EXTENSIONAL TECTONICS IN SOUTHERN BASINS AND RANGES, USA AND IN WESTERN TURKEY: A REVIEW OF SIMILARITIES, DIFFERENCES AND PROBLEMS

Western Turkey and the southern Basins and Ranges, USA, are two of the best examples of large continental extensions and exhibit remarkable similarities and some unique differences. The two regions contains structural features unique to extension such as metamorphic core complexes, extensional folds, turtleback faults, shear zones, detachment surfaces, and extensional basins with syn-extensional sedimentary rocks, although the origin of extension is different.

The Basins and Ranges extension was initiated by the formation of the San Andreas fault zone about 30 Ma ago. The rolling hinge model is proposed as the mechanism responsible for the isostatic rise of the metamorphic core complexes which were formed about 20 Ma ago as the ductile extension began to subside. Brittle extension was initiated about 16 Ma ago and produced many extensional basins, including the Furnace Creek, and Death Valley basins. Current problems in the southern Basins and Ranges include determining a) the amount and percentage of cumulative extension; b) the role of strike-slip faulting in the extensional processes; c) amount of slip rate on detachment surfaces; and d) whether the extensional basins are related to the rolling hinge or to deeply rooted normal faults.

There are three proposed models of extension in western Turkey: 1) tectonic escape/ lateral extrusion; 2) back-arc spreading/subduction roll back; and 3) orogenic collapse. The first model suggests that the N- trending basins were developed by the N-S post Paleogene compression and cut by E-W trending basins initiated in Tortonian. The second model proposes that N-S extension is related to the Aegean/Hellenic subduction zone. Proposed timing of the initiation of the roll back process ranges from latest Oligocene to Pliocene. The third model suggests that N-S extension is related to the spreading and thinning of the crust after the Paleogene shortening. Recently, the E-trending basins are interpreted as being formed by a process similar to the rolling hinge/flexural rotation models of extension. Current geological problems in western Turkey include determining a) age, nature and exhumation history of the Menderes massif, b) the amount and percentage of cumulative extension; and c) the origin of the N-S and E-W trending basins and the structural relationship between them.