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Magmatic crystallization, isobaric cooling, and decompression of the garnet-bearing assemblages of the Jijal Sequence (Kohistan Terrane, western Himalayas)

Lucie Ringuette, Jacques Martignole and Brian F. Windley
Magmatic crystallization, isobaric cooling, and decompression of the garnet-bearing assemblages of the Jijal Sequence (Kohistan Terrane, western Himalayas)
Geology (Boulder) (February 1999) 27 (2): 139-142

Abstract

The Jijal ultramafic-mafic sequence is the lowermost exposed part of the Kohistan terrane. Petrography and geothermobarometry show that garnet-bearing assemblages of the Jijal sequence consist of a mosaic of magmatic and metamorphic equilibria. Garnet-bearing magmatic assemblages started their crystallization at a depth >50 km, either at the base of a thickened arc-type crust or within rising magmatic batches in the upper mantle. Quasi-isobaric cooling of magmatic assemblages occurred in the high-P, high-T granulite field without reaching the eclogite field. Subsequently, these assemblages were partly retrograded under amphibolite- to greenschist-facies conditions. This succession of equilibria attests to a switch from a high-P quasi-isobaric cooling regime to a major decompression followed by final cooling at the upper-crustal level. This P-T evolution is best explained by a yet unrecognized tectonic event that consists of partial exhumation of the base of the Kohistan terrane during its accretion to the Asian plate. Final cooling and unloading in turn, could be related to extension following the obduction of the Kohistan terrane onto the Indian plate.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 27
Serial Issue: 2
Title: Magmatic crystallization, isobaric cooling, and decompression of the garnet-bearing assemblages of the Jijal Sequence (Kohistan Terrane, western Himalayas)
Affiliation: Universite de Montreal, Departement de Geologie, Montreal, QC, Canada
Pages: 139-142
Published: 199902
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 22
Accession Number: 1999-021262
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N35°30'00" - N36°15'00", E73°00'00" - E74°00'00"
Secondary Affiliation: University of Leicester, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199908
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