Record details

    K-Ar dating of illite fundamental particles separated from illite-smectite
Statement of responsibility
    N. Clauer, J. Srodon, Juraj Franců, Vladimír Šucha
    Clauer, N.
    Franců, Juraj, 1957-
    Srodon, J.
    Šucha, Vladimír
Source title - serial
    Clay minerals
    Vol. 32, no. 2
    p. 181-196
    6 obr., 1 fot., 1 tab., 3 s.bibl.
    Zkr. název ser.: Clay Miner.
Subject group
    datování K/Ar
    ložisko bentonitu
    minerály jílové
    separační technika
Geographical name
Abstract (in english)
   Fundamental particles of illite-smectite from bentonites were separated into classes by high-speed centrifugation after infinitive osmotic swelling of mixed-layer crystals, achieved by Na-exchange and dispersion in distilled water. In samples free of detrial contamination, the thinnest fundamental particles yield older K-Ar ages than the kicker fundamental particles. This implies that they do not preferentially lose radiogenic 40Ar due to size, and the illitization process is a crystal growth mechanism (not nucleation plus growth). As a result, any K-Ar age of fundamental illite particles from bentonites is an integral over longer or shorter periods of time, depending on the thermal history of the rocks. In thick bentonite beds, the measured age difference between the beginning of the illitization process at the contact with the host rocks and the end in the centre of the bed records extremely slow K diffusion in these well compacted rocks.
   These data explain why measured K-Ar ages of illite-smectite from bentonites are younger that the corresponding age of shale illitization, inferred from the burial history of the basin. The finest technically separable size-fractions of associated shales (<0.02 m) yield K-Ar dates* greater than the stratigraphic age. This observation points to incomplete recrystallization of detrial illite during burial diagenesis
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    21. 3. 2008
Import date
    8. 8. 2012