U–Pb and Hf isotopic study of detrital zircons from the meta-sedimentary rocks in central Jiangxi Province, South China: Implications for the Neoproterozoic tectonic evolution of South China Block

Abstract

The Zhoutan Group, made of meta-sedimentary rocks and mafic volcanic, outcrops at the western margin of the Cathaysia Block. These rocks have been previously considered to represent a Mesoproterozoic sequence. However, this study shows that the ages of detrital zircons from the garnet–mica schists of this group are predominantly Neoproterozoic (1.0–0.82 Ga), and the youngest detrital zircon grains clearly constrain that the maximum depositional age of the meta-sedimentary sequence (i.e. the Zhoutan Group) is ca. 826 Ma. Subordinate detrital zircons give Paleo- to Mesoproterozoic (1.9–1.4 Ga) ages and minor zircons yield Neoarchaean (∼2.5 Ga) ages. Because 1.0–0.82 Ga old rocks are common at the southeastern margin of the Yangtze Block, while the 1.9–1.4 Ga rocks occur in the northwestern Fujian and southeastern Zhejiang Provinces, Cathaysia Block, our data suggest that these Neoproterozoic sediments may be derived both from the Yangtze Block and the Cathaysia Block. We proposed that these sediments deposited in a small remnant ocean between the passive margin of the Cathaysia Block and the active margin of the Yangtze Block, thus the timing of the final assembly between the Yangtze and the Cathaysia Block was after 826 Ma. Paleoproterozoic detrital zircons mostly have negative ε Hf values, suggesting that much of the Paleoproterozoic crust in South China came from reworked Archean crust. Detrital zircons with oscillatory growth zoning in the 1.0–0.82 Ga age population have approximately the same proportion of positive and negative ε Hf values ranging from +17.8 to −27.3. This favors the growth of a significant volume of juvenile crust in the Neoproterozoic time in South China, possibly caused by the subduction before the assembly between the Yangtze and the Cathaysia Block.