Contact metamorphism in the Malashan dome, North Himalayan gneiss domes, southern Tibet: An example of shallow extensional tectonics in the Tethys Himalaya

Authors

Tetsuo Kawakami, Kyoto University
Mutsuki Aoya, National Institute of Advanced Industrial Sciences and Technology Tsukuba
Simon Wallis, Nagoya University
Jeffrey Lee, Central Washington UniversityFollow
Kentaro Terada, Hiroshima University
Yu Wang, China University of Geoscience Beijing
Matt Heizler, New Mexico Bureau of Mines and Mineral Resources

Document Type

Article

Department or Administrative Unit

Geological Sciences

Publication Date

9-26-2007

Abstract

Combined petrographic, structural and geochronological study of the Malashan dome, one of the North Himalayan gneiss domes, reveals that it is cored by a Miocene granite, the Malashan granite, that intruded into the Jurassic sedimentary rocks of Tethys Himalaya. Two other granites in the area are referred to as the Paiku and Cuobu granites. New zircon SHRIMP U-Pb and muscovite and biotite ⁴⁰Ar-³⁹Ar dating show that the Paiku granite was emplaced during 22.2–16.2 Ma (average 19.3 ± 3.9 Ma) and cooled rapidly to 350–400 °C at around 15.9 Ma. Whole-rock granite chemistry suggests the original granitic magma may have formed by muscovite dehydration melting of a protolith chemically similar to the High Himalayan Crystalline Sequence. Abundant calcareous metasedimentary rocks and minor garnet-staurolite-biotite-muscovite ± andalusite schists record contact metamorphism by three granites that intruded intermittently into the Jurassic sediments between 18.5 and 15.3 Ma. Two stages of widespread penetrative ductile deformation, D1 and D2, can be defined. Microstructural studies of metapelites combined with geothermobarometry and pseudosection analyses yield P–T conditions of 4.8 ± 0.8 kbar at 550 ± 50 °C during a non-deformational stage between D1 and D2, and 3.1–4.1 kbar at 530–575 °C during syn- to post-D2. The pressure estimates for the syn- to post-D2 growth of andalusite suggest relatively shallow (depth of ∼15.2 km) extensional ductile deformation that took place within a shear zone of the South Tibetan Detachment System. Close temporal association between intrusion of the Malashan granite and onset of D2 suggests extension may have been triggered by the intrusion of the Malashan granite.

Comments

This article was originally published in Journal of Metamorphic Geology. The full-text article from the publisher can be found here.

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Recommended Citation

Kawakami , T., et al. (2007). Contact metamorphism in the Malashan dome, North Himalayan gneiss domes, southern Tibet: An example of shallow extensional tectonics in the Tethys Himalaya. Journal of Metamorphic Geology, 25(8), 831-853. DOI: 10.1111/j.1525-1314.2007.00731.x