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Collision zone between the Kohistan arc and the Asian plate in NW Pakistan

Published online by Cambridge University Press:  03 November 2011

C. J. Pudsey
Affiliation:
Department of Geology, The University, Leicester LEI 7RH, England
M. P. Coward
Affiliation:
Department of Geology, Imperial College, Prince Consort Road, London SW7 5BP, England.
I. W. Luff
Affiliation:
Department of Geology, The University, Leicester LEI 7RH, England.
R. M. Shackleton
Affiliation:
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK43 7BB, England.
B. F. Windley
Affiliation:
Department of Geology, The University, Leicester LEI 7RH, England.
M. Q. Jan
Affiliation:
Centre of Excellence in Geology, University of Peshawar, Peshawar, N.W.F.P., Pakistan.

Abstract

This paper describes the suture zone between the Asian plate and the accreted Kohistan island arc in the Chitral district of NW Pakistan.

The southern part of the Asian plate consists of two tectonic units separated by the N-dipping Reshun fault. The northwestern unit comprises Devonian carbonates and quartzites overlain by Devonian to Permian shales and slates with some limestones (Lun shales). Its structure is complex with S-verging thrusts and isoclinal folds. Along the Reshun fault, the relatively undeformed Reshun Formation may represent molasse. The central unit includes N-dipping Upper Palaeozoic slates and quartzites (Darkot Group), probably faulted against an antiformal tract of slates, schists derived from a volcanic assemblage and Cretaceous limestones (Chitral slate, Koghozi greenschist, Krinj and Gahiret limestones). Asian plate sediments are intruded by granitic and granodioritic plutons, variably deformed and locally porphyritic.

The Northern suture melange of volcanic, sedimentary and serpentinite blocks in a slate matrix separates the Asian plate from the southeastern unit, the Kohistan arc. This comprises Cretaceous volcanic rocks with some sediments (Shamran Volcanic Group, Drosh, Purit and Gawuch Formations) intruded by aphyric diorites, tonalites and granites. These intermediate plutonic rocks pass southwards into a mafic layered complex and amphibolites representing deep levels of the arc. The volcanic rocks and sediments dip to the N and have a horizontal lineation. The structural history of southern Asia and Kohistan is consistent with an originally curved Northern suture: motion of the arc was initially to the NE relative to Asia and subsequently to the NW.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 1985

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