Tectono-stratigraphic evolution of the Ayhan Basin, Central Anatolia, Turkey: A Late Cretaceous to Early-Eocene supra detachment basin that underwent post-Lutetian compression and tilting

Abstract

The Ayhan basin is located in the center of the Central Anatolian Crystallyne Complex (CACC). Adjacent to the Ayhan basin are the metamorphic blocks of Hırkadağ to the west and İdis Daği to the east. These expose Cretaceous metamorphic rocks of amphibolite to upper amphibolite facies which are intruded by granites and syenitoids with an assumed Maastrichtian age. The formation of the Ayhan Basin was caused by N-S directed extensional faulting, evidenced by the steep N-dipping normal fault which forms the southern boundary of the basin. This fault was activated during emplacement of the Karahidir volcanics in the Campanian-Maastrichtian. These volcanics are reworked throughout the complete sedimentary sequence of the Ayhan basin. The history of the Ayhan Basin is characterised by pre-Lutetian syn-sedimentary extension, evidenced by syn-sedimentary normal faults. During this extension the basin is dominated by continental sediments assiociated with fluvial and lacustrine paleo-environments. Only during the Lutetian, marine nummulitic limestones are deposited. N-S directed compression started after the Lutetian. During this compression the basin is deformed by folds and south dipping thrust faults. The volcanics at the southern boundary are thrusted northwards over the sedimentary sequence. After this compression the basin is tilted and uplifted. Northernly dipping clastic sediments are deposited, which unconformably overly the Campanian – Lutetian sediments. The post-Lutetian sediments are covered by the volcanic tuffs of the Ürgüp Formation. After the stage of tilting, the metamorphic Hırkadağ and İdis Daği Block are uplifted by steeply dipping normal faults. Based on detailed mapping of the Ayhan Basin, balanced cross-section are created. Restoration of these cross-sections quantify a shortening of ~2 km. Exhumation of the Hırkadağ Block is accomodated by a low angle detachment fault. Unroofing of the Hırkadağ and İdis Daği blocks is only recorded in the Upper Group of the sedimentary sequence of the Ayhan Basin. At the base of this Upper Group metamorphic detritus is found. Therefore, in the study area, the unroofing of the surrounding metamorphic blocks can only be dated to be post-Lutetian. This is opposed to the regional geology of the CACC, where unroofing is pre-Eocene, indicated by middle-Eocene deposits which unconformably overly the metamorphic rocks of the CACC.