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Journal: |
Nature & Nature Geoscience 2012 No.5
clicks:1012 |
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Title:
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Author:
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E. Wang,E. Kirby,K. P. Furlong,M. van Soest,G. Xu,X. Shi,P. J. J. Kamp & K. V. Hodges |
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Adress: |
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 10029, China |
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Abstract:
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High topography in eastern Tibet is thought to have formed when deep crust beneath the central Tibetan Plateau flowed towards the plateau margin, causing crustal thickening and surface uplift1, 2. Rapid exhumation starting about 10–15 million years ago is inferred to mark the onset of surface uplift and fluvial incision3, 4, 5, 6. Although geophysical data are consistent with weak crust capable of flow7, 8, it is unclear how the timing9 and amount of deformation adjacent to the Sichuan Basin during the Cenozoic era can be explained in this way10, 11. Here we use thermochronology to measure the cooling histories of rocks exposed in a section that stretches vertically over 3 km adjacent to the Sichuan Basin. Our thermal models of exhumation-driven cooling show that these rocks, and hence the plateau margin, were subject to slow, steady exhumation during early Cenozoic time, followed by two pulses of rapid exhumation, one beginning 30–25 million years ago and a second 10–15 million years ago that continues to present. Our findings imply that significant topographic relief existed adjacent to the Sichuan Basin before the Indo-Asian collision. Furthermore, the onset of Cenozoic mountain building probably pre-dated development of the weak lower crust, implying that early topography was instead formed during thickening of the upper crust along faults. We suggest that episodes of mountain building may reflect distinct geodynamic mechanisms of crustal thickening. |
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