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Modification of the subcontinental mantle beneath East Serbia: Evidence from orthopyroxene-rich xenoliths |
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| Authors: | Vladica Cvetkovi&#x; Marina Lazarov Hilary Downes Dejan Prelevi&#x; |
| Institution: | aFaculty of Mining and Geology, University of Belgrade, ?u?ina 7, 11000 Belgrade, Serbia and Montenegro bFachbereich für Geographie, Geologie und Mineralogie, Fakultät für Naturwissenschaften, Universität Salzburg, Hellbrunnerstraße 34/III, A-5020 Salzburg, Austria cInstitut für Mineralogie, Johann Wolfgang Goethe-Universität, Seckenberganlage 28, 60054 Frankfurt am Main, Germany dResearch School of Earth Sciences, Birkbeck College, Malet St., London, WC1E 7HX, UK eJohannes Gutenberg-Universität, Institut für Geowissenschaften FB 22 Mineralogie, Becherweg 21, 55099 Mainz, Germany |
| Abstract: | Orthopyroxene-rich olivine websterite xenoliths (OWB2) in Palaeogene basanites in East Serbia are mostly composed of tabular low-Al2O3 orthopyroxene (> 70 vol.%, Mg# 85–87) containing tiny Cr spinel inclusions. Orthopyroxene shows a slightly U-shaped primitive mantle-normalized trace element pattern with strong peaks at U and Pb, similar to that of orthopyroxene from normal regional peridotitic mantle. In between the orthopyroxenes are interstitial spaces composed of partially altered olivine (Mg# 85–87), clinopyroxene, Ti-rich spinel, Mg-bearing calcite, K-feldspar, apatite, ilmenite and relicts of a hydrous mineral. Clinopyroxene appears as selvages around orthopyroxene and as coarser euhedral crystals. Trace element patterns of the clinopyroxene selvages resemble those of adjacent orthopyroxene, whereas the coarser ones have flatter and more LREE- and LILE-enriched patterns, similar to that of metasomatic clinopyroxene. The OWB2 xenoliths are interpreted as having formed in two stages. During Stage I orthopyroxene crystallized, along with some spinel, olivine and probably hydrous phase(s). This original OWB2 lithology was a hydrous olivine-bearing orthopyroxenite that crystallised from subduction-related SiO2-saturated, boninite-like magmas. During Stage II the interstitial minerals formed due to infiltration of a low-SiO2, high-CaO and CO2-rich external melt, accompanied by decomposition of original H2O-bearing minerals. The calculated composition of the infiltrating liquid corresponds to a mafic alkaline melt similar to the basanitic host but more enriched in CO2, LREE and LILE. Metasomatism is interpreted in terms of small degree melts related to the Palaeogene mafic alkaline magmatism. |
| Keywords: | Geochemistry Orthopyroxenite Mantle Xenoliths East Serbia |
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