Geochemistry of plagioclase weathering in Nabari gabbroic body, Southwest Japan, and a kinetic model of neoformation mechanism in open system
| Autor: | Okumura, Shigeru |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 1990 |
| Zdroj: | Périodiques Scientifiques en Édition Électronique. |
| Popis: | At the top of the Nabari gabbroic body, several weathering zones can be distinguished, based on the association of authigenic minerals in the saprolite : these include a kaolin minerals-goethite zone, a kaolin minerals-sraectite-goethite(±) zone, and a smectite zone. Plagioclase weathers to gibbsite directly or via allophane at the top of the gabbroic body, dissolves congruently in the middle zone, and changes into kaolinite or into halloysite at the lower zone. The aqueous chemistry in the Nabari gabbroic terrain is presented : [Ca+4]/[H+]2 increases with depth, and the compositional change of the pore water along the circulation path is explained by kinetic dissolution of plagioclase under non-equilibrium conditions, and nearly equilibrium precipitation of authigenic minerals. When a potential gap exists at the plagioclase/water interface, boundary conditions for local equilibrium theory are taken away ; chemical potentials of dissolved species, especially of weakly dissolved species such as aqueous aluminum species, increase toward the interface by a diffusion mechanism in aqueous media. Halloysite formation under locally high aluminum concentrations is explained by this model. Okumura Shigeru. Geochemistry of plagioclase weathering in Nabari gabbroic body, Southwest Japan, and a kinetic model of neoformation mechanism in open system. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol I : Clay-organic interactions. Clay minerals in soils. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 129-138. (Sciences Géologiques. Mémoire, 85) |
| Databáze: | OpenAIRE |
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