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Layered deformation in the Taiwan orogen

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Science  14 Aug 2015:
Vol. 349, Issue 6249, pp. 720-723
DOI: 10.1126/science.aab1879

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Lower crustal deformation takes a turn

Collisions creating mountain belts frequently involve a tectonic plate plunging into the mantle. Huang et al. connect the deformation of rock from the subducting plate to the surface topography in Taiwan (see the Perspective by Long). Subsurface deformation mapping required interpreting certain seismic wave velocities as they travel through the crust. The subsequent images of Taiwan's deep crust show two distinct layers of deformation. The bottom layer comprises the subducting slab, which is being pulled into the mantle. This mechanically couples with the upper layer of crust, compressing it into a mountain range.

Science, this issue p. 720; see also p. 687

Abstract

The underthrusting of continental crust during mountain building is an issue of debate for orogens at convergent continental margins. We report three-dimensional seismic anisotropic tomography of Taiwan that shows a nearly 90° rotation of anisotropic fabrics across a 10- to 20-kilometer depth, consistent with the presence of two layers of deformation. The upper crust is dominated by collision-related compressional deformation, whereas the lower crust of Taiwan, mostly the crust of the subducted Eurasian plate, is dominated by convergence-parallel shear deformation. We interpret this lower crustal shearing as driven by the continuous sinking of the Eurasian mantle lithosphere when the surface of the subducted plate is coupled with the orogen. The two-layer deformation clearly defines the role of subduction in the formation of the Taiwan mountain belt.

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