The geodynamic evolution of the Western Mediterranean related to the closure of the Ligurian-Tethys ocean is not yet fully resolved. We present a new 3D numerical model of double subduction with opposite polarities fostered by the inherited segmentation of the Ligurian-Tethys margins and rifting system between Iberia and NW Africa. The model is constrained by plate kinematic reconstructions and assumes that both Alboran-Tethys and Algerian-Tethys plate segments are separated by a NW-SE transform zone enabling that subduction polarity changes from SE-dipping in the Alboran-Tethys segment to NW-dipping in the Algerian-Tethys segment. The model starts about late Eocene times at 36.5 Ma and the temporal evolution of the simulation is tied to the geological evolution by comparing the rates of convergence and trench retreat, and the onset and end of opening in the Alboran Basin. Curvature of the Alboran- Tethys slab is imposed by the pinning of its western edge when reaching the end of the transform zone in the adjacent west-Africa continental block. The progressive curvature of the trench explains the observed regional stress reorientation changing from N-S to NW-SE and to E-W in the central and western regions of the Alboran Basin. The increase of the retreat rates from the Alboran- Tethys to the Algerian-Tethys slabs is compatible with the west-to-east transition from continental-to-magmatic-to-oceanic crustal nature and with the massive and partially synchronous calc-alkaline and alkaline magmatism. Alkaline magmatism is related to the induced sublithospheric mantle flow by the double subduction system depicting a NE-SW upwelling trend.

This work is funded by the SUBTETIS (PIE-CSIC-201830E039, CSIC), ALORBE (PIE- CSIC-202030E310), GeoCAM (PGC2018-095154-B-I00, Spanish Government), Equinor R&T Fornebu (Norway), and the Generalitat de Catalunya grant (AGAUR 2017 SGR 847). We also thank the computer resources at MareNostrum and the technical support provided by the Barcelona Supercomputing Center (BSC) through several projects (AECT-2019-1-0013 and AECT-2019-2-0005). S. Z. has been funded by the Spanish Ministry through Grant DPI2017-85139-C2-2-R, by the Catalan Government through Grant 2017-SGR-1278, and by the EU's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement 777778. This work has been done in the framework of the Unidad Asociada of LACAN-UPC with CSIC and using the facilities of the Laboratory of Geodynamic Modeling from Geo3BCN-CSIC.

Numerical experiments are named M1 and M2. M1: Alboran-Algerian system; M2: Alboran system, according to Figure S2 in Peral et al., 2022. Increasing numbers indicate different timesteps of each experiment.

Peer reviewed