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
2010 (English)In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 99, no 6, 1267-1303 p.Article in journal (Refereed) Published
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 E-1-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 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 (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 E-1-phase; (3) fastest rates of extrusion of the lower boundaries of the STDSU and the STDSL during the E-2a- and E-2b-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.
Place, publisher, year, edition, pages
2010. Vol. 99, no 6, 1267-1303 p.
Higher Himalayan Shear Zone, Extrusion, Ductile shearing, Channel flow, Brittle shearing, Detachment
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:uu:diva-105528DOI: 10.1007/s00531-009-0459-8ISI: 000281026800007OAI: oai:DiVA.org:uu-105528DiVA: diva2:221436
Uppdaterad från In press till Published 201012062009-06-042009-06-042010-12-06Bibliographically approved