Granitoid intrusions at the periphery of Kursk block as a part of Paleoproterozoic silica large igneous province at the Eastern Sarmatia

Abstract

At the eastern border of the Archean Kursk block of Sarmatia the Paleoprotorozoic 2.04–2.08 Ga diorite-granodiorite magmatism is widespread. The intrusive massifs granitoids are metaluminous calc-silica I-type rocks enriched with incoherent elements (LILE and LREE) with negative Ti, P and Nb anomalies. They have wide variety of εNd(T) values in rocks and εHf(T) values in zircons, and vary greatly in melt origin depths with the heterogenous Archean lower crust mafic sources. The diorites have the less radiogenic ancient crustal sources. Granodiorites have Paleo- and Mesoarchean and more juvenile Neoarchean sources. The reason of intensive 2.06 Ga magmatism was the astenospheric mantle uplift during the breakdown of pushed oceanic plate due to flat subduction. The plate breakdown and the mafic underplating lead to intracrustal melting in the upper plate consisting of different age Archean and Paleoproterozoic crustal fragments which were joint as a result of previous accretion. Diorite-granodiorite magmas were formed at melting points of different depths in the ancient Archean crust at the periphery of Kursk block with involvement of the Eastern Sarmarian orogen Paleoproterozoic lithosphere fragments into the melting sources.