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1 Department of Geosciences, Penn State University, University Park, Pennsylvania 16802, USA
2 Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA
3 Geosciences Department, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
4 ExxonMobil Exploration Company, P.O. Box 4778, Houston, Texas 77210-4778, USA
Recent observations of cleavage patterns, strain histories, and kinematics across the Taiwan mountain belt depict systematic orogen-scale variations with respect to the synorogenic divide and suggest that the pattern of cleavage development is a predictable consequence of orogen stresses and kinematics. In Taiwan, continental crust within the collision is accreted in the prowedge facing Asia, but is advected eastward into the east-verging retrowedge, where the most deeply exhumed rocks are exposed. Wedge mechanics predict a reversal in the direction of plunge of the principal compressive stress at the topographic divide between the opposing wedges. The observation of a single cleavage in western Taiwan suggests that the cleavage in the prowedge remains stable with respect to the stress orientation. In contrast, the existence of a second crenulation cleavage in the retrowedge is evidence for an abrupt change in stress orientation and unstable buckling of preexisting prowedge fabrics. Advection of a fabric across a topographic divide in a doubly vergent wedge provides an explanation for the occurrence of cleavage fronts and fans in natural systems such as Taiwan.
Key Words: cleavage fan • cleavage front • Taiwan • slaty cleavage • incremental strain
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