Excess argon in amphiboles linked to greenschist facies alteration in the Kamila amphibolite belt, Kohistan island arc system, northern Pakistan; insights from 40Ar/39Ar step-heating and acid leaching experiments

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Authors:Wartho, J. A.; Rex, D. C.; Guise, P. G.
Author Affiliations:Primary:
University of Leeds, Leeds, United Kingdom
Volume Title:Geological Magazine
Source:Geological Magazine, 133(5), p.595-609. Publisher: Cambridge University Press, London, United Kingdom. ISSN: 0016-7568
Publication Date:1996
Note:In English. 56 refs.; illus., incl. 3 tables, geol. sketch map
Summary:A mineralogical and 40Ar/39Ar study of 13 hornblendes from the Kamila amphibolite belt and Kamila shear zone in N Pakistan has revealed a correlation between the degree of greenschist-facies alteration and quantity of excess 40Ar. There is also a N-S divide, with amphibole from the N region showing greater degrees of greenschist-facies alteration, brittle deformation and excess 40Ar incorporation compared to the predominantly plastically deformed, less altered amphibole samples from the Kamila shear zone in the S. Acid leaching of two hornblendes from the Kamila amphibolite belt indicates that a large proportion of the excess 40Ar is correlated with later greenschist-facies alteration phases, and can be easily removed by acid etching, thus revealing acceptable regional 40Ar/39Ar plateau ages of ∼ 76 ± 4 m.y. [R.A.H.]
Subjects:Absolute age; Alteration; Amphibolites; Ar/Ar; Argon; Brittle deformation; Cretaceous; Dates; Deformation; Facies; Greenschist facies; Isotope ratios; Isotopes; Mesozoic; Metamorphic rocks; Metavolcanic rocks; Noble gases; Radioactive isotopes; Stable isotopes; Asia; Indian Peninsula; Indus Valley; Kohistan; Pakistan; Kamila amphibolite belt; Kamila shear zone; Northern Pakistan
Abstract Numbers:97M/1808
Record ID:1997010791
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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