Late Cretaceous extension and Palaeogene rotation-related contraction in Central Anatolia recorded in the Ayhan-Buyukkisla basin

摘要

The configuration and evolution of subduction zones in the Eastern Mediterranean region in Cretaceous time accommodating Africa-Europe convergence remain poorly quantitatively reconstructed, owing to a lack of kinematic constraints. A recent palaeomagnetic study suggested that the triangular Central Anatolian Crystalline Complex (CACC) consists of three blocks that once formed an similar to N-S elongated continental body, underthrusted below ophiolites in Late Cretaceous time. After extensional exhumation and upon Palaeogene collision of the CACC with the Pontides of the southern Eurasian margin, the CACC broke into three fragments that rotated and converged relative to each other. Here, we date the extension and contraction history of the boundary between two of the rotating massifs of the CACC by studying the Upper Cretaceous-Palaeogene Ayhan-Buyukkisla basin. We report an Ar-40/Ar-39 age of an andesite at the base of the sequence to show that the deposition started in an E-W extensional basin around 72.11 +/- 1.46. The basin developed contemporaneously with regional exhumation of the CACC metamorphics. The lower basin sedimentary rocks were unconformably covered by mid-Eocene limestones and redbeds, followed by intense folding and thrust faulting. Two balanced cross-sections in the study area yield a minimum of 17-27km of post-mid-Eocene similar to N-S shortening. We thus demonstrate the Cenozoic compressional nature of the Kirsehir-Nigde-Hirkadag block boundary and show that the extensional exhumation of the CACC predates collision-related contraction. A plate kinematic scenario is required to explain these observations that involves two Late Cretaceous-Palaeogene subduction zones to the north and south of the CACC, for which we show a possible plate boundary configuration.