THE PETROGENESIS OF THE EDOUGH MUSCOVITE ORTHOGNEISSES, ANNABA, NORTHEAST ALGERIA

The Edough muscovite orthogneisses, which are restricted to the lower part of a tectonic slice of andalusite metapelites and predate the dom ing of the massif, are well differentiated, S-type metagranites genera ted by 10-30% partial melting followed by 50-60% fractional crystalliz ation of a melt derived from the structurally underlying biotite gneis ses or a crustal material of a similar composition. These metagranites predate the Ms Tertiary metamorphism, were isochemically metamorphose d, tectonically emplaced and preserve syn-collisional affinities and h ence are believed to have formed at the end of the M(2) metamorphism. The composition of these metagranites and that of the 16-15 Ma post M( 3) Edough igneous rocks are then used to discuss the tectonic evolutio n of the Edough metamorphic core complex.