Sr‐Nd‐Hf‐O isotope geochemistry of the Ertaibei pluton, East Junggar, NWChina: Implications for development of a crustal‐scale granitoid pluton and crustal growth

Abstract

AbstractTo better understand the compositional diversity of plutonic complexes and crustal growth of the Central Asian Orogenic Belt (CAOB), we conducted an integrated study of the Ertaibei pluton, which obtained geochronological, petrological, geochemical, and isotopic (including whole rock Sr‐Nd, in situ zircon Hf‐O) data. The pluton (ca. 300 Ma) is composed of granodiorites that contain mafic microgranular enclaves (MMEs), dolerite dikes, and granite dikes containing quartz‐tourmaline orbicules. The dolerite dikes were possibly generated by melting of an asthenospheric mantle source, with discrete assimilation of lower crustal components in the MASH (melting, assimilation, storage, and homogenization) zone. The MMEs originated from hybridization between mantle and crust‐derived magmas, which spanned a range of melting depths (∼25–30 km) in the MASH zone and were episodically tapped. Melting of the basaltic lower crust in the core of the MASH zone generated magmas to form the granodiorites. The granite dikes originated from melting of an arc‐derived volcanogenic sedimentary source with a minor underplated basaltic source in the roof of the MASH zone (∼25 km). The compositional diversity reflects both the magma sources and the degree of maturation of the MASH zone. Although having mantle‐like radiogenic isotope compositions, the Ertaibei and other postcollisional granitoids show high zircon δ18O values (mostly between +6 and +9‰), indicating a negligible contribution to the CAOB crustal growth during the postcollisional period.