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The Ophiolitic Sequence of the Sivas Basin (Turkey) : Implications for Tethyan Dynamics in Anatolia

Abstract

The closure of the various oceanic branch of the Neotethys is classically associated with the obduction of ophiolitic rocks, defining several suture zones. These oceanic sutures extending from the Eastern Alps to the Oman reflect a complex and still poorly understood paleogeographic framework. Reconstructions of the Anatolian continent assume the amalgamation of one or more continental fragments during the Mesozoic–Early Cenozoic time. In that context, the Sivas Basin is located in a key position at the junction of three crustal domains: the Pontides to the North, the Anatolide – Tauride platforms to the South, and the Central Anatolian Crystalline Complex to the West. This Tertiary basin is formed during the closure of the Northern branch of Neotethys. Notably, this basin developed over an ophiolitic basement obducted from the North during the Maastrichtian, outcropping mainly to the North and South of the basin boundaries. The Tertiary sedimentary succession developed directly on the ophiolitic basement, characterized by Paleocene to Eocene carbonate plateform followed by more continental and evaportic deposits during the Oligocene. This basement has been previously related to the ophiolitic melange from the Izmir - Ankara – Erzincan suture. Based on new field data from the Gürlevik Daği, we will show that the ophiolitic complex preserved, from the bottom to the top: 1) a large volume of intensely serpentinized peridotites, strongly veined with chrysotile, with locally minor gabbroic intrusions 2) upward, serpentinized mantle rocks are affected by a cataclastic deformation associated with tectonic breccias and ophicalcites, eventually 3) on the top of the mantle radiolarian cherts, sedimentary breccia with mantle clasts are deposited. We interpret this ophiolitic succession as related to an ocean-continent transition characterized by the exhumation of subcontinental mantle rocks, along low-angle detachment faults. The serpentinized peridotites record the final rifting stage leading to the exposure of the mantle rocks at the sea floor and their reworking in tectonosedimentary breccias (ophicalcites). The age of initiation of detachment is constrained by radiolarites datations and U-Pb geochronology from zircon of the gabbros sampled in the field. Eventually, a new structural scheme is proposed for the Gürlevik Daği area.