A precursor of the North Anatolian Fault in the Marmara Sea region

Abstract

Abstract Apatite (U-Th)/He and fission-track analyses of both basement and sedimentary cover samples collected around the Marmara Sea point to the existence of a system of major E–W-trending structural discontinuities active at least from the Late Oligocene. In the Early Pliocene, inception of the present-day North Anatolian Fault (NAF) system in the Marmara region occurred by reactivation of these older tectonic structures. This is particularly evident across the Ganos fault in southern Thrace, as exhumation south of it occurred during the latest Oligocene and north of it during the mid-Miocene. In this area, large tectonic structures long interpreted as the results of Plio-Quaternary NAF-related transpressional deformation (i.e. the Ganos monocline, the Korudag anticline, and the Gelibolu folds) were in fact produced during the Late Oligocene – Early Miocene. The overall lack of significant (U-Th)/He age differences across the NAF indicates that the Early Pliocene inception of strike–slip motion in the Marmara region represents a relatively minor episode. At the scale of the entire Marmara region, the geographic pattern of exhumation ages shown in this study results instead from the complex superposition of older tectonic events including: (i) the amalgamation of Sakarya and Anatolide–Tauride terranes and (ii) Aegean-related extension.