Neotectonics of East Anatolian Plateau (Turkey) and Lesser Caucasus: implication for transition from thrusting to strike-slip faulting

The east Anatolian plateau and the Lesser Caucasus are characterised and sh aped by three major structures: (1) NW-and NE-trending dextral to sinistral active strike-slip faults, (2) N-S to NNW-trending fissures and /or Plio-Q uaternary volcanoes, and (3) a 5-km thick, undeformed Plio-Quaternary conti nental volcanosedimentary sequence accumulated in Various strike-slip basin s. In contrast to the situation in the east Anatolian plateau and the Lesse r Caucasus, the Transcaucasus and the Great Caucasus are characterised by W NW-trending active thrust to reverse faults, folds, and 6-km thick, undefor med (except for the fault-bounded basin margins) continuous Oligocene-Quate rnary molassic sequence accumulated in actively developing ramp basins. Hen ce, the neotectonic regime in the Great Caucasus and the Transcaucasus is c ompressional-contractional, and Oligocene-Quaternary in age; whereas it is compressional-extensional, and Plio-Quaternary in age in the east Anatolian plateau and the Lesser Caucasus. Middle and Upper Miocene volcano-sedimentary sequences are folded and thrus t-to-reverse-faulted as a result of compressional-contractional tectonic re gime accompanied by mostly calc-alkaline volcanic activity, whereas Middle Pliocene-Quaternary sequences, which rest with angular unconformity on the pre-Middle Pliocene rocks, are nearly flat-lying and dominated by strike-sl ip faulting accompanied by mostly alkali volcanic activity implying an inve rsion in tectonic regime. The strike-slip faults cut and displace dykes, re verse to thrust faults and fold axes of Late Miocene age up to maximum 7 km : hence these faults are younger than Late Miocene, i.e., these formed afte r Late Miocene. Therefore, the time period between late Serravalian (simila r to 12 Ma) continent-continent collision of Arabian and Eurasian plates an d the late Early Pliocene inversion in both the tectonic regime, basin type and deformation pattern (from folding and thrusting to strike-slip faultin g) is here termed as the Transitional period. Orientation patterns of various neotectonic structures and focal mechanism solutions of recent earthquakes that occurred in the east Anatolian plateau and the Caucasus fit well with the NS directed intracontinental convergenc e between the Arabian plate in the south and the Eurasian plate in the nort h lasting since Late Miocene or Early Pliocene in places. (C) 2001 Editions scientifiques et medicales Elsevier SAS.