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Timing of midcrustal metamorphism, melting and deformation in the Mount Everest Region of Southern Tibet revealed by U(Th)-Pb geochronology

By John Cottle, M.P. Searle, Matthew Horstwood and D.J. Waters


U(‐Th)‐Pb dating of zircon, monazite, and xenotime from metamorphic and igneous rocks at two outcrops along a north‐south transect in the Mount Everest region of southern Tibet provide new constraints on the timing and duration of thermal events associated with channel flow and the ductile extrusion of the Greater Himalayan Series (GHS). At the southernmost outcrop in the Kangshung Valley, Th‐Pb ages from monazite indicate that prograde metamorphism associated with crustal thickening following the India‐Asia collision occurred at least as early as Ma. A subsequent sillimanite‐grade metamorphic event at Ma was followed by two phases of leucogranite emplacement at and Ma. At Thongmön, 40 km to the northeast of the Kangshung Valley, prograde metamorphism was occurring at 25.4 Ma and lasted until Ma, reaching 740°C and 5 kbar at Ma. Immediately following metamorphism, two phases of leucogranite were emplaced at and Ma, with an intervening phase of ductile deformation. These data combined with ages from the Rongbuk glacier and Ama Drime range, north and east of Everest and the North Himalayan Mabja dome 100–140 km to the northeast, suggest that GHS metamorphism lasted 20 m.yr. and that migmatization and south‐directed channel flow peaked around 23–20 Ma and ended by 16 Ma. The youngest leucogranites crosscut all ductile fabrics related to the Miocene channel flow

Publisher: University of Chicago Press
Year: 2009
DOI identifier: 10.1086/605994
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