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. AOYA 1 , S. R. WALLIS 2 , T. KAWAKAMI 3 , J. LEE 4 , Y. WANG 5 & H. MAEDA 6 1 Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Tsukuba 305-8567, Japan (e-mail: aoya.m@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 (Present address: Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Tsukuba 305-8567, 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 Abstract: Despite the importance of Tethys Himalayan or North Himalayan gneiss domes for dis- cussing 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 defor- mation stages, D 1 and D 2 , with D 2 showing an increasing strength towards the granite contacts; and (iii) the development of a strong D 2 foliation (gneissosity) in the outermost part of the granite cores. In addition, field and bulk-chemical studies show: (i) D 2 is associated with a domi- nant 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 base- ment, 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. Contemporaneous activity of thrust faults, with top- to-the-south movement, and normal faults, with top-to-the-north movement, is one of the most strik- ing characteristics of the Himalayan orogeny (e.g. Burg et al. 1984a; Burchfiel et al. 1992; Hodges et al. 1992; Hodges 2000). The south Himalayan thrust systems such as the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) are over- lain by a normal fault system, the South Tibetan Detachment (STD), which stretches roughly along the length of the main Himalayan range (Fig. 1). Southward extrusion of the Greater Himalaya, a high-grade metamorphic sequence sandwiched between the MCT and the STD (Fig. 1), is com- monly presented as one of the best documented examples of large-scale channel flow and extrusion of middle to lower continental crust (e.g. Beaumont et al. 2001, 2004; Jamieson et al. 2004). In this tec- tonic framework, the Greater Himalaya forms the footwall of the north-dipping STD with the Tethys From:LAW, R. D., SEARLE, M. P. & GODIN, L. (eds) Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. Geological Society, London, Special Publications, 268, 471–495. 0305-8719/06/$15.00 # The Geological Society of London 2006.