FN Archimer Export Format PT J TI The Moroccan Anti-Atlas ophiolites: Timing and melting processes in an intra-oceanic arc-back-arc environment BT AF Hodel, F. Triantafyllou, A. Berger, J. Macouin, M. Baele, J.-M. Mattielli, N. Monnier, C. Trindade, R.I.F. Ducea, M.N. Chatir, A. Ennih, N. Langlade, Jessica Poujol, M. AS 1:1;2:2,3;3:1;4:1;5:4;6:5;7:6;8:7;9:3,8;10:9;11:9;12:10;13:11; FF 1:;2:;3:;4:;5:;6:;7:;8:;9:;10:;11:;12:;13:; C1 Géosciences Environnement Toulouse (GET), Observatoire de Midi-Pyrénées, CNRS, IRD, Université Toulouse III Paul Sabatier, 14, Avenue Edouard Belin, 31400 Toulouse, France Department of Geology, University of Liège, Sart Tilman, Liège, Belgium Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA Geology and Applied Geology Unit – Mining Geology, Université de Mons, 20, Place du Parc, B-7000, Belgium Department of Earth and Environmental Sciences – G-Time Laboratory, Université Libre de Bruxelles, 50 Avenue Franklin Roosevelt, 1050 Brussels, Belgium Laboratoire de Planétologie et Géodynamique – Nantes (LPGN), UFR Sciences et Techniques, Université de Nantes, UMR-CNRS 6112, France Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universitad de São Paulo, 05508-900 São Paulo, Brazil Faculty of Geology and Geophysics, University of Bucharest, Bucharest, Romania EGGPG, Département de Géologie, Faculté des Sciences, Université Chouaïb Doukkali, 24000 El Jadida, Morocco Microsonde Ouest, Ifremer–Centre de Bretagne, Technopole Brest Iroise, BP70, F-29280 Plouzané, France Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France C2 OBSERV MIDI PYRENEES, FRANCE UNIV LIEGE, BELGIUM UNIV ARIZONA, USA UNIV MONS, BELGIUM UNIV LIBRE BRUXELLES, BELGIUM UNIV NANTES, FRANCE UNIV SAO PAULO, BRAZIL UNIV BUCHAREST, ROMANIA UNIV CHOUAIB DOUKKALI, MOROCCO CNRS, FRANCE UNIV RENNES, FRANCE IF 0.452 TC 21 UR https://archimer.ifremer.fr/doc/00636/74780/74967.pdf LA English DT Article DE ;Neoproterozoic;SSZ;Ophiolite;Back-arc;U-Pb dating;Serpentinite;West African Craton AB The Moroccan Anti-Atlas orogenic belt encloses several Precambrian inliers comprising two major Neoproterozoic ophiolitic complexes: the Sirwa and Bou Azzer ophiolites. These ophiolites expose crustal and mantle units, thrusting over fragments of a long-lived intra-oceanic arc system. We present a detailed geochronological and petro-geochemical study of three mafic/ultramafic units of these two ophiolites: the Khzama sequence (Sirwa ophiolite) and the Northern and Southern Aït Ahmane sequences (Bou Azzer ophiolite). The crystallization of layered metagabbros from the Bou Azzer ophiolite (North Aït Ahmane sequence) has been dated here at 759 ± 2 Ma (U-Pb on zircons). This new age for the Bou Azzer ophiolite is similar to the formation of the Sirwa ophiolite (762 Ma) and suggests that both units formed during the same spreading event. Metabasalts of the three units show tholeiitic signature but with variable subduction-related imprints marked by LILE enrichments, HFSE depletions and variable Ti contents, similar to modern back-arc basin basalts (BABB). Their back-arc origin is also supported by the geochemical signature of ultramafic units showing very low contents in major and trace incompatible elements (Al2O3: 0.12–1.53 wt%, Ti: 3.5–64.2 ppm and Nb: 0.004–0.10 ppm), attesting of a highly refractory protolith. This is in agreement with the high Cr# (0.44–0.81) and low to intermediate Mg# (0.25–0.73) of their constitutive Cr-spinels. Dynamic melting models suggest that these serpentinites experienced intense and polyphased hydrous melting events, strongly influenced by supra-subduction zone SSZ-fluid influx and subduction-related melt percolation. Being particularly affected by these SSZ-melt/rock interactions and closer to arc units to the south, the Sirwa ophiolite and the South Aït Ahmane unit of the Bou Azzer ophiolite likely represent an early stage of the arc-back-arc system, which has been more influenced by the magmatic products of the arc activity compared to the North Aït Ahmane unit of the Bou Azzer ophiolite. PY 2020 PD OCT SO Gondwana Research SN 1342-937X PU Elsevier BV VL 86 UT 000567037800010 BP 182 EP 202 DI 10.1016/j.gr.2020.05.014 ID 74780 ER EF