ملخص: A geochronological study was carried out on rocks from the “Petite Kabylie Massif” in northeastern Algeria to determine the timing of magmatic and metamorphic events affecting a metamorphic complex involved in a major phase of Alpine overthrusting. This type of metamorphic complex is known throughout the northwestern African orogenic domain: the Maghrebide Chain (northern Algeria), the Betic Cordilliera (southeastern Spain) and Calabria (southern Italy). The study, which is mainly focused on the Petite Kabylie area, is supplemented with the dating of rocks from a key occurrence of synkinematic granite in the “Grande Kabylie Massif”. In Petite Kabylie, an early phase of magmatism at 455 +/- 19 Ma and a second phase in the range 270-280 Ma (278 +/- 3 Ma and 273 +/- 6 Ma) are dated using the U---Pb zircon method. A Hercynian metamorphic event is recorded in detrital zircons dated at 370 +/- 6 Ma. Rb---Sr micas ages are scattered between 280 Ma and 7 Ma, suggesting a mixing system or a history of complex cooling between the late Hercynian and the Alpine events. The basement here is also characterized by two superimposed metamorphic events, the first one of LP and the second of HP type. The earlier event could be around 280 Ma or older (370 Ma?), while the second event is thought to be either late Hercynian, Eoalpine or even Alpine in age. The petrological and geochronological data can best be explained by a continuous evolution of the 280 Ma-old granite and its associated HP metamorphism taking place over a short time span and ending with extensive deformation around 270 Ma ago as suggested by the fast cooling of the crust. This interpretation is in agreement with the U---Pb zircon age of the synkinematic granite from Grande Kabylie, dated between 284 +/- 2 Ma and 273 +/- 6 Ma, which corresponds to a late-Hercynian transtensional regime. The Eoalpine tectono-metarmorphic events are not constrained from geochronological data. A low-grade Alpine event is recorded during the Eocene-Oligocene (40-25 Ma) from Rb---Sr biotite ages, which agrees with the age of basement overthrusting. Late stage of low temperature activity continued up to 7-10 Ma as indicated by some biotite ages.

لغة: إنجليزية