Role of a Late Cretaceous Volcanic Arc and Related Units in Tectonic Assembly of the Tethyan Suture Zone, Central and Eastern Pontides, North Turkey

The Izmir-Ankara-Erzincan suture zone (IAEZ) in the Central and the Eastern Pontides, N Turkey comprises a stack of mainly Upper Cretaceous-Early Tertiary thrust sheets that record the development of: 1) a subduction­-accretion complex; 2) a rifted continental margin volcanic arc and associated fore-arc basin, and 3) a backarc basin and its sedimentary fill. Alternative tectonic models are considered in this thesis in the light of structural, sedimentary, igneous geochemical and palaeontological evidence. A tectonostratigraphic revision of the Late Cretaceous-Early Tertiary Neotethyan units in the Central and Eastern Pontides, combined with new biostratigraphic ages is used to constrain the timing of events associated with the assembly of the suture zone. All of the Late Cretaceous Neotethyan units exhibit a pervasive north-vergent shear. The age of north vergent deformation is constrained by the oldest overlying sediments (Kadikizi Formation and Sipikör Formation) as pre-Eocene. Large-scale southward thrusting followed, forming the present thrust stack. Whole-rock geochemical analyses of basic igneous rocks obtained by X-ray fluorescence indicate the presence of a volcanic arc within the suture zone. The geochemistry of the Neotethyan ophiolites (found to the north of the arc units in both areas) suggests they may represent emplaced backarc basin lithosphere. Screens of metamorphic rocks within the ophiolite in the Eastern Pontides, together with geochemical evidence for a partially enriched mantle source of arc volcanic rocks in the Central Pontides suggest that the arc-backarc system formed by rifting of the continental margin of Eurasia. Using petrographic evidence thick (<1500 m) sedimentary successions found within the suture zone are interpreted as arc apron, forearc, backarc and syn-collisional basins respectively. It is inferred that Neotethys was subducted northwards beneath the Eurasian margin associated with oceanwards trench-retreat, development of a volcanic arc and a backarc basin during Late Cretaceous time.