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Pre-collisional anastomosing shear zones in the Kohistan Complex (NW Pakistan)

Abstract : Ductile strain localisation commonly forms a pattern of shear zones anastomosing around lenses of less deformed rock. Initiation and development history of anastomosing shear zones, which are little documented, are studied through the description of the structures and the deformation history of plutonic rocks that form the lower crust of the Kohistan Complex. Structures and textures developed in these rocks result from primary magmatic to solid state regional strain overprinted by anastomosing shear zones. The primary strain was mainly acquired during magmatic emplacement at 100-90 Ma. Strain localisation took place continuously from magmatic emplacement to solid state deformation during cooling of the plutons and formed 3 successive sets of shear zones. Set 1 is composed of associated discrete Riedel and thrust shear zones developed above solidus conditions during SW-ward thrusting. Continuous deformation from solidus to amphibolite facies conditions between 100 and 83 Ma formed the second set of shear zones. The lower amphibolite facies set 3 shear zones are differentiated by larger strain recorded in the thicker mylonitic zones and enlargement of the spacing between shear zones during cooling. The anastomosing pattern of shear zones described here probably represents arc-related deformation during subduction of the Tethys oceanic lithosphere below the Kohistan Arc Complex.
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Submitted on : Monday, November 20, 2006 - 4:44:27 PM
Last modification on : Wednesday, August 7, 2019 - 2:48:08 PM

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Laurent Arbaret, Jean-Pierre Burg, G. Zeilinger, N. Chaudrhy, S. Hussains, et al.. Pre-collisional anastomosing shear zones in the Kohistan Complex (NW Pakistan). The Geological Society, London, Special Publications, Geological Society of London, 2000, 170, pp.295-311. ⟨10.1144/GSL.SP.2000.170.01.16⟩. ⟨hal-00115233⟩

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