Slab decapitation in the Hindu Kush

Date & time

1–2pm 19 October 2017

Location

Jaeger 1 Seminar Room, RSES

Speakers

Gordon Lister (RSES)

Event series

Contacts

 Adele Morrison

A slab decapitation event may actively be in progress beneath the Hindu Kush, at the forefront of the modern India-Asia collision. We argue that the underlying tectonics involves a south-facing subduction zone that has rolled back as far north as it is able. The continued northward motion of India means that deviatoric stress levels have increased, leading to the creation of back thrusts at the northern margin of the once-connected Tarim and Tadjik Basins. In such circumstances, with the passage of time, since the sense-of-relative-displacement on the back-thrust opposes that of the older subduction megathrust, the adjacent lithosphere eventually rammed the subducting slab, initiating its decapitation. To verify this hypothesis, the eQuakes program has been used to re-examine slab geometry, revealing evidence that can be interpreted as indicating slab boudinage in a south-facing subduction zone. This potentially resolves the paradoxical occurrence of Pliocene metamorphic core complexes in the north of the Himalayan Ranges while in the modern day there is abundant evidence of compressional orogeny. The indentors that formed during the closure of Tethys collapsed internal basins and created rolling-back subduction zones that subjected the leading edge of the advancing terrane-stack to extreme horizontal extension.  Roll-back of a south-facing subduction system thus creates and then exhumes metamorphic core complexes, some now subject to rapid uplift because rebound takes place after decapitation removes the slab pull force.

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