Time constraints on Early Tonian Rifting and Cryogenian Arc terrane-continent convergence along the northern margin of the West African craton: Insights from SHRIMP and LA-ICP-MS zircon geochronology in the Pan-African Anti-Atlas belt (Morocco) |
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| Institution: | 1. Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, P.O. Box 2390, Marrakech, Morocco;2. LGE. Department of Geology, ENS, Cadi Ayyad University, BP S2400, Marrakech, Morocco;3. Em. Pr. Université de Paris-Sud, 10 rue des Jeûneurs, 75002, Paris, France;4. Department of Mineralogy and Petrology, University of Granada, Campus Fuentenueva, 18002, Granada, Spain;5. UMR Geoazur, 250 rue A. Einstein, Université de Nice - Sophia-Antipolis, 06560, Valbonne, France;6. Direction de la Géologie, Ministère de l''Energie et des Mines, B.P. 6208, Rabat Instituts, Haut Agdal, Rabat, Morocco;7. Laboratoire Géosciences, Université Hassan II-Casablanca, BP 5366, Maârif, Casablanca, Morocco;8. Marine Science, Safety and Environmental Protection Department, Massachusetts Maritime Academy, Buzzards Bay, MA, USA, 02532;1. Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, Prince Moulay Abdellah Boulevard, P.O. Box 2390, 40 000, Marrakech, Morocco;2. LAGAGE Laboratory, Department of Geology, Faculty of Sciences, Ibn Zohr University, P.O. Box 28/S, 80 000, Agadir, Morocco;3. Université de Lorraine, CNRS, CRPG, F-54000, Nancy, France;4. Ottawa-Carleton Geoscience Centre, Department of Earth Sciences Carleton University, 1125 Colonel By Drive Ottawa, Ontario, K1S5B6, Canada;5. LGCA, Département de Géologie, Université Hassan II de Casablanca, Morocco;6. Managem Group, Twin Center, 20100, Casablanca, Morocco;1. BRGM, BP 6009, 45060 Orléans Cédex, France;2. Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, P.O. Box 2390, Marrakech 40005, Morocco;3. Department of Geology, ENS, Cadi Ayyad University, P.O. Box 24000, Marrakech 40005, Morocco;4. ENSEGID, Univ. Bordeaux III, 33607 Pessac Cedex, France;5. GEODE Terre et Patrimoine, B.P. 7004, 40014 Marrakech, Morocco;6. Department of Geology, Faculty of Sciences & Technics Guéliz, Cadi Ayyad University, P.O. Box 549, Guéliz, Marrakech 40005, Morocco;1. Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain;2. Ecole Nationale de l’Industrie Minérale, Département des Sciences de la Terre, BP 753 Agdal – Rabat, Morocco;3. Council for Geoscience, P.O. Box 572, Bellville 7535, South Africa;4. United States Geological Survey, P.O. Box 628, Montpelier, VT 05601, USA |
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| Abstract: | The Neoproterozoic Anti-Atlas belt (Morocco) is a key segment in tracing the history of the northern margin of the West African craton (WAC) from Rodinia breakup to Gondwana assembly. In order to constrain geodynamic events related to rifting and convergence and their stratigraphic records, a radiometric study was carried out on the volcano-sedimentary Tachdamt and Bleïda Formations. The volcaniclastic deposits of Tachdamt Fm. yield an age of ca. 883 Ma and provide a new constraint for the timing of the subaqueous volcanic eruption and the initiation of rifting in the Anti-Atlas. This age is ~100 my older than the previous age of 788 ± 10 Ma obtained from Rb/Sr isotope dating (Clauer, 1976). Available zircon data from the interbedded clastic deposits from Tachdamt Fm. indicate major shifts in provenance during the rifting with sediments sourced from the WAC and a nearby Grenvillian terrane. Detrital zircon ages from metasiltstones of Bleïda Fm. set a maximum depositional age at ca. 700 Ma. The age spectra discloses a major shift in sediment input with provenance from the WAC, Grenvillian terrane and an arc-related terrane (ca. 770–700 Ma) lying along the Anti-Atlas margin. The newly obtained results combined with existing radiometric data allowed the refinement of the stratigraphic and geotectonic framework of the pre-Pan-African strata in the WAC. The Early Tonian syn-rift volcanism has much in common with similar events in other cratons and provides a stratigraphic record for incipient Rodinia breakup. The overlying Bleïda Fm. deposited in a peripheral foreland basin chronicles the Cryogenian arrival of the ca. 770–700 Ma Bou Azzer-Siroua arc-related terrane at the Anti-Atlas margin, and correlates with initial accretion in West Gondwana. The new results indicate that the Grenvillian detrital input in the Anti-Atlas during both geodynamic stages points toward a possible Mesoproterozoic terrane existing along the western margin of the WAC. |
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