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The effect of natural weathering on the chemical and isotopic compositions of biotites

Geochimica et Cosmochimica Acta

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Abstract

The effect of progressive natural weathering on the isotopic (Rb-Sr, K-Ar, ??D, ??18O) and chemical (REE, H2O+) compositions of biotite has been studied on a suite of migmatitic biotites from the Chad Republic. During the early stages of weathering the Rb-Sr system is strongly affected, the hydrogen and oxygen isotope compositions change markedly, the minerals are depleted in light REE, the water content increases by a factor of two, and the K-Ar system is relatively little disturbed. During intensive weathering the K-Ar system is more strongly disturbed than the Rb-Sr system. Most of the isotopic and chemical modifications take place under nonequilibrium conditions and occur before newly formed kaolinite and/or smectite can be detected. These observations suggest that 1. (a) "protominerals" may form within the biotite structure during the initial period of weathering, and 2. (b) only when chemical equilibrium is approached in the weathering profile are new minerals able to form. ?? 1982.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The effect of natural weathering on the chemical and isotopic compositions of biotites
Series title:
Geochimica et Cosmochimica Acta
Volume
46
Issue:
10
Year Published:
1982
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
1755
Last page:
1762
Number of Pages:
8