Finite element modelling of the formation of supercritical wedges by coulomb-plastic deformation of the wedge-base: Implications for the deformation in the Darjeeling-Sikkim-Tibet Himalayan Wedge

Mukul, Malay (1999) Finite element modelling of the formation of supercritical wedges by coulomb-plastic deformation of the wedge-base: Implications for the deformation in the Darjeeling-Sikkim-Tibet Himalayan Wedge. Technical Report. C-MMACS/National Aerospace Laboratories, Bangalore, India.

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Abstract

The current understanding of wedge-scale compressive tectonics is based on theoretical, experimental and observational models which address the intermediate- and finitestage deformation in a sedimentary wedge . Numerical models can provide an insight into the deformation characteristics of the plastic basement in basement-involved wedges (like the Himalayas) at the onset ofdeformation and improve our understanding of the deformation in the basement-involved wedges in a compressive stress regime . Finite element models of appropriately constrained Coulomb-plastic granitic basement (under mid-crustal confining stresses) reveal the existence of a horizontal stress threshold below which engineering plastic strains are comparatively small (0.2 km) and a convex upwards, high shear stress zone forms near the back-end of the modelled body where the horizontal stresses are applied . Above the horizontal stress threshold, the plastic strains increase drastically (11 km) and a high shear stress zone (with boundary dipping about 30xB0; towards the back-end of body) forms near the front-end of the modelled body . These observations imply that in fold-and-thrust wedges with a plastic base and decollement, supercritical tapers are likely to form due to high plastic deformation within the plastic base if applied horizontal stresses exceed the threshold value. The basement-cored Kangmar ramp-anticline observed during the INDEPTH profiling of the Tibetan Higher Himalayas (Tethyan belt) was formed over a ramp in the basal decollement of the Himalayan fold-and-thrust belt at about 15 km depth ; this structure probably formed due to high plastic strain that developed at the base of the wedge during the onset of the Himalayan collision-tectonics. Supercritical tapers generated in the Darjeeling-Sikkim-Tibet wedge in the above manner was reduced both by hinterland collapse in the Higher Himalayas13; by normal faulting along the South Tibetan detachment system and extensive frontal imbrication in the Darjeeling-Sikkim Himalayas

Item Type:	Monograph (Technical Report)
Uncontrolled Keywords:	Finite element modelling;Coulomb-plastic deformation
Subjects:	MATHEMATICAL AND COMPUTER SCIENCES > Mathematical and Computer Scienes(General)
Depositing User:	Ms Indrani V
Date Deposited:	13 Jul 2006
Last Modified:	24 May 2010 04:14
URI:	http://nal-ir.nal.res.in/id/eprint/1892

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