2.6 Ga high-Si rhyolites and granites in the Kursk Domain, Eastern Sarmatia: Petrology and application for the Archaean palaeocontinental correlations

Abstract

A 2.61 Ga intraplate magmatism took place locally within the Kursk Domain of the Eastern Sarmatia forming a volcanic-plutonic association of rhyolites and granites. The zircon Lu-Hf and Sm-Nd whole rocks isotope data indicate the crustal source heterogeneity of these Neoarchaean intraplate granitoids. Their protoliths were dominated by Palaeoarchaean metapelites and Mesoarchaean TTG associations.The Neoarchaean rhyolites of the Kursk Domain are characterized by the high crystallization temperatures of c. 900 °C according to the data of mineral geothermobarometry and geochemistry of zircons (TiQ and TiZr). The magmatic chambers were located at a depth of no more than 7 km. The silicic melt, parental for these 2.61 Ga old rhyolites and granites could be formed as a result of 20% dehydration melting of the metapelite-TTG mixture in equilibrium with the Ilm-Bt-Opx-Pl restite at a pressure of no more than 4 kbar. The Atamansky Complex granites crystallized at deeper levels and contain an admixture of Opx-Pl restite or cumulus component. This caused their geochemical differences from rhyolites when these phases were removed during the melts migration to higher levels of the crust. The Atamansky granites are considered as intermediate chambers where differentiation of the initial silicic magmas took place with the formation of the residual rhyolitic melts.The heat source could be a mafic plume magmatism, known in the Eastern Sarmatia. There, in intraplate settings, hot deep plume generated mafic magmas intruded into the crust forming shallow interim chambers; the latter initiated melting of the felsic host-rocks (predominantly metapelites and TTG) in the upper parts of the crust producing the silicic volcanic-plutonic association.The simultaneous 2.61 Ga old granitoid intraplate magmatism in the Eastern Sarmatia and Dharwar Craton, caused by the mafic heat source, adds one more argument in favor of an assumption that the Sarmatia, Pilbara, Kaapvaal and, possibly, Dharwar Cratons composed a single supercontinent Vaalbara in the Neoarchaean. The Dharwar Craton, perhaps, was at the periphery of the Vaalbara supercontinent next to the Eastern Sarmatia.