ALASEHIR SUPRADETACHMENT BASIN: A UNIQUE PRODUCT OF EARLY CENOZOIC EXTENSIONAL DEFORMATION IN WESTERN ANATOLIA, TURKEY

Alasehir basin is a well-preserved, Early Miocene – Plio-Quaternary supradetachment basin formed above the Alasehir Detachment fault (ADF) of the Central Menderes metamorphic core complex (MMC). At the south, the north-dipping ADF separates high-grade metamorphic rocks of Gondwana origin intruded by calcalkaline granitoids from Neogene sedimentary rocks of the E-W-trending Alasehir supradetachment basin (ASB). The basin is bounded by high-angle, seismically active normal fault separating Plio-Quaternary Alasehir graben from older units. Petrographic investigation of ADF rocks indicates top-to-the NNE sense of shearing. The sedimentary fill of ASB records critical information about uplift and exhumation of MMC along ADF since the latest Oligocene. Deposition begins in a lacustrine and fluvial/alluvial environment in the Early Miocene. Debris flow deposits alternating within fluvial/alluvial deposits indicate that the region has been disturbed by seismic activities on high-angle normal faults. Early Miocene units overlain by Plio-Quaternary lacustrine-to-alluvial deposits with an angular unconformity. Complex structural architecture of the basin consists of mainly 4 different fault types controlling deposition, subsidence and extension rates: 1- ~E-W-striking ADF 2-Range-perpendicular high-angle normal faults forming step-like structure 3- Range-perpendicular low-angle normal faults mimicking the detachment fault 4-Range-parallel, rotational, high-angle, scissor faults accommodating differential extension and exhumation rates. Due to back-tilting and block-rotation, the older Early Miocene units display steeper dip angles in comparison to those in Plio-Quaternary units. Scissor faults are significant structures that their strike orientation coincides with alkaline-to-hyper alkaline magmatism centers of Kula Volcanic province in the northern margin of the Alasehir graben. Distribution of volcanic rocks and their plutonic equivalents with shoshonitic to alkaline composition along N-S-striking scissor faults can be an indicator of presence of lithospheric-scale, deep fracture zones in the region. ASB is one of the best locations to observe these important regional-scale structures and other endmembers of the continuous Early Cenozoic extensional deformation.