, R. & Mengel, K. (1999). Trace element partitioning between phlogopite, clinopyroxene and leucite lamproite melt. Earth and Planetary Science Letters 168, 287–299.[CrossRef][Web of Science]
Shaw, D. M. (1970). Trace element fractionation during anatexis. Geochimica et Cosmochimica Acta 34, 237–243.[CrossRef][Web of Science]
Stoppa, F. & Cundari, A. (1995). A new Italian carbonatite occurrence at Cupaello (Rieti) and its genetic significance. Contributions to Mineralogy and Petrology 122, 275–288.[CrossRef][Web of Science]
Sun, S. S. & McDonough, W. F. (1989). Chemical and isotopic systematics of oceanic basalts; implications for mantle composition and processes. In: Saunders, A. D. & Norry, M. J. (eds) Magmatism in the Ocean Basins. Geological Society, London, Special Publications 42, 313–345.
Tappe, S., Foley, S. F. & Pearson, D. G. (2003). The kamafugites of Uganda: a mineralogical and geochemical comparison with their Italian and Brazilian analogues. Periodico di Mineralogia 72, 51–77.
Terzi, M. & Svenjikova, E. V. (1991). Age of leucite-bearing rocks in Yugoslavia. Comptes Rendus des Séances de la Société Serbe de Géologie 283–287.
Thy, P., Stecher, O. & Korstgard, J. A. (1987). Mineral chemistry and crystallization sequences in kimberlite and lamproite dikes from the Sisimiut area, central West Greenland. Lithos 20, 391–417.[CrossRef][Web of Science]
Treuil, M. & Joron, J. L. (1975). Utilisation des éléments hydromagmatophiles pour la simplification de la modelisation quantitative des processus magmatiques; exemples de l'Afar et la Dorsale Medioatlantique. In: Societa Italiana di Mineralogia e Petrologia; Atti della Riunione; Tavola Rotonda. Geochimica e Geochimica Isotopica. 56, 125–174.
Turner, S., Arnaud, N., Liu, J., Rogers, N., Hawkesworth, C., Harris, N., Kelley, S., van Calsteren, P. & Deng, W. (1996). Post-collision, shoshonitic volcanism on the Tibetan Plateau: implications for convective thinning of the lithosphere and the source of ocean island basalts. Journal of Petrology 37, 45–71.
Turner, S., Platt, J. P., George, R. M. M., Kelley, S. P., Pearson, D. G. & Nowell, G. M. (1999). Magmatism associated with orogenic collapse of the Betic–Alboran domain, SE Spain. Journal of Petrology 40, 1011–1036.[CrossRef][Web of Science]
Vaselli, O., Downes, H., Thirlwall, M. F., Dobosi, G., Coradossi, N., Seghedi, I., Szakacs, A. & Vannucci, R. (1995). Ultramafic xenoliths in Plio-Pleistocene alkali basalts from the eastern Transylvanian Basin; depleted mantle enriched by vein metasomatism. Journal of Petrology 36, 23–53.
Vaskovi, N., Jovi, V. & Matovi, V. (1996). Petrochemical characteristics of Tertiary volcanic rocks from Avala Mt. Annales Géologiques de la Peninsule Balkanique LX/2, 291–312.
Vaughan, A. P. M. (1996). A tectonomagmatic model for the genesis and emplacement of Caledonian calc-alkaline lamprophyres. Journal of the Geological Society, London 153, 613–623.
Vaughan, A. P. M. & Scarrow, J. H. (2003). K-rich mantle metasomatism control of localization and initiation of lithospheric strike-slip faulting. Terra Nova 15, 163–169.[CrossRef][Web of Science]
Venturelli, G., Capedri, S., Battistini, G. D., Crawford, A., Kogarko, L. & Celestini, S. (1984a). The ultrapotassic rocks from southeastern Spain. Lithos 17, 37–54.[CrossRef][Web of Science]
Venturelli, G., Thorpe, R., Piaz, G. D., Moro, A. D. & Potts, P. (1984b). Petrogenesis of calc-alkaline, shoshonitic and associated ultrapotassic Oligocene volcanic rocks from the Northwestern Alps, Italy. Contributions to Mineralogy and Petrology 86, 209–220.[CrossRef][Web of Science]
Venturelli, G., Mariani, E. S., Foley, S. F., Capedri, S. & Crawford, A. J. (1988). Petrogenesis and conditions of crystallization of Spanish lamproitic rocks. Canadian Mineralogist 26, 67–79.[Web of Science]
Venturelli, G., Capedri, S., Barbieri, M., Toscani, L., Mariani, E. S. & Zerbi, M. (1991). The Jumilla lamproite revisited—a petrological oddity. European Journal of Mineralogy 3, 123–145.
