Plate velocity exhumation of ultrahigh-pressure eclogites in the Pakistan Himalaya
- 1Department of Geology, University of Leicester, and Natural Environment Research Council Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottinghamshire NG12 5GG, UK
- 2Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK
Abstract
U-Pb ages of zircon and allanite from the coesite-bearing ultrahigh-pressure (UHP) units in the Kaghan Valley, northern Pakistan, demonstrate that peak UHP metamorphism along the northern margin of the Indian plate occurred at 46.4 ± 0.1 Ma at peak pressure-temperature conditions of >27.5 kbar (>100 km) and 720–770 °C. Much lower pressure retrogressive growth of titanite took place between 46.4 and ca. 44 Ma, indicating that the eclogites were exhumed to 35 km depth at or before 44 Ma, implying very rapid exhumation rates within the mantle of ∼30–80 mm/yr or more, comparable to rapid plate velocities. Once entrained in the base of the crust, the eclogites followed a slower cooling history from 45 Ma, similar to the amphibolite facies gneisses of the Pakistan Himalaya.
- ultrahigh-pressure metamorphism
- exhumation
- Pakistan
- Himalaya
- allanite
- UTh-Pb dating
- zircon
- coesite
- continental collision
Footnotes
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↵GSA Data Repository item 2006214, analytical methods and Tables DR1 and DR2, 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 19 June 2006.
- Received 21 March 2006.
- Revision received 16 June 2006.
- The Geological Society of America, Inc.
