Depositional and Tectonic Evolution of the Late Cenozoic Alasehir Supradetachment Basin, Western Anatolia (Turkey)
Z. Öner and Y. Dilek
Geology, Miami University, 116 Shideler Hall, Oxford, OH 45056
The sedimentary record of the extensional graben systems developed on the Menderes core complex (MCC) in western Anatolia provides critical information on the timing, nature and kinematics of Cenozoic extensional deformation in the Aegean province. The study area, located on the southern shoulder of the Alasehir graben, includes high-grade metamorphic rocks of the MCC overlain by the Miocene & younger sedimentary rocks above a N-dipping detachment surface. The ~100-m-thick cataclastic shear zone beneath this surface contain S-C fabrics, microfaults, Riedel shears, mica-fish structures & shear bands, all consistently indicating top-tothe North shearing. Granodioritic plutons crosscutting the MCC & the detachment surface are exposed within this cataclastic zone, displaying extensional ductile & brittle structures. The oldest sedimentary units overlying the detachment surface are the Lower-Middle Miocene shale and limestone of lacustrine & fan delta facies (Gerentas & Kaypaktepe Units). Stratigraphically upward these rocks are overlain by the U. Miocene (Acidere Frm), Plio-Pleistocene (Göbekli, Yenipazar, Asartepe & Erendali Frms) & Quaternary fluvial and alluvial fan sediments. Several major unconformities exist in these Miocene-Quaternary strata that likely developed as a result of extensional tilt-block faulting during the evolution of the Alasehir graben and its L. Cenozoic predecessor in a supradetachment basin (SDB). The internal structure & stratigraphy of the basinal strata suggest that the paleo-drainage patterns may have changed from predominantly S to N during MCC exhumation to E to W as rotational block faulting fully developed within the Alasehir SDB in the latest Cenozoic. High-angle, oblique-slip scissor faults crosscut the MCC rocks, the detachment surface & the basinal strata, offsetting them for more than few 100 meters. Fault blocks locally show different structural architecture & metamorphic grades, suggesting differential uplift along these scissor faults, which also controlled the kinematics of faulting & the distribution, shape and depth of the accommodation space within the SDB. Identification of these extension-perpendicular scissor faults in highly extended terrains is important for correctly reconstructing the crustal exhumation history & paleogeography of SDBs.
AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas