MULTISCALE RETRODEFORMABLE TRANSECT OF THE ACTIVE TAIWAN ARC-CONTINENT COLLISION: STRATEGIES AND RESULTS

We have developed a multiscale transect of the active ~90mm/y Taiwan arc-continent collision encompassing both the deforming Eurasian and Philippine-Sea plates and extending from the surface to the base of the subducted Eurasian slab at ~500km to provide a data-rich framework for studies of this classic collisional mountain belt. In this presentation we highlight the strategies that we have applied and the results obtained by data integration in [i] the upper crust and in [ii] the deep subducting continent-ocean transition. We integrated and interpreted multiscale geophysical and geological data in 2D and 3D using the Gocad environment, including high-quality regional and local tomographies (Vp, Vs, Vp/Vs, dVp, dVs), wide-angle refraction data, multichannel seismic reflection data, surface structural and stratigraphic data, well data, and abundant well-located seismicity to understand the structure of Taiwan arc-continent collision from surface to Moho. We applied advanced balancing techniques, aided by StructureSolver software, to test and iteratively refine interpretations of the deformed upper crust of the Eurasian continental margin and accreted Luzon Arc and to restore the subducting Eurasian lithosphere. Our strategy in the upper crust makes use of a widespread velocity inversion at ~10km depth marking the main Eurasian subduction interface. This interface is at the base of the higher velocity deformed and metamorphosed Eurasian continental shelf, slope and rise sediments. Below this interface are subducting Paleogene rift basins and lower crust that are interpreted using tomographic velocities and reactivated faults illuminated by seismicity. Above the main detachment we made detailed use of surface structural and stratigraphic data using advanced balancing techniques and StructureSolver software to predict the downward continuation of major faults, which were successfully integrated with tomographic images and abundant seismicity illuminating active faults. Under eastern Taiwan the Eurasian subduction interface dives abruptly downward and the middle and lower crust thins marking the subducted edge of the continent, followed by a transition to a 10-15km thick layer with velocities Vp>8.0km/s, interpreted as eclogite within mafic rocks near the base of the former continental slope.