Growth of the imbrication zone along the southeast Anatolian orogenic belt: evidencefrom fission track thermochronology from Gölbaşı region (SE Turkey)

Abstract

: One of the major components of continental collision zones is their imbricated zones. Such a zone along the Southeast Anatolian Orogenic Belt (SAOB) is solely controlled by a still-active convergence and accretion system between the Anatolian Plate and Arabian platform since at least Late Cretaceous. The zone is characterized by NEE/SWW-trending, northward-dipping thrust slices that are squeezed between the Tauride Block to the north and the Arabian platform to the south. The units cropping out within the zone comprise Neo-Tethys-related magmatic, ophiolitic, sedimentary and metamorphic rocks with Late Cretaceous to Miocene formation/metamorphism ages. The Karanlıkdere granitoid intrudes into Late Cretaceous Meydan ophiolite, Helete volcanics, and Malatya metamorphics. These units thrust over Cenozoic volcanic and sedimentary rocks. Although various scenarios have been proposed for the late Cretaceous to Neogene evolution of the complex region, quantitative data aiming to understand the growth mechanism of the imbrication zone in the region are limited. The zircon U-Pb and the apatite fission track (AFT) thermochronology were applied to the Karanlıkdere granitoid within the imbrication zone of the Southeast Anatolian Orogenic Belt (SAOB). The LA-ICP-MS zircon U-Pb age yields 79.67 ± 0.24 Ma with 0.23–0.65 Th/U ratios. This age is slightly younger than the previously published ages, indicating that the main body of the Karanlıkdere granitoid formed 3-4 Ma later than the small dikes intruded into other units. The AFT ages are directly controlled by altitude and range between 40.38 ± 3.4 Ma and 22.81 ± 0.63 Ma. The oldest AFT age has the highest altitude, whereas the youngest has the lowest height. The age-temperature models show a slow uplift rate between 40 Ma and 22 Ma. The results indicate that the growth of the imbrication zone in front of the Nappes of the SAOB continued in a steady-state mode with a slow uplift rate of 0.02 ± 0.005 mm/a, during middle-late Eocene to early Miocene and increasing uplift rate during early-middle Miocene, which might be explained by continental collision during early-middle Miocene.