Imaging high-pressure rock exhumation in eastern Taiwan

Abstract

Increasingly detailed studies of out crops of high-pressure rock terranes in combination with rapidly evolving numerical modeling studies have given rise to a number of possible explanations for the processes by which these rocks are exhumed. Imaging actively exhuming high-pressure terranes remains one of the fundamental, but elusive, tasks that could advance the understanding of how these important rocks reach Earth's surface. Seismic tomography along the active arc-continent collision in eastern Taiwan images a high P- and S-wave velocity zone that extends from the shallow subsurface beneath a high-pressure metamorphic terrane to ∼50 km depth. We present a petrophysical analysis of this high-velocity zone that indicates the presence of rock types common to high-pressure terranes. The high-velocity zone is seismically active throughout. We determine focal mechanisms for 57 earthquakes, and carry out full waveform modeling on 10; these have double-couple focal mechanisms with a compensated linear vector dipole component up to 20.6%. We suggest that the high-velocity zone comprises an exhuming high-pressure terrane. Focal mechanisms for earthquakes within it indicate that shear faulting dominates in the deformation, but high fluid pressure may also play a role.

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