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Perthitic alkali feldspar as indicator mineral in the Central Swiss Alps; dip and extension of the surface of the microcline/sanidine transition isograd

Hans Ulrich Bambauer, Walter Bernotat, Udo Breit and Herbert Kroll
Perthitic alkali feldspar as indicator mineral in the Central Swiss Alps; dip and extension of the surface of the microcline/sanidine transition isograd
European Journal of Mineralogy (February 2005) 17 (1): 69-80

Abstract

The K-feldspar and plagioclase components of the microperthites in granitic rocks from 20 traverses through the Swiss Central Alps have been studied by XRD. Pre-Alpine structural states are preserved in the northern region where maximum temperatures did not exceed 350 degrees C; the northern boundary of this region coincides roughly with the stilpnomelane-out boundary. The southern (central) region is subdivided into two zones. In the northern zone microcline structural states were transformed into sanidine, but in zone 2a the pre-Alpine structural states have all been homogenized to stable low microcline. In zone 2b, the T (sub max) exceeded 450-480 degrees C so that microcline states were transformed into sanidine, which on subsequent cooling back-reacted to various microcline states. Thus from N to S the first occurrence of 'X-ray orthoclase' or intermediate microcline is indicative of the microcline/sanidine isograd. The An content of the microperthitic plagioclase distinguishes two main zones: 1) a northern zone extending to the south beyond the K-feldspar discontinuity where the plagioclase is more or less albitic and 2) a southern zone separated from the northern zone by a discontinuous increase of the An content to oligoclase. The northern boundary of the oligoclase zone closely matches the staurolite-in boundary ( approximately 550 degrees C).


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 17
Serial Issue: 1
Title: Perthitic alkali feldspar as indicator mineral in the Central Swiss Alps; dip and extension of the surface of the microcline/sanidine transition isograd
Affiliation: Westfaelische Wilhelms-Universitaet, Institut fuer Mineralogie,, Munster, Federal Republic of Germany
Pages: 69-80
Published: 200502
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 58
Accession Number: 2005-031131
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N46°10'00" - N46°45'00", E08°00'00" - E09°30'00"
Secondary Affiliation: Forschungszentrum Karlsruhe, DEU, Federal Republic of Germany
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 200517
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