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

https://doi.org/10.1016/0016-7037(82)90115-6Get rights and content

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.

References (39)

  • G. Bocquier et al.

    Un nouveau type d'accumulation oblique dans les paysages géochimiques: l'invasion remontante de la montmorillonite

    C.R. Acad. Sci. Paris

    (1970)
  • T.E. Cerling et al.

    Isotopic evidence for dramatic climatic changes in East Africa during the Pleistocene

    Nature

    (1977)
  • N. Clauer

    Géochimie isotopique du strontium des milieux sédimentaires. Application à la géochronologie de la couverture du craton ouest-africain

    Mém. Sci. Géol., Strasbourg

    (1976)
  • N. Clauer

    Behaviour of strontium and argon isotopes in biotites during progressive natural weathering

  • C.D. Coryell et al.

    A procedure for geochemical interpretation of terrestrial rare earth abundances patterns

    J. Geophys. Res.

    (1963)
  • H. Craig

    Isotopic variations in meteoric waters

    Science

    (1961)
  • Environmental Isotope Data N° 6

    World survey of isotope concentration in precipitation, 1972–1975

    I.A.E.A. Technical Reports Series N° 192

    (1979)
  • I. Friedman et al.

    Hydrogen

  • R.M. Hazen et al.

    The effect of cation substitutions on the physical properties of trioctahedral micas

    Amer. Mineral.

    (1972)
  • Cited by (46)

    • Micas from mariupolite of the Oktiabrski massif (SE Ukraine): An insight into the host rock evolution - Geochemical data supported by Raman microspectroscopy

      2015, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
      Citation Excerpt :

      Hence, the trioctahedral mica is quite fresh. Clauer et al. [29] noted that fresh micas are enriched in K and impoverished in Na and Ca. The chemical composition of fresh dark mica indicates the total Al values of 1.963–2.239 a.p.f.u, pronounced variations of Mg contents, i.e. 0.842–2.135 a.p.f.u. and the average Fe2+/(Fe2+ + Mg) ratio of 0.725.

    • Dating deformation in the Gran Paradiso Massif (NW Italian Alps): Implications for the exhumation of high-pressure rocks in a collisional belt

      2012, Lithos
      Citation Excerpt :

      It cannot be ruled out that biotite, as the main carrier of radiogenic Sr in this domain, was affected by post-deformational alteration or incipient weathering. Biotite is known to be easily oxidised or chloritised during such processes, which tends to disturb and usually rejuvenate apparent Rb/Sr (and K-Ar) ages (Chen et al., 2007; Clauer et al., 1982; Jeong et al., 2006). If this assertion is correct, the apparent age of 30.1 ± 5.4 Ma can be interpreted as a minimum age for the end of ductile deformation in this sample or, alternatively, as a minimum age of pre-alteration closure of the Rb/Sr system in biotite of this sample.

    • Chemical and K-Ar systematics of a mylonitic mica after natural and experimental interactions with varied fluids

      2012, Chemical Geology
      Citation Excerpt :

      The experiments were also designed to provide a basis for an evaluation of the “conventional” wisdom that holds that radiogenic 40Ar is preferentially removed from mica-type particles with respect to K under alteration conditions of any kind. Only a limited literature is presently available on this topic that is critical for a reliable application of the K–Ar and 40Ar/39Ar methods to mica-type materials during natural hydrothermal alteration (e.g., Grove and Harrison, 1996) or continental weathering (e.g., Clauer et al., 1982). A mylonite rock sample from the Riedel faulting zone in the Scottish Highlands was collected at Ben Oss Gully, which is located about 5 km to the S of the Tyndrum city and near a Pb–Zn mine, both about 60 km NNE of Glasgow.

    View all citing articles on Scopus
    View full text