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Marine and supergene alteration processes in a chloritized amphibole-schist, Deux-Sevres, France

Published online by Cambridge University Press:  09 July 2018

D. Proust ,
P. Dudoignon ,
A. Bouchet  and
A. Meunier
D. Proust
Affiliation:
Laboratoire de Pétrologie de la Surface, Université de Poitiers, 86022 Poitiers Cédex
P. Dudoignon
Affiliation:
Laboratoire de Pétrologie des Altérations Hydrothermales, Université de Poitiers, 86022 Poitiers Cédex, France
A. Bouchet
Affiliation:
Laboratoire de Pétrologie des Altérations Hydrothermales, Université de Poitiers, 86022 Poitiers Cédex, France
A. Meunier
Affiliation:
Laboratoire de Pétrologie des Altérations Hydrothermales, Université de Poitiers, 86022 Poitiers Cédex, France
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Abstract

Mineralogical examination of a strongly chloritized amphibole-schist indicated that it had been subjected to two alteration episodes of different origin. Structural and petrographic evidence showed that the alteration processes operated per descensum from the bedrock surface down to shallow depth, thus eliminating any hydrothermal episode due to fluid ascension through deep fractures. The rock was first altered into interstratified chlorite-vermiculite minerals with potassic interlayers. These potassic clay minerals occur in an originally K-deficient rock and seem to have been generated by a marine alteration episode; this episode appears to be contemporaneous with the Cenomanian transgression which covered the amphibole-schist with sandy-clayey deposits. The potassic clay minerals were replaced during a later meteoric alteration episode by kaolinites, iron oxides, and smectites with Mg, Ca interlayer cations.

Type
Research Article
Information
Clay Minerals , Volume 22 , Issue 2 , June 1987 , pp. 129 - 143
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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