Collision tectonics of the Ladakh-Zanskar Himalaya

Abstract

The collision of the Indian Plate with the Karakoram-Lhasa Blocks and the closing of Neo-Tethys along the Indus Suture Zone (ISZ) is well constrained by sedimentologic, structural and palaeomagnetic data at ca. 50 Ma. Pre-collision high P— low T blueschist facies metamorphism in the ISZ is related to subduction of Tethyan oceanic crust northwards beneath the Jurassic-early Cretaceous Dras island arc. The Spontang ophiolite was obducted south westwards onto the Zanskar shelf before the Eocene closure (Dl). The youngest marine sediments on the Zanskar shelf and along the ISZ are Lower Eocene, after which continental molasse deposition occurred. After ocean closure, thrusting followed a SW-directed piggy-back sequence (D2). This has been modified by late-stage breakback thrusts, overturned thrusts and extensional normal faulting associated with culmination collapse and underplating. The ISZ and northern Zanskar shelf sequence are affected by late Tertiary redirected backthrusting (D3), which also affects the Indus molasse. A 50 km wide ‘pop-up’ zone with divergent thrust vergence was developed across the Zanskar Range. Balanced and restored cross sections indicate a minimum of 150 km of shortening across the Zanskar shelf and ISZ. Post-collision crustal thickening by thrust stacking resulted in widespread Barrovian metamorphism in the High Himalaya that reached a thermal climax during Oligocene-Miocene times. Garnet-biotite-muscovite + tourmaline granites were generated by intracrustal partial melting during the Miocene within the Central Crystalline Complex. Their emplacement on the hangingwall of localized ductile shear zones was associated with SW-directed thrusting along the Main Central Thrust (MCT) zone and concomitant culmination collapse normal faulting along the Zanskar Shear Zone (ZSZ) at the top of the slab. Metamorphic isograds have become inverted by post-metamorphic SW-verging recumbent folding and thrusting along the base of the High Himalayan slab. Along the top of the slab, isograds are the right way up but are structurally and thermally telescoped by normal faulting along the ZSZ. 1

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

“…The metamorphic isograds can be deformed passively according to various kinematic models that are compatible with either extrusion or channel flow, or both (e.g. Searle et al 1988Searle et al , 1999Searle & Rex 1989;Jain & Manickavasagam 1993;Grujic et al 1996Grujic et al , 2002Hubbard 1996;Jamieson et al 1996;Davidson et al 1997;Daniel et al 2003). Coupled thermal mechanical finite element modelling ) has been successful in replicating the distribution of the metamorphic isograds and P-T-t data obtained through field and laboratory studies, although it failed to predict the timing of the low temperature metamorphic overprint.…”

“…Recent structural restorations and isotopic studies, however, propose the lower Tethyan sedimentary sequence as a potential protolith for some of the GHS (Vannay & Grasemann 2001;Argles et al 2003;Gehrels et al 2003;Searle & Godin 2003;Richards et al 2005). The STD is generally interpreted as either a d6collement surface (stretching fault), where the thick pile of continental margin rocks (Tethyan sedimentary sequence) has been decoupled without much internal disturbance to the stratigraphy, or a passive roof thrust within the MCT system, with a hanging-wall flat-footwall flat geometry (Searle et al 1988;Yin 2002).…”

Evolution of North Himalayan gneiss domes: structural and metamorphic studies in Mabja Dome, southern Tibet

“…As in studies in Kangmar Dome Chen et al, 1990;Lee et al, 2000), this investigation does not constrain the timing of D1 NS-contractional structures. Studies in the Annupurna Vannay and Hodges, 1996;Godin et al, 1999) and Ladakh -Zanskar regions (Searle et al, 1988) led to the inference of an early to middle Eocene age for this contractional event. Because we did not observe normal faults that could have accommodated the syn-metamorphic penetrative D2 extensional deformation, we follow Lee et al's (2000) interpretation that to maintain strain compatibility, middle crustal collapse (thinning) was accommodated at shallow crustal levels by normal slip along the Southern Tibetan detachment system.…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…We define the final India-Asia collision as the timing of the final marine sedimentation (planktonic foraminifera zone P8; shallow benthic zone SBZ10; Green et al 2008) in the suture zone and along the north Indian plate margin (Garzanti et al 1987;Searle et al 1988Searle et al , 1997bRowley 1998;Zhu et al 2005;Green et al 2008). Ophiolite obduction southward onto the passive margin of Indian preceded India-Asia collision and most probably occurred during the Late Cretaceous-Palaeocene (Searle et al 1988(Searle et al , 1997b.…”