Kinematics of a former oceanic plate of the Neotethys revealed by deformation in the Ulukışla basin (Turkey), Tectonics
- D. Gürer, D.J.J. van Hinsbergen, L. Matenco, F. Corfu, A. Cascella
Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Suprasubduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers) were generated during this subduction event and are today distributed in the eastern Mediterranean region along three ~E-W trending ophiolitic belts. Several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra-Neo-Tethyan subduction zone. Here we present new paleospreading directions from six Upper Cretaceous ophiolites of Turkey, Cyprus, and Syria, calculated by using new and published paleomagnetic data from sheeted dyke complexes. Our results show that ~NNE-SSW subduction zones were formed within the Neo-Tethys during the Late Cretaceous, which we propose were part of a major step-shaped subduction system composed of ~NNE-SSW and ~WNW-ESE segments. We infer that this subduction system developed within old (Triassic?) lithosphere, along fracture zones and perpendicular weakness zones, since the Neo-Tethyan spreading ridge formed during Gondwana fragmentation would have already been subducted at the Pontides subduction zone by the Late Cretaceous. Our new results provide an alternative kinematic model of Cretaceous Neo-Tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old (and cold) lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges. Plain Language Summary The inception of new subduction zones is one of the most critical and at the same time still unclear processes of the solid earth cycle. A major subduction initiation event started in the Late Cretaceous (~95 Ma) in the vast Neo-Tethys Ocean separating Gondwana and Eurasia landmasses. Several contrasting hypotheses have been put forward to explain the kinematics of such a regional-scale event, but most of these models invoked an unlikely simultaneous initiation of multiple subduction zones. Here we present new data from six suprasubduction zone ophiolites of Turkey, Cyprus, and Syria providing the first quantitative constraints on the kinematics of Late Cretaceous subduction initiation in the Neo-Tethys. Suprasubduction zone ophiolites are emerged fragments of oceanic crust formed during subduction inception above the embryonic subduction zone. Paleospreading directions calculated from these ophiolites indicate that the Neo-Tethyan Cretaceous subduction did not start at ~E-W trending active plate boundaries (i.e. spreading ridges) as commonly proposed, but rather along ~NNE-SSW trending fracture zones connected by ~WNW-ESE segments parallel to passive margins, in ancient (Triassic?), cold, and thick lithosphere.