SOUTH CHINA IN RODINIA REVISITED

South China may hold some key clues for understanding the assembly and break-up of Rodinia. On the assembly and configuration of Rodinia, recent work confirm the existence of ca. 1430 Ma granitoids and 1300-1000 Ma amphibolite-facies metamorphism in the Hainan Island, at the southwestern end of Cathaysia. The presence in southern Yangtze craton of ca. 1000 Ma granitoids, and similar-aged clastic rocks likely sourced from Cathaysia, suggest that the collision between Cathaysia and Yangtze likely peaked at ca. 1000 Ma in western Sibao Orogen. However, the presence of ca. 970 Ma adakitic granites along southeastern Yangtze craton indicates that subduction was still on-going at that time, and 900 Ma arc volcanism on both northern and southeastern margins of the Yangtze Craton could represent the youngest rocks formed during the continental collision/accretion. Further considering that the Neoproterozoic rift history of South China is almost identical to that of eastern Australia, South China is geologically plausible to be between southern Laurentia and eastern Australia in Rodinia. If this was the case, it would imply that major segments of Rodinia did not come together until after 1000 Ma, and possibly as young as ca. 900 Ma. This could explain some geological mismatches in various Australia-East Antarctica-Laurentia fits. However, other configurations are also feasible, such as having South China adjacent to India and western Australia. Currently available paleomagnetic data permit both configurations.

On the break-up of Rodinia, recent work identified largely coeval anorogenic magmatism in central and western Rodinia that spread over 100 My but fall mostly within two major episodes: one at ca. 830-795 Ma, and the other at ca. 780-745 Ma. Both episodes have mafic rocks of mantle plume origin (e.g., in western Laurentia, South China, Australia and southern Africa), and the pre-rift start of the first episode argues against the possibility of them being decompressional melt of a stretched and thinned continental lithosphere. It has thus been proposed that there was a mantle superplume beneath Rodinia which caused anatectic magmatism from at least ca. 830 Ma, and continental rifting from ca. 820 Ma within the supercontinent. This eventually led to the break-up of Rodinia at around the time of the Sturtian glaciation.