Journal of Petrology Advance Access originally published online on April 25, 2007
Journal of Petrology 2007 48(5):1001-1019; doi:10.1093/petrology/egm008
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High-Pressure Melting of Eclogite and the P–T–X History of Tonalitic to Trondhjemitic Zoisite-Pegmatites, Münchberg Massif, Germany
1Geoforschungszentrum Potsdam, Section 4.1 Experimental Geochemistry and Mineral Physics, Telegrafenberg, D-14473 Potsdam, Germany
2Technische Universität Berlin, Fachgebiet Petrologie, Ackerstrasse 71–79, D-13355 Berlin, Germany
3Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 København K, Denmark
4Geoforschungszentrum Potsdam, Section 3.3 Climate Dynamics and Sediments, Telegrafenberg, D-14473 Potsdam, Germany
RECEIVED DECEMBER 5, 2005; ACCEPTED FEBRUARY 19, 2007
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ABSTRACT |
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TOP
ABSTRACT
INTRODUCTIONZoisite-bearing high-pressure pegmatites from the Münchberg Massif, Germany, provide an excellent example of the characteristics of the onset of metabasite melting at eclogite-facies conditions. The pegmatites were derived by partial melting of a mid-ocean ridge basalt (MORB)-like eclogite at T
680°C/2·3 GPa to 750°C/3·1 GPa, which produced small amounts of tonalitic to trondhjemitic melt. The melt concentrated locally in isolated, small melt pockets and crystallized primary zoisite as liquidus phase at P 2·3 GPa/680°C to 2·1 GPa/750°C. Compositional zoning of pegmatite zoisite records an ensuing multi-stage uplift history with successive, discrete crystallization events at 1·4 ± 0·2 GPa/650–700°C and 1·0 ± 0·1 GPa/620–650°C. Resorption textures indicate reheating and thermal perturbation of the whole system prior to each successive crystallization event. Final solidification of zoisite-pegmatites occurred at 0·9 ± 0·1 GPa/620–650°C. The data suggest that isolated melt + zoisite crystal mush pockets formed an integral part of the eclogite throughout uplift from melt formation at T 680°C/2·3 GPa to 750°C/3·1 GPa to final solidification at 
0·9 GPa/620–630°C; that is, over a depth range of 45–60 km. The entire pegmatite-forming process was probably fluid conserving: fluid present during melt formation was trapped by fully or nearly water-saturated siliceous melts, whereas fluid liberated during pegmatite crystallization interacted with dehydrated eclogite-facies assemblages to form amphibolite-facies hydrous minerals. A set of empirical Dmelt/eclogite values based on mean zoisite-pegmatite and eclogite composition were used to model the onset of partial high-pressure melting of metabasites. KEY WORDS: adakite; high-pressure melting; pegmatite; trondhjemite; zoisite
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INTRODUCTION |
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High-pressure pegmatites in high-pressure metabasites offer a unique opportunity for studying the geochemical characteristics of high-pressure melting of metabasites. High-pressure melting of metabasites plays the key role in the formation of the tonalite–trondhjemite–granodiorite (TTG) series that form large proportions of many Archaean terrains, and in the formation of adakites in modern subduction zones (Martin, 1999
; Foley et al., 2002; Condie, 2005; and references therein). Adakitic high-pressure melts could also enrich the overlying mantle wedge in Si, Al, large ion lithophile elements (LILE), light rare earth elements (LREE), and H2O and could play an important role in the genesis of typical, subduction-related calc-alkaline magmas. Knowledge of the geochemical processes during high-pressure melting of metabasite is therefore not only essential for the understanding of continental crust formation during the Archaean, but also for the interpretation of recent magma-generation processes at subduction zones. High-pressure melting of mafic lithologies at deep levels of the thickened crust of orogenic belts will also influence the rheological properties of the crust and may aid in weakening the crust sufficiently to lead to orogenic collapse (Skjerlie & Patiño Douce, 2002).
High-pressure pegmatites in metabasites have been reported from several locations; for example, the Münchberg Massif, Germany (Erdmannsdörffer, 1931; Bauberger, 1957; Matthes et al., 1974; Franz & Smelik, 1995), the Norwegian eclogite province (Green & Mysen, 1972), the Massif Central, France (Nicollet et al., 1979), the Cabo Ortegal, Spain (Maaskant, 1985), and the Catalina Schist, California (Sorensen & Barton, 1987). Zoisite-bearing high-pressure pegmatites are of special interest as they allow the study of the geochemical characteristics of zoisite–melt relations at high pressure. Eclogite-facies metabasites often contain zoisite and phengite as hydrous phases and may form under high PH2O (Holland, 1979). In these plagioclase-free high- and ultrahigh-pressure metabasites zoisite is the main carrier of Sr, Pb, light rare earth elements (LREE) and middle REE (MREE) (Hickmott et al., 1992; Nagasaki & Enami, 1998; Brunsmann et al., 2000) and controls the geochemical behaviour of these elements during melting. High-pressure melting of metabasites triggered by the breakdown of zoisite is a process that potentially produces Sr- and LREE-rich tonalitic–trondhjemitic melts (Skjerlie & Patiño Douce, 2002).
Within the Münchberg Massif two types of high-pressure pegmatites occur: phengite-pegmatites with characteristic centimetre-size phengite crystals [named ‘albite-pegmatites’ by Bauberger (1957)] and zoisite-pegmatites with characteristic centimetre-size zoisite crystals [named ‘zoisite–plagioclase-pegmatites’ by Erdmannsdörfer (1931); see also Matthes et al. (1974) and Franz & Smelik (1995)]. Franz & Smelik (1995) studied these high-pressure pegmatites in detail with a focus on the zoisite-pegmatites and established a three-stage P–T path for the zoisite-pegmatites from 2·0 GPa/690°C to 1·5 GPa/680°C to 1·3 GPa/650°C.
Here we re-examine the high-pressure pegmatites from the Münchberg Massif. We present new P–T estimates for the zoisite-pegmatites, whole-rock chemical data for zoisite- and phengite-pegmatites, mineral trace element data for zoisite, plagioclase and amphibole from zoisite-pegmatites, as well as a set of empirical trace element partition coefficients between high-pressure melt and eclogite. Based on these data we derive a likely petrogenetic model for the zoisite-pegmatites, which suggests that: (1) melting occurred at higher pressure (>2·5 GPa) than assumed by Franz & Smelik (1995); (2) the zoisite crystals record a prolonged crystallization history from 2·1 to 2·3 GPa/680–750°C down to 1·0 ± 0·1 GPa/620–650°C; (3) their exhumation path was not continuous but multi-stage and disturbed by at least two reheating events; (4) pockets of tonalitic to trondhjemitic melt + zoisite crystal mush formed a stable, integral part of the bulk-rock system during uplift from pressures of >2·5 GPa to 1·0 GPa.
