Rapid Late Eocene Exhumation of the Sivas Basin (Central Anatolia) Driven by Initial Arabia-Eurasia Collision

Continental collisions exert a profound influence on the configuration and evolution of orogenic systems. The effects of Arabia-Eurasia collision on the geodynamics of the eastern Mediterranean are difficult to unravel, however, because the timing of initial collision (i.e., intercontinental contact) remains controversial. We present the first detrital and bedrock apatite fission track and (U-Th-Sm)/He thermochronology, and detrital zircon U-Pb constraints from the Sivas Basin and eastern Taurides in central Anatolia (Turkey), which provide a detailed record of Cenozoic orogenesis in the hinterland of the Arabia-Eurasia collision zone. Our results indicate rapid middle Eocene burial followed by shortening, rapid cooling (up to ~25–45 °C/myr), and initiation of the southern Sivas fold-thrust belt (SSFTB) during the late Eocene (~40–34 Ma), consistent with evidence of a coeval basin-wide unconformity. We interpret that rapid late Eocene cooling of the SSFTB reflects exhumation driven by the northward propagation of retroforeland contraction into the Sivas Basin from the middle to late Eocene, and we propose that these events were due to initial soft collision of the thinned Arabian passive margin by ~45 Ma. This timing of the inception of collision is supported by a regional compilation of apatite fission track data that indicates rapid cooling and hinterland exhumation throughout central and eastern Anatolia from ~45 to 20 Ma, which was synchronous with a widespread magmatic lull from ~40 to 20 Ma. The data presented here are compatible with a widely accepted transition to more mature or hard collision at ~20 Ma, probably related to the arrival of thick Arabian crust along the Bitlis suture zone.