Geochemical and zircon U-Pb-Hf-O isotopic evidence for a coherent Paleoproterozoic basement beneath the Yangtze Block, South China

The early history of the Yangtze Block is not well constrained owing to the scarce outcrops of the Archean to Paleoproterozoic rocks. Here, we report an integrated study of zircon U-Pb and Hf-O isotopes, as well as whole rock major and trace elements and Nd isotopes for the orthogneisses of the Dongling Complex in the eastern Yangtze Block. LA-ICP-MS zircon U-Pb dating yields a Pb-207/Pb-206 age of ca. 1.85 Ga for the protolith age of the orthogneiss, revealing a reliable Paleoproterozoic basement in the eastern Yangtze Block. Zircons from the orthogneiss have epsilon(Hf)(t) values ranging from -13.4 to -9.0, corresponding to T-DM2(hf) model ages of 3.03-2.80 Ga. The zircon delta O-18 values range between 6.5 parts per thousand and 8.8 parts per thousand with an average of 7.8 parts per thousand. In addition, the whole rock epsilon(Nd)(t) values of the orthogneisses range from -9.3 to -8.0 and T-DM2(Nd) model ages from 2.98 Ga to 3.05 Ga. The orthogneisses have relatively high SiO2, K2O + Na2O, Rb, Ga, Zr, Nb, Y and Ce contents and show low CaO, Eu, Ba and Sr concentrations. Their 10,000*Ga/Al ratios range between 3.0 and 3.5. All these geochemical and Nd-Hf-O isotopic signatures suggest A-type granite protolith for orthogneisses in the Dongling Complex. They were generated by partial melting of Archean crustal materials in a post-collisional tectonic setting. When our data is combined with the existing geochronological data in other parts of the Yangtze Block, it demonstrates a coherent Paleoproterozoic basement beneath the Yangtze Block, representing an important part of the Columbia supercontinent. The ca. 1.85 Ga A-type magmatism may have led to craton stabilization over all of the Yangtze Block. In addition, a potential Precambrian dual basement structure may exist in the eastern Yangtze Block, which is supported by Paleoproterozoic metamorphic basement and overlaying Neoproterozoic sedimentary cover. (C) 2016 Elsevier B.V. All rights reserved.