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GEOLOGICAL SETTING |
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The Münchberg Massif forms part of the Central European Variscan Belt and is an inverted nappe pile consisting of four major lithotectonic units (Fig. 1a). The tectonically lower units are the Phyllite–Prasinite series and the Randamphibolite, which crop out along the southeastern and southwestern border of the Münchberg Massif. Muscovite K–Ar ages indicate metamorphism at
360 Ma in the Phyllite–Prasinite series whereas hornblende K–Ar ages for the Randamphibolite scatter between 400 and 370 Ma (Kreutzer et al., 1989). The central part of the Münchberg Massif consists of the tectonically higher units Liegend (=lower) series and Hangend (=upper) series. The former is a meta-clastic sequence with intercalated augengneiss, meta-gabbros and meta-granodiorites, the latter a sequence of different types of amphibolite and phengite-bearing amphibole-gneisses with intercalated relics of eclogite. Metamorphism of the Liegendseries occurred at 380 Ma with intrusion ages for the protoliths of the augengneiss and meta-gabbro of 500 Ma (Gebauer & Grünenfelder, 1979; Kreutzer et al., 1989). Eclogite-facies metamorphism within the Hangendseries occurred at 395–380 Ma (Gebauer & Grünenfelder, 1979; Stosch & Lugmair, 1990), phengites from eclogites have yielded Ar–Ar plateau and isochron ages of 365 ± 7 Ma (Hammerschmidt & Franz, 1992); intrusion ages of the mafic protoliths are 480 ± 23 Ma (Stosch & Lugmair, 1990).
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Two eclogite types exist within the Hangendseries (Matthes et al., 1974
, 1975): (1) a dark variety with clinopyroxene + garnet + quartz + rutile ± amphibole ± phengite ± zoisite; (2) a light variety with kyanite in addition to the paragenesis of (1). The dark variety probably represents former mid-ocean-ridge basalt (MORB) whereas the light variety resembles high-Al basalt and gabbro (Matthes et al., 1975; Stosch & Lugmair, 1990). The eclogites of the Hangendseries record minimum peak metamorphic conditions of 2·0–2·5 GPa/600–700°C, a re-equilibration stage at 1·4–1·5 GPa/600–700°C, and an intense amphibolite-facies overprint at 0·8–1·0 GPa/600–650°C (Franz et al., 1986; Klemd, 1989; Klemd et al., 1991; Massonne, 1991; O’Brien, 1993; Fig. 1b). Calc-silicate boudins, which are intimately interlayered with the eclogites, indicate minimum pressures of 3·1 GPa at 630°C (Klemd et al., 1994; Fig. 1b). The available P–T data for the Hangendseries suggest that (1) maximum temperatures did not significantly exceed 700°C, (2) the eclogites probably crossed the water-saturated MORB solidus during exhumation, and (3) the eclogites were at temperatures above the water-saturated trondhjemite solidus throughout most of their exhumation history. |
PETROGRAPHY OF HIGH-PRESSURE PHENGITE- AND ZOISITE-PEGMATITES |
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The phengite-pegmatite bodies (Bauberger, 1957
) range in size from only a few centimetres to several tens of metres, the larger of which have been mined for feldspar. They occur in all lithologies of the Hangendseries but are heterogeneously distributed. They comprise about 1·5–2·5 vol. % of the whole series, and are uniformly composed of 70 vol. % albite-rich plagioclase, 25 vol. % quartz, and 5 vol. % phengite. The characteristic centrimetre-size phengite crystals are situated within a plagioclase–quartz matrix. Accessory phases (<1 vol. %) are clinozoisite–epidote, amphibole, chlorite, and K-feldspar. The phengite-pegmatites are syn-tectonic and show a sharp, clearly intrusive contact to the country rocks. In eclogites, they are mostly discordant and tend to follow fractures, whereas in amphibolites and gneisses they are dominantly concordant to the main foliation (Bauberger, 1957; Franz & Smelik, 1995). At the contacts between eclogite and phengite-pegmatite the eclogite is retrograded into a zoisite- and garnet-bearing amphibolite (see Hammerschmidt & Franz, 1992, fig. 2a). The phengite-pegmatites formed during the re-equilibration stage at 1·4–1·5 GPa/600–700°C and subsequently experienced the same deformation and cooling history as the metabasites (Bauberger, 1957; Hammerschmidt & Franz, 1992). Ar–Ar isochron ages of phengites from phengite-pegmatites yielded 351 ± 3 Ma (Hammerschmidt & Franz, 1992).
Contrary to the phengite-pegmatites, the zoisite-pegmatites within the Hangendseries have so far only been described from the 300 m thick Weissenstein eclogite body, the largest eclogite body of the Münchberg Massif (Erdmannsdörffer, 1931; Matthes et al., 1974; Franz & Smelik, 1995; Fig. 1a). The Weissenstein eclogite is predominantly of the dark variety, with a variable modal composition, comprising 28–64 vol. % garnet, 18–70 vol. % clinopyroxene, 0–13 vol. % quartz, 0–4 vol. % rutile and phengite each, and 0–10 vol. % zoisite (Matthes et al., 1974). Texture and mineralogy of the zoisite-pegmatites have been described in detail by Franz & Smelik (1995) and we will refer to their results in the following discussion. Representative microprobe analyses of zoisite, clinozoisite, amphibole, and plagioclase compiled from their data are given in Table 1. The zoisite-pegmatites are characterized by centimetre- to decimetre-size euhedral prismatic zoisite crystals (Fig. 2a), which are embedded in a matrix of graphic plagioclase–quartz intergrowth. The zoisite crystals show resorption features as well as ductile and brittle deformation textures (Fig. 2a). They exhibit three distinct growth zones, which reflect three stages of zoisite crystallization. Relic cores are relatively iron-rich [zoisite 1; 
, where XFe = Fe/(Fe + Al – 2)] and rimmed by iron-poorer zoisite that consists of an inner part with 
(zoisite 2) and an outer part with 
(zoisite 3) (Fig. 2b). Partial resorption of zoisite 1 predates crystallization of zoisite 2, partial resorption of zoisite 1 + 2 predates crystallization of zoisite 3. Within the zoisite crystals small lamellae of clinozoisite 
, albite (An1–5), and calcic amphibole occur in textural equilibrium with zoisites 2 and 3. Clinozoisite with 
also occurs as small crystals around zoisite, whereas amphibole may also form larger clusters within the plagioclase–quartz matrix (Fig. 2a). Matrix plagioclase has an anorthite content of 10–15 mol % (=An10–15). Crystallization of the plagioclase–quartz matrix postdates zoisite crystallization and indicates final solidification.
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SAMPLE DESCRIPTION AND ANALYTICAL TECHNIQUE |
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We have studied six zoisite-pegmatite samples [85-1, 85-2, 85-4, 85-5, 89-1, and 93-24; samples 85-1, 85-2 and 85-5 were previously described and discussed by Hammerschmidt & Franz (1992
) and Franz & Smelik (1995)] from the Weissenstein eclogite and one phengite-pegmatite sample (1129) from Bärenhügel, Höflas, 1·5 km south of Weissenstein. There is no zoisite-pegmatite outcrop within the Weissenstein eclogite, and the zoisite-pegmatite samples were collected from the talus in the vicinity of the view tower at Weissenstein. We therefore have no information about textural relations between zoisite-pegmatite and eclogite host rock, nor do we know whether the samples represent one common or several different zoisite-pegmatite bodies, nor can we be certain whether the collected samples are representative parts of the zoisite-pegmatites.
For whole-rock analysis representative parts of the collected samples were crushed and milled in an agate mortar. Zoisite separates from zoisite-pegmatites were obtained by crushing the samples and careful handpicking to optical purity under the binocular. Whole-rock samples were analysed for major and minor elements (Table 2) by X-ray fluorescence (XRF) on melt and powder pellets at the Technical University of Berlin. Trace element concentrations (Tables 2 and 3) in whole-rock samples and zoisite separates were determined from solutions by inductively coupled plasma-mass spectrometry (ICP-MS; Fisons VG PlasmaQuad 2+) at the GeoForschungsZentrum Potsdam following the methods described in detail by Dulski (2001).
