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Abstract
Abstract Himalayan high-pressure metamorphic rocks are restricted to three environments: the suture zone; close to the suture zone; and (mostly) far (>100 km) from the suture zone. In the NW Himalaya and South Tibet, Cretaceous-age blueschists (glaucophane-, lawsonite- or carpholite-bearing schists) formed in the accretionary wedge of the subducting Neo-Tethys. Microdiamond and associated phases from suture-zone ophiolites (Luobusa and Nidar) are, however, unrelated to Himalayan subduction–collision processes. Deeply subducted and rapidly exhumed Indian Plate basement and cover rocks directly adjacent to the suture zone enclose eclogites of Eocene age, some coesite-bearing (Kaghan/Neelum and Tso Morari), formed from Permian Panjal Trap, continental-type, basaltic magmatic rocks. Eclogites with a granulite-facies overprint, yielding Oligocene–Miocene ages, occur in the anatectic cordierite ± sillimanite-grade Indian Plate mostly significantly south of the suture zone (Kharta/Ama Drime/Arun, north Sikkim and NW Bhutan) but also directly at the suture zone at Namche Barwa. The sequence carpholite-, coesite-, kyanite- and cordierite-bearing rocks of these different units demonstrates the transition from oceanic subduction to continental collision via continental subduction. The granulitized eclogites in anatectic gneisses preserve evidence of former thick crust as in other wide hot orogens, such as the European Variscides.
Highlights
High-pressure metamorphic rocks such as blueschists, eclogites and high-pressure granulites are the products of major geodynamic processes such as subduction, collision and crustal thickening
Himalayan high-pressure metamorphic rocks are restricted to three environments: the suture zone; close to the suture zone; and far (>100 km) from the suture zone
Eclogite can form at a wide range of temperatures and if not completely retrogressed, can yield evidence of high pressures reached through the processes in crustal thickening as well as subduction
Summary
High-pressure metamorphic rocks such as blueschists (glaucophane ± lawsonite-bearing rocks), eclogites and high-pressure granulites are the products of major geodynamic processes such as subduction, collision and crustal thickening. Schertl & O’Brien 2013) All of these rock types, blueschist, eclogite and high-pressure granulite, as well as rocks containing coesite and diamond occur within the Himalaya. The Himalayan–Tibetan orogen can be most subdivided into a number of roughly parallel belts, running for over 2500 km along strike of the collision zone, separated by major faults and thrusts (Fig. 1) (Gansser 1964; Hodges 2000; Yin & Harrison 2000) These are, from north to south, the Trans-Himalayan Batholith, the Indus–Tsangpo
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