Turbidite record of a middle Neoproterozoic active continental margin in the West Cathaysia terrane, South China: Implications for the relationships between the Yangtze and Cathaysia blocks and their positions in Rodinia.

South China is the largest block of Rodinia in southeastern Asia. It consists of the Yangtze and Cathaysia blocks, separated by the Jiangshan-Shaoxing-Pingxiang Fault. Most studies suggest that the two blocks were amalgamated in the early Neoproterozoic, and the middle Neoproterozoic vocano-sedimentary sequences on both blocks were deposited in a post-collisional rift basin (the Nanhua rift basin). Here, we conducted a geochemical and geochronological study of a turbidite sequence at the western margin of the Cathaysia Block that was previously considered to have been deposited in the Nanhua rift basin. The sedimentary rocks are characterized by bathypelagic to bathyal facies. They are composed of siliciclastic sedimentary rocks interlayered with tuffaceous materials and have geochemical compositions between felsic to intermediate arc igneous rocks. Abundant euhedral detrital zircons define a major age peak at ca. 790–770 Ma, indicating that the detrital grains were derived mostly from locally distributed syn-sedimentary middle Neoproterozoic arc igneous rocks. Predominance of zircons with ages close to the time of deposition and the whole-rock trace element compositions of the turbidite sequence also imply a convergent plate margin setting for the turbidite. The Hf isotopic compositions of the Neoproterozoic detrital zircons suggest that their provenance consisted of largely reworked crustal materials, inconsistent with a potential interpretation that similarly aged igneous rocks in the Jiangnan Orogen were the provenance. These lines of evidence, combined with other available data, suggest that the western margin of the Cathaysia Block (the West Cathaysia terrane) bears more similarities to the western and northern margins of the Yangtze Block and northern India and formed part of a Neoproterozoic subduction-accretion system located along the margin of Rodinia. We suggest that early Paleozoic strike-slip movement along the Jiangshan-Shaoxing-Pingxiang Fault played a significant role in shaping the current tectonic framework of South China by bringing the West Cathaysia terrane to its present position with respect to the Yangtze Block. [ABSTRACT FROM AUTHOR]