Tibetan basement rocks near Amdo reveal “missing” Mesozoic tectonism along the Bangong suture, central Tibet
- 1 Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
- 2New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
- 3Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
- 4Institute of Tibetan Plateau Research and Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Abstract
The U-Pb and 40Ar/39Ar studies of a unique exposure of crystalline basement along the Jurassic–Early Cretaceous Bangong suture of central Tibet reveal previously unrecognized records of Mesozoic metamorphism, magmatism, and exhumation. The basement includes Cambrian and older orthogneisses that underwent amphibolite facies metamorphism coeval with extensive granitoid emplacement at 185–170 Ma. The basement cooled to ∼300 °C by 165 Ma and was exhumed to upper crustal levels in the hanging wall of a south-directed thrust system during Early Cretaceous time. We attribute Jurassic metamorphism and magmatism to the development of a continental arc during Bangong Ocean subduction, and Early Cretaceous exhumation to northward continental underthrusting of the Lhasa terrane beneath the Qiangtang terrane. We speculate that a Jurassic arc extended regionally along the length of the Bangong suture, but in all other places in Tibet has been buried, either depositionally or structurally, beneath supracrustal assemblages.
Footnotes
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↵GSA Data Repository item 2006094, supplementary geochronologic and thermochronologic data, is available online at www.geosociety.org/pubs/ft2006.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
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- Accepted 23 January 2006.
- Received 21 November 2005.
- Revision received 20 January 2006.
- The Geological Society of America, Inc.
