The Eglab massif in the West African Craton (Algeria), an original segment of the Eburnean orogenic belt: petrology, geochemistry and geochronology

The Eglab massif, situated in the northern part of the West African Craton (WAC), exhibits a specific Eburnean evolution compared to that known in the southern part of the WAC. Two major orogenic stages are recognized in the Eglab massif. The first one corresponds mainly to 2.21-2.18 Ga magmatic activity forming a metamorphosed batholith composed of various juvenile calc-alkaline orogenic suites, compatible with a mature island-arc setting. Together, these suites make up a metamorphic basement that includes some 2.7 Ga-old relics of Archean ocean crust. The second orogenic stage is characterized by active-margin magmatic suites emplaced and deformed at ca. 2.09 Ga. They are intruded by large volumes of high-K post-orogenic magmas, covering over half of the present area of the Eglab massif, which are interpreted as resulting from stab roll-back processes and asthenospheric upwelling at 2.07 Ga. This high-K magmatism is not present on such a wide scale in the southern WAC. Furthermore, the specific character of the Eglab terrains is also highlighted by mafic rocks that are chemically compatible with mature arc and active-margin settings. By contrast, the mafic suites of the southern WAC have compositions more compatible with oceanic plateau and oceanic island-arc settings where they form greenstone belts never observed in the Eglab massif. (C) 2005 Elsevier B.V. All rights reserved.