Deformational and strain patterns of an intracontinental collision ductile shear zone—an example from the Higher Garhwal Himalaya

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Abstract

The Higher Himalayan metamorphic belt of Garhwal appears to have evolved in a major 15–20 km wide, NE-dipping ductile shear zone of the overthrust-type due to intracontinental crustal shortening during Cenozoic continental collision within the Indian Plate. Out of the four major distinct deformation phases, the most widespread D2 deformation phase is marked by a prominent S2 foliation axial-planar to the reclined and recumbent F2 folds, a coaxial NE-plunging L2 stretching lineation and syntectonic growth of index metamorphic minerals. These deformational structures are developed during the SW-directed D2 ductile shear deformation, irrespective of the orientation of the S2 foliation and thrust zones.

Regional strain patterns in quartzite of the Lesser Himalayan Garhwal Group beneath the Main Central Thrust (MCT) and the Central Crystalline Zone using Rf/φ data on quartz clasts and aggregates reveal that the maximum values of finite strain εs are attained within narrow mylonitic shear zones within the broad ductile shear zone. During its progressive translation towards higher structural levels in late D2 and D3 deformation phases, the shortening was accommodated by development of thrust sheets with the MCT and Jutogh Thrust surfaces coinciding with zones of mylonite and maximum strain. At higher levels, ductile shear zones became compressional brittle-ductile zones which resulted in the development of SW-verging F3a and F3b folds during the southward migration of the thrust sheets in the Lesser Himalaya.

References (53)

  • N Fry

    Random point distribution and strain measurement in rocks

    Tectonophysics

    (1979)
  • K Honegger et al.

    Magmatism and metamorphim in the Lakakh Himalayas (the Indus-Tsangpo suture zone)

    Earth Planet. Sci. Lett.

    (1982)
  • J.R Hossack

    Pebble deformation and thrusting in the Bygdin area (S. Norway)

    Tectonophysics

    (1968)
  • R Kligfield et al.

    Strain analysis of a Northern Apennine shear zone using deformed marble breccias

    J. Struct. Geol.

    (1981)
  • N.E Odling

    Strain Analysis and strain path modelling in the Loch Tollier gneisses, Gairloch, NW Scotland

    J. Struct. Geol.

    (1984)
  • J.P Platt et al.

    Structures and fabrics in a crustal-scale shear zone, Betic Cordillera, SE Spain

    J. Struct. Geol.

    (1986)
  • D.J Sanderson

    The development of fold axes oblique to the regional trend

    Tectonophysics

    (1973)
  • M.P Searle

    Structural evolution and sequence of thrusting in the High Himalayan, Tibetan-Tethys and Indus suture zones in Zanskar and Ladakh, Western Himalaya

    J. Struct. Geol.

    (1986)
  • A.W.B Siddans et al.

    Finite strain patterns and their significance in Permian rocks of the Alps Maritime (France)

    J. Struct. Geol.

    (1984)
  • H Takagi

    Implications of mylonitic microstructures for the geotectonic evolution of the Median Tectonic Line, central Japan

    J. Struct. Geol.

    (1986)
  • V.C Thakur

    Development of major structures across the northwestern Himalaya, India

  • G.D Williams

    Rotation of contemporary folds into the X direction during overthrust processes in Laksefjord, Finmark

    Tectonophysics

    (1978)
  • A Anand

    Deformation and strain patterns of the Central Himalayan metamorphics from Northwestern Garhwal

    (1986)
  • V.B Bhanot et al.

    RbSr ages for some granitic and gneissic rocks of Kumaun and Himachal Himalaya

  • O.N Bhargava

    Outline of the stratigraphy of Eastern Himachal Pradesh, with special reference to the Jutogh Group

  • M Brunel

    Ductile thrusting in the Himalaya: shear sense criteria and stretching lineation

    Tectonics

    (1986)
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