A Miocene onset of the modern extensional regime in the Isparta Angle: constraints from the Yalva‡ Basin (southwest Turkey)

The pre-Neogene Tauride fold-and-thrust belt, comprising Cretaceous ophiolites and metamorphic rocks and non-metamorphic carbonate thrust slices in southern Turkey, is flanked and overlain by Neogene sedimentary basins. These include poorly studied intra-montane basins including the Yalva double dagger Basin. In this paper, we study the stratigraphy, sedimentology and structure of the Yalva double dagger Basin, which has a Middle Miocene and younger stratigraphy. Our results show that the basin formed as a result of multi-directional extension, with NE-SW to E-W extension dominating over subordinate NW-SE to N-S extension. We show that faults bounding the modern basin also governed basin formation, with proximal facies close to the basin margins grading upwards and basinwards into lacustrine deposits representing the local depocentre. The Yalvac Basin was a local basin, but a similar, contemporaneous history recently reconstructed from the AltA +/- napa Basin, similar to 100 km to the south, shows that multi-directional extension dominated by E-W extension was a regional phenomenon. Extension is still active today, and we conclude that this tectonic regime in the study area has prevailed since Middle Miocene times. Previously documented E-W shortening in the Isparta Angle along the Aksu Thrust, similar to 100 km to the southwest of our study area, is synchronous with the extensional history documented here, and E-W extension to its east shows that Anatolian westwards push is likely not the cause. Synchronous E-W shortening in the heart and E-W extension in the east of the Isparta Angle may be explained by an eastwards-dipping subduction zone previously documented with seismic tomography and earthquake hypocentres. We suggest that this slab surfaces along the Aksu thrust and creates E-W overriding plate extension in the east of the Isparta Angle. Neogene and modern Anatolian geodynamics may thus have been driven by an Aegean, Antalya and Cyprus slab segment that each had their own specific evolution.