Scale-Independence, Uniformitarianism and the Genetic Relationship between Strike-Slip and Thrust Tectonics

William J. Sercombe, Wayne P. Wilson, David A. Pivnik, and Richard A. Beck

Two standard geologic tools, scale independence and uniformitarianism elucidate the genetic relationship between thrust and strike-slip (wrench) systems which geologists have traditionally separated in tectonic theory. A world-wide review of deformed belts indicates a transition from wrenched hinterland cores into compressional thrusts at the outermost frontal fringes. This transition from thrust to strike-slip varies between a gradual increase in structural complexity and three-dimensional strain, as in the Canadian Rockies, to direct contact of thrust sheets with a transpressional metamorphic core as in the Eastern Alps. Wrench faulting produces strike-slip cores that are transitional to outward vergent thrust "petals". Flower structures are scale-independent and are do umented at the laboratory, outcrop, oilfield and continental scale. Compressional structuring in thrust dominated systems are considered here as large scale petals generated as deformation is driven to the foreland from the hinterland/core by transpression. The thrust/wrench relationship is further documented from the heterogeneous mixture of strike-slip, tensional and thrust fault plane focal mechanism solutions calculated from worldwide neotectonic studies in active deformed belts. Simple shear predicts the same combination of fault types. Flower-type structures will produce both thrust and strike-slip earthquakes and are found in seismic areas that have a combination of thrust and strike-slip earthquakes. Tensional earthquakes develop with transtensional zones associated with wrenchin .

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California