Record details

    Possible effects of tectonic shear strain on phyllosilicates: a case study from the Kandersteg area, Helvetic domain, Central Alps, Switzerland
Statement of responsibility
    Péter Árkai, Rafael Ferreiro Mählmann, Václav Suchý, Kadosa Balogh, Ivana Sýkorová, Martin Frey
Other titles
    Diagenesis and Low-Grade Metamorphism (Variant.)
    Árkai, Péter
    Balogh, Kadosa
    Frey, Martin
    Mählmann, Rafael Ferreiro
    Suchý, Václav
    Sýkorová, Ivana, 1969-
Source title - serial
    Schweizerische mineralogische und petrographische Mitteilungen
    Vol. 82, no. 2
    p. 273-290
    9 obr., 5 tab., 2 s. bibl.
    Zkr. název ser.: Schweiz. mineral. petrogr. Mitt.
Subject group
    břidlice jílová
    datování K/Ar
    vrásnění alpinské
Geographical name
Abstract (in english)
   Relatively few and rather controversial data exist on the effects of tectonic shear strain on phyllosilicates properties under conditions of incipient metamorhism. In the present paper, X-ray powder diffractometric illite and chlorite "crystallinity", apparent mean crystallite thickness and lattice strain data provided from a shale-slate-mylonitized slate sample series. These results are compared with published and new organic petrographic data and microstructural observations. The sample series represents a characteristic vertical section from the Helvetic domain (Central Alps, Switzerland). From top the bottom, this section crosses the boundaries between the Wildhorn nappe, the Gellihorn nappe, and the Doldenhorn nappe.
   The diagenetic/metamorphic grade increases downwards, as shown by phyllosilicate characteristics: Mainly diagenetic conditions prevail in the Wildhorn, partly diagenetic, partly anchizonal conditions in the Gellihorn, and mostly anchizonal conditions in the studied part of the Doldenhorn nappe. This pattern confirms the previously published trend for the Helvetic domain in general. Compared with the retarded phyllosilicates reaction progress, high grades of coalfication, expressed in vitrinite reflectance and graphitization data, are demonstrated throughout the profile. Most probably, this discrepancy can be attributed to differences in kinetic factors influencing metamorphism of phyllosilicates and coalified organic matter during the relatively short-term regional heating. A local, but systematic increase in metamorphic grade in the vicinity of nappe boundaries and also within each nappe, marked by a decrease in "crystallinity" values of clay-size phyllosilicate reaction progress.
   High tectonic strain near the thrust planes has been well established also by the occureence of highly coalfied organic particles and by the development of graphitized organic matter. In addition to shear-strain, migration of fluid also affected the phyllosilicates, especially in the lower, cataclastic-mylonitic zone of the Gellihorn nappe. K-Ar dates obtained on the 0.1-2 um illite-muscovite fraction samples indicate incomplete, partial rejuvenation in the low anchiozonal part of the Wildhorn nappe and in the low to high anchizonal parts of the Gellihorn nappe, but almost complete resetting in the anchizonal Doldenhorn nappe
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    26. 9. 2007
Import date
    8. 8. 2012