Precambrian crustal evolution of the Yangtze Block tracked by detrital zircons from Neoproterozoic sedimentary rocks

Integrated U–Pb dating, Hf-isotope and trace-element analysis of detrital zircons from the Fanjingshan and Xiajiang sediments in the southeastern part of the Yangtze Block has been used to identify ancient crustal remnants and the provenance of clastic sediments, and to provide an overview of crustal evolution in the now-covered parts of the Yangtze Block. The zircon dating indicates that the Fanjingshan Group, which previously was regarded as 870 Ma old, actually was deposited in a ∼800 Ma rift basin similar to other contemporaneous basins in the Yangtze Block; the regional unconformity separating the Fanjingshan Group from the overlying Xiajing Group is dated to 800–740 Ma. Differences in clast compositions and the trace-element and Hf-isotope signatures of zircons between the Fanjingshan Group and the Xiajiang Group suggest changes in the source areas within the Yangtze Block. The combined ages and Hf-isotope data for each group show different histories of crustal evolution in their source areas. In the Yangtze Block, a previously unrecognized source (∼4.3 Ga) is suggested by the Hf model ages of the oldest zircons. Both recycling of ancient crustal materials and minor addition of juvenile material took place in the time intervals 2.5–2.4 Ga, 2.0–1.7 Ga and 0.85–0.8 Ga. The most important generation of juvenile crust appears to have occurred at 1.6–1.4 Ga in the source area of the Fanjingshan Group, and at 0.95–0.85 Ga and 0.78–0.74 Ga in the source area of the Xiajiang Group. This is the first documentation of early Mesoproterozoic (1.6–1.4 Ga) juvenile crust in South China.