Article (Scientific journals)
The Moroccan Anti-Atlas ophiolites: Timing and melting processes in an intra-oceanic arc-back-arc environment
Hodel, F.; Triantafyllou, Antoine; Berger, J. et al.
2020In Gondwana Research, 86, p. 182-202
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Keywords :
Back-arc; Neoproterozoic; Ophiolite; Serpentinite; SSZ; U-Pb dating; West African Craton
Abstract :
[en] 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. © 2020 International Association for Gondwana Research
Disciplines :
Earth sciences & physical geography
Author, co-author :
Hodel, F.;  Géosciences Environnement Toulouse (GET), Observatoire de Midi-Pyrénées, CNRS, IRD, Université Toulouse III Paul Sabatier, 14, Avenue Edouard Belin, Toulouse, 31400, France
Triantafyllou, Antoine ;  Université de Liège - ULiège > Département de géologie > Pétrologie, géochimie endogènes et pétrophysique
Berger, J.;  Géosciences Environnement Toulouse (GET), Observatoire de Midi-Pyrénées, CNRS, IRD, Université Toulouse III Paul Sabatier, 14, Avenue Edouard Belin, Toulouse, 31400, France
Macouin, M.;  Géosciences Environnement Toulouse (GET), Observatoire de Midi-Pyrénées, CNRS, IRD, Université Toulouse III Paul Sabatier, 14, Avenue Edouard Belin, Toulouse, 31400, France
Baele, J.-M.;  Geology and Applied Geology Unit – Mining Geology, Université de Mons, 20, Place du ParcB-7000, Belgium
Mattielli, N.;  Department of Earth and Environmental Sciences – G-Time Laboratory, Université Libre de Bruxelles, 50 Avenue Franklin Roosevelt, Brussels, 1050, Belgium
Monnier, C.;  Laboratoire de Planétologie et Géodynamique – Nantes (LPGN), UFR Sciences et Techniques, université de Nantes, UMR-CNRS 6112, France
Trindade, R. I. F.;  Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universitad de São Paulo, São Paulo, 05508-900, Brazil
Ducea, M. N.;  Department of Geosciences, University of Arizona, Tucson, AZ 85721, United States, Faculty of Geology and Geophysics, University of Bucharest, Bucharest, Romania
Chatir, A.;  EGGPG, Département de Géologie, Faculté des Sciences, Université Chouaïb Doukkali, El Jadida, 24000, Morocco
Ennih, N.;  EGGPG, Département de Géologie, Faculté des Sciences, Université Chouaïb Doukkali, El Jadida, 24000, Morocco
Langlade, J.;  Microsonde Ouest, Ifremer–Centre de Bretagne, Technopole Brest Iroise, BP70, Plouzané, F-29280, France
Poujol, M.;  Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, Rennes, 35000, France
More authors (3 more) Less
Language :
English
Title :
The Moroccan Anti-Atlas ophiolites: Timing and melting processes in an intra-oceanic arc-back-arc environment
Publication date :
2020
Journal title :
Gondwana Research
ISSN :
1342-937X
eISSN :
1878-0571
Publisher :
International Association for Godwana Research, Japan
Volume :
86
Pages :
182-202
Peer reviewed :
Peer Reviewed verified by ORBi
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