Paleo- and Neo-Tethyan subducted slabs beneath the Eastern Mediterranean region

Douwe J.J. van Hinsbergen , Douwe van der Meer, Wim Spakman 

The late Paleozoic to recent Alpine-Himalayan orogen contains the geological remnants of subducted lithosphere of the Paleotethys and Neotethys oceans and of microcontinents within these. Along its ~12,000 km length, this orogenic belt is divided into segments marked by abrupt changes along-strike. These discontinuities align with paleo-transform faults, across which the histories of ocean opening and closure changed, as indicated by plate reconstructions. Here, we test whether seismic tomography revealing slab remnants and corresponding segments in the mantle below the Tethyan realm may be correlated to Paleo- and Neotethyan subduction zones. We focus on the Anatolian segment and its neighboring Aegean and Iranian segments, where deep-mantle slabs were previously not studied in detail. Using a recent, detailed plate tectonic reconstruction placed in a mantle reference frame, to predict where and when slabs were subducted. We then compare these predictions with seismic tomographic images of the mantle beneath the Eastern Mediterranean and Middle Eastern regions. Building on previously interpreted slabs in the Aegean and Iranian region, we identify anomalies of the Anatolian segment. Notably, we identify a sub-horizontal slab between 2200 and 1500 km depth as the remnant of Paleotethyan oceanic lithosphere that subducted between ~240 and 180 Ma. Subsequent Neotethyan subduction generated three major slabs. Two of these (Pontides and Egypt slabs) detached in the late Cretaceous and are now located in the upper part of the lower mantle. The third one (Cyprus slab) resides predominantly in the upper mantle but penetrates the top of the lower mantle where it is overturned, and is still subducting, or possibly detaching, today. The present positions of these slabs likely reflect their past slab detachment locations, whereas their geometries reflect absolute motions (advancing, stationary, or retreating) of their associated paleo-trenches through time. We show that slabs associated with the Aegean, Anatolian, Iranian, and previously identified Tibetan segments define mantle provinces. The transitions between these provinces closely align with the transform-related boundaries that are expressed in orogenic segmentation. Their stability implies minimal paleo-longitudinal mantle flow in the mantle reference frame since the Early Mesozoic. These observations suggests that upper and lower mantle structure is largely explained by near-vertical slab sinking of slabs after their detachment since the Triassic without significant modification by bottom-up-driven, or lateral mantle convective flow.