Recent tectonic reorganization of the Nubia-Eurasia convergent boundary heading for the closure of the western Mediterranean ANDREA BILLI 1* ,CLAUDIO FACCENNA 1,2 ,OLIVIER BELLIER 3 ,LILIANA MINELLI 4 ,GIANCARLO NERI 4,5 , CLAUDIA PIROMALLO 4 ,DEBORA PRESTI 2,5 ,DAVIDE SCROCCA 1 and ENRICO SERPELLONI 6 Key-words. – Western Mediterranean, Convergent boundary, Tectonic reorganization, subduction, Back-arc basin, Basin inversion. Abstract. – In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian (W-Africa) northward subduction beneath Eurasia, subduction has almost ceased, as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic re- flection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the conver- gent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two back-arc oceanic bas- ins (Algerian-Liguro-Provençal and Tyrrhenian basins) and it is now mainly active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provençal, Algerian, and Alboran (partly) margins. Onset of compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins fol- lowing a similar propagation of the cessation of the subduction, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced on the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to really start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. Part of the contractional deformation may have shifted toward the north in the Liguro-Provençal basin possibly because of its weak rheological properties compared with those of the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are strongly heterogeneous along the boundary. These fea- tures prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred to follow a Wilson Cycle (at a small scale) with the following main steps : (1) northward Nubian subduction with Mediterranean back-arc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive onset of compression, from west to east, in the former back-arc domain and consequent basin inversion (since ~8-10 Ma); (4) possible future subduction of former back-arc basins. Réorganisation tectonique récente du domaine de convergence de plaque Nubie-Eurasie en Méditerranée occidentale Mots-clés. – Méditerranée occidentale, Frontière de plaque en convergence, Réorganisation tectonique, Subduction, Bassin d’arrière arc, Inversion tectonique. Résumé. – En Méditerranée occidentale, après une longue période (Paléogène supérieur et Néogène) de subduction de la plaque nubienne sous l’Eurasie, la subduction s’arrête et la convergence doit alors être accommodée par d’autres pro- cessus géodynamiques impliquant une réorganisation tectonique de la méditerranée occidentale. Une synthèse des données tectoniques, séismologiques, géodésiques, tomographiques, et de sismique réflexion complétée par de nouvelles mesures géodésiques, nous permet de proposer un modèle de cette réorganisation tectonique intégré à l’échelle de la Méditerranée occidentale. Entre le Nord du Maroc et le Nord de la Sicile, la déformation com- pressive résultant de la convergence s’est déplacée de la zone de subduction vers les marges des bassins océaniques d’arrière arc, que sont les bassins algéro-liguro-provençal et tyrrhénien. Les marges tyrrhénienne (Nord de la Sicile), li- guro provençale (SE de la France), algérienne et de l’Alboran sont par ailleurs toujours actives. La compression, ainsi que l’inversion tectonique associée, se sont propagées, du bassin d’Alboran (c. 8 Ma) vers le domaine tyrrhénien (c.2 Ma), parallèlement à la rupture du slab due à l’arrêt de la subduction. Ensuite l’inversion s’est propagée vers la Bull. Soc. géol. France, 2011, t. 182, n o 4, pp. 279-303 Bull. Soc. géol. Fr., 2011, n o 4 1. Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy. * Corresponding author : Istituto di Geologia Ambientale e Geoingegneria (IGAG), CNR, Area della Ricerca Roma 1, Via Salaria km 29,300, Monterotondo, 00016, Roma, Italy, Tel. +39 06-90672732, email : andrea.billi@cnr.it 2. Dipartimento di Scienze Geologiche, Università Roma Tre, Rome, Italy. 3. UMR CEREGE – 6635, CNRS, Université Paul Cézanne, Aix-Marseille Université, IRD, Collège de France, Europôle de l’Arbois, BP. 80, 13545 Aix-en-Provence, France. 4. Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy. 5. Dipartimento di Scienze della Terra, Università di Messina, Messina, Italy. 6. Istituto Nazionale di Geofisica e Vulcanologia, Centro Nazionale Terremoti, Bologna, Italy. Manuscript received July 16, 2010; accepted on Decembre 23, 2010.