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 similar to 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 similar to 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. Plain Language Summary Taiwan was formed by the northwestward convergence of the North Luzon Arc (NLA) with the Eurasian continental margin. Most of the uppermost parts of the arc volcanoes and orogens have been intensely eroded; nevertheless, their detritus is well preserved in the Taiyuan Basin in the southern Coastal Range, eastern Taiwan. In this study, zircons separated from remnant arc volcanic and sedimentary sequences are dated by an in situ U-Pb method to offer temporal constraints and provide insight into the arc-continental collision evolution in Taiwan. The latest ages from the NLA volcanoes reveal a southward cessation of magmatism from similar to 5.3 to <1.2 Ma, which is consistent with an oblique collision. Detritus from the Yuli Belt, a Miocene accretionary prism in the eastern Taiwan orogen, started to fill the Taiyuan Basin beginning at <4.3 Ma. Meanwhile, three embedded tuff layers dated at 1.74, 1.58, and <1.2 Ma indicate eruptions associated with Lutao, an offshore NLA volcanic islet, and suggest an abrupt increase in the deposition rate at similar to 2 Ma, corresponding to rapid and extensive exhumation of the Taiwan orogen.