ZusammenfassungEine Klassifizierung der Geometrie von Dilatationsbrtichen wird vorgeschlagen. Sie wird angewendet auf Strukturen die charakterisiert werden k6nnen als die Kombination eines Bruchsystems und eines Dilatationsvektorfeldes. Die Klassifizierung wird illustriert dutch Beispiele von magmatischen Gfingen, Pegmatitien und Pseudotachyliten. Segmentierung in Form yon Vers~itzen, StoBfugen oder Gabelungen sind hfiufig in vielen Bruchsystemen. Vier Grundtypen von Dilatationsbruchsystemen k6nnen an Hand der Segmentierungsgeometile unterschieden werden, diese sind: Unregelm~i-gige -, verzweigte -, kulissenf6rmige -und zickzack Typen. Die Zickzack-Bruchsysteme werden weiter untergliedert. Sie bestehen aus neu gebildeten sich schief ausdehenden Brtichen, oder aber aus bereits bestehenden Flfichen des Muttergesteins, welche yon der schiefen Erweiterung reaktiviert wurden. Dies ist die erste Ver6ffentlichung, die von magmatischen Zickzack-Gfingen berichtet, die neu geformte Brtiche entwickeln.Die
AbstractA classification of dilational fracture geometry is proposed. It applies to structures that can be characterized by the combination of a fracture system and a dilation vector field. The classification is illustrated with examples of igneous dykes, pegmatites, and pseudotachylites. Segmentation in the form of offsets, jogs, or bifurcations is common to most fracture systems. Four basic types of dilational fracture systems are distinguished on the basis of the geometry of segmentation. These are: irregular, braided, en-echelon, and zigzag. Zigzag fracture systems are further differentiated. They consist of newly formed, obliquely dilated fractures or, alternatively, of pre-existing planes in the host-rock that are reactivated by oblique dilation. This paper is the first to actually report an igneous zigzag-dyke involving newly formed fractures.Rotation of the regional stress field in the direction of propagation leads to en-echelon segmentation. Braided fracture systems reflect high local stress-intensities, probably related to propagation rate. Two possibilities exist for the formation of zigzag dykes consisting of newly formed fractures that are obliquely dilated. They may form by extreme interaction of tensile fracture segments in a regional stress field with a low differential stress. Alternatively, they may form in a regional stress field with high differential stress through the propagation of shear fractures.Segmentation of dykes, characterized by offsets, is common. Such segmentation can be the result of protrusions of the fracture termination. Offsets also occur where a dyke cuts an older planar structure. Such offsets are the result of the local inhibition of fracture propagation. The resulting apparent offset can lead to a misinterpretation of relative age.Apophyses form as a result of the dilation of a segmented fracture system.
R6sum6Cette note propose une classification des fractures de dilatation, basge sur leur g6om6trie. Elle s'applique aux structures que l'on peut caractdriser par la combinaison d'...