CLIMATE MODULATED EROSION AND SEDIMENT FLUX CONTROL OFFSHORE CRUSTAL STRUCTURE AT SOUTH CHINA SEA CONTINENTAL MARGIN

Rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling. Rifting on passive margins is not always just an extreme version of intra-continental extentsion. Basins on some continental margins experience anomalous subsidence events that postdate active extension. Deep basins on the northern margin of the South China Sea, notably the Baiyun Sag, show basement subsidence accelerating after ~21 Ma, postdating extension by several million years. Similar subsidence events are seen after 5 Ma in the Song Hong-Yinggehai Basin and after 11 Ma in the Qiongdongnan Basin. We combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following Early Miocene monsoon intensification is a viable trigger for ductile flow towards the continent after the cessation of active extension. Flow towards the rift during break-up has been recognized in several hot rift systems. Loading works in conjunction with onshore uplift to drive flow of the lower crust away from the rift axis. As well as sediment supply rates distribution patterns and drainage capture can be significant in controlling crustal flow and thinning. This illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate-tectonic coupling.