EVOLUTION OF THE PRECAMBRIAN IN-OUZZAL BLOCK (CENTRAL SAHARA, ALGERIA)

New structural and geochronological data are used to constrain the evolution of the Precambrian In-Ouzzal block situated on the eastern side of the West African Craton. The results of this study can be summarized as follows: (i) The block can be subdivided into two series; one is mainly composed of Archaean granitic gneisses (3.2-2.5 Ga old), while the other contains metasedimentary and basic to ultrabasic rocks which can be compared with those described in Archaean supracrustal terrains. (ii) The entire block is affected by very high temperature granulite-facies metamorphism. (iii) The metamorphism is associated with two main deformational phases, the first of which is responsible for a regional foliation refolded during the second phase. (iv) The major tectono-metamorphic event in the area is related to a 2.0 Ga-old (Eburnian) orogeny which ended with carbonatite emplacement. Nearly all evidence of the earliest crustal evolution events (i.e. the initial emplacement and deformation of the granitic and supracrustal materials) has been erased by the Eburnian event.