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GEOREF RECORD

A re-evaluation of the stratigraphy and evolution of the Kohistan Arc sequence, Pakistan Himalaya; implications for magmatic and tectonic arc-building processes

Peter J. Treloar, Michael G. Petterson, M. Qasim Jan and M. A. Sullivan
A re-evaluation of the stratigraphy and evolution of the Kohistan Arc sequence, Pakistan Himalaya; implications for magmatic and tectonic arc-building processes
Journal of the Geological Society of London (September 1996) 153, Part 5: 681-693

Abstract

New field mapping and structural data from the Kohistan arc allow a re-evaluation of the arc stratigraphy. The oldest units are transitional oceanic-type basalts, which form the basement to the subduction-related sequence. Arc-type gabbroic sheets and plutons intrude the oceanic basalts; together these form the Kamila amphibolite belt. Metasediments and basaltic lavas were deposited, within an extensional basin, onto the Kamila amphibolite belt basement. This sequence, exposed across the arc, forms a distinct stratigraphic unit defined here as the Jaglot group. Sediment-charged turbidity currents transported material into the basin, and submarine eruptions contributed the basaltic component. This period of extension culminated in the eruption of high-Mg boninites of the Chalt Volcanic group which overlie the rocks of the Jaglot group. The earliest granitic rocks of the Kohistan batholith predate suturing and intrude the Jaglot and Chalt sequences. At approximately 100 m.y. Kohistan sutured to Asia, suturing being accompanied by thickening of the arc with the development of major intra-arc shear zones and a penetrative, regionally developed steep cleavage. At approximately 85 m.y. intra-arc rifting permitted emplacement of the voluminous gabbronorites of the Chilas complex which clearly intrudes the Kamila amphibolite belt and also the Jaglot group. Heat advection associated with the emplacement of the Chilas complex caused amphibolite-facies regional metamorphism, melting of the lower arc and plutonism. Some of the resultant granitic plutons were unroofed and eroded between 80 and 55 m.y., before emplacement of further plutons and extrusion of basaltic to rhyolitic volcanic rocks at between 55 and 40 m.y. Much of the magmatism was controlled by extensional tectonics within the overriding plate of the kind commonly associated with a retreating subduction zone.


ISSN: 0016-7649
EISSN: 2041-479X
Coden: JGSLAS
Serial Title: Journal of the Geological Society of London
Serial Volume: 153, Part 5
Title: A re-evaluation of the stratigraphy and evolution of the Kohistan Arc sequence, Pakistan Himalaya; implications for magmatic and tectonic arc-building processes
Affiliation: Kingston University, School of Geological Sciences, Kingston-upon-Thames, United Kingdom
Pages: 681-693
Published: 199609
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 55
Accession Number: 1996-076119
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N32°00'00" - N37°00'00", E71°00'00" - E76°00'00"
Secondary Affiliation: British Geological Survey, GBR, United KingdomUniversity of Peshawar, PAK, PakistanVassar College, USA, United States
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
Update Code: 199623
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