Contribution to a geodynamic reconstruction of the Anti-Atlas (Morocco) during Pan-African times with the emphasis on inversion tectonics and metallogenic activity at the Precambrian–Cambrian transition |
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Authors: | Dominique Gasquet Gilles Levresse Alain Cheilletz Moulay Rachid Azizi-Samir Abdellah Mouttaqi |
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Institution: | aUniversité de Savoie, CISM-EDYTEM, CNRS-UMR 5204, Campus Scientifique, 73376 Le Bourget du Lac Cédex, France;bUNAM, Centro de Geociencias, Campus Juriquilla, 76230 Santiago de Queretaro, Mexico;cCRPG-CNRS UPR A2300 and ENSG-INPL, BP 20, 54501 Vandoeuvre-lès-Nancy Cédex, France;dReminex, Groupe ONA, 26 Av. Allal El Fassi, Tissir 36-40, Marrakech, Morocco;eONHYM, 5 Charia My Hassan, BP 99, Rabat, Morocco |
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Abstract: | New geochronological analyses (U–Pb SIMS zircon ages) have yielded ages of 552 ± 5 Ma for the Bou Madine rhyolitic dome (Ougnat, eastern Anti-Atlas), 543 ± 9 Ma for the Tachkakacht rhyolitic dyke (Saghro–Imiter, eastern Anti-Atlas), and 531 ± 5 Ma for the Aghbar trachytic sill (Bou Azzer, central Anti-Atlas). Inherited zircon cores from the Aghbar trachytic sill and from the Bou Madine rhyolitic dome have been shown to be of Statherian age (ca. 1600–1800 Ma) and Palæoproterozoic (>2100 Ma) age, respectively, suggesting that a significantly older protolith underlies the Pan-African rocks in the Central and Eastern Anti-Atlas. Granodiorites and rhyolites from the Saghro–Imiter area have similar low 87Sr/86Sr (0.702–0.706) and 143Nd/144Nd (0.5116–0.5119) initial ratios, suggesting a mixture of mantle and lower crust sources. This can also be inferred from the low 187Os/188Os ratios obtained on pyrite crystals from the rhyolites.A recently published lithostratigraphic framework has been combined with these new geochemical and geochronological data, and those from the literature to produce a new reconstruction of the complex orogenic front that developed at the northern edge of the Eburnian West African craton during Pan-African times. Three Neoproterozoic magmatic series can be distinguished in the Anti-Atlas belt, i.e., high-K calc-alkaline granites, high-K calc-alkaline to shoshonitic rhyolites and andesites, and alkaline-shoshonitic trachytes and syenites, which have been dated at 595–570, 570–545 and 530 Ma, respectively.The accretion of the Pan-African Anti-Atlas belt to the West African super continent (WAC) was a four-stage event, involving extension, subduction, moderate collision and extension. The calc-alkaline magmatism of the subduction stage was associated with large-scale base metal and gold mineralisation. Metallogenic activity was greatest during the final extensional stage, at the Precambrian–Cambrian boundary. It is characterised by world-class precious metal deposits, base–metal porphyry and SEDEX-type occurrences. |
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Keywords: | Neoproterozoic Zircon U– Pb dating Sr– Nd isotopes Anti-Atlas Morocco West African Craton |
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