Hostname: page-component-cd9895bd7-fscjk Total loading time: 0 Render date: 2024-12-25T18:03:55.342Z Has data issue: false hasContentIssue false
  • English
  • Français

Weathering mineral facies in altered granites: The importance of local small-scale equilibria

Published online by Cambridge University Press:  05 July 2018

A. Meunier  and
B. Velde
A. Meunier
Affiliation:
Laboratoire de Pédologie, Faculté des Sciences, Université de Poitiers, 86022, France
B. Velde
Affiliation:
Laboratoire de Pétrographie, Université Pierre et Marie Curie, 4 place Jussieu, 75230, Paris, Cedex 05, France
Get access Rights & Permissions [Opens in a new window]

Summary

Classical clay mineralogy determinations and electron microprobe analyses of weathering minerals developed in altered two-mica granites indicate that the chemical forces that produce new minerals are often constrained to small volumes, frequently on the scale of a mineral grain or contact between two grains in the granite.

Chemical potentials such as pH, alkali and alkaline earth and silica activity in the altering aqueous solutions provoke a destabilization of pre-existing minerals, which recrystallize locally to give a new multimineral product. The chemical composition of the new phases is largely governed by the relative concentrations of the elements present in the former minerals.

Three mineral facies were observed in the weathered granites: initially a sericite-beidellitic type, then a beidellite-kaolinitic type, and finally a last stage kaolinite-oxide facies assemblage. The position of each facies is not restricted to a given depth in the profile but the relative proportions of each facies found in a thin-section size sample change towards the kaolinite-oxide facies.

The global rock chemistry reflects the type facies predominant in each sample. The first two facies are roughly silica conservative while the kaolinite-oxide facies loses silica as well as alkali and alkaline earths.

Geochemical and clay mineral studies of rock alteration should consider problems of mineral genesis at very localized sites.

Type
Research Article
Information
Mineralogical Magazine , Volume 43 , Issue 326 , June 1979 , pp. 261 - 268
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1979

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bisdom, (E. B. A.), 1967. Leid. Geol. Med. 37, 33.Google Scholar
Boulet, (R.), 1974. Thesis, Strasbourg University, 330 pp.Google Scholar
Dejou, (J.), 1958. Thesis, Clermont-Ferrand, 164 pp.Google Scholar
Delvigne, (J.), 1965. Cah. Off. Rech. Sci. Territ. Outre-Mer, Dunod, Paris.Google Scholar
Feth, (J. M.), Robertson, (C. E.), and Polzed, (W. L.), 1964. US Geol. Survey. Water supply paper, 15351, 70 PP.Google Scholar
Grant, (W. H.), 1963. Clays and Clay Minerals (11th Nat. Clay Conf.), 65.CrossRefGoogle Scholar
Hoda, (S. N.) and Hood, (W. C.), 1972. Clays and Clay Minerals. 20, 343.CrossRefGoogle Scholar
Jackson, (M. L.), 1965. Soil Sci. 99, 1, 15.CrossRefGoogle Scholar
Lelong, (F.), 1969. Mem. Sci. Terre (Thesis), Nancy University, 14, 187 pp.Google Scholar
Leneuf, (N.), 1959. Thesis, Off. Rech. Sci. Territ. Outre-Mer.Google Scholar
Meunier, (A.), 1975. C.R. Acad. Sci. Paris. 280, 221.Google Scholar
Meunier, (A.) and Velde, (B.), 1976. Clay Minerals. 11, 235.CrossRefGoogle Scholar
Meunier, (A.) 1977. Thesis, Poitiers University (in press).Google Scholar
Novikoff, (A.), 1974. Thesis, Strasbourg University, 298 pp.Google Scholar
Pédro, (G.), 1964. Thesis, Inst. Nat. Rech. Agron. Versailles, 344 PP.Google Scholar
Seddoh, (F. K.), 1973. Mem. Univ. Dijon (Thesis), 377 PP.Google Scholar
Tardy, (Y.), Bocquier, (G.), Paquet, (H.), and Millot, (G.), 1973. Geoderma. 10, 4, 271.CrossRefGoogle Scholar
Thompson, (J.B.,jr.), 1959. Researches in Geochemistry. Wiley: New York Google Scholar