KINEMATICS OF A COMPLEX ALPINE SEGMENT - SUPERIMPOSED TECTONIC AND METAMORPHIC EVENTS IN THE PETITE KABYLIE MASSIF (NORTHERN ALGERIA)

This study presents an investigation of two superimposed high-grade te ctonometamorphic events (M1/D1-M2/D2) recorded in two distinct crystal line units of the Petite Kabylie Massif (NE Algeria). The lower unit, which is characterized by the presence of both metamorphic inprints, i s known as the Beni-Ferguen nappe. D1 deformation is characterized by a low-dipping regional cleavage with an Est-West extensional shearing componant, and is associated in the upper unit with HT/LP metamorphism (MI : 725 degrees C, 4 kbar) and granite emplacement dated at 274 +/- 6 Ma. The following deformational phase (D2) corresponds to northward -directed shearing and is mainly seen to effect the lower unit; it is linked to high grade metamorphism (M2) during which M1 andalusite was transformed into M2 kyanite in the metapelites. In this lower unit, PI T conditions are estimated at 550-650 degrees C and 9-10 kb. The 280-M a old granites are affected by M2/D2, If M1/DI is accepted as a late H ercynian event, then the age of M2/D2 needs to be discussed: it could correspond to an eo-Alpine event.