TURBIDITE RECORD OF A NEOPROTEROZOIC ACTIVE CONTINENTAL MARGIN IN THE WESTERN CATHAYSIA BLOCK, SOUTH CHINA: IMPLICATIONS FOR THE RELATIONSHIPS BETWEEN THE YANGTZE AND CATHYSIA BLOCKS AND THEIR POSITIONS IN RODINIA

South China consists of the Yangtze and Cathaysia blocks and is the largest block of Rodinia in southeastern Asia. The boundary between the two blocks is considered to be the Jiangshan-Shaoxing-Pingxiang Fault Zone. Although most studies suggested that the two blocks were amalgamated in the early Neoproterozoic and underwent regional extension afterwards, the completely different sedimentary successions and source characteristics from Cryogenian to early Paleozoic implis that they were unlikely to develop in the same rift basin. We carried out a geochemical and geochronological study of a turbidite sequence at the western margin of the Cathaysia Block which was previously considered as being 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. The overwhelming populations of 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 Neoproterozoic arc igneous rocks. Furthermore, a predominance of zircons with ages close to the time of deposition and the whole rock trace element compositions of the turbidite sequence imply a convergent plate margin setting for the turbidite. The Hf isotopic compositions of the Neoproterozoic detrital zircons suggest their provenance consist of largely reworked crustal materials, in consistent with a potential interpretation that similarly-aged igneous rocks in the Jiangnan Orogen are the provenance. These lines of evidence suggest that the western margin of the Cathaysia Block bears more similarities with the western and northern margin of the Yangtze Block and both of them were part of the same subduction-accretion system in the Neoproterozoic that was located along the margin of Rodinia. We suggest that the early Paleozoic strike-slip movement along the Jiangshan-Shaoxing-Chenzhou fault zone played a significant role in shaping up the current framework of South China by bringing the Cathaysia Block to its present position with respect to the Yangtze Block.