Petrogenesis of Late Carboniferous to Early Permian Granitoid Plutons in the Chinese South Tianshan:Implications for Crustal Accretion

Abstract

A large volume of granitoid plutons formed in the South Tianshan orogenic belt during Late Carboniferous to Early Permian.These rocks can be generally classified as Late Carboniferous I-type granites,Early Permian I and S-type granites,and A-type granites that formed at ~275 Ma.The different rocks have some differences in features of source regions and temperature and pressure conditions under which magma evolves,which reflect the development process of tectonic environment during that period.In this paper,seven granitoid plutons in the Chinese South Tianshan orogenic belt,including Tielieke pluton,Mangqisu pluton,Yingmailai pluton,Chuanwulu pluton,Baleigong pluton,Huoshibulake pluton and Mazhashan pluton,were chosen for geochronological,petrological,and geochemical investigations.The Tielieke and Mangqisu plutons are Late Carboniferous I-type granites and the magmas formed due to partial melting of the metaigneous rocks in the lower crust under the condition of the syn-collisional tectonics.The Early Permian S-type granite is represented by the Yingmailai pluton,which was the result of remelting of Mesoproterozoic metasedimentary rocks induced by the radiogenic heating.Felsic rocks in the Chuanwulu pluton are Early Permian I-type granites,representing the hybrid magmas derived from the lower part of the thickened continental crust.The mafic rocks in the Chuanwulu pluton represent underplating mantle-derived magma resulted from partial melting of enrichment metasomatized lithospheric mantle.The Yingmailai and Chuanwulu plutons formed in a transition stage of tectonic regimes from syn-collisional compression to post-collisional extension.A-type granites forming at ~275 Ma represents a high temperature granitic magma,which resulted from the interaction between asthenosphere and lower crust under a condition of low pressures.The Baleigong pluton is A2-type granite representing the epilogue of the post-collisional setting.The Huoshibulake and Mazhashan plutons,however,are A1-type granite indicative of intra-plate rifting regime.