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TEM study of the mechanism of transformation of detrital kaolinite and muscovite to illite/smectite in sediments of the Salton Sea geothermal field

Giovanna Giorgetti, M. Pilar Mata and Donald R. Peacor
TEM study of the mechanism of transformation of detrital kaolinite and muscovite to illite/smectite in sediments of the Salton Sea geothermal field
European Journal of Mineralogy (October 2000) 12 (5): 923-934

Abstract

The reaction by which kaolinite transforms to I-S has been studied by SEM and TEM using core samples from the Salton Sea Scientific Drilling Project. Kaolinite is abundant from the surface to a depth of approximately 300 m ( approximately 115 degrees C), decreasing in abundance and becoming undetectable at a depth of approximately 500 m ( approximately 160 degrees C), with a concomitant increase in abundance of I-S. In a 256-m deep sample, kaolinite occurs as large ( approximately 100 mu m) detrital grains, in the fine-grained (<1 mu m) matrix, and as packets forming stacks in detrital biotite and muscovite. In sharp contrast, no kaolinite was detected in the sample from a depth of 477 m but illite and minor I-S occur in the matrix. Authigenic chlorite occurs as subhedral crystals in the matrix with subparallel illite crystals, and as muscovite-chlorite stacks. I-S occurs in three ways: (1) Interlayered within kaolinite as a few, curved layers with 10- and 20-Aa periodicities with the characteristics of collapsed, dehydrated I-S. Along-layer transitions with change in (001) d-value from 7 to 10 Aa occur. (2) As coalescent, randomly oriented packets filling pore space in the matrix. (3) Interlayered with detrital muscovite. These observations show that R1 I-S in Salton Sea-area sediments forms primarily through alteration of kaolinite and muscovite of detrital origin over a temperature interval of approximately 100 to <200 degrees C, with I-S serving as a precursor to illite. Reaction occurs both by direct layer-by-layer replacement of kaolinite and muscovite, and by dissolution, ion transport and crystallization in pore space. Both processes involve dissolution and crystallization, with only the scale of transport varying from that of along-layer interfaces to the dimensions of pore space. The pH value and activity of K (super +) in the hydrothermal brines play important roles in the alteration process and control the simultaneous transformation of both kaolinite and muscovite to I-S.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 12
Serial Issue: 5
Title: TEM study of the mechanism of transformation of detrital kaolinite and muscovite to illite/smectite in sediments of the Salton Sea geothermal field
Affiliation: University of Siena, Department of Earth Sciences, Siena, Italy
Pages: 923-934
Published: 200010
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 33
Accession Number: 2001-000767
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
N32°34'60" - N33°25'00", W116°10'00" - W114°25'00"
Secondary Affiliation: University of Cadiz, ESP, SpainUniversity of Michigan, USA, United States
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 200101
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