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Chlorine-rich amphiboles; interplay between amphibole composition and an evolving fluid

Kare Kullerud
Chlorine-rich amphiboles; interplay between amphibole composition and an evolving fluid
European Journal of Mineralogy (April 1996) 8 (2): 355-370

Abstract

Cl-rich amphiboles (Cl 0.59-3.78 wt.%) occur with garnet, plagioclase and Ba-, Ti- and Cl-rich biotite in narrow shear zones in 1800 m.y. noritic granulites in the Flakstadphi y basic complex, Lofoten, N Norway. The granulite-facies assemblage was partially replaced by an amphibolite-facies assemblage (including Cl-rich amphibole) formed during shear deformation associated with the infiltration of a Cl- and Ba-rich fluid. The Cl content of the amphiboles ranges from 0.1 to 1.0 atom pfu; there are strong correlations between Cl and K, Fe, Mg, (super [6]) Al, (super [4]) Al and Si. The compositional variation can be described in terms of a Cl-free additive component (K (sub 0.1) Na (sub 0.6) )(Ca (sub 1.9) Mg (sub 2.9) Fe (sub 1.7) Ti (sub 0.9) Al (sub 0.4) ) (Al (sub 1.2) Si (sub 6.8) )(OH) (sub 2) and a completely coupled exchange component (Si (sub -1.6) (super [4]) Al (sub 1.6) (super [6]) Al (sub 0.9) Fe (sub 1.3) Mg (sub -2.1) K (sub 0.4) Cl (sub 1) OH (sub -1) ). It is inferred that the compositional variation of amphiboles along the exchange vector were caused by variations in only one chemical variable, i.e. the ratio a (super fluid) (sub HCl) /a (super fluid) (sub H sub 2O) of the grain-boundary fluid. Formation of amphibole and biotite during interaction between the primary igneous minerals and the fluid resulted in an increase in the Cl content of the fluid, since H is preferentially incorporated relative to Cl into these minerals. The composition of the amphibole provides a pattern for how the fluid phase gradually disappeared through the rock.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 8
Serial Issue: 2
Title: Chlorine-rich amphiboles; interplay between amphibole composition and an evolving fluid
Author(s): Kullerud, Kare
Affiliation: University of Tromso, Department of Geology, Tromso, Norway
Pages: 355-370
Published: 199604
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 27
Accession Number: 1996-044108
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N63°30'00" - N71°10'00", E09°30'00" - E31°04'60"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199615
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