Developing lithospheric strain fabrics and complex asthenospheric flow in the eastern Mediterranean: evidence from shear-wave splitting

Abstract:

Since 20 Ma the Anatolian plate has experienced rapid westward motion relative to Eurasia, up to 2 km of uplift, and widespread volcanism. Processes that have been proposed to explain these phenomena include large scale asthenospheric flow, tearing and/or break-off of subducting slabs, and lithospheric dripping and/or delamination. We investigate these processes by measuring upper mantle seismic anisotropy via teleseismic shear-wave splitting, using SKS, SKKS and PKS phases observed at seismograph stations throughout the eastern Mediterranean from the period 1991-2020. In the north of our study area, we present evidence for lithospheric anisotropy along the North Anatolian Fault (NAF). Elsewhere, anisotropy is consistent with asthenospheric flow through tomographically-imaged slab gaps and flow driven by Hellenic trench retreat. Shorter splitting delay times and nulls in central Anatolia suggest weaker azimuthal anisotropy in the asthenosphere, supporting models that invoke vertical mantle flow patterns (lithospheric dripping and/or asthenospheric upwelling). Evidence for westward flow of asthenosphere driving Anatolian plate motion is lacking, suggesting plate motions are not driven by basal drag.