An anorogenic pulse in a typical orogenic setting: The geochemical and geochronological record in the East Serbian latest Cretaceous to Palaeocene alkaline rocks

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• 作者：Vladica Cvetkovi膰 ; Kristina 艩ari膰 ; Dejan Prelevi膰 ; Johann Genser ; Franz Neubauer ; Volker H枚ck ; Albrecht von Quadt
• 关键词：Intraplate magmatism ; Post-collisional setting ; Sr ; Nd ; Pb isotopes ; Balkan Peninsula
• 刊名：Lithos
• 出版年：November, 2013
• 年：2013
• 卷：180-181
• 期：Complete
• 页码：181-199
• 全文大小：2789 K

文摘

This study focuses on the East Serbian latest Cretaceous to Palaeocene Mafic Alkaline Rocks (hereafter, ES-MAR). This alkaline magmatism developed along the Eurasian border after the closure of the Mesozoic Tethys in the Balkan sector. Olivine(卤 clinopyroxene)-phyric and olivine- and nepheline-normative basanite, tephrite and theralite rocks are studied using Ar/Ar ages and major elements, trace elements and Sr-Nd-Pb isotopes. The ES-MAR are geochemically similar to other alkaline rocks of the Circum-Mediterranean Anorogenic Cenozoic Igneous (CiMACI) province, showing elevated contents of high field strength elements (HFSE) (e.g., Nb = 50-100 ppm) and high HFSE/LILE (large ion lithophile elements) ratios coupled with relatively low ⁸⁷Sr/⁸⁶Sr_i (mostly 0.7028-0.7040) and high ¹⁴³Nd/¹⁴⁴Nd_i (mostly > 0.5127). In contrast to the majority of CiMACI rocks, the ES-MAR exhibit low ²⁰⁶Pb/²⁰⁴Pb_i (< 18.5) ratios, similar to those displayed by Plio-Pleistocene volcanics of Sardinia. The Pb-unradiogenic signature of the ES-MAR is explained as the involvement of either an enriched mantle I-like source or highly depleted mantle. However, Sr-Nd-Pb and trace element variations (U/Nb, Ce/Pb, Th/Nb, and Th/La ratios and K₂O and Th contents) suggest that mixing between an asthenospheric magma (similar to the average primitive CiMACI) and a lamproite-like melt also played a significant role in the ES-MAR petrogenesis. It is assumed that the lamproite-like magma originated by the melting of crustally modified lithosphere. A similar mantle is believed to be the source of primitive Serbian Oligocene lamproites. The model fails to explain the elevated K₂O contents shown by samples that have low Th/Nb, Th/La and U/Nb and low Ce/Pb ratios. This subset of ES-MAR samples probably implies that there was an additional, presumably 鈥榓norogenic鈥?source of potassium.