Petrogenesis of Jurassic granitic rocks in South China Block: Implications for events related to subduction of Paleo-Pacific plate

Abstract

Frequent magmatic intrusion and eruption during the early Yanshanian in South China formed a unique and diverse igneous rock assemblage, mainly comprising granite, rhyolite, and some basic rocks. Nevertheless, the tectonic regime responsible for the formation of these granitic rocks remains controversial. The comprehensive available data suggest that the Jurassic granitic rocks formed during the period from 180 to 145 Ma, with an age peak at ca. 160 Ma. Jurassic rocks are predominantly concentrated in Wuyi, southern Hunan, northeast Guangdong, and southern Jiangxi, followed by the eastern Guangxi-western Guangdong areas, mainly including I-, S-, and A-type granites, and a few I–S transformation-type granites. These granitic rocks invariably exhibit enrichment in Rb, Th, U, and Pb, while Ba, Nb, Sr, P, and Ti are depleted, and variable Eu/Eu* ratios. The whole-rock Sr–Nd isotopic and zircon Hf isotopic compositions show that the Jurassic granitic rocks are mainly recirculation products of Paleo-Mesoproterozoic rocks, as well as the mantle-derived magma, which played a major role in the formation process. Among them, the granites in eastern Guangxi-western Guangdong and Northeast Guangdong areas display higher ε Nd(t) and ε Hf(t) values, suggesting a relatively larger contribution from mantle-derived materials. Based on the comprehensive regional geological data, we interpret that these Jurassic granitic rocks as a product of lithosphere extensional-thinning, tectonic-magmatic interaction formed during the process of flat-slab subduction.