Geochemistry and Geochronology of OIB‐type Early Jurassic Magmatism in the Zhangguangcai Range, NE China, as a Result of Continental Back‐arc Extension

Abstract

AbstractThe Zhangguangcai Range in the Xing'an(Hinggan) Mongolian Orogenic Belt, NE China, contains Early Jurassic (c. 188 Ma) Dabaizigou (DBZG) porphyritic dolerite. Compared with other island‐arc mafic rocks, the DBZG dolerite is characterized by high trace‐element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB‐type rocks. Analysed rocks have (87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive ∊Nd(t) values of 2.3–3.2 and positive ∊Hf(t) values of 8.5–17.1. Trace‐element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet‐to spinel‐facies conditions. The occurrence of OIB‐like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back‐arc environment in the upper plate of a palaeo‐Pacific slab subducting W–NW beneath East Asia.