STRIKE-SLIP FAULTING AND RELATED BASIN FORMATION IN ZONES OF TECTONIC ESCAPE: TURKEY AS A CASE STUDY

Abstract

Abstract During large-scale convergence of oceanic and arc-type lithospheric fragments towards a cratonic promontory along western North America from Middle Jurassic through Paleogene time, non-subductable crust of the approaching Pacific realm was deflected dextrally northward or sinistrally southward from this ‘reverse indenter’ in the California-Nevada region. Paleontologic and paleomagnetic data suggest oblique dextral displacements on the order of 1.500 to 2,000 km for the accreted terranes in the western Cordillera of Canada. These dextral displacements were first concentrated along closing sutures (from Middle Jurassic to Early Cretaceous time); later they were also taken up by pericollisional fault zones, which propagated into the western parts of the Cordilleran thrust belt and involved the Coast Plutonic Complex (mid-Cretaceous to Paleocene). A-subduction in the thrust belt and inferred B-subduction west of the Coast Plutonic Complex were thus accompanied by dextral displacements within the Omineca and Coast fault arrays respectively, imparling northwest-directed stretching fabrics onto ductile metamorphic or igneous rocks, and discrete fault strands on high-level crustal rocks. The convergent strike-slip fault motions in the Canadian Cordillera created mainly sedimentary source areas rather than subsiding basins. Pericollisional basins that did receive clastic materials from zones of oblique convergence were (1) marginal basins in the process of closing, (2) relict or tectonically overloaded depressions on accreting terranes, (3) foreland basins created by thrust propagation in the miogeoclinal succession, and (4) small pull-apart or restraining bend depressions near high-angle strike-slip faults. Basins in the accreted terrene complexes west of the Cordilleran thrust belt received most of their detrital material from exposed volcanic, plutonic, and oceanic sedimentary rocks; the predominantly turbiditic basin fill suffered repeated deformation, high sustained heat flow, and intrusive activity. The foreland basin to the east of the thrust belt, on the other hand, received most of its detrital input from carbonate and quartz-rich clastic rocks of the miogeocline and metamorphosed equivalents; the predominantly shallow-water clastic deposits of the foreland basin experienced considerably less deformation and thermal alteration than the varied sedimentary assemblages of the accreted belt.