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In situ trace element analyses by laser ablation (LA)-ICP-MS were obtained on zoisite at the Geochemisches Institut, Universität Göttingen, and on plagioclase and amphibole at the Geological Survey of Denmark and Greenland, Copenhagen.
The LA-ICP-MS system at Göttingen consists of a frequency quadrupled Nd:YAG laser system emitting at 266 nm (Cetac LSX 100) coupled to a Fisons VG PlasmaQuad PQ2+ STE ICP-MS system. Analyses were made on 50–80 µm diameter spots. The ablated material was transferred to the mass spectrometer in an argon gas stream. 43Ca was used as internal standard and NIST SRM 612 glass [values from Pearce et al. (1997)] as external calibration standard. In a typical analytical sequence, two standards were analysed, followed by three to four unknowns, then two standards, and so on. For each analysis an ablation time of 60 s was applied. Background was measured for 30 s prior to and after ablation. Data acquisition was performed by peak hopping (two points per isotope) with a dwell time of 10 ms and a quad settling time of 5 ms per peak. Raw counts were converted to counts per second (c.p.s.) by the Fisons time-resolved computer software package. All subsequent data reduction (e.g. background subtraction, instrumental drift correction, isobaric interference correction) was done off-line using Excel-based spreadsheets developed by ourselves. The NIST SRM 614 glass standard was analysed routinely as an unknown, and the results are consistently within 2
of published concentrations. The detection limits are in the mid ppb range for most of the elements analysed.
In Copenhagen, the LA-ICP-MS system consists of a frequency quintupled Nd:YAG laser system emitting at 213 nm (New Wave UP 213) coupled to a ThermoFinnigan Element2 magnetic sectorfield ICP-MS system. Because for most of the REE the expected concentrations in plagioclase are in the ppb to ppt range, all analyses were made on 250 µm diameter spots. Ablation was performed in helium that was mixed downstream into the argon sample gas of the mass spectrometer. 29Si was used for internal standardization and NIST SRM 612 glass [values from Pearce et al. (1997)] was used as external calibration standard. In a typical analytical sequence, one standard was analysed, followed by six unknowns, then one standard, and so on. For each analysis an ablation time of 45 s was applied. Background was measured for 30 s prior to and after ablation. Data acquisition was performed by electrostatic scanning (one point per isotope) with a dwell time of 10 ms at fixed magnet masses. Reduction of time-resolved data and concentration calculations were subsequently performed off-line using the GLITTER software package. One analysis of the NIST SRM 614 glass standard was performed with every five unknowns for quality control and the results are consistently within 1 of the average concentrations reported by Kurosawa et al. (2002). The detection limit for most of the elements is in the lower mid ppt range.
The trace element patterns are normalized to the primitive mantle and the REE patterns to the chondrite values of Sun & McDonough (1989).
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WHOLE-ROCK COMPOSITION OF ZOISITE- AND PHENGITE-PEGMATITES |
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Major and minor element composition
The zoisite-pegmatites are essentially composed of SiO2 (
46–66 wt %), Al2O3 (21–29 wt %), CaO (5–20 wt %) and Na2O (1·5–8 wt %); Fe2O3 varies from 0·4 to 2·6 wt %, MgO is <1·2 wt %, and MnO, K2O, TiO2 and P2O5 are all <<1 wt % (Table 2). The variable concentrations of SiO2, Al2O3, CaO, Na2O and Fe2O3 reflect variable amounts of the major phases zoisite, plagioclase, and quartz within the different samples. Phengite-pegmatite differs in terms of higher SiO2 (75·59 wt %) and K2O (0·68 wt %) and lower Al2O3 (16·16 wt %), Fe2O3 (0·34 wt %) and CaO (1·57 wt %); MnO, MgO, Na2O, TiO2 and P2O5 in phengite-pegmatite are comparable with concentrations in the zoisite-pegmatites (Table 2). Zoisite-pegmatites have very low normative orthoclase, high normative anorthite and resemble tonalites except for 85-2, which has a trondhjemitic composition; phengite-pegmatite has higher normative orthoclase and albite and is of typical trondhjemitic composition (Fig. 3a).
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Trace element composition
The trace element characteristics of zoisite-pegmatite samples 85-1, 85-2, 85-5, 89-1 and 93-24 are comparable, although some elements show considerable scatter between the different samples: they contain 21–61 ppm Cr, 0·08–0·13 ppm Cs, 3·4–4·2 ppm Rb, 186–1558 ppm Ba, 16·6–28·8 ppm Pb, 545–1238 ppm Sr, and 139–654 ppm
REE + Y (Table 2). Sample 85-4 differs in having notably higher Pb (58·9 ppm) and Sr (1238 ppm), and higher Cr (75 ppm), Cs (0·18 ppm) and Rb (7·4 ppm); the concentrations of the other elements in 85-4 are in the range observed for the other zoisite-pegmatite samples (Table 2). Zr/Hf ratios are consistently between 18·8 and 20·6 in all zoisite-pegmatite samples, except for 93-24 (Zr/Hf = 25·8); Nb/Ta ratios are uniformly in the range 10·1–10·9, except for 85-5 (Nb/Ta = 6·7) and 93-24 (Nb/Ta = 17·8). Primitive mantle-normalized trace element patterns of all zoisite-pegmatites are coherent and characterized by an enrichment of incompatible elements, with overall distinct negative Nb–Ta, K, Zr–Hf, Ti and Li anomalies and a positive Pb anomaly (Fig. 3b). Additionally, samples 85-1, 85-5, and 89-1 display slightly negative Sr anomalies. Chondrite-normalized REE patterns of samples 85-1, 85-2, 85-5, 89-1, and 93-24 parallel each other and are straight, LREE-enriched with (La/Lu)N = 21·4–31·5 (Fig. 3c). The variable absolute REE concentrations in these samples reflect variable zoisite contents. The chondrite-normalized REE pattern of 85-4 is bell-shaped with (La/Lu)N = 6·9, (La/Gd)N = 0·50, and (Gd/Lu)N = 13·6 (Fig. 3c).
The La–Yb signatures of the zoisite-pegmatites resemble those of typical adakites and Archaean TTGs, although the normalized La–Nb ratio of 85-4 overlaps with that of typical island arc magmas and post-Archaean TTGs (Fig. 3d). Contrary to adakites and TTGs, which typically have high Zr/Sm ratios >25 (Foley et al., 2002), zoisite-pegmatites have extremely low Zr/Sm ratios of only 0·2–1·1 (Table 2). Like typical adakites and TTGs (Foley et al., 2002) all zoisite-pegmatites have Nb/Ta ratios lower than primitive mantle, except for zoisite-pegmatite sample 93-24, which has a primitive mantle-like Nb/Ta ratio of 17·8.
