Lithospheric Structure Beneath The Western Mediterranean From The Receiver-function Kirchhoff-Radon Transform Method

The western Mediterranean is located at the adjacent area between the European and African plates.Underlying the center of the western Mediteranean is an～700 km long,near-vertical,called the Alboran Slab.The basin extension resulting from the slab rollback and the continents collision together created complex geology in the research area of this study.According to the discussion about the apparently thin crust under the Betics,the controversies about the current relationship between the edges of the Alboran Slab and the crustal base beneath the Gilbraltar Arc,and the debate about the origin of the thin lithosphere beneath the Middle Atlas(MA)and eastern High Atlas(HA),we utilized 179 teleseismic events got from 230 temporary or permanent stations in the research area,applied a three-dimensional Kirchhoff-GRT method to image their P-to-S receiver functions,and test the stability of our results by Bootstrap method.Finally,we obtained high-resolution results about lithospheric structure beneath the western Mediterranean,and made conclusions and explanations as below:1.The results came from Bootstrap method to find that when the percentage of chosen events was over 83%,the stacking results became steady,which comfirmed that our results were stable.2.The crustal thickness between the western and eastern Betics is different.But the range of thick crust(～40-45km)estimated by our method was smaller than the range from some previous studies,we think that the range of delamination happened under the Betics is larger than theirs.3.The current relationship between the top of the Alboran Slab and the crustal base beneath the Betics-Rif orogens still has conflicts.The images obtained in this research have shown that the top of the Alboran Slab has totally detached from the crustal base beneath the Betics,but still attached to the crust of Rif Mountains,which may comfirm the tearing of the slab and explain the intermediate-focus earthquake happened in this area.4.Our results find that the range of thin lithosphere in the Atlas was not extended to the western High Atlas,which didn’t support the theory that the Canary mantle plume beneath the Canary Islands is the source of the heat flow beneath the MA and eastern HA.5.The thin lithosphere under the Atlas resulted from upwelling asthenospheric materials beneath the eastern Rif.The edge-driven convection(EDC)cells beneath the Atlas orogenic system would have led the upwelling asthenospheric materials under the Rif to the base of the Atlas lithosphere,which resulted in thermal erosion and thin lithosphere under the Atlas orogens.