Strong Neotectonic Block-Rotations, Related to the Africa-Eurasia Convergence in Northern Algeria: Paleomagnetic Evidence From the Mitidja Basin

摘要

Significant tectonic clockwise rotations were evidenced in the Tell Atlas (Neogene Algerian Cheliff basin) by previous paleomagnetic studies. For northwestern Africa and in the context of the Africa-Eurasia convergence, they provided a new argument validating a kinematic model, based on transpression with shortening accommodated by clockwise block rotations. To corroborate this deformation pattern at a larger scale, new paleomagnetic studies were performed on 349 cores in the Mitidja basin, of Mio-Plio-Quaternary age, in the Algerian Tell Atlas. This intramontaneous basin is structured by two regional major E-W to WNW-ESE dextral shear zones. Primary magnetization data were obtained in 43 out of the 49 sampled sites. This magnetization is carried by Ti-poor titanomagnetite. Its direction shows that significant tectonic block rotations affected this basin since 16 Ma. Zones located between the E-W and WNW-ESE major structures are affected by coherent clockwise rotations (average magnitude of 48 degrees) of large blocks, compartmented by presently associated sinistral NE-SW faults. Along the shearing structures, smaller blocks, resulting from the fragmentation of the large blocks, show various rotations, many of which are of large magnitude. These rotations, similar to those highlighted previously in the Cheliff basin, are interpreted as resulting from bookshelf, consequence of the Africa-Eurasia plates convergence in the Tell Atlas.