Plio-Pleistocene fluvial dynamics in the pro-foreland basins of Taiwan: Thermochronological constraints and tectonic implications from the syn-orogenic deposits.

In order to tackle the relationship between the exhumed Taiwan Orogeny and the associated sediment routing systems, new results from zircon fission track (ZFT) dating, calcareous nannofossil biostratigraphy, and the occurrence of the diagnostic magnetic mineral pyrrhotite in modern and ancient syn-orogenic sediments from pro-foreland basins in western Taiwan are reported. The ZFT age spectra of modern river sediments correspond well to the thermochronometric ages of exposed bedrock and indicate a rapidly exhumed source with a young ZFT peak age of 1.7 Myr in central Taiwan, which has not been widely reported. ZFT results from the Pleistocene successions show diachronous deposition of totally-reset zircons from south to north, accompanied by a trend of younging up-section. The progression of these ZFT signals in conjunction with changes in petrography and pyrrhotite occurrence suggest transient developments of sediment routing systems in central Taiwan and the importance of paleo sediment routing systems. In the Dadu River, totally-reset zircons did not appear until 1–0.45 Myr, when the flux of thermally mature material became prominent. The course of the Choshui river migrated during the past 1 Myr and the reorganization of the river reflects activity of frontal thrusts in Pleistocene times. Exhumation rates recorded by detrital sediments of the Choshui River catchment have been consistently higher than those of the Dadu River, suggesting inherited heterogeneity of exhumation in the orogen. • Modern and ancient pro-foreland deposits of Taiwan were subjected to ZFT, calcareous nannofossils, and pyrrhotite studies. • Detrital ZFT spectra revealed reorganization of sediment routing systems in central Taiwan. • ZFT spectra of modern sediments recognize fast exhumed source areas with the young 1.7 Myr peak age. • Differences of exhumation rates suggest heterogeneity of unroofing between catchments. [ABSTRACT FROM AUTHOR]