Identification of deep magnetized structures in the tectonically active Chlef area (Algeria) from aeromagnetic data analyzed with 2-D and 3-D imaging derived from the wavelet and ridgelet transforms

International audienceThe Chlef region constitutes a key area to study neotectonics structures and their geodynamical context. Aeromagnetic data analyzed using different processing methods (shaded relief technique, computation of vertical gradient, upward continuation, use of the continuous wavelet transform and ridgelet transform), allow establishing a structural image of emerging and deep structures both onshore and offshore. Magnetic anomalies, over the Mediterranean Sea, the Chlef basin and the Ouarsenis Mounts, are well-correlated with the known geological structures. Long and short wavelength anomalies have been distinguished. The short wavelength anomalies are associated with the volcanic rocks on the coast from Chenoua to El Marsa and with the basement in the Boukadir zone in the sedimentary Chlef basin. The long wavelength anomalies to the South are associated mainly with deep E-W structures, limiting the Chlef basin. To the North, similar structures have been identified in the Mediterranean Sea. The compilation of the identified magnetic features leads to geometrical shape corroborating the structure in blocks of the Chlef basin

New African Lower Carboniferous paleomagnetic pole from intrusive rocks of the Tin Serririne basin (Southern border of the Hoggar, Algeria)

International audienceA paleomagnetic study has been conducted on intrusive doleritic rocks cropping out within Devonian horizontal tabular formations of the Saharan craton (Tin Serririne basin, South of Hoggar shield). The 40K/40Ar dating of the dolerites gave an age of 347.6 ± 8.1 Ma, i.e. Tournaisian. The paleomagnetic data present three different directions. The first has a paleomagnetic pole close to the previous African poles of Permian age. This direction is therefore interpreted as a Permian remagnetization. The second direction, which is defined by both linear regression and remagnetization circles analysis, is considered as the primary magnetization. It yields a new African Tournaisian paleomagnetic pole (λ = 18.8° S, phi = 31.2° E, K = 29, A95 = 7.5°) very close to the Ben Zireg Tounaisian pole [Aifa, T., Feinberg, H., Pozzi, J.P., 1990. Devonian/Carboniferous paleopoles for Africa. Consequences for Hercynian geodynamics. Tectonophysics, 179, 288–304]. The third direction has intermediate orientation between those of the first or second directions and that of the Upper Cenozoic field. It is interpreted as related to a composite magnetization. This new Tin Serririne pole improves the APWP of Gondwana, for this key period of the evolution of the Pangea. This APWP confirms the previous paleogeographic reconstruction which shows that the pre-Hercynian ocean between Gondwana and Laurussia is still not close during the beginning of the Carboniferous

Eburnean and Pan-African granitoids and the Raghane mega-shear zone evolution: Image analysis, U-Pb zircon age and AMS study in the Arokam Ténéré (Tuareg shield, Algeria)

info:eu-repo/semantics/publishe

Repeated granitoid intrusions during the Neoproterozoic along the western boundary of the Saharan metacraton, Eastern Hoggar, Tuareg shield, Algeria: An AMS and U–Pb zircon age study

IF=1.677info:eu-repo/semantics/publishe

Relative importance of the Hercynian and post-Jurassic tectonic phases in the Saharan platform: a palaeomagnetic study of Jurassic sills in the Reggane Basin (Algeria)

International audienceIn the intracontinental domain of the northwestern Saharan platform, the deformation of the Palaeozoic sedimentary cover is mainly attributed to a far-field effect of the Hercynian orogeny having occurred at the African-Laurusian plate boundary in the Late Carboniferous to Early Permian times. However, geological observations from different parts of Africa and Arabia provide evidence that several minor but widespread tectonic events occurred later, particularly during the Cretaceous. Contrary to elsewhere in the northwestern part of Africa, in the Reggane Basin, outcropping doleritic sills of Early Jurassic age are intruded in folded Palaeozoic sediments of Devonian to Carboniferous ages deposited before the Hercynian orogeny. In this favourable situation, a palaeomagnetic study of the Liassic dolerite is able to provide information on the tectonic history of the surrounding area independently from geological observations. The present study aims to quantify the relative proportion of tilting related to, respectively, the Hercynian and a post-intrusion phase, using a fold test based on the small circle analysis. This method proved to be very efficient to unravel these tectonic events. It shows that, in the studied area, the folds were initiated during the Hercynian phase, but mainly amplified during the post-intrusion phase which turned out to be the dominant one. In the Reggane Basin, the age of this second event is not geologically well constrained between probably Late Jurassic and Early Cretaceous. It could be the far-field effect of either the Cimmerian phase (∼140 Ma) or more likely the Austrian tectonic phase (Late Barremian, ∼125 Ma). The Late Barremian tectonic episode corresponds to a major event: the break-up of Western Gondwana, which led to the separation of Africa from South America and to the incipient fragmentation of the African plate into three major blocks. The conclusion drawn from the palaeomagnetic study in the Reggane Basin is consistent with the geological observations and representative of the intraplate Cretaceous deformations recorded in many other places in Africa. It emphasizes once again that stresses can be transferred far from the plate boundaries, into the continental plate interiors