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

Abstract 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(± 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/86Sri (mostly 0.7028–0.7040) and high 143Nd/144Ndi (mostly > 0.5127). In contrast to the majority of CiMACI rocks, the ES-MAR exhibit low 206Pb/204Pbi (< 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 ‘anorogenic’ source of potassium.