The Pre-Obduction to Post-Obduction Evolution of the Sivas Ophiolite (Turkey) and Implications for the Precollisional History of Eastern Anatolia

Abstract

The Anatolian block preserves remnants of Tethyan oceanic basins consumed by north dipping subduction zones until the Late Cretaceous prior to Paleogene collision. The Sivas Basin, which belongs to the Maastrichtian to Cenozoic Central Anatolian basins, is located in a key position limited to the north and the south by respectively the Pontides and Tauride ophiolitic bodies and to the west by the Kırşehir block. This study focuses on the southern margin of the Sivas Basin, where an obducted ophiolite is capped by Maastrichtian-Paleocene sediments. We present new field observations, with U-Pb zircon dating on magmatic rocks and geochemical analyses to (1) unravel the pre-obduction nature and origin of the ophiolitic basement and (2) describe the post-obduction tectonosedimentary evolution. The pre-obduction evolution shows that (i) the Sivas ophiolite is characterized by serpentinized peridotites, with minor magmatic intrusions, (ii) the top of the serpentinized mantle is characterized by a cataclastic deformation with ophicalcites interpreted as an extensional detachment fault, (iii) the U-Pb zircon dating of two magmatic intrusions yield age of 91.49 ± 0.8 Ma and 72.7 ± 0.5 Ma, and (iv) petrological and geochemical data show that the magmatic intrusions were affected by hydrothermal metamorphism. These data suggest that the Sivas ophiolite may have recorded forearc hyperextension in frame of a Late Cretaceous suprasubduction zone. The post-obduction evolution is characterized by the deposition of a Maastrichtian-Paleocene carbonate platform on the ophiolite, followed by clastic sediments containing reworked ophiolitic and Tauride Mesozoic clasts. ©2019. American Geophysical Union. All Rights Reserved.