Speaker:Chung Huang (黃鐘)
University of Connecticut
Title:Tectonic evolution of a major tectonostratigraphic boundary fault in an active accretionary wedge: an example from the Tulungwan Fault, southern Taiwan
The Taiwan orogeny is located in the convergent boundary between the Philippine Sea Plate and the Eurasian Plate and has grown during the last few million years as the Philippine Sea Plate collided with the continental margin of China. The resulting collision zone is composed of several tectonostratigraphic units separated by major structural boundaries. To better understand the kinematics of one of these major boundaries, we completed a 3-week field program along the Laonung River in southern Taiwan and integrated available geodetic data. In this area, the geometry of penetrative slaty cleavage and associated stretching lineations indicate a regional-scale, SSW-plunging antiform is located in the east of the boundary and verges to the NW. The absence of a crenulation cleavage in outcrops and thin sections and the abundance of late-stage faults and brittle structures suggest that the fold is a post-metamorphic structure. The vertical displacement rate provided by leveling and GPS surveys from the past decade and the dated strath terraces along the Laonung River show higher uplift rates, suggesting the boundary is an active structure. We then use the geometry of the folded cleavage and a trishear folding mechanism to model the development of this regional-scale fold, and proposed a multiple stages deformation model of the antiform. This antiform is located in the hanging wall of an active blind thrust. The depth of the fault tip is not clear, but after the tip of the blind thrust migrates upward, the Tulungwan Fault could be reactivated and become a seismogenic fault in the future.
Time : 1:30 p.m. - 3:00 p.m., Tuesday, Oct 8th, 2013
Location : Room 213, Department of Geosciences