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K/Ar Systematics of an Acid-Treated Illite/Smectite: Implications for Evaluating Age and Crystal Structure

Published online by Cambridge University Press:  02 April 2024

James L. Aronson  and
C. B. Douthitt
James L. Aronson
Affiliation:
Case Western Reserve University, Cleveland, Ohio 44106
C. B. Douthitt*
Affiliation:
Case Western Reserve University, Cleveland, Ohio 44106
*
1Present address: Geology Department, Melbourne University, Parkville, Victoria 3052, Australia.
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Abstract

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On the basis of progressive acid dissolution the Thompson-Hower model states that mixed-layer glauconite/smectite and illite/smectite contain potassium in two structural sites: a mica-type K position (site 1) and a position of uncertain structural status more prone to dissolution (site 2). Site 2 was thought not to retain radiogenic argon (40Ar*). Using extensive progressive acid dissolution and K/Ar studies on a sized illite/smectite (I/S), determining the amount of K in site 2 is shown to be somewhat more complicated than previously thought because the dissolution pattern depends on acid normality. More important, site 2 fully retains 40Ar*, and no age correction is thus necessary as is required by the Thompson-Hower model, further affirming the geochronologic value of illite in mixed-layer clay. These data are also relevant to understanding the crystal and particle structure of I/S. Site 2 is probably a partly filled K interlayer that develops as an intermediate kinematic step on the way to being fully filled during the transformation of smectite to illite.

Keywords

Acid dissolutionAge datingGlauconiteIllite/smectiteInterstratificationOrderingPotassium
Type
Research Article
Information
Clays and Clay Minerals , Volume 34 , Issue 4 , August 1986 , pp. 473 - 482
Copyright
Copyright © 1986, The Clay Minerals Society

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