Zircon U–Pb geochronology and Hf isotopic compositions of the Mesozoic granites in southern Anhui Province, China

Abstract

Mesozoic magmatism is extensively developed in eastern China along the eastern Asian continental margin, but the geochronological framework is not well understood for each area. In this study, seventy-eight samples were collected from the Mesozoic igneous rocks in south Anhui Province, east-central China, in order to precisely constrain their formation ages and contributions to crustal growth. Zircon U–Pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages: at 150–136 and 136–120Ma, respectively. The first stage of granitic rocks, not documented in other areas of eastern China, is mostly composed of hornblende-bearing I-type granodiorite and monzogranite, and is considered to be formed by slab-tearing during Pacific subduction. The second stage of magmatism, coeval to that in other areas of eastern China, is characterized by the occurrence of A-type granite and syenite, and their volcanic counterparts, although I-type granitic rocks are also developed locally. These rocks are mostly distributed around and within the fault-controlled volcanic basins, and some are closely related to detachment shearing, indicating their formation in an extensional setting. Zircon Hf isotopic analyses indicate that Archean material might be present in the area, but that the main episode of crustal growth took place during the Mesoproterozoic, with very little juvenile material in the Mesozoic.