Record details

    Geochemistry and Rb-Sr geochronology of a ductile shear zone in the Orlica-Śnieznik dome (West Sudetes, Poland)
Statement of responsibility
    Ulrich Lange, Michael Bröcker, Klaus Mezger, Jerzy Don
    Bröcker, Michael
    Don, Jerzy
    Lange, Ulrich
    Mezger, Klaus
Source title - serial
    International journal of Earth sciences (Geologische Rundschau)
    Vol. 91, no. 6
    p. 1005-1016
    8 obr., 1 fot., 6 tab., 2 s. bibl.
    Zkr. název ser.: Int. J. Earth Sci. (Geol. Rdsch.)
Subject group
    chemismus hornin
    datování Rb/Sr
    deformace duktilní
    facie amfibolitová
    orlicko-sněžnické krystalinikum
    vrásnění variské
    vzorek celé horniny
    zóna střižná
Geographical name
    Polsko - jihozápad
Abstract (in english)
   Amphibolite-facies orthogneisses of the Orlica-Snieznik dome in the West Sudetes (Poland) show a local continuous transition from weakly deformed augen gneisses to finely laminated mylonites. Field evidence indicates that ductile shearing developed pre- or syntectonically to a migmatization event. Bulk-rock compositions of variably deformed samples yield no indications for deformation- and/or fluid-enhanced element mobility and redistribution. 87Rb-86Sr geochronology (biotite, phengite, whole rock) places time constraints on the deformation process and the post-orogenic cooling history. Phengite-and biotite-whole-rock pairs yield Rb-Sr ages of 340 to 334 Ma and 335 to 294 Ma, respectively, independent of the degree of deformation. The weighted mean of phengite-whole-rock pairs indicates an age of 337.4+-2.3 Ma. Combining most of the biotite-whole-rock data yields a weighted mean age of 328.6+-4.4 Ma.
   Because of their different closure temperatures for the Rb-Sr system, these differences are interpreted to date cooling after a thermal event. Direct dating of the deformation is not possible, but the cooling history record defines a minimum age for the development of ductile shearing and the last migmatization event. These time constraints provide evidence for the initiation of crustal collapse during or immediately following peak metamorphic conditions. The results of this study further document the importance of Variscan metamorphism in the Orlica-Snieznik dome
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    7. 4. 2008
Import date
    8. 8. 2012