Abstract

The high-grade, partially melted metamorphic core of the Himalaya formed at depth after the collision of India with Asia, was extruded southwards at about 25 and 15 Myr ago, and now forms a slab of crystalline rocks (the Greater Himalayan Sequence) along the full length of the Himalaya. It happens that its upper boundary, a system of extensional faults and ductile shear zones (the South Tibetan Detachment System), passes through Mt Everest, where the summit is of Ordovician limestone, while the base camps are in granite and migmatitic gneiss. On the 1933 British Everest Expedition, L.R. Wager, later Professor of Geology at Oxford University, collected more than 60 samples across the transition in the Rongbuk Valley and on Everest itself. After retracing his steps (in the virtual realm) to relocate the samples, I have combined structural and metamorphic studies on them, along with existing data, to produce the most complete account to date of the mechanism and timing of the ductile shear zone responsible for exhuming the Himalayan metamorphic core.