[S-IT20] New perspectives on accretion and exhumation processes during oblique plate convergence

[SIT20-10] Out of Sequence Faulting in Backbone Range and its Implication to Exhumation Process of the Taiwan Orogen

*Yuan Hsi Lee¹, Timothy B Byrne², Wei Lo³, Shao-Jyun Wang⁴, Shuh-Jong Tsao⁵, Cheng-Hong Chen⁶ (1.National Chung Cheng University, 2.Center for Integrative Geosciences, University of Connecticut, Storrs, Connecticut, USA, 3.Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taiwan, 4.Department of Earth and Environmental Sciences, National Chung Cheng University, Taiwan, 5.Central Geological Survey, MOEA, Taiwan, 6.Department of Geosciences, National Taiwan University, Taiwan)

Keywords:Taiwan orogen, Out-of-sequence-thrust, exhumation process

The Taiwan orogenic belt results from convergence between the Philippine Sea plate and Eurasia plate since the late Cenozoic. An extremely high exhumation rate has been observed in the Backbone, which has motivated interpretive models that show underplating as the primary process in driving uplift and thickening. Here we integrate new U-Th/He and fission-track dates of detrital zircons with previously published thermochronology to document a significant out-of-sequence thrust (OOST) fault in the core of Taiwan orogen. The OOST, informally named the Tayulin fault system, is identified by structural kinematics and offset metamorphic temperature trends, low-temperature thermochronometric dates, and seismic tomography. The OOST appears to be composed of three segments that crop out along the western flank of the Central Range. Vertical apparent age-elevation profiles from the hanging wall suggest a nearly constant rate of exhumation of 2-5 mm/yr from about 2 Ma. The OOST also can be identify by seismic tomography. The temporal correlation between slip on the OOST and rapid exhumation in the Backbone Ranger(i.e., the hanging wall) suggests that the OOST also played an important role in the exhumation of the Taiwan orogen.