Higher Himalayan Shear Zone, Sutlej section: structural geology and extrusion mechanism by various combinations of simple shear, pure shear and channel flow in shifting modes

Abstract

The Higher Himalayan Shear Zone (HHSZ) in the Sutlej section reveals (1) top-to-SW ductile shearing, (2) top-to-NE ductile shearing in the upper-and the lower strands of the South Tibetan Detachment System (STDS U , STDS L ), and (3) top-to-SW brittle shearing corroborated by trapezoid-shaped minerals in micro-scale. In the proposed extrusion model of the HHSZ, the E 1 -phase during 25-19 Ma is marked by simple shearing of the upper subchannel defined by the upper strand of the Main Central Thrust (MCT U ) and the top of STDS U as the lower-and the upper boundaries, respectively. Subsequently, the E 2a -pulse during 15-14 Ma was characterized by simple shear, pure shear, and channel flow of the entire HHSZ. Finally, the E 2b -pulse during 14-12 Ma observed simple shearing and channel flow of the lower sub-channel defined by the lower strand of the Main Central Thrust (MCT L ) and the top of the STDS L as the lower-and the upper boundaries, respectively. The model explains the constraints of thicknesses of the STDS U and the STDS L along with spatially variable extrusion rate and the inverted metamorphism of the HHSZ. The model predicts (1) shear strain after ductile extrusion to be maximum at the boundaries of the HHSZ, which crudely matches with the existing data. The other speculations that cannot be checked are (2) uniform shear strain from the MCT U to the top of the HHSZ in the E 1 -phase; (3) fastest rates of extrusion of the lower boundaries of the STDS U and the STDS L during the E 2a -and E 2b -pulses, respectively; and (4) variable thickness of the STDS L and rare absence of the STDS U . Non-parabolic shear fabrics of the HHSZ possibly indicate heterogeneous strain. The top-to-SW brittle shearing around 12 Ma augmented the ductile extruded rocks to arrive a shallower depth. The brittle-ductile extension leading to boudinage possibly did not enhance the extrusion.

Shallow-generated damage within non-planar strike-slip fault zones: role of sedimentary rocks in slip accommodation, SW Holy Cross Mountains, Poland

“…Such angular relation conforms with the field observations from other areas (e.g. Mukherjee and Koyi 2010;Mukherjee 2010Mukherjee , 2013a. It is significant that this type of Riedel shears may be linked to the P or Y deformation bands within a very narrow, up to few centimetre wide zones that covers the area in the close vicinity of the fault surface.…”

Higher Himalayan Shear Zone, Zanskar Indian Himalaya: microstructural studies and extrusion mechanism by a combination of simple shear and channel flow

“…In other words, trapezium-shaped grains with straight grain boundaries were only considered as thrust slices. A similar precaution was also adopted by Mukherjee (2007Mukherjee ( ), (2008 and Mukherjee and Koyi (2009a) in sorting out trapezoidal grains from the HHSZ in other Himalayan sections.…”

“…On larger scales as well, the thickness of the continuation of the ZSZ along the trend of the Himalaya is spatially variable (Vannay and Grasemann 2001). For example, it is 5.2-7.3 km in the Sutlej section (Mukherjee and Koyi 2009a), at least 5 km in eastern Himalaya (Carosi et al 1999), 1.5 km in the Dhaulagiri area in Nepal Himalaya (Kellet 2006;Kellet and Godin 2009), 1 km in the eastern Himalaya (Molli, Internet Reference) and especially in the Dzakaa Chu section (Cottle et al 2007), and is as low as 350-400 m in the Annapurna section (Searle and Godin 2003).…”

Implications of channel flow analogue models for extrusion of the Higher Himalayan Shear Zone with special reference to the out-of-sequence thrusting

“…; Mukherjee 2007Mukherjee , 2010aMukherjee and Koyi 2010a,b). The lower boundary of this belt is the Main Central Thrust (Jain and Anand 1988) and the upper boundary is the South Tibetan Detachment SystemUpper (STDS U ) (Mukherjee 2007(Mukherjee , 2010a; Mukherjee and Koyi 2010a). The rocks of the HHSZ could be one of the following: (i) a high-grade metamorphosed lower tectonic unit of the Lesser Himalaya; (ii) that of an upper unit of Tethyan sediments; (iii) diverse crustal elements mixed with Greater India during a major early Palaeozoic tectonism (review by Robinson et al 2006).…”