Journal of Geophysical Research Atmospheres · 1978 · 469 citations · 35 references
Natural SciencesEarth SciencesGeologyPetrologyTectonicsTectonophysicsCollision TectonicsFault MechanicsPlate TectonicsTectonic StressCollisional OrogenyCrustal ShorteningHimalayan-type OrogenyShear StressStress Near FaultsSubduction InitiationTectonic ShorteningThrust Generation
Upper limits of 200–300 bars for shear stress on the intracontinental thrust fault indicate that Himalayan granites could not have formed by friction alone, implying that metamorphism likely resulted from exposure of continental crust to hot asthenosphere before thrusting. The Indian subcrustal lithosphere peeled away under the Tethyan slab’s force, detaching buoyant crust from dense lithosphere and initiating intracontinental subduction, which better explains the metamorphic pattern and the shift to localized thrusting. The stresses required to form the granites would need an overthrusting velocity exceeding 30 cm yr⁻¹, and the detachment of buoyant crust provides a more plausible explanation for the observed metamorphism and the transition from distributed shortening to localized thrusting.
Independent arguments based on topographic stress and crustal strength give upper limits of 200 bars and 300 bars, respectively, for the average shear stress on the intracontinental thrust fault that formed the Himalaya. According to either a one‐dimensional or a two‐dimensional fault model, such stresses could not have produced the Himalayan granites by friction, unless overthrusting velocity exceeded 30 cm/yr. More probably, Himalayan metamorphism was caused by exposure of continental crust to hot asthenosphere prior to the formation of the intracontinental thrust. Crust was exposed by peeling away of Indian subcrustal lithosphere in response to the force and moment exerted by the Tethyan slab. This detachment of buoyant crust from dense lithosphere better explains the metamorphic pattern and also explains why the distributed crustal shortening at the beginning of the collision orogeny was replaced by localized thrusting or intracontinental subduction.
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