Lithospheric structure of the Atakor metacratonic volcanic swell (Hoggar, Tuareg Shield, southern Algeria): Electrical constraints from magnetotelluric data

