International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

RELATIONSHIPS BETWEEN FOLDING AND FRACTURING IN OROGENIC BELTS: EXAMPLES FROM THE RHENOHERCYNIAN ZONE (GERMANY) AND THE EXTERNAL HELLENIDES (GREECE)

Pages: 153 - 162

Authors: SOTIRIOS KOKKALAS, PARASKEVAS XYPOLIAS, IOANNIS K. KOUKOUVELAS, THEODOR DOUTSOS

Abstract: The kinematic similarities of small-scale structures in the Rhenohercynian Zone and the external zones of the Hellenides are illustrated. Both orogenic domains comprise asymmetric folds verging toward the foreland and are affected by extensional joints (ac and bc) associated with hybrid joints as well as with shear fractures (hk0a and hk0b). Joints were formed during layer bending which took place throughout the fold evolution and were symmetrically arranged with respect to principal stresses σ1, σ2 and σ3. Although the magnitude of the stress axes changed during folding, their orientation with respect to layering remained constant: one of them is orientated perpendicular to the layering, whereas the other two are parallel and perpendicular to the dip direction of the layering respectively. As expressed by ac and hybrid joints the extension normal to the dip direction of layering progressively increased during fold tightening. Layer parallel shear responsible for the asymmetry of the folds caused joint rotation toward the fold hinge within the long limb. Furthermore, these movements controlled at both limbs the formation of bc and associated hybrid joints during the folding.

Keywords: Rhenohercynian, Hellenides, folding, extensional joints, hybrid joints, shear fractures

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