Kinematics of the Greater Himalayan sequence, Dhaulagiri Himal: implications for the structural framework of central Nepal

Abstract

In the Dhaulagiri region of central Nepal quartz-rich specimens sampled from the Greater Himalayan sequence yield well-defined quartz c -axis fabrics with a dominant top-to-the-SW sense of shear. These fabrics reflect pervasive crystal-plastic deformation extending more than 8 km structurally below previously mapped locations of the Main Central thrust fault. Quartz c -axis fabric opening angles suggest deformation temperatures of c . 500 ± 50 °C within the lower portion of the Greater Himalayan sequence and up to c . 670 ± 50 °C within the migmatitic upper portion. These temperatures generally plot within error of garnet–biotite temperature estimates for metamorphic assemblages and are interpreted to reflect Tertiary deformation during extrusion of the mid-crust. The quartz c -axis data, and a new, detailed tectonostratigraphic map, constrain the position of the Ramgarh thrust in the Dhaulagiri region to be coincident with the Main Central thrust at the base of the pervasively deformed exhumed mid-crustal core. Mean kinematic vorticity numbers ( W m ) measured in specimens sampled from the lower portion of the Greater Himalayan sequence range between 0.49 and 0.80 ( c . 66–41% pure shear) with an average value of 0.67 ( c . 53% pure shear). These data indicate that extrusion of the mid-crust was facilitated by a significant component of pure shear strain.

Evidence for Pleistocene Low-Angle Normal Faulting in the Annapurna-Dhaulagiri Region, Nepal

“…Leucogranitic intrusions persist across the detachment into the lower-grade Tibetan Sedimentary Sequence calc-schists in the hanging wall. Ductile deformational fabrics, similar to those observed in the Kali Gandaki Valley, are also found in the footwall and hanging wall in the Myagdi Khola Valley (Larson and Godin 2009). Brittle deformation is evidenced by a narrow brecciated zone along the fault that dips ca.…”

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

“…This means there is a possibility that the MCT U , the STDS L and the STDS U were active between 19 and 14 Ma; and the MCT L , the STDS L and the STDS U at 14-12 Ma. (ix) A heterogeneous ductile shear regime was dominated by central pure shear and marginal simple shear (Grasemann et al 2006;Law et al 2004;review by Exner 2005;Jessup et al 2006;Carosi et al 2007;Larson and Godin 2009). (x) The sub-horizontal channel at mid-crustal depth beneath the Tibetan plateau contains 3-7% partially molten rocks (Caldwell et al 2009).…”

Pressure–temperature–time–deformation path of kyanite-bearing migmatitic paragneiss in the Kali Gandaki valley (Central Nepal): Investigation of Late Eocene–Early Oligocene melting processes

“…Deformation within the GHS is dominantly characterized by general shear (e.g. Larson and Godin, 2009 and references therein). The GHS is tectonically overlaid by the Tethyan Sedimentary Sequence (TSS) via a large scale ductile to brittle system of normal faults, named South Tibetan Detachment System (Burchfiel et al, 1992;Burg et al, 1984;Caby et al, 1983;Carosi et al, 1998Carosi et al, , 2002Searle, 2010).…”