Caledonian reworking of Paleoproterozoic basement in the Cathaysia Block: Constraints from zircon U-Pb dating,Hf isotopes and trace elements

A combined study of zircon U-Pb dating, Hf isotopes and trace elements has been carried out for granodioritic neosomes of migmatites from the Tianjingping area in northwestern Fujian Province. Zircons are characterized by zoning, higher Th/U ratios (mostly ⩾0.1), HREE enrichment, and positive Ce and negative Eu anomalies, and show features similar to magmatic or anatectic zircons. Apparent ²⁰⁶Pb/²³⁸U ages for the zircons are 447±2 Ma (95% conf., MSWD = 0.88), corresponding to a Caledonian event. ε_Hf(t) values are −13.3 to −9.7, indicating a crustal source. Two-stage Hf model ages are 1.7 to 1.9 Ga, suggesting that protolith of the migmates was probably formed in the Paleoproterozoic. The granodioritic neosomes have the characteristics of peraluminous calc-alkaline granite, and their REE patterns and trace elements spidergrams show features of middle to upper crustal rocks. Together with previous studies, we conclude that the protolith of the Cathaysia basement in the Tianjingping area was likely formed in the middle-late Paleoproterozoic and experienced partial melting during the Caledonian period. The recognition of Caledonian reworking of the Paleoproterozoic basement in the Cathaysia Block provides a new insight into the tectonic evolution of the Cathaysia Block in the Caledonian period and the interaction between the Cathaysia Block and the Yangtze Block. Supported by the National Natural Science Foundation of China (Grant No. 40372094), the Opening Foundation of State Key Laboratory of Continental Dynamics, Northwest University (Grant No. 06LCD12) and the project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)