The trace element characteristics of the phengite-pegmatite sample analysed (1129) differ notably from those of zoisite-pegmatites: it has significantly lower contents of Cr, Ga, Sc, V, Th, U, and REE + Y (REE + Y only 4·7 ppm), but is richer in Cs and Rb (Table 2). Its Zr/Hf ratio of 24·2 is comparable with that of zoisite-pegmatite 93-24 but is higher than in the other zoisite-pegmatite samples. The Nb/Ta ratio of 25·5 is notably higher than in the zoisite-pegmatites. The primitive mantle-normalized trace element pattern displays enrichment of Cs, Rb, and Ba and pronounced positive K, Pb, Sr, and Li anomalies (Fig. 3b); the chondrite-normalized REE pattern is almost flat with (La/Lu)N = 4·6 (Fig. 3c). As a consequence of the very low REE content, the La–Yb ratio of the phengite-pegmatite neither resembles those of adakites and Archaean TTGs nor those of island arc magmas and post-Archaean TTGs (Fig. 3d). Its high Zr/Sm ratio of 67 is typical for adakites and TTGs, whereas the higher than primitive mantle Nb/Ta ratio is at variance with typical adakites and TTGs (Foley et al., 2002).
Source rocks for zoisite- and phengite-pegmatites
The overall chemical affinity of the zoisite- and phengite-pegmatites to tonalites, trondhjemites, and adakites suggests that both pegmatite types could have been derived by partial melting of metabasic source rocks. Their different spatial distribution within the Hangendseries (zoisite-pegmatites only in the Weissenstein eclogite; phengite-pegmatites throughout the entire Hangendseries) and the observed differences in whole-rock composition between the zoisite- and phengite-pegmatites, however, suggest that the two pegmatite types were derived from different source rocks. The low K, Cs, and Rb concentrations of the zoisite-pegmatites suggest a K-, Cs-, and Rb- (and probably phengite-) poor source rock. As phengite content (<<4 vol. %) and K2O (0·19 wt %) and Rb (5 ppm) concentrations in the Weissenstein eclogite are very low (Matthes et al., 1974), the chemical data and spatial restriction of zoisite-pegmatites to the Weissenstein eclogite are consistent with melt formation within the eclogite itself. In contrast, the higher K, Cs, and Rb contents of the phengite-pegmatite compared with the zoisite-pegmatite point to more potassium- and probably phengite-rich source rocks. The major part of the Hangendseries consists of different types of amphibolite and phengite-bearing amphibole-gneisses (see above). Here, potassium concentration and phengite content vary on a local scale (Stettner, 1960) and may reach levels high enough to produce melts with higher potassium concentrations as observed for the phengite-pegmatites. The chemical and spatial distribution data therefore strongly suggest that the phengite-pegmatites were derived from the phengite-bearing amphibole-gneisses of the Hangendseries (see also Franz & Smelik, 1995).
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TRACE ELEMENT CONTENTS OF ZOISITE-PEGMATITE MINERALS |
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Zoisite
Zoisite separates from 85-1, 85-5, 89-1, and 93-24 have almost identical trace element concentrations except for Rb and Ba (Table 3): they contain 1358–1419 ppm Sr, 28·0–44·6 ppm Pb, 9·2–14·0 ppm Th, 3·19–4·64 ppm U, and 930–1199 ppm
REE + Y. Zoisite from 85-4 (Table 3) differs in terms of its lower Th (2·78 ppm), U (2·61 ppm), and REE + Y (659 ppm) but higher Pb (70·9 ppm) and Sr (1610 ppm) contents. Zr/Hf ratios (18·8–24·2) are similar in all zoisite separates and resemble the corresponding whole-rock values. Zoisite trace element patterns from 85-1, 85-5, 89-1, and 93-24 (Fig. 4a) are enriched in incompatible elements with pronounced negative Zr–Hf, small negative Sr, and small positive Pb anomalies. The corresponding REE patterns are straight and enriched in LREE with (La/Lu)N = 24·9–43·8 (Fig. 4b). The zoisite trace element pattern from 85-4 is bell-shaped with pronounced positive Pb and U and negative Zr–Hf anomalies and a very small positive Sr anomaly (Fig. 4a). The corresponding REE pattern displays highest concentration of Gd and (La/Lu)N = 5·4, (La/Gd)N = 0·38, and (Gd/Lu)N = 14·3 (Fig. 4b).
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Trace element patterns in zoisites 1–3 from 85-1 and 85-4 as determined by in situ analysis are strikingly coherent in each sample (except for zoisite 3 in 85-4) and broadly resemble the corresponding mineral separate analyses.
Zoisites 1–3 from sample 85-1 are enriched in incompatible elements with negative Sr and Hf and small positive Pb anomalies (Fig. 4c). REE patterns are straight and enriched in LREE with (La/Lu)N = 43–59. The data suggest a slight, coherent decrease of Hf, Y, and REE and an increase of Sr and Pb from zoisite 1 to zoisite 3. Pb and Sr concentrations in zoisites 1–3 closely resemble those in the host pegmatite, whereas REE and Hf are consistently higher and Ba significantly lower than in the host pegmatite.
In 85-4 only zoisites 1 and 2 have coherent trace element concentrations whereas zoisite 3 differs notably (Table 4). Trace element patterns of zoisites 1 and 2 are bell-shaped with distinct positive Pb and negative Hf, and very small negative Sr anomalies (Fig. 4d). The REE patterns of zoisites 1 and 2 are enriched in MREE with (La/Lu)N = 6·5 and 7·0, (La/Gd)N = 0·28 and 0·32, and (Gd/Lu)N = 22 and 23, which is also observed in zoisite separate 85-4 (Fig. 4b). The data suggest a slight, coherent decrease of Hf, Y, and REE from zoisite 1 to zoisite 2, whereas Pb and Sr increase. Pb, Sr, and LREE concentrations in zoisites 1 and 2 closely resemble those in the host pegmatite, whereas MREE and heavy REE (HREE) and Hf are consistently higher, and Ba significantly lower, than in the host pegmatite. However, zoisite 3 has significantly lower LREE and MREE concentrations than zoisites 1 and 2 (Fig. 4d). Its REE pattern is somewhat erratic but still bell-shaped, but with (La/Lu)N = 3·2, (La/Gd)N = 0·3, and (Gd/Lu)N = 10·5. Pb and Sr concentrations are comparable with those in zoisites 1 and 2, whereas Ba is higher and Hf lower in zoisite 3 than in zoisites 1 and 2.
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Plagioclase
Mean trace element concentrations in plagioclase as determined by in situ LA-ICP-MS (Table 5) are low except for Rb (2·8–64 ppm), Ba (498–2515 ppm), Pb (2·3–26·5 ppm), and Sr (346–1069 ppm). REE concentrations are extremely low with
REE + Y = 0·25–1·35 ppm. Pronounced positive Pb and Sr anomalies and high Cs, Rb, and Ba characterize the plagioclase trace element patterns (Fig. 5a). REE patterns are straight, slightly LREE-enriched with (La/Lu)N = 9·6–14·6.
