Development of extensional stresses in the compressional setting of the Himalayan thrust wedge: inference from numerical modelling

Abstract

The estimation of contemporary tectonic stress field and deformation in active fold-and-thrust belts are imperative in identifying active geodynamics and resulting faulting phenomenon. In this paper, we focus on contemporary extensional tectonics in the overall compressive setting of the Himalayan orogen. Here we examine the regional tectonic stress field and upper crustal deformation in the Himalayan thrust wedge using a 2D finite element technique, incorporating elastic rheology under plain strain condition. The elastic models demonstrate that the extensional tectonic stress and related normal faulting is extensively developed in the southern front of the Himalaya at shallow crustal level (< 10 km in depth). Our modelling shows a good consistency with the geological field evidences of active faulting, focal mechanism solutions of medium size earthquakes in the several sectors of the Himalaya. Results based on numerical simulation, tectonic analysis and taking geological and geophysical data into account, we interpret that the present-day extensional tectonic activity is not restricted in the southern Tibet but distributed in the different sectors of the Himalayan fold-and-thrust belt co-exist with compressional structures. Modelling results also indicate that the nature, distribution and orientation of the maximum compressive stress ( 1 ) of the Himalaya are mainly controlled by the intra crustal Main Himalayan décollement (MHT). The significant amount of shear stress/strain concentration along the MHT in the western Nepal predict that the region is prone to moderate and great future earthquakes.

Extension driven brittle exhumation of the lower-middle crustal rocks, a paleostress reconstruction of the Neoproterozoic Ambaji Granulite, NW India

“…6b). Extension oriented perpendicular to the long axis of the orogen in the Higher Himalayas is also thought to have produced large normal faults running parallel to the axis of the orogen, in this case associated with Southern Tibet Detachment and the formation Tethys ocean (Grujic et al, 1996;Nelson et al, 1996;Beaumont et al, 2001;Vannay and Grasemann, 2001;Jessup et al, 2006;Joshi and Hayashi, 2010;Searle, 2010;Cooper et al, 2012). In addition, transverse faults resulting from extension oriented parallel to the orogen have also been observed in the Himalayas (Hintersberger et al, 2010;Liu et al, 2012).…”

Finite element modelling of the pull-apart formation: implication for tectonics of Bengo Co pull-apart basin, southern Tibet

“…FEM has successfully proved to be a powerful method for simulating pull-apart basin geometries and deformation mechanisms, [1,2,7,16,18,19]. In this study, we applied a 2D-finite element software package developed by Hayashi [24], which has been used widely by Joshi and Hayashi, [25][26][27]. Similar to most mesh-based numerical methods, bodies of rocks in this program are represented by triangular elements and each element is assigned appropriate material properties, such as density, Young's modulus, cohesion and angle of internal friction.…”

Quaternary extensional and compressional tectonics revealed from Quaternary landforms along Kosi River valley, outer Kumaun Lesser Himalaya, Uttarakhand

“…Along the South Almora Thrust and Ramgarh Thrust zones, the valleys are narrow and V-shaped where Quaternary deposits are sparse due to relatively rapid uplift across these thrusts. Along the South Almora Thrust zone, three to four levels of fluvial terraces thrusts (Searle et al 1988(Searle et al , 2008 or local adjustment of tectonics regime due to the taper angle readjustment of the Himalayan décollement (Joshi and Hayashi 2010). Normal faults are reported from various mountainous regions of the world, from the high plateaus of the Andes, Basin and Range provinces, western Apennines, Pamir, Central Himalaya and Tibet (England and Molnar 1993, and references therein).…”

“…However, post-orogenic structures, e.g. normal faults, are well distributed in the Himalaya (Joshi and Hayashi 2010). Secondly, out-ofsequence thrusting (Mukherjee et al 2012;Mukherjee 2015) and back thrusts (Mukherjee 2013) are also present in the Himalayan orogen.…”