How much strain can continental crust accommodate without developing obvious through-going faults?
B.C. Burchfiel, C. Studnicki-Gizbert, J.W. Geissman, R.W. King, Z. Chen, L. Chen, E. Wang, 2007. "How much strain can continental crust accommodate without developing obvious through-going faults?", Whence the Mountains? Inquiries into the Evolution of Orogenic Systems: A Volume in Honor of Raymond A. Price, James W. Sears, Tekla A. Harms, Carol A. Evenchick
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Geologic data combined with global positioning system (GPS) and paleomagnetic data from SW China indicate that continental crust can absorb tens to perhaps at least hundreds of kilometers of horizontal shear without developing either through-going faults or obvious structures capable of accommodating shear strain. The arcuate, left-lateral Xianshuihe-Xiaojiang and Dali fault systems bound crustal fragments that have rotated clockwise around the eastern Himalayan syntaxis. The two fault systems terminate to the south, but faults reappear farther south, and these continue the GPS velocity gradient. The shear must be transmitted across the Lanping-Simao fold belt without forming through-going faults. West of the Longmen Shan, a geodetically determined velocity gradient of ∼10 mm/yr at N60°E lies in an area not marked by through-going faults. If this deformation has been active for the past 8–11 m.y., it should have accumulated ∼100 km of shear across a belt ∼100 km wide. In both regions, there are no obvious structures that are capable of accommodating the shear. Paleomagnetic data from the southern Lanping-Simao belt are interpreted to indicate an unexpected zone of left-lateral shear present (Burchfiel and Wang, 2007) where rotation of crustal material is locally more than 90° across a zone unmarked by any mapped through-going faults. In these examples, the mechanism of deformation is not obvious, but we suggest it is distributed brittle deformation at a range of scales, from closely spaced faults to cataclastic deformation. In older terranes, recognition of such zones potentially adds an unknown uncertainty to field study and tectonic analyses.