Zircon U-Pb and Hf isotopic study of Mesozoic felsic rocks from eastern Zhejiang, South China: Geochemical contrast between the Yangtze and Cathaysia blocks

Abstract

The Jiangshan-Shaoxing Fault Zone (JSFZ) in Zhejiang Province has been proposed to represent a suture between the Yangtze and Cathaysia blocks in South China. In this study, in-situ zircon U-Pb and Hf isotopic analysis and whole-rock major- and trace-element measurement of early to middle Cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone. Twelve Cretaceous granitoid bodies were sampled from the NW and SE sides of the fault zone, respectively, with composition ranging from diorite to granite (SiO2=56.2-76.6wt.%). These granitoids yielded U-Pb ages ranging from 135-100Ma, with a systematic variation in zircon Hf isotopic compositions (εHf(t)=+6.9 to -7.0 in the NW side vs. +1.9 to -12.9 in the SE side). The TDM2 values for the granitoids from the NW side are 0.34 to 1.33Ga, with two peaks at ca. 876 and 1170Ma respectively, whereas those from the SE side are 0.70 to 1.62Ga, with a single peak at ca. 1126Ma. The Hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the Yangtze and Cathaysia blocks, supporting that the JSFZ is possibly a suture zone between the two blocks. Our results together with the available geological data suggest that the Mesoproterozoic materials are important for both the Yangtze and Cathaysia basement and the Neoproterozoic magmatic activities were important in the Yangtze Block, possibly related to the break-up of the Rodinia supercontinent, but less significant in the Cathaysia Block. This may imply that the two blocks have not completely juxtaposed in the Neoproterozoic. © 2010 International Association for Gondwana Research.