Topographic architecture and drainage reorganization in Southeast China: Zircon U-Pb chronology and Hf isotope evidence from Taiwan

Abstract

The uplift of Tibet Plateau and the marginal sea spreading have had important influence on the tectonic, landform and drainage system in East Asia, although the marginal sea spreading in shaping the topography and drainage reorganization in East Asia has been still controversial. Here we present U-Pb age and Hf isotopic composition of detrital zircon grains from Cenozoic sedimentary rocks in Taiwan to understand how the provenance and river systems evolved. Our data show that the U-Pb age spectra of detrital zircon grains in Paleogene sandstones are dominated by Yanshanian (180–67Ma) zircon grains and with subordinate or nil Proterozoic and Archean zircon grains. These results are in contrast to those in Miocene rocks that are dominated by the Indosinian (257–205Ma) zircon grains together with Yanshanian, Proterozoic and Archean population. The initial Hf isotope ratios [εHf(t)] of the zircon grains also display systematic change in Paleogene and Neogene strata. Our data demonstrate that the Hsuehshan Range and Western Foothills in Taiwan have the same sedimentary sources. The source region of Paleogene strata was mainly located at the coast in southeast China and migrated inland over time. The source might have reached the Lower Yangtze region during early Miocene. Although the mechanism of transport of sediments from the Lower Yangtze region to Taiwan is unclear, we speculate that the Minjiang River might have been larger in Early Miocene than the present and might have delivered inland material along the boundary of Yangtze and Cathaysia Blocks to Taiwan. These were then captured by the Yangtze River systems at some time after Late Miocene. This change corresponds to the time of the drainage reorganization in East Tibet, such as Yangtze River, and the regional subsidence resulting from the opening of marginal sea. The combined effects of Tibet uplift and opening of marginal sea might have shaped the topography and river system reorganization in East Tibet. The evolution of topography and drainage systems in southeast China seems to be mainly controlled by the opening of marginal sea.