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TEM evidence for high-temperature (300 degrees C) smectite in multistage clay-mineral pseudomorphs in pelitic rocks (Rif, Morocco)

Philippe Agard, Michael Jullien, Bruno Goffe, Alain Baronnet and Mohammed Bouybaouene
TEM evidence for high-temperature (300 degrees C) smectite in multistage clay-mineral pseudomorphs in pelitic rocks (Rif, Morocco)
European Journal of Mineralogy (August 1999) 11 (4): 655-668

Abstract

Optically homogeneous pseudomorphs occur in high-Pressure metapelites from the Alpine Rif chain, Morocco, along with talc and kyanite. Further characterization using optical microscopy, electron microprobe, single-crystal X-ray diffraction, and HRTEM reveals a complex metamorphic replacement sequence of a previous high-pressure metamorphic mineral, possibly magnesiochloritoid. Within the pseudomorphs, three zones are recognized based on the occurrence of distinct layer silicates, which crystallized under different P-T conditions along the retrograde metamorphic P-T path. These layer silicates are, from core to rim: (1) a relic mixture of margarite and chlorite, (2) oriented chlorite-smectite intergrowths+ or -pyrophyllite, and (3) chlorite and abundant smectite (at the periphery of the pseudomorph). These pseudomorphs represent an uncommon record of the retrograde metamorphic P-T path because the earliest smectite formed while the rocks still experienced P-T conditions in the stability field of pyrophyllite. This observation suggests that clay minerals may crystallize as regional metamorphic products, and that their stability field might not be restricted to late shallow-depth alteration.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 11
Serial Issue: 4
Title: TEM evidence for high-temperature (300 degrees C) smectite in multistage clay-mineral pseudomorphs in pelitic rocks (Rif, Morocco)
Affiliation: CNRS, UMR, Ecole Normale Superieure, Paris, France
Pages: 655-668
Published: 199908
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 58
Accession Number: 1999-066200
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
N34°00'00" - N36°00'00", W06°34'60" - W02°04'60"
Secondary Affiliation: CEA Saclay, FRA, FranceCNRS, CRMC2, FRA, FranceUniversite Mohamed V, MAR, Morocco
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 199922
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