Retro-Foredeep Basin Evolution in Taiwan: Zircon U-Pb and Hf Isotope Constraints From the Coastal Range

The evolution of the Taiwan orogen, an active arc–continent collision zone between the North Luzon Arc (NLA) and the Eurasian continent, is recorded in arc volcanic and sedimentary rocks from the Taiyuan retro-foredeep basin of the Coastal Range, eastern Taiwan. Arc volcanism in the northern NLA experienced a magmatic culmination at 9–7 Ma and a cessation at 5.3–4.3 Ma, based on new U-Pb zircon ages. Young zircon U-Pb ages (1.74, 1.58, and <1.2 Ma) and low Hf isotope signatures also indicate that three biotite-bearing lapilli tuff layers deposited in the retro-foredeep basin are associated with eruptions of the Lutao volcano in the southern NLA. NLA volcanism terminated progressively from ∼5.3 to <1.2 Ma in response to a southward-propagating collision zone that followed the uplift of the orogenic wedge by <3 myr. The detrital zircon U-Pb age spectra suggest no significant shift in provenance during the Plio-Pleistocene period and indicate that the synorogenic sediments in the Taiyuan Basin were mainly derived from the Yuli Belt, a Miocene accretionary complex in the eastern Taiwan orogen. The accumulation rate of synorogenic deposits varies from 0.53 to 5.14 km/myr, with an abrupt increase at ∼2 Ma. This new rate is higher than the previously proposed rates and that of the pro-foreland basin to the west, suggesting asymmetric and rapid uplift of the Taiwan orogen.