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

Abstract

Thin-section studies of the Zanskar Shear Zone (ZSZ) rocks reveal a top-to-SW and subsequent primary and secondary top-to-NE ductile shearing; brittle-ductile and brittle extensions; top-to-SW brittle shear, steep normal faulting and fracturing. In the proposed two-phase model of ductile extrusion of the Higher Himalayan Shear Zone (HHSZ), a top-to-SW simple shearing during 22-18 Ma was followed by a combination of top-to-SW simple shear and channel flow at 18-16 Ma. The second phase simulates a thin ZSZ characterized by a top-to-NE shearing. The channel flow component ceased around 16 Ma, the extruding HHSZ entered the brittle regime but the topto-SW shearing continued until perturbed by faults and fractures. Variation in the extrusion parameters led to variable thickness of the ZSZ. Shear strain after the extrusion is presumably maximum at the boundaries of the HHSZ and falls towards the base of the ZSZ, which crudely matches with the existing data. The other predictions: (1) spatially uniform shear strain after the first stage, (2) fastest extrusion rate at the base of the ZSZ, and (3) a lack of continuation of the ZSZ along the Himalayan trend are not possible to validate due to paucity of suitable data. Nonparabolic shear fabrics of the ZSZ indicate their heterogeneous deformation.

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

“…2, Eq. 4 in ''Appendix'') has evolved as an almost unanimously accepted extrusion mechanism of the HHSZ through the wedge-shaped HHSZ in the Bhutan Himalaya (Grujic et al 1996(Grujic et al , 2002Hollister and Grujic 2006), implicitly for the Zanskar section (Stephenson et al 2001; also see Mukherjee and Koyi 2009b), and eventually for all the Himalayan sections by the Dalhousie research group (e.g. Beaumont et al 2001Beaumont et al , 2004Jamieson et al 2002Jamieson et al , 2004; also see reviews by Burbank 2005;Jain et al 2005a, b;Mukherjee 2005;Godin et al 2006;Hodges 2006;Jessup et al 2006;Grujic 2006;Dewey 2008;Mukherjee 2009a).…”

“…1). From structural pxoint of view, the Higher Himalaya has been referred as the 'Higher Himalayan Shear Zone' (HHSZ) by the Roorkee school (Jain and Anand 1988;Jain and Manickavasagam 1993;Manickavasagam et al 1999;Jain et al 2000Jain et al , 2002Jain et al , 2005aMukherjee 2007Mukherjee , 2008; Mukherjee and Koyi 2009b) and recently as an 'orogenic channel' by the tectonic modelers at Dalhousie (e.g. Beaumont et al 2001Beaumont et al , 2004Jamieson et al 2004).…”

The lithospheric density structure below the western Himalayan syntaxis: tectonic implications

“…The exception to this simplification is also documented in terms of out-of-sequence thrusting (Pandey et al 2004;Mukherjee, this volume, in prep. ) and backthrusting (Mukherjee & Koyi 2010;Mukherjee 2013a). In western Himalaya, the tectonic regime can be broadly categorized into (i) the Himalayan collision zone, orthogonal to the plate convergence, (ii) the western syntaxis including Pamir, Nanga Parbat and the Kashmir -Hazara syntaxis and (iii) the Western Fold Belt (WFB) of the Kirthar and Sulaiman ranges until the Chaman Fault, which marks the boundary of the Indian plate towards the west (Fig.…”

Kinematics and Timing of Brittle-Ductile Shearing of Mylonites along the Bok Bak Fault, Peninsular Malaysia

“…In Peninsular Malaysia, the fault systems which encompasses the Bok Bak fault, Kuala Lumpur fault, Bukit Tinggi fault, Mersing fault, and Lebir fault show trends parallel to the large-scale faults of SE Asia such as the Three Pagoda fault, Mae Ping fault and Ailao Shan-Red-River fault. The faults of Peninsular Malaysia are considered to have pre-dated the India-Asia collision event [2][3][4][5][6][7][8][9][10] , although information on kinematics and dating of these faults is lacking. As such, their implication to the regional tectonics is inconclusive.…”

“…Here we examine the kinematics of the Bok Bak fault, and date its timing by the 40 Ar/ 39 Ar method. The Bok Bak fault is classified as one of the terrane crossing faults of Peninsular Malaysia 3 . It is visible as NNW and NW trending of en echelon tectonic lineaments sets spanning of ~200 km (Figure 1).…”