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Geological Society, London, Special Publications; 2006; v. 268; p. 471-495;
DOI: 10.1144/GSL.SP.2006.268.01.22
© 2006 Geological Society of London

Himalaya-Tibetan Plateau

The Malashan gneiss dome in south Tibet: comparative study with the Kangmar dome with special reference to kinematics of deformation and origin of associated granites

M. Aoya1, S. R. Wallis2, T. Kawakami3,6, J. Lee4, Y. Wang5 & H. Maeda6

1 Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Tsukuba 305-8567, Japan aoya.m{at}aist.go.jp
2 Department of Earth & Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan
3 Department of Earth Sciences, Faculty of Education, Okayama University, Okayama, 700-8530, Japan
4 Department of Geological Sciences, Central Washington University, Ellensburg, WA 98926, USA
5 Department of Geology, China University of Geosciences, Beijing 100083, China
6 Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

Despite the importance of Tethys Himalayan or North Himalayan gneiss domes for discussing extrusive flow of the underlying Greater Himalayan Sequence, these metamorphic domes in general remain poorly documented. The main exception is the Kangmar dome. The Malashan metamorphic complex, a newly documented North Himalayan gneiss dome, is shown to have strong similarities with the Kangmar dome, suggesting that the North Himalayan gneiss domes have the following features in common: (i) Barrovian-type metamorphism with grade increasing towards a centrally located two-mica granite; (ii) the presence of two dominant ductile deformation stages, D1 and D2, with D2 showing an increasing strength towards the granite contacts; and (iii) the development of a strong D2 foliation (gneissosity) in the outermost part of the granite cores. In addition, field and bulk-chemical studies show: (i) D2 is associated with a dominant top-to-the-north sense of shear (in disagreement with the most recent kinematic studies in Kangmar dome); (ii) the deposition age of associated metasediments is upper Jurassic suggesting that the Malashan dome is located not at the base, but within the middle section of the Tethys Himalaya; and (iii) in contrast to the Kangmar granitic gneiss that is interpreted as Indian basement, three granitic bodies in Malashan all formed as young intrusive bodies during the Himalayan orogeny. These results suggest that the formation mechanism of the North Himalayan gneiss domes needs to be re-evaluated to test the rigidity of the hanging wall assumed in channel flow models.





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J. Lee, W. McClelland, Y. Wang, A. Blythe, and M. McWilliams
Oligocene-Miocene middle crustal flow in southern Tibet: geochronology of Mabja Dome
Geological Society, London, Special Publications, 2006; 268: 445 - 469.
[Abstract] [PDF]