Vollmer, R. (1976). Rb–Sr and U–Th–Pb systematics of alkaline rocks; the alkaline rocks from Italy. Geochimica et Cosmochimica Acta 40, 283–295.[CrossRef][Web of Science]
Vollmer, R. (1989). On the origin of the Italian potassic magmas; 1, A discussion contribution. Chemical Geology 74, 229–239.[CrossRef][Web of Science]
Vollmer, R. (1991). On the origin of the Italian potassic magmas; a one-dimensional diffusion-controlled model of source metasomatism. Earth and Planetary Science Letters 107, 487–498.[CrossRef][Web of Science]
von Quadt, A., Peytcheva, I., Heinrich, C., Frank, M., Cvetkovi, V. & Banjeevi, M. (2003). Evolution of the Cretaceous magmatism in the Apuseni–Timok–Srednogorie metallogenic belt and implications for the geodynamic reconstructions: new insight from geochronology, geochemistry and isotope studies. Final GEODE-ABCD Workshop, Programme and Abstracts, 60 pp.
Watson, E. B. & Green, T. H. (1981). Apatite/liquid partition coefficients for the rare earth elements and strontium. Earth and Planetary Science Letters 56, 405–421.[CrossRef][Web of Science]
Wendlandt, R. F. (1991). Oxygen diffusion in basalt and andesite melts; experimental results and discussion of chemical versus tracer diffusion. Contributions to Mineralogy and Petrology 108, 463–471.[CrossRef][Web of Science]
Wilson, M. & Bianchini, G. (1999). Tertiary–Quaternary magmatism within the Mediterranean and surrounding regions. In: Durand, B., Jolivet, L., Horvath, F. & Seranne, M. (eds) The Mediterranean Basins; Tertiary Extension within the Alpine Orogen. Geological Society, London, Special Publications 156, 141–168.
Wilson, M. & Downes, H. (1991). Tertiary–Quaternary extension-related alkaline magmatism in western and central Europe. Journal of Petrology 32, 811–849.
Wilson, M. & Patterson, R. (2001). Intraplate magmatism related to short-wavelength convective instabilities in the upper mantle: evidence from the Tertiary–Quaternary volcanic province of western and central Europe. In: Ernst, R. & Buchan, K. L. (eds) Mantle Plumes: their Identification through Time. Geological Society of America, Special Papers 352, 37–58.
Woolley, A. R., Bergman, S. C., Edgar, A. D., Le Bas, M. J., Mitchell, R., H., Rock, N. M. S. & Scott Smith, B. H. (1996). Classification of lamprophyres, lamproites, kimberlites, and kalsilitic, melilitic, and leucitic rocks. Canadian Mineralogist 34, 175–186.[Web of Science]
Zindler, A. & Hart, S. (1986). Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493–571.[CrossRef][Web of Science]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  C. AKAL K-richterite-olivine-phlogopite-diopside-sanidine lamproites from the Afyon volcanic province, Turkey Geological Magazine, July 1, 2008; 145(4): 570 - 585. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 I. Seghedi, T. Ntaflos, and Z. Pecskay The Gataia Pleistocene lamproite: a new occurrence at the southeastern edge of the Pannonian Basin, Romania Geological Society, London, Special Publications, January 1, 2008; 293(1): 83 - 100. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. Cvetkovic, G. Poli, G. Christofides, A. Koroneos, Z. Pecskay, K. Resimic-Saric, and V. Eric The Miocene granitoid rocks of Mt. Bukulja (central Serbia): evidence for pannonian extension-related granitoid magmatism in the northern Dinarides European Journal of Mineralogy, July 1, 2007; 19(4): 513 - 532. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. Hurai, M. Huraiova, P. Konecny, and R. Thomas Mineral-melt-fluid composition of carbonate-bearing cumulate xenoliths in Tertiary alkali basalts of southern Slovakia Mineralogical Magazine, February 1, 2007; 71(1): 63 - 79. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Harangi and L. Lenkey Genesis of the Neogene to Quaternary volcanism in the Carpathian-Pannonian region: Role of subduction, extension, and mantle plume Geological Society of America Special Papers, January 1, 2007; 418(0): 67 - 92. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Kovacs, L. Csontos, Cs. Szabo, E. Bali, Gy. Falus, K. Benedek, and Z. Zajacz Paleogene-early Miocene igneous rocks and geodynamics of the Alpine-Carpathian-Pannonian-Dinaric region: An integrated approach Geological Society of America Special Papers, January 1, 2007; 418(0): 93 - 112. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Prelevic, S.F. Foley, and V. Cvetkovic A review of petrogenesis of Mediterranean Tertiary lamproites: A perspective from the Serbian ultrapotassic province Geological Society of America Special Papers, January 1, 2007; 418(0): 113 - 129. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. TAPPE, S. F. FOLEY, G. A. JENNER, L. M. HEAMAN, B. A. KJARSGAARD, R. L. ROMER, A. STRACKE, N. JOYCE, and J. HOEFS Genesis of Ultramafic Lamprophyres and Carbonatites at Aillik Bay, Labrador: a Consequence of Incipient Lithospheric Thinning beneath the North Atlantic Craton J. Petrology, July 1, 2006; 47(7): 1261 - 1315. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||