Professor Yi Yan Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry Chinese Academy of Sciences
Uplift of Tibet Plateau, as eastern Asia reversed its regional tilt from westward to eastward is at the centre of debates over how tectonic forces can influence topography, regional drainage pattern and Asian monsoonal climate. However the growth of eastern Tibet Plateau and drainage patterns which are sensitive to changes in the regional gradient are still debated and how tectonic, climate and river drainage processes have interacted in this part of the world during the latter part of the Cenozoic are unclear at present.
As one of the biggest marginal sea in East Asia the spreading history of the South China Sea mainly determined from magnetic anomaly lineaments is still disputed. During transition from rifting to seafloor spreading, a breakup-unconformity often develops on rifted margins adjacent to the new oceanic crust. SHRIMP U-Pb dating of zircon from the Pinglin Tuff in Taiwan indicates the breakup-unconformity formed before 39 Ma, which may indicate that seafloor spreading had started in South China Sea by that time. Most of this old oceanic crust may have been subducted eastward beneath the Philippine Sea Plate since Late Miocene. The diachronism of breakup-unconformities and the transition of provenance in the surrounding rift basins on the northern periphery of South China Sea is consistent with a propagation of seafloor spreading from east to west.
Initial uplift of eastern Tibet and significant river reorganization have been thought occurred at around 25 Myr closely linked to the formation of the Yangtze River system. However sediments from the Yangtze River Delta and geomorphologic studies in the Three Gorges even support a more recent initiation of the Yangtze River younger than 5 Myr. We reconstruct the river drainage evolution over 25 million years using marine sedimentary record from the South China Sea. Our study shows that the river system experienced two major reorganization events. One occurred after ca.25 Myr that the Yangtze River or Pearl River expanded westward and captured parts of the Paleo-Red River. The second one occurred after ca.11 Ma that the headwaters of the Pearl and Minjiang Rivers lost to the south-westward expansion of the Yangtze River.
We propose that the river drainage reorganization reflect the protracted and episodic growth of eastern Tibet, evolution of East Asia marginal seas and Asian monsoonal climate.