HR: 0800h
AN: T11B-0371    [Abstracts]
TI: Oblique Northeastward Lateral Extrusion of a Crustal Block in North-central Taiwan: a Mechanism for Syn-tectonic Extension
AU: * Gourley, J R
EM: jonathan.gourley@uconn.edu
AF: Center for Integrated Geosciences, University of Connecticut, 354 Mansfield Road U-2045, Storrs, CT 06269 United States
AU: Byrne, T
EM: tim.byrne@uconn.edu
AF: Center for Integrated Geosciences, University of Connecticut, 354 Mansfield Road U-2045, Storrs, CT 06269 United States
AB: An integrated data set of earthquake locations (Taiwan's Central Weather Bureau), focal mechanisms from the Broadband Array of Taiwan Seismicity (BATS), GPS velocities and geologic data are combined to constrain the geometry and kinematics of a crustal block within the metamorphic basement of Taiwan's northeastern Central Range. The active block is bounded by two parallel seismic zones that accommodate uplift and northeastward oblique lateral extrusion. The western shear zone is a region that dips vertically to steeply west and projects generally to the western boundary between the Slate Belt and pre-Tertiary metamorphic basement. BATS focal mechanisms consistently show east-side-up, left-lateral normal displacements. Late-stage geologic structures published previously show left-lateral faulting followed by east-west extension. The eastern shear zone dips vertically to steeply west and projects to the eastern boundary of the metamorphic basement, which correlates with the eastern mountain front in this area. BATS focal mechanisms show west-side-up reverse displacements. The kinematics of these two zones define a crustal scale block that is interpreted to be moving up and northeast towards the Okinawa Trough. The extrusion of this crustal block may be driven in part by the topographic difference between the Central Range and the Okinawa Trough, as well as by the active collision between the Philippine Sea Plate and the Eurasian basement high. This proposed northeastern lateral extrusion mirrors the active lateral extrusion in southwestern Taiwan which is observed on the southern side of the Eurasian basement high collision. The involvement of the basement high in the collision and adjacent regions appears to be an important factor in understanding local structural variations in the arc-continent collision and should be considered in both forward and reverse modeling of Taiwan deformation.
DE: 8038 Regional crustal structure
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: Fall Meeting 2005