Petrogenesis of keratophyes in the Pingshui Group, Zhejiang: Constraints from zircon U-Pb ages and Hf isotopes

Zircon LA-ICP-MS U-Pb ages and Hf isotopic as well as whole-rock geochemical data are reported for keratophyes in the Pingshui Group, Zhejiang. The results are used to discuss their petrogenesis and geological significance. The keratophyes were dated at 904±8 to 906±10 Ma. These intermediate-felsic rocks are characterized by high LREE contents and depletion of HREE and HFSE (e.g., Nb, Ta, Ti, P), resembling arc-derived rocks. The keratophyes exhibit positive ε_Hf(t) values of 8.6 to 15.4, consistent with their ε_Nd(t) values of 6.4 to 7.9 but far away from those of crust-derived rocks. Such features indicate that they were likely originated from prompt reworking of juvenile crust by arc-continent collision during the early-Neoproterozoic assembly between the Cathaysia and Yangtze Blocks. Combining with their Hf model ages, we suggest that there may exist not only remarkable growth of juvenile crust at ca.1.3—1.1 Ga but also production of juvenile arc-derived crust along the southeastern margin of the Yangtze Block (e.g., the Pingshui area) at ca.1.0–0.9 Ga. Supported by China Geological Survey (Grant No. 1212010610611) and the Ministry of Land and Resources (Grant No. 200811015)