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The Pan-African orogeny along the boundaries of the West African craton |
1 Institut für Geowissenschaften, Universität Potsdam, Karl Liebknecht Strasse 24, 14476 Potsdam-Golm, Germany (e-mail: romain{at}geo.uni-potsdam.de)
2 Département de géologie, Université Hassan II—Aïn Chock, Route d'El Jadida, B.P. 5366 Maârif, Casablanca, Morocco
3 Laboratoire de Géologie, UMR 8538, Ecole Normale Supérieure Paris, 24 rue Lhomond, 75231 Paris cedex 05, France
4 Akka Gold Mining, MANAGEM-ONA, Rabbat, Morocco
5 Present address: Department of Geology, Kansas University, 1475 Jayhawk Boulevard, Lawrence, Kansas 66045-5276, USA
Since the discovery of ophiolite sequences, the Bou-Azzer inlier has been considered a key area for understanding the evolution of the northern margin of the West African craton during the Pan-African orogeny. For about 20 years, it had been commonly accepted that the Bou-Azzer inlier represents an accretionary mélange accreted onto the West African craton under blueschist metamorphic conditions, similar to the Franciscan Complex and the Sanbagawa facies series. This would imply that a low geothermal gradient was prevalent during the subduction of the Pan-African oceanic plate, and that the ocean was subducted with a high convergence rate. A reinvestigation of the metamorphic conditions by a thermodynamic approach shows that the ophiolite sequence of Bou-Azzer underwent HT greenschist metamorphic conditions instead of blueschist metamorphic conditions. We propose that the ophiolites of Bou-Azzer are not similar to the Sanbagawa facies series or to the Franciscan Complex, but bear similarities to the Albanian or Cyprus ophiolites, which represent dismembered ophiolite sequences overprinted by greenschist conditions.
