Geochemical evolution of the Late Carboniferous to Early Permian igneous rocks from the Baolidao magmatic belt, eastern Central Asian Orogenic Belt

Abstract

The Late Palaeozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB) and the genesis of magmatic rocks in the terrane have been topics of debate for decades. We have tried to understand the processes involved in the evolution of the Late Palaeozoic Baolidao belt and magma generation by compiling data from more than 200 samples along with new age estimates and geochemical data. Spinel stability field melting of the subduction hydrated juvenile depleted mantle (DM) is the dominant mafic magma generating process. The crustal granitoids from the Late Carboniferous suite (320 ~ 300 Ma) and the Early Permian suite (300 ~ 280 Ma) have contrasting characteristics. The Late Carboniferous suite is characterized by lower crustal AFC process at hornblende-dominated and plagioclase-free pressure, which resulted in considerable growth of continental crust, while the Early Permian suite is characterized by low pressure partial melting (plagioclase stable in residue) of a thinned juvenile crust. The process of the extension of hydrous mantle coupled with crustal thinning from the Late Carboniferous to Early Permian can be used to explain the chemical and petrogenetic features of the Late Palaeozoic magmatism along the Baolidao belt. We propose that lithosphere-scale extension should have been a key process in the tectonic evolution of the eastern CAOB during the Late Palaeozoic. Show more