Crustal structure of the pre-collision passive margin from seismic reflection imaging offshore southwest Taiwan

New multi-channel seismic reflection data collected offshore Taiwan as part of the 2009 TAIGER project provide images of the crustal structure of the southern Chinese continental margin in its pre-collision state. Although geodynamic models indicate surfacial, crustal, and upper mantle processes involved in the Taiwan arc-continent collision are all influenced by the behavior of the impinging continental crust, these models lack any real constraints on the buoyancy and rheology of upper and lower continental crust. Knowledge of the thickness, geometry, and density structure of the southern Chinese margin is then necessary to determine if, and to what extent, subduction of continental crust may occur in the Taiwan arc-continent collision. Preliminary processing and analysis of the new multi-channel seismic reflection data have been performed to image the southern Chinese margin before it enters the collision. These images show ~4 seconds of passive margin sediments overlying ~6 seconds of continental crust at the Chinese continental shelf, as well as strong mid-crustal reflectors arriving at ~5-8 seconds and reflections from Moho arriving at ~11-12 seconds. Away from the continental shelf, the crust thins to a two-way time thickness of ~3 seconds, while the Moho reflection rises to 9 seconds over a ~250 km transition zone. Normal faults are also observed to penetrate deep into the crust, in some places potentially as deep as the Moho. Integration of these images with gravity and OBS data also acquired as part of the TAIGER project will provide further constraints on key parameters governing the behavior of continental crust in arc-continent collision.