GEOLOGY OF THE SAROS GRABEN AND ITS IMPLICATIONS FOR THE EVOLUTION OFTHE NORTH ANATOLIAN FAULT IN THE GANOS-SAROS REGION, NORTHWESTERN TURKEY

Palaeo- and neo-tectonic evolutions of the Gulf of Saros, northwestern Turkey, were investigated based on geological mapping, geomorphology, seismicity and GPS measurements. In this area three overlapping basin s were differentiated: the Thrace, Enez and Saros basins. The Thrace b asin opened during the middle Eocene on the continental Strandja Massi f as a post-collisional, fault-controlled extensional basin after the closing of the Intra-Pontide Ocean to the south. This basin reached it s greatest extent during the Late Eocene-Early Oligocene and then, tur ned into an intramontane terrestrial basin from the middle Miocene onw ards. The Enez basin opened along the southern margin of the former Th race basin as an E-W-trending half graben during the middle Miocene. T he, age and geometry of this basin corresponds to the extensional basi ns of the Aegean graben system to the south. Stratigraphy and structur es related to the North Anatolian fault indicate that the fault starte d to be active since Pliocene and modified older structures. The fault zone evolved in two stages in and around the Gulf of Saros. During th e initial stage the fault was trending as a single segment with a tran spressional nature and without any stepping, and caused thrusting and folding subparallel to the main trace of the fault. Since the Late Pli ocene the fault was left-stepping in the Saros area, giving rise to th e Saros pull-apart basin. We modelled these two stages by using bounda ry element method, and found that there is a good correlation between the modelling results and geology and geomorphology. (C) 1998 Elsevier Science B.V. All rights reserved.