Geochemistry Results of Clastic Rocks from the Late Carboniferous Cameng Formation, South Qiangtang, Tibet: Preliminary Constraints for Provenance, Weathering and Tectonic Setting.

Tectonic setting of the Late Carboniferous Cameng Formation in the north of South Qiangtang terranes (SQT) remains controversial. Here, we report new geochemical results for clastic rocks from the Cameng Formation. Our results show that the Index of Compositional Variability (ICV) is greater than 1, indicating these sediments experienced limited recycling and were probably derived from acid to intermediate magmatic rocks. The extent of weathering, with the Index of CIA vary from 67 to 75 (mean = 71), ICV > 1 (mean = 1.25) and the Th/U ratios > 4, is moderate in the source area. These new findings show that the Cameng Formation was most likely deposited in an unstable environment (continental island arc or active continental margin). Combined with other evidence, we further infer that the Early Paleozoic rocks (²⁰⁶Pb/²³⁸U ages varying from 438 to 502 Ma) presently exposed in the South Qiangtang terrane are the potential source of the Late Carboniferous depositions in the northern SQT, and were most likely deposited in a forearc basin under the in situ suture model, that is, the southward subduction of the Longmu Co-Shuanghu Tethys Ocean beneath the SQT. [ABSTRACT FROM AUTHOR]