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Clay mineral mixtures as alteration products in pillow basalts from the eastern flank of Juan de Fuca Ridge: a TEM-AEM study

Published online by Cambridge University Press:  09 July 2018

G. Giorgetti ,
P. Marescotti ,
R. Cabella  and
G. Lucchetti
G. Giorgetti*
Affiliation:
Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, 53100 Siena, Italy
P. Marescotti
Affiliation:
Dipartimento per lo Studio del Territorio e delle sue Risorse, C.so Europa, 26, 16132, GenovaItaly
R. Cabella
Affiliation:
Dipartimento per lo Studio del Territorio e delle sue Risorse, C.so Europa, 26, 16132, GenovaItaly
G. Lucchetti
Affiliation:
Dipartimento per lo Studio del Territorio e delle sue Risorse, C.so Europa, 26, 16132, GenovaItaly
*
*E-mail: [email protected]
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Abstract

Transmission electron microscope-analytical electron microscope analyses have been carried out on secondary minerals from pillow basalts with various degrees of alteration from the Juan de Fuca Ridge (ODP Leg 168). The electron microscopic data indicate that the alteration products consist mainly of phyllosilicate mixtures. The least altered sample shows poorly crystalline phyllosilicates occurrring as flakes with 10 Å -spaced lattice fringes. They have compositions of celadonite mixed with smectite and/or Fe oxyhydroxides and Mg-rich smectite. Proceeding towards older, more altered basalts, the alteration products consist of: (1) poorly crystalline celadonite mixtures and Mg-rich smectite; and (2) phyllosilicates with a higher degree of crystallinity, showing lattice fringes with 9.1 Å -spacing and with a talc-like composition. Changes in phyllosilicate association occur as the type of alteration changes from an oxidizing, water-dominated system (occurrence of celadonite mixtures with Fe hydroxides) to a reducing, rock-dominated system (occurrence of Fe-smectite and talc-like mixtures).

Keywords

clay mineralsbasalt alterationTEM-AEMJuan de Fuca Ridge
Type
Research Article
Information
Clay Minerals , Volume 36 , Issue 1 , March 2001 , pp. 75 - 91
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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