Distributed deformation in southern and western Tibet during and after the India‐Asia collision

Abstract

Field and radiometric data are used to describe and date strain and stress states in southern (longitude 88° to 91°E, latitude 28° to 30°N) and western Tibet (longitude 79° to 82°E, latitude 30° to 34°N). We factorize deformation into syncollisional and postcollisional, and we present stretching lineation and displacement orientation maps, two sections across the Indian shelf sequence, and stress orientations calculated from mesoscale fault slip data. In southern Tibet, syncollisional stretching and displacement directions trend 9°±46° and displacement is top to south. Synkinematic, low‐grade metamorphism is dated at 50 Ma at one locality in the Indian shelf sequence underlying the main mantle thrust of the Indus‐Yarlung suture. This implies Paleocene onset of continental collision for the investigated section. Postcollisional structures comprise a “backthrust” group, which includes foreland‐ and hinterland‐directed thrusts, reverse and strike‐slip faults, and folds. It dominates postcollisional deformation, is concentrated along the Indus‐Yarlung suture, and portrays N‐S compression (σ1 trend of 8°±17°, σ2 of 97°±17°). A “strike‐slip” group consists of conjugate strike‐slip faults, is concentrated in east trending, narrow, highly deformed zones, and indicates that N‐S compression is locally compensated by E‐W extension (σ1 of 15°±29°, σ3 of 103°±30°). Synkinematic muscovite dates postcollisional deformation as late early Miocene (17.5 Ma) at one locality at the suture. Strike‐slip and oblique normal (σ3 of 60°±23°, σ1 of 144°±21°) and normal (σ3:114°±16°) faulting, dated between late Miocene and Recent and including active deformation, represents (dominant) E‐W and minor N‐S extension due to E‐W stretching of southern Tibet and oroclinal bending along the Himalayan arc. Restoring syncollisional and postcollisional deformation yields a minimum of 67% (258 km) shortening across the Indian shelf sequence. Incorporating recently published contraction estimates across the eastern Himalaya yields minimum shortening between undeformed India and the Indus‐Yarlung suture of 66% (536 km). The Himalaya‐Tibet orogenic system south of the Indus‐Yarlung suture had an initial width of ≥811 km in the southern Tibetan section. In western Tibet, imbrication of an ophiolite sequence of the Bangong‐Nujiang suture is top to south (stretching lineation trend of 15°±18°), and σ3 of active deformation trends ESE. Faulting along the Shiquanhe fault zone, which transfers displacement from the northern part of the Karakorum fault to a system of rifts in western central Tibet, indicates dextral strike‐slip alternating with sinistral‐oblique normal faulting and block rotations around vertical axes during a prolonged shearing history. The Indian Shelf sequence south of Mount Kailas shows top to south imbrication (stretching lineation trend of 52°±60°). Both Indian shelf rocks and (?Oligocene‐Miocene) Kailas conglomerates record backthrusting and backfolding (σ1 of 33°) and Recent E‐W extension (σ3 of 85°±28°).

Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction

“…Some of this late stage overprinting may relate to north-dipping thrust faults in the Tethyan sedimentary sequence, between the suture zone and the STD (e.g. Ratschbacher et al 1994). Geodynamic modelling ) supports this possibility if the weak channel overburden fails and glides towards the foreland causing relative thrusting along the upper boundary of the channel.…”

Testing the effects of topography, geometry, and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya

“…This approach allows topography to respond to deformational loading and erosional unloading. For models using the static and responsive topographies, the initial topography assigned to the restored section simulates a preexisting foldthrust belt in the Tethyan sequence before the initiation of the MCT (Ratschbacher et al, 1994;Murphy and Yin, 2003;Webb et al, 2011). This topography maintains 0 km of elevation from the southern end of the restored cross section to the lower Lesser Himalaya.…”

Tectonic and climatic forcing on the Panj river system during the Quaternary

“…1B). Kinematic models of the active extension in the Pamir discuss topographic collapse (Brunel et al, 1994), radial overthrusting (Strecker et al, 1995), and links to the right-slip KFZ (Ratschbacher et al, 1994). Along the eastern boundary of the Pamir, the crustal extension is accommodated along the Kongur Shan extensional system (e.g.…”