The effect of natural weathering on the chemical and isotopic compositions of biotites
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Abstract
The effect of progressive natural weathering on the isotopic (Rb-Sr, K-Ar, δD, δ18O) 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.
| 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 |
| DOI | 10.1016/0016-7037(82)90115-6 |
| Volume | 46 |
| Issue | 10 |
| Year Published | 1982 |
| Language | English |
| Publisher | Elsevier |
| Description | 8 p. |
| First page | 1755 |
| Last page | 1762 |
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