Folding and imbrication of the Indian crust during Himalayan collision

Abstract

India collided with a northern Kohistan-Asian Plate at about 50 Ma ago, the time of ocean closure being fairly accurately defined from syntectonic sediments as well as the effect on magnetic stripes on the Indian Ocean floor. Since collision, Asia has over-ridden India, developing a wide range of thrust scrapings at the top of the Indian Plate. Sections through the imbricated sedimentary cover suggest a minimum displacement of over 500 km during Eocene to recent plate convergence. This requires the Kohistan region to the north to be underlain by underthrusted middle to lower Indian crust, deformed by ductile shears and recumbent folds. These structures are well seen in the gneisses immediately south of the suture, where they are uplifted in the Indus and Nanga Parbat syntaxes. Here there are several phases of thrust-related small-scale folding and the development of a large folded thrust stack involving basement rocks, the imbrication of metamorphic zones and the local development of large backfolds. Some of the important local structures: the large late backfolds, the Salt Ranges and the Peshawar Basin, can all be related to the necessary changes in thrust wedge shape as it climbs through the crust and the three dimensional nature of the thrust movements associated with interference between the Kohistan and western Himalayan trends.

Deformation migration in an orogen-scale shear zone array: an example from the Basal Briançonnais Thrust, internal Franco-Italian Alps

“…Coward et al 1988;Jadoon, Lawrence & Lillie, 1992). Attempts have been made to interpret these crustal-scale structures in terms of thrust belt tectonics (e.g.…”

Composite mesoscopic and magnetic fabrics of the Paleo-Proterozoic Wangtu Gneissic Complex, Himachal Himalaya, India: Implications for ductile deformation and superposed folding of the Himalayan basement rocks

“…Whilst volumetric analysis suggests shortening of 1815-2100 km in west and 2750-2800 km in eastern part of the Himalaya (Dewey et al, 1989;Le Pichon et al, 1992), cross section balancing estimates shortening of only 85-700 km (c.f. Johnson, 2002) (Coward and Butler, 1985;Coward et al, 1988;Searle et al, 1988;Schelling and Arita, 1991;Ratschbacher et al, 1994;Srivastava and Mitra, 1994, etc.). One possible reason behind the much lower values obtained from cross section balancing is that it does not consider internal deformation of the basement, i.e.…”

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

“…Coward and others, 1988;Treloar and others, 1989;DiPietro and others, 2008), but is now resolved by the succession of FIA data and crustal shortening directions recorded by these microstructures (Figure 1d). In addition, two separate kyanite-grade metamorphic cycles have been identified associated with N-S (FIA set 2) and E-W (FIA set 3) shortening.…”

“…These temperatures are all too high to represent earth-surface temperatures but are reasonable burial temperatures given estimates of the burial history of the region. The total thickness of Cenozoic basin sediments in this area are estimated to be between 3-5 km, with our section composing the base of this succession (Liu and Wang, 2001;Coward and others, 1988). Vitrinite reflectance data (personal communication, Haisheng Yi, CITS, Chengdu) from the overlying Yaxicuo Group suggest FHSG sediments have been exposed to maximum burial temperatures of up to 180°C, depending on actual thicknesses of the FHSG.…”