Variation of kinematics at the brittle-ductile transition in the eastern Central Range, Taiwan

Abstract:

Kinematic evolution of exhumation process is always a fascinating mystery for solid earth sciences. Analyses of structures and strain distribution associated with exhumation of the eastern Central Range in Taiwan provide a unique opportunity to understanding the structural history and kinematic evolution of orogenic belts.

It is well known that sub-horizontally along-strike stretching lineation is noticeable on the foliation and slaty cleavage with moderate dip at the eastern Central Range, contrast to the down-dip stretching lineation at the western Central Range. The observation of sub-horizontal stretching lineation is compatible with results of orogeny-parallel anisotropy of shear wave splitting in Taiwan. Small shear band and kink band is overprinted on the penetrative foliation. With shear-sense indicators, it illustrated that along-strike shearing associated with almost N-S compression took place during ductile and semi-ductile deformation under the strike-slip faulting stress regime. Conversely, sub-horizontal crenulation cleavages and listric normal faults and also sub-vertical quartz veins and sub-vertical joints subparallel to the motion of the Philippine Sea Plate and quite often locally cut the foliation and slaty cleavage throughout the eastern Central Range, displaying that sub-vertical ductile thinning associated with N 20-30E extension was active during semi-brittle and brittle deformation under normal faulting stress regime. Variation of kinematics at the brittle-ductile transition might indicate that dynamics changes dramatically in the orogenic exhumation system and might further suggest that the existence of a lid separated brittle from ductile deformation to facilitate the exhumation in the eastern Central Range, Taiwan.