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Amphibole
Mean trace element concentrations in amphibole as determined by in situ LA-ICP-MS (Table 5) are generally low except for Rb (5·2 and 9·2 ppm), Ba (57·1 and 115 ppm), Zr (13·2 and 19·7 ppm), and Hf (0·76 and 1·10 ppm). Sr and Pb, which have considerably higher abundances in zoisite and plagioclase, are present at low concentrations, ranging from 28·4 to 28·8 ppm and 3·68 to 7·29 ppm, respectively. Zr/Hf ratios of 20·1 and 27·4 are comparable with those in zoisite. REE concentrations are low with
REE + Y = 14·04 and 42·8 ppm. The trace element patterns resemble each other and are characterized by a pronounced positive Pb anomaly, small positive U, Sr, and Hf anomalies and high Cs, Rb, and Ba contents (Fig. 5b). The REE patterns of amphibole are straight and slightly enriched in HREE with (La/Lu)N between 0·089 and 0·28. |
P–T EVOLUTION OF ZOISITE-PEGMATITES |
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The uniform textures and comparable mineralogical and chemical compositions of the zoisite-pegmatite samples suggest a common P–T evolution. This can be reconstructed based on the Fe3+ contents of zoisites 1–3 in conjunction with simultaneously crystallized phases and melt relations in the MORB and trondhjemite systems as proxies for the host eclogite and zoisite-pegmatites, respectively (Fig. 6). For coexisting zoisite and clinozoisite
is always less than 
and increases with increasing pressure and temperature (Fig. 6a); the maximum Fe3+ content in zoisite as function of P and T is given by the equation |
|
).
|
We used this
relation to calculate isopleths for 
, 0·12, and 0·10 as observed in zoisites 1–3 (Fig. 6b). Textures suggest that zoisite 1 is the only phase to crystallize during crystallization Stage 1, and its Fe3+ content thus only yields minimum P–T conditions between 2·5 GPa/690°C and 2·1 GPa/750°C for Stage 1. For crystallization Stages 2 and 3, the simultaneously crystallized clinozoisite (with 
) indicates Fe3+ saturation in zoisite and the calculated isopleths yield actual P–T conditions between 1·75 GPa/640°C and 1·2 GPa/730°C for Stage 2 and between 1·3 GPa/610°C and 0·8 GPa/690°C for Stage 3. The uncertainties of the calculated isopleths are about ±0·3 GPa and ±50°C (Brunsmann et al., 2002). Additional constraints on the P–T evolution of the zoisite-pegmatites are as follows (Fig. 6b).
- To melt, the eclogite host rocks must have crossed the water-saturated MORB solidus. This places the minimum temperatures at 680°C/2·3 GPa to 750°C/3·1 GPa.
- Nearly pure albite, which crystallized with zoisite during crystallization Stage 2, and plagioclase with composition An10–15 crystallizing during Stage 3 place the P–T conditions for these stages below the albite = jadeite + quartz equilibrium, and Stage 3 at lower pressure than Stage 2.
- The lower temperature limit for crystallization Stage 3 is given by the water-saturated trondhjemite solidus at 610°C at 0·8–1·2 GPa pressure.
Textures indicate partial resorption of zoisite 1 and zoisite 1 + 2 prior to crystallization of zoisite 2 and zoisite 3, respectively (see Fig. 2b). These resorption textures either may reflect changes in melt composition leading to chemical disequilibrium between zoisite and melt, or may reflect reheating leading to decreasing modal amounts of zoisite. The almost identical trace element concentrations in zoisites 1–3 (see Fig. 4c and d) indicate more or less identical melt composition throughout the entire crystallization history and strongly suggest that reheating is responsible for the observed resorption textures. Unfortunately, our samples do not allow us to determine either the P–T conditions of these resorption events or the P–T evolution between the different crystallization stages. We therefore cannot definitely preclude cooling below the solidus and complete solidification of the pegmatites before successive reheating events. It appears nevertheless reasonable, and most probable, based on the regional geology and published P–T data for the Hagendseries, that the entire P–T evolution of the zoisite-pegmatites happened at supersolidus conditions.
Assuming supersolidus conditions throughout the entire crystallization history and Tmax 
750°C, based on published P–T data for the Hangendseries, the P–T evolution of the zoisite-pegmatites can be, albeit somewhat speculatively, summarized as follows (Fig. 6b).
- The Weissenstein eclogite crossed the water-saturated MORB solidus between 680°C/2·3 GPa and 750°C/3·1 GPa and small amounts of tonalitic to trondhjemitic melts formed.
- Cooling led to crystallization of zoisite 1 at P 2·3 GPa/680°C to 2·1 GPa/750°C (crystallization Stage 1).
- At some P–T between crystallizations Stages 1 and 2 reheating of the system led to partial resorption of zoisite 1.
- At 1·4 ± 0·2 GPa/650–700°C zoisite 2 (rimming relic zoisite 1) crystallized together with clinozoisite and nearly pure albite (crystallization Stage 2).
- At some P–T between crystallization Stages 2 and 3 reheating of the system led to partial resorption of zoisite 1 + 2.
- Crystallization of zoisite 3 (rimming relic zoisite 1 + 2) together with clinozoisite and anorthite An10–15 occurred at 1·0 ± 0·1 GPa/620–650°C (crystallization Stage 3).
- Crystallization of the plagioclase–quartz matrix and final solidification of the tonalitic to trondhjemitic melts occurred at 0·9 ± 0·1 GPa/620–630°C.
The P–T conditions for crystallization Stages 1–3 broadly correspond to the P–T conditions of the metamorphic stages recorded in the Weissenstein eclogite (Fig. 6b). Only for pegmatite Stage 1 does the P–T estimate for the zoisite-pegmatites suggest a slightly higher temperature and pressure than previously estimated for the high-pressure event 1 of the eclogites (Fig. 6b). The agreement between the P–T conditions recorded by the crystallization stages of the zoisite-pegmatites and the metamorphic stages of the Weissenstein eclogite strongly suggests that the pockets of tonalitic to trondhjemitic melt + zoisite crystal mush formed an integral part of the Weissenstein eclogite during the entire uplift from the melt-forming event at 680°C/2·3 GPa to 750°C/3·1 GPa to final solidification at 0·9 ± 0·1 GPa/620–630°C; that is, over a depth range of 60 km. Our data further suggest that this uplift was not continuous, but multi-stage, with successive, discrete events, in line with earlier results by O’Brien (1993).
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ECLOGITE–MELT RELATIONS |
|---|
If we take the measured whole-rock composition of the zoisite-pegmatites as representative of the initial high-pressure melt, our data allow us to address the geochemical characteristics of early stages of high-pressure melting of MORB-like metabasites. However, because of the lack of zoisite-pegmatite outcrops within the Weissenstein eclogite (see above) we have no in situ information about the textural and chemical relationships between the eclogite and zoisite-pegmatites, and thus any discussion on eclogite–melt relations is necessarily speculative.
Major element characteristics
Despite their overall chemical affinity to TTGs and adakites, the zoisite-pegmatites differ from typical TTG and adakites by their lower SiO2, TiO2, Fe2O3, MgO, and K2O and notably higher Al2O3 and CaO contents. Compared to experimentally produced partial high-pressure melts of metabasites (Rapp et al., 1991; Skjerlie & Patiño Douce, 2002), zoisite-pegmatites tend to be poorer in SiO2 and K2O but richer in Al2O3 and CaO (Table 6). The experimental studies were performed at pressures of 2·1–3·2 GPa, comparable with the estimated pressure conditions for the formation of the zoisite-pegmatites, but at notably higher temperatures of 975–1150°C than those recorded by the zoisite-pegmatites. Additionally, all experiments were carried out under fluid-absent conditions. As the starting materials for the experiments by Rapp et al. (1991) and Skjerlie & Patiño Douce (2002) are almost perfect analogues to the Weissenstein eclogite, the observed compositional differences between zoisite-pegmatites and experimental high-pressure melts are due to either the higher temperatures of the experimental studies or different melting processes [e.g. water-saturated (zoisite-pegmatites) vs fluid-absent (experiments)].
|
Trace element characteristics
The differences in trace element contents between the zoisite-pegmatite samples, especially the varying Nb/Ta and Zr/Hf ratios and the higher Pb, Sr, Cs, Cr, and Rb and different REE pattern in one sample, indicate trace element heterogeneity of the Weissenstein eclogite on a local scale, consistent with the data of Stosch & Lugmair (1990
), who reported subtle to notable trace element variations within the Weissenstein eclogite body. The data therefore point to a local control on the trace element characteristics of the zoisite-pegmatites and strongly suggest that melting within the eclogite was a small-scale process. This process produced numerous small, isolated melt pockets without homogenizing the different melt pools. However, given the lack of in situ information, our data are insufficient to address these local trace element heterogeneities and the local control on melt trace element composition; consequently, we refer to a mean eclogite and mean zoisite-pegmatite composition in the following discussion.
Based on the degree of post-eclogite facies alteration, Matthes et al. (1974) distinguished three types of eclogite within the Weissenstein eclogite body: Type E with <5 vol. % alteration, type e with 5–50 vol. % alteration, and type 
with >50 vol. % alteration. We used whole-rock chemical data for eclogite types E and e of Matthes et al. (1974) and Stosch & Lugmair (1990) to calculate the mean composition of the Weissenstein eclogite (Table 7). A mean zoisite-pegmatite composition was calculated as the mean of zoisite-pegmatite samples 85-1, 85-2, 85-5, 89-1 and 93-24, neglecting the unusual sample 85-4 (Table 7). The primitive mantle-normalized trace element pattern of the mean eclogite is almost flat, slightly enriched in all elements, with a positive Pb anomaly and small negative Th, K, Sr, Zr–Hf, and Ti anomalies (Fig. 7a). Rubidium, K, and Er in the mean zoisite-pegmatite are comparable with the mean eclogite, whereas Ta (and probably Nb), Zr, Hf, Ti, Tm, Yb, Lu, V, Sc, Cr, Cu, and Ni are lower; all other elements are enriched in the mean zoisite-pegmatite (Fig. 7a, Table 7). Comparing the primitive mantle-normalized trace element patterns of the mean eclogite and mean zoisite-pegmatite indicates that the pronounced positive Pb and small negative Sr anomalies observed in the zoisite-pegmatite samples are at least partly inherited from the host eclogite (Fig. 7a). Unfortunately, no Nb data are available for the Weissenstein eclogite, and therefore we cannot test whether the low Nb/Ta ratios found in most zoisite-pegmatite samples are due to the melting process or at least partly inherited from the host eclogite.
|
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Set of empirical Dmelt/eclogite
Based on the compositions of the mean zoisite-pegmatite, as representative of the tonalitic to trondhjemitic high-pressure melt, and the mean eclogite we calculated a set of empirical melt/eclogite partition coefficients (Fig. 7b; Table 7). The elements Ta, Zr, Hf, Tm, Yb, Lu, V, Sc, Cr, Cu, and Ni are compatible with respect to eclogite, with Dmelt/eclogite ranging from
to 
, whereas all other elements are moderately incompatible, with Dmelt/eclogite ranging from 
to 
(Table 7). To compare our empirical Dmelt/eclogite values with experimental results we calculated bulk partition coefficients between tonalitic to trondhjemitic melt and eclogite based on a mean eclogite with 47 vol. % clinopyroxene, 41 vol. % garnet, and 1·0 vol. % rutile (Weissenstein; Matthes et al., 1974) and experimentally derived Dmelt/rutile (Foley et al., 2000) and Dmelt/clinopyroxene and Dmelt/garnet data (Barth et al., 2002). The experimentally determined Dmelt/mineral data were obtained at substantially higher temperatures (900–1100°C) than those recorded by the Weissenstein eclogite and zoisite-pegmatite and are, therefore, not directly comparable. Some principal features are nevertheless evident from Figure 7b: (1) decreasing empirical 
values from LREE to HREE are compatible with experimental predictions and reflect residual garnet; (2) empirical 
and 
are generally higher than the experimental data except for Yb and Lu; (3) empirical Dmelt/eclogite for Rb, Ba, Pb, Sr, Zr and Hf are significantly lower than the experimental data, which predict pronounced positive Pb and Sr and slightly positive Zr–Hf anomalies in the melt. The observed low 
and 
probably reflect small amounts of residual phengite, low 
and 
reflect residual zircon; two phases that were not considered in the determination of the experimental bulk partition coefficients. Ubiquitous quartz within the Weissenstein eclogite (Matthes et al., 1974) indicates SiO2 saturation in the eclogite and high-pressure melts. Residual zircon would therefore also indicate Zr saturation in the high-pressure melts, in which case calculation of would become meaningless. Our empirically determined Dmelt/eclogite values for high-pressure melting of eclogite at low temperature are different from available experimental data at high temperatures. Both methods have their distinct disadvantages—for natural samples it is not clear whether they are representative of the whole-rock and often the source rocks of the high-pressure melts cannot be clearly defined; experimentally produced melts, on the other hand, are often heterogeneous and vary unsystematically, and temperature has to be high to reach melt fractions high enough to allow analysis of the produced melt pools. Our dataset, therefore, provides an alternative to the experimental data for modelling the composition of high-pressure partial melts of metabasites at conditions just above the onset of melting.
Water-saturated vs dehydration melting
Eclogite melting may have occurred under either water-saturated conditions in the presence of an aqueous fluid phase along the water-saturated MORB solidus or via dehydration melting triggered by the breakdown of OH-bearing phases at temperatures above the water-saturated MORB solidus. High-pressure veins with omphacite, zoisite, quartz, and rutile within the Weissenstein eclogite point to the presence of a free aqueous fluid phase, at least during parts of its high-pressure evolution (Matthes et al., 1970; Klemd, 1989). However, it remains unclear whether this fluid phase also triggered the observed high-pressure melting. Potential internal fluid sources at T > 680°C/2·3 GPa to 750°C/3·1 GPa, as determined for the onset of partial melting of the eclogite host-rock, are zoisite, phengite and amphibole (Fig. 6). Zoisite and phengite might be present as minor phases within the Weissenstein eclogite (Matthes et al., 1974; see above), whereas primary amphibole is only rarely found. In the zoisite-bearing quartz eclogite studied by Skjerlie & Patiño Douce (2002) the onset of dehydration-melting triggered by the breakdown of phengite occurred at 900–1000°C within the pressure range 2·2–3·2 GPa. As these temperatures are 300°C higher than anything recorded so far for the Weissenstein eclogite, breakdown of phengite may be ruled out as being responsible for melt formation within the Weissenstein eclogite. This is in line with the observed low K2O content of the zoisite-pegmatites: the zoisite-bearing quartz eclogite studied by Skjerlie & Patiño Douce (2002) contains 0·14 wt % K2O, comparable with 0·16 ± 0·11 wt % K2O as determined for the Weissenstein eclogite (Matthes et al., 1974; Stosch & Lugmair, 1990). The experimental melts produced by breakdown of phengite, however, have up to 5·13 wt % K2O (Skjerlie & Patiño Douce, 2002), much higher than the values observed in the studied zoisite-pegmatites. Within the P–T range determined for the onset of partial melting of the Weissenstein eclogite, potential internal fluid sources are therefore amphibole and zoisite, the upper stability limits of which roughly coincide in this P–T range (Fig. 6b). Based on our data we cannot distinguish between water-saturated conditions and dehydration melting triggered by the breakdown of zoisite and/or amphibole. However, as zoisite (if present) is the main carrier of Pb, Sr, and the LREE and MREE in high-pressure metabasites (Hickmott et al., 1992; Nagasaki & Enami, 1998; Brunsmann et al., 2000), the observed high concentrations of LREE and MREE and especially Pb within zoisite-pegmatites indicate that the melt-forming reaction has zoisite as an educt phase.
