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How much strain can continental crust accommodate without developing obvious through-going faults?

By
B.C. Burchfiel
B.C. Burchfiel
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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C. Studnicki-Gizbert
C. Studnicki-Gizbert
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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J.W. Geissman
J.W. Geissman
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA
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R.W. King
R.W. King
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Z. Chen
Z. Chen
Chengdu Institute of Geology and Mineral Resources, Chengdu, Sichuan, 610082, People's Republic of China
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L. Chen
L. Chen
Yunnan Institute of Geological Sciences, No. 87 Dongfong Lane, Kunming, Yunnan 650051, People's Republic of China
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E. Wang
E. Wang
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, People's Republic of China
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Published:
January 01, 2007

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.

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Contents

GSA Special Papers

Whence the Mountains? Inquiries into the Evolution of Orogenic Systems: A Volume in Honor of Raymond A. Price

James W. Sears
James W. Sears
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Tekla A. Harms
Tekla A. Harms
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Carol A. Evenchick
Carol A. Evenchick
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Geological Society of America
Volume
433
ISBN print:
9780813724331
Publication date:
January 01, 2007

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