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Tectonics and topographic evolution of Namche Barwa and the easternmost Lhasa block, Tibet

By
Peter K. Zeitler
Peter K. Zeitler
Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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Anne S. Meltzer
Anne S. Meltzer
Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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Lucy Brown
Lucy Brown
Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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William S.F. Kidd
William S.F. Kidd
Department of Earth and Atmospheric Sciences, University at Albany, Albany, New York 12222, USA
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Chul Lim
Chul Lim
Department of Earth and Atmospheric Sciences, University at Albany, Albany, New York 12222, USA
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Eva Enkelmann
Eva Enkelmann
Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221, USA
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Published:
August 01, 2014

In the easternmost Himalaya and southeastern Tibet, the Namche Barwa–Gyala Peri massif and adjacent Lhasa block host some of the Earth’s most active geologic processes and extreme topography. Synthesis of U-Th/He and Ar-Ar thermochronology, anatectic history, seismicity, and structural geology shows the important role that surface processes have played in this region in both local and orogen-scale crustal dynamics. Basement rocks of the massif underwent an episode of metamorphism, partial melting, and focused deformation that began ca. 10 Ma and likely remains active due to thermally mediated feedbacks between these processes and erosion. Strong differential rock uplift at Namche Barwa established the immense Namche Barwa knickzone on the Yarlung Tsangpo River, which has been stabilized through coupling between erosion driven by high stream power and localized deformation. This knickzone has maintained a high secondary base level of ~3000 m for the upper Yarlung Tsangpo watershed and so has shielded a large region of southeastern Tibet from excavation by the river, which in turn could alter the morphology and so the dynamics of the eastern Himalayan orogenic wedge. The landscape evolution of the southeast Lhasa block involved slow regional unroofing or incision in the Neogene, a significant pulse of ~5 km of rapid exhumation from ca. 10 to 5 Ma, and since then a great reduction in exhumation started once the Namche Barwa knickzone on the Yarlung Tsangpo was established. The low-relief high-elevation surface in the area is a relatively young feature, developed after the rapid 10–5 Ma exhumation pulse.

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Contents

GSA Special Papers

Toward an Improved Understanding of Uplift Mechanisms and the Elevation History of the Tibetan Plateau

Junsheng Nie
Junsheng Nie
MOE Key Laboratory of Western China's Environmental Systems, Collaborative Innovation Centre for Arid Environments and Climate Change, Lanzhou University, 222 South Tianshui Road, Lanzhou, Gansu 730000, China
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Brian K. Horton
Brian K. Horton
Institute for Geophysics and Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA
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Gregory D. Hoke
Gregory D. Hoke
Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA
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Geological Society of America
Volume
507
ISBN print:
9780813725079
Publication date:
August 01, 2014

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