Zoisite from the studied zoisite-pegmatites contains primary two-phase (liquid and vapour) aqueous fluid inclusions with <6 wt % NaCl and densities of <1 g/cm3 (Klemd, 2004). These fluid inclusions provide unambiguous evidence for the exsolution of an aqueous, low-density fluid during zoisite crystallization (Klemd, 2004) and indicate fully or nearly water-saturated conditions for the tonalitic to trondhjemitic melts, regardless of the actual melting process.
|
SUMMARY |
|---|
The zoisite-pegmatites provide an excellent example of the onset of metabasite melting at eclogite-facies conditions. Such conditions can be expected in a down-going oceanic slab as well as in collision zones. The newly produced melt in a metabasaltic rock of MORB composition is tonalitic (to trondhjemitic) and shares some characteristics with the TTG series or with adakites. The amount of melt, forming at a temperature of less than 750°C, however, is small, as a result of the combined effect of relatively low temperature and restricted availability of water, and the melt does not separate from the rock unit. Only if the melt fraction increases will the melt segregate and might migrate upwards, influencing melting in the overlying mantle wedge. Because of the poor outcrop situation of the Münchberg area in the Variscan chain of Central Europe, it is unfortunately impossible to give an estimate of the amount of melt produced. This will be a crucial question to solve: at what degree of melting, at what temperature in a given composition and at what geological (mechanical) conditions the melt will effectively separate.
Our data suggest the following model: high-pressure partial melting and pegmatite formation occurred at conditions only slightly above the water-saturated solidus and can be a fluid-conserving or fluid-recycling process. Any fluid released from hydrous minerals such as zoisite, epidote or amphibole is trapped in small fractions of fully to nearly water-saturated siliceous melt (for true dehydration melting, a free fluid phase never exists). Neither the fluid nor the siliceous melt will separate and migrate into the overlying rock units. During uplift, cooling and crystallization, the water, which is stored in the siliceous melt, is again liberated and encounters a dehydrated eclogite-facies assemblage. Here, it hydrates the eclogite-facies assemblage, leading to crystallization of hydrous minerals such as amphibole or mica. This model of fluid conservation or fluid recycling implies also that the trace element budget of the whole-rock does not change during melting and subsequent crystallization. The pegmatites from the Hangendserie of the Münchberg area still preserve some trace element signatures of their individual protoliths, which means that the partial melts did not mix and were not homogenized. Element transport occurs only on a restricted scale of probably much less than the present thickness of the Hangendserie.
The coarse grain size of the pegmatitic rocks is, however, a good condition to preserve textural disequilibrium and to record different stages of the uplift and cooling history. Reheating is indicated in the pegmatites by partial resorption of zoisite and crystallization of a second and third generation with distinctly different composition. This observation is in line with the idea that uplift occurred during the collision event and shortly after or simultaneously with stacking of the nappes; that is, in a short time frame, which is in many cases close to the time resolution of available geochronometric methods.
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ACKNOWLEDGEMENTS |
|---|
This paper benefited from careful reading of an earlier version by W. Heinrich. Thorough and critical reviews by R. Klemd, A. Patiño Douce and M. Schmidt significantly improved the final manuscript. Editorial handling by R. Gieré is gratefully acknowledged. This paper is published with the permission of the Geological Survey of Denmark and Greenland, Copenhagen.
*Corresponding author. Present address: Technische Universität Berlin, Fachgebeit Petrologie Ackerstrasse 71–79, D-13355 Berlin, Germany. Telephone: +49-(0)30-314 72091. Fax: +49-(0)30-314 72218. E-mail: axel.liebscher{at}tu-berlin.de
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REFERENCES |
|---|
Barth MG, Foley SF, Horn I. Partial melting in Archaean subduction zones: constraints from experimentally determined trace element partition coefficients between eclogitic minerals and tonalitic melts under upper mantle conditions. Precambrian Research (2002) 113:323–340.[CrossRef][Web of Science]
Bauberger W. Über die ‘Albit-Pegmatite’ der Münchberger Gneismasse und ihre Nebengesteine. Geologica Bavarica (1957) 36:1–77. [Translated title: About the ‘albite-pegmatites’ of the Muenchberg Gneiss Massif and their country rocks.].[Medline]
Brunsmann A, Franz G, Erzinger J, Landwehr D. Zoisite- and clinozoisite-segregations in metabasites (Tauern Window, Austria) as evidence for high-pressure fluid–rock interaction. Journal of Metamorphic Geology (2000) 18:1–21.[CrossRef][Web of Science]
Brunsmann A, Franz G, Heinrich W. Experimental determination of zoisite–clinozoisite phase equilibria in the system CaO–Al2O3–Fe2O3–SiO2–H2O. Contributions to Mineralogy and Petrology (2002) 143:115–130.[Web of Science]
Condie KC. TTGs and adakites: are they both slab melts? Lithos (2005) 80:33–44.[CrossRef][Web of Science]
Dulski P. Reference materials for geochemical studies; new analytical data by ICP-MS and critical discussion of reference values. Geostandards Newsletter (2001) 25:87–125.[Web of Science]
Erdmannsdörffer OH. Über Zoisitoligoklaspegmatit und seine Beziehung zu anorthositischen Magmen. In: Sitzungsberichte der Heidelberger Akademie der Wissenschaften, Mathematisch-naturwissenschaftkiche Klasse, 4. Abhandlung, 1–9 (1931) [Translated title: About zoisite–oligoclase-pegmatite and its relation to anorthositic melts.].
Foley SF, Barth MG, Jenner GA. 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 (2000) 64:933–938.[CrossRef][Web of Science]
Foley S, Tiepolo M, Vannucci R. Growth of early continental crust controlled by melting of amphibolite in subduction zones. Nature (2002) 417:837–840.[CrossRef]
Franz G, Selverstone J. An empirical phase diagram for the clinozoisite–zoisite transformation in the system Ca2Al3Si3O12(OH)–Ca2Al2Fe3+Si3O12(OH). American Mineralogist (1992) 77:631–642.[Abstract]
Franz G, Smelik G. Zoisite–clinozoisite bearing pegmatites and their importance for decompressional melting in eclogites. European Journal of Mineralogy (1995) 7:1421–1436.
Franz G, Thomas S, Smith DC. High-pressure phengite decomposition in the Weissenstein eclogite, Münchberger Gneiss Massif, Germany. Contributions to Mineralogy and Petrology (1986) 92:71–85.[CrossRef][Web of Science]
Gebauer D, Grünenfelder M. U–Pb zircon and Rb–Sr mineral dating of eclogites and their country rocks. Example: Münchberg Gneiss Massif, northeast Bavaria. Earth and Planetary Science Letters (1979) 42:35–44.[CrossRef][Web of Science]
Green DH, Mysen BO. Genetic relationship between eclogites and hornblende + plagioclase pegmatite in western Norway. Lithos (1972) 5:147–161.[CrossRef]
Hammerschmidt K, Franz G. Retrograde evolution of eclogites: evidences from microstructures and 40Ar/39Ar white mica dates, Münchberg Massif, northern Bavaria. Contributions to Mineralogy and Petrology (1992) 111:113–125.[CrossRef][Web of Science]
Hickmott DD, Sorensen SS, Rogers PSZ. Metasomatism in a subduction complex: constraints from microanalysis of trace elements in minerals from garnet amphibolite from the Catalina Schist. Geology (1992) 20:347–350.
Holland TJB. High water activities in the generation of high-pressure kyanite eclogites of the Tauern Window, Austria. Journal of Geology (1979) 87:1–27.[Web of Science]
Klemd R. P–T evolution and fluid inclusion characteristics of retrograded eclogites, Münchberg Gneiss Complex, Germany. Contributions to Mineralogy and Petrology (1989) 102:221–229.[CrossRef][Web of Science]
Klemd R. Fluid inclusions in epidote minerals and fluid development in epidote-bearing rocks. Epidotes. Mineralogical Society of America, Reviews in Mineralogy and Geochemistry—Liebscher A, Franz G, eds. (2004) 56:197–234.
Klemd R, Matthes S, Okrusch M. High-pressure relics in meta-sediments intercalated with the Weissenstein eclogite, Münchberg gneiss complex, Bavaria. Contributions to Mineralogy and Petrology (1991) 107:328–342.[CrossRef][Web of Science]
Klemd R, Matthes S, Schüssler U. Reaction textures and fluid behaviour in very high-pressure calc-silicate rocks of the Münchberg gneiss complex, Bavaria, Germany. Journal of Metamorphic Geology (1994) 12:735–745.[Web of Science]
Kreuzer H, Seidel E, Schüßler U, Okrusch M, Lenz KL, Raschka H. K–Ar geochronology of different tectonic units at the northwestern margin of the Bohemian Massif. Tectonophysics (1989) 157:149–178.[CrossRef][Web of Science]
Kurosawa M, Jackson SE, Sueno S. Trace element analysis of NIST SRM 614 and 616 glass reference materials by laser ablation microprobe-inductively coupled plasma-mass spectrometry. Geostandards Newsletter (2002) 26:75–84.[Web of Science]
Maaskant P. The iron content and the optic axial angle in zoisites from Galicia, NW Spain. Mineralogical Magazine (1985) 49:97–100.[CrossRef][Web of Science]
Martin H. Adakitic magmas: modern analogues of Archaean granitoids. Lithos (1999) 46:411–429.[CrossRef][Web of Science]
Massonne HJ. High-pressure, low-temperature metamorphism of pelitic and other protoliths based on experiments in the system K2O–MgO–Al2O3–SiO2–H2O. In: Habilitation thesis (1991) Bochum: Ruhr Universität. 172.
Matthes S, Richter P, Schmidt K. Die Eklogitvorkommen des kristallinen Grundgebirges in NE-Bayern. II. Der Disthen (Kyanit) der Eklogite und Eklogitamphibolite des Münchberger Gneisgebietes. Neues Jahrbuch für Mineralogie, Abhandlungen (1970) 113:111–137. [Translated title: Eclogites from the gneiss area of NE Bavaria. II. Kyanite from eclogites and eclogitic amphibolites from the Münchberg Gneiss Massif.].
Matthes S, Richter P, Schmidt K. Die Eklogitvorkommen des kristallinen Grundgebirges in NE-Bayern. VII. Ergebnisse aus einer Kernbohrung durch den Eklogitkörper des Weissensteins. Neues Jahrbuch für Mineralogie, Abhandlungen (1974) 120:270–314. [Translated title: Eclogites from the gneiss area of NE Bavaria. VII. The Weissenstein eclogite body: results of a drill core.].
Matthes S, Richter P, Schmidt K. Die Eklogitvorkommen des kristallinen Grundgebirges in NE-Bayern. IX. Petrographie, Geochemie und Petrogenese der Eklogite des Münchberger Gneisgebietes. Neues Jahrbuch für Mineralogie, Abhandlungen (1975) 126:45–86. [Translated title: Eclogites from the gneiss area of NE Bavaria. IX. Petrography, geochemistry, and petrogenesis of the eclogites of the Muenchberg gneiss area.].
Nagasaki A, Enami M. Sr-bearing zoisite and epidote in ultra-high pressure (UHP) metamorphic rocks from the Su-Lu province, eastern China: an important Sr reservoir under UHP conditions. American Mineralogist (1998) 83:240–247.[Abstract]
Nicollet C, Leyreloup A, Dupuy C. Petrogenesis of high-pressure trondhjemitic layers in eclogites and amphibolites form southern Massif Central, France. Trondhjemites, Dacites and Related Rocks—Barker F, ed. (1979) Amsterdam: Elsevier. 435–463.
O’Brien PJ. Partially retrograded eclogites of the Münchberg Massif, Germany: records of a multi-stage Variscan uplift history in the Bohemian Massif. Journal of Metamorphic Geology (1993) 11:241–260.[Web of Science]
O’Connor JT. A classification of quartz-rich igneous rocks based on feldspar ratios. US Geological Survey Professional Papers (1965) 525-B:79–84.
Pearce NJG, Perkins WT, Westgate JA, Gorton MP, Jackson SE, Neal CR, Chenery SP. A compilation of new and published trace element data for NIST SRM 610 and NIST SRM 612 glass reference material. Geostandards Newsletter (1997) 21:115–144.[CrossRef][Web of Science]
Rapp RP, Watson EB, Miller CF. Partial melting of amphibolite/eclogite and the origin of Archean trondhjemites and tonalities. Precambrian Research (1991) 51:1–25.[CrossRef][Web of Science]
Liebscher A, Franz G. Magmatic epidote. Epidotes. Mineralogical Society of America, Reviews in Mineralogy and Geochemistry (2004) 56:399–430.
Skjerlie KP, Patiño Douce AE. The fluid-absent partial melting of a zoisite-bearing quartz eclogite from 1·0 to 3·2 GPa; implications for melting in thickened continental crust and for subduction-zone processes. Journal of Petrology (2002) 43:291–314.
Sorensen SS, Barton MD. Metasomatism and partial melting in a subduction complex: Catalina Schist, southern California. Geology (1987) 15:115–118.
Stettner G. Erläuterungen zur Geologischen Karte von Bayern 1:25 000, Blatt Nr. 5836 Münchberg. (1960) München: Bayerisches Geologisches Landesamt. 163. [Translated title: Explanation to the geological map of Bavaria 1:25 000, Sheet No. 5836 Münchberg.].
Stosch H-G, Lugmair GW. Geochemistry and evolution of MORB-type eclogites from the Münchberg Massif, southern Germany. Earth and Planetary Science Letters (1990) 99:230–249.[CrossRef][Web of Science]
Sun S-s, McDonough WF. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Magmatism in the Ocean Basins. Geological Society, London, Special Publications—Saunders AD, Norry MJ, eds. (1989) 42:313–345.
Vielzeuf D, Schmidt MW. Melting relations in hydrous systems revisited: application to metapelites, metagreywackes and metabasalts. Contributions to Mineralogy and Petrology (2001) 141:251–267.[Web of Science]
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