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
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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
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
* 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
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