TY - JOUR
T1 - Higher Himalayan Shear Zone, Sutlej section
T2 - Structural geology and extrusion mechanism by various combinations of simple shear, pure shear and channel flow in shifting modes
AU - Mukherjee, Soumyajit
AU - Koyi, Hemin A.
N1 - Funding Information:
Acknowledgments SM acknowledges the Guest Scholarship (2005– 2006) of Swedish Institute, 2002–2007 Junior and Senior Research Fellowships (grant numbers: F.NO.2-48/2001(II)EU.II and 9/143(441)/ 2003-EMR-I, respectively) of the Council of Scientific and Industrial Research (India), 2008 Research Associateship of Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR, India) and 2009 onwards ‘Seed Grant’ (Spons/GS/SM-1/2009) of Indian Institute of Technology Bombay. Swedish Research Council supported HAK. Discussions with K. C. Sahu (Imperial College) and C. J. Talbot (Uppsala University) on channel flow, and with A. K. Jain (Indian Institute of Technology Roorkee) on Himalayan geology were beneficial. C. J. Talbot owes additional thanks to help us in designing the ‘channel flow box’ (Fig. 22), fine tuning the English and sharpening research problems. R. Chakrabarti (Harvard University), S. Bhattacharyya (Alabama University) and A. Ghatak (Rochester University) constantly updated us on Himalayan Geology. Several interactions with R. Govindarajan (JNCASR) led SM to correlate channel flow with the Himalayan tectonics. The ‘channel flow box’ was manufactured by Sören Karlson (Uppsala University). A number of constructive reviews by B. C. Bur-chfiel (Massachusetts Institute of Technology) significantly improved the manuscript. W-C. Dullo, M. Dullo and the Indian Springer team are thanked for their efficient editorial handling of the manuscript.
PY - 2010
Y1 - 2010
N2 - 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 (STDSU, STDSL), and (3) top-to-SW brittle shearing corroborated by trapezoid-shaped minerals in micro-scale. In the proposed extrusion model of the HHSZ, the E1-phase during 25-19 Ma is marked by simple shearing of the upper sub-channel defined by the upper strand of the Main Central Thrust (MCTU) and the top of STDSU as the lower- and the upper boundaries, respectively. Subsequently, the E2a-pulse during 15-14 Ma was characterized by simple shear, pure shear, and channel flow of the entire HHSZ. Finally, the E2b-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 (MCTL) and the top of the STDSL as the lower- and the upper boundaries, respectively. The model explains the constraints of thicknesses of the STDSU and the STDSL 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 MCTU to the top of the HHSZ in the E1-phase; (3) fastest rates of extrusion of the lower boundaries of the STDSU and the STDSL during the E2a- and E2b-pulses, respectively; and (4) variable thickness of the STDSL and rare absence of the STDSU. 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.
AB - 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 (STDSU, STDSL), and (3) top-to-SW brittle shearing corroborated by trapezoid-shaped minerals in micro-scale. In the proposed extrusion model of the HHSZ, the E1-phase during 25-19 Ma is marked by simple shearing of the upper sub-channel defined by the upper strand of the Main Central Thrust (MCTU) and the top of STDSU as the lower- and the upper boundaries, respectively. Subsequently, the E2a-pulse during 15-14 Ma was characterized by simple shear, pure shear, and channel flow of the entire HHSZ. Finally, the E2b-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 (MCTL) and the top of the STDSL as the lower- and the upper boundaries, respectively. The model explains the constraints of thicknesses of the STDSU and the STDSL 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 MCTU to the top of the HHSZ in the E1-phase; (3) fastest rates of extrusion of the lower boundaries of the STDSU and the STDSL during the E2a- and E2b-pulses, respectively; and (4) variable thickness of the STDSL and rare absence of the STDSU. 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.
KW - Brittle shearing
KW - Channel flow
KW - Detachment
KW - Ductile shearing
KW - Extrusion
KW - Higher Himalayan Shear Zone
UR - http://www.scopus.com/inward/record.url?scp=77955774015&partnerID=8YFLogxK
U2 - 10.1007/s00531-009-0459-8
DO - 10.1007/s00531-009-0459-8
M3 - Article
AN - SCOPUS:77955774015
SN - 1437-3254
VL - 99
SP - 1267
EP - 1303
JO - International Journal of Earth Sciences
JF - International Journal of Earth Sciences
IS - 6
ER -