Early Jurassic A-type granitoids in the Xing'an block constrain on the spatial extent of the Paleo-Pacific tectonic regime

Abstract

Northeast (NE) China underwent complex tectonic processes during the early Mesozoic era, influenced by both the Paleo-Pacific and Mongol-Okhotsk tectonic regimes. However, the dominant factor responsible for the early Jurassic magmatism in the Xing'an block, whether it was the Mongol-Okhotsk or the Paleo-Pacific tectonic regime, remains uncertain. This study aims to investigate the geochemical characteristics, petrogenesis, and geodynamic implications of the early Jurassic A-type granitoids in Heihe, Xing'an block, in order to shed light on the evolution and spatial extent of the Paleo-Pacific tectonic regime. The Heihe A-type granitoids were formed by partial melting of calc-alkaline meta-andesite/basalt under high-temperature and low-pressure conditions. During the later stages of magma evolution, fractional crystallization of K-feldspar played a significant role. The geochemical characteristics of the Heihe A-type granitoids resemble both A1-type and intraplate granite, similar to the early Jurassic A-type granites in the Songnen block. The Xing'an block, at least its southeastern margin, was mainly overprinted by the subduction of the Paleo-Pacific oceanic plate during the early Jurassic. This is evidenced by the north-south distribution pattern and the decreasing zirconium saturation temperature from east to west of the early Jurassic igneous rocks in the Xing'an block. The occurrence of early Jurassic various types of A-type granitoids and coeval OIB mafic rocks in NE China could be attributed to the back-arc extension and asthenosphere upwelling triggered by the Paleo-Pacific slab rollback.