First evidence for Cambrian rift-related magmatism in the West African Craton margin: The Derraman Peralkaline Felsic Complex |
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| Institution: | 1. Department of Mineralogy and Petrology, University of Granada, Campus Fuentenueva, 18002 Granada, Spain;2. LGAGE, Départementde Géologie, Université Hassan II, Casablanca, Morocco;3. Em. Pr. Université Paris-Sud (Orsay), 10 Rue des Jeuneurs, 75002 Paris, France;4. Office National des Hydrocarbures et des Mines, 5 Avenue Moulay Hassan, Rabat, Morocco;1. Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Sektion Geochronologie, GeoPlasma Lab, Königsbrücker Landstraße 159, 01109 Dresden, Germany;2. CEREGE, Aix-Marseille Université, Centre Saint-Charles, case 67, 3 place Victor Hugo, 13331 Marseille, France;3. Institut für Geowissenschaften, Mineralogie, Goethe Universität Frankfurt, Altenhoeferallee 1, 60438 Frankfurt, Germany;4. Department of Earth Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa;5. Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, Prince Moulay Abdellah Boulevard, P.O. Box, 2390 Marrakech, Morocco;6. Instituto Dom Luiz (IDL-LA) Universidade de Lisboa, Faculdade de Ciências (FCUL), Departamento de Geologia (GeoFCUL), Campo Grande Edificio C8, 1749-016 Lisboa, Portugal;1. Institut für Geowissenschaften, Universität Kiel, 24118, Germany;2. GEOMAR, Helmholtz Centre for Ocean Research, 24148 Kiel, Germany;3. Faculté des sciences, Université My Ismail, Meknes, Morocco;4. Managem Group, Marrakech, Morocco;1. Ruhr-Universität Bochum, Institut für Geologie, Mineralogie & Geophysik, Univertsitätsstrasse 150, 44801 Bochum, Germany;2. Departamento de Mineralogía y Petrología, Universidad de Granada (UGR), Fuentenueva s/n, E-18002 Granada, Spain;3. Instituto de Geociências, Rua do Lago, 562, Universidade de São Paulo, 05505-080 São Paulo, Brazil |
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| Abstract: | West of the southern, Archean, part of the Reguibat Rise of the West African Craton the Oulad Dlim Massif consists of metamorphic nappes stacked during the Mauritanides (Variscan) orogeny. In the Derraman region, about 12 km west of the nappes, we have found strongly deformed hypersolvus aegirine-riebeckite A1-type granites with SHRIMP zircon U–Pb ages of ca. 525 ± 3 Ma, ε(Nd)525Ma (? 5.2 to ? 6.8.) and Nd model ages TCR ≈ 1.85 Ga. These granites define two km-sized bodies and a few smaller satellites. One body is emplaced within a 3.12 Ga leucocratic gneiss. The other body and its satellites are emplaced within an Archean low-grade metasedimentary sequence with detrital zircons that have ages that peak at 2.84 Ga, 2.91 Ga, and 3.15 Ga. These Archean gneisses and metapelite rocks define a tectonic unit, hereafter called the Derraman-Bulautad-Leglat (DBL) unit, which was formed from the Reguibat basement at the very margin of the WAC. The ~ 525 Ma Derraman granites are the oldest post-Archean rocks in this unit and were generated in an intraplate rifting environment from melting of crustal fenites during the ubiquitous Cambrian rifting event that affected this part of northern Gondwana. At the present level of knowledge, however, we cannot decide whether the “old” Nd isotope signature of Derraman granites resulted from melting of an old (Paleoproterozoic) fenite source or reflects the signature of the mantle-derived metasomatising fluids. The just-discovered Derraman granites are strikingly similar to other rift-related Cambrian–Ordovician hypersolvus aegirine–riebeckite granites widespread in North Gondwana. Understanding the potential connections between them would help to understand the Cambrian–Ordovician breakdown of northern Gondwana. |
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