We have chosen
to present here only models where exhumation and extensional tectonics
are associated with crustal shortening and thickening and not with crustal
extension as proposed by Platt (1986) or Ruppel et al.(1988).
of extrusion is to place the high-grade rocks of the HHCS in contact with
the overlying low-grade sedimentary series of the Tethys Himalaya along
the low-angle normal Zanskar Shear Zone but in a tectonic setting without
any net extension of the overall system.
On the basis
of these various models and from our own observation, we infer that ductile
extention along the ZSZ and conjugated thrusting along the MCT are the
result of the south-westward extrusion of the HHCS. The HHCS represents
a slab of upper crustal material that was first underthrusted below a
buttress formed by the Sedimentary series of the Tethys Himalaya (the
Nyimaling-Tsarap nappe), until it reached a critical point where the downwards-pulling
forces were counteracted by buoyancy. When this critical point was reached,
the upper crust failed and the HHCS slab became detached from the subsiding
lithosphere. Once detached, the HHCS was sandwiched beween the still subsiding
lithosphere and the rigid buttress formed by the TH. The compressive forces
exerted by the ongoing collision lead to the deformation of the HHCS through
conjugated simple shear and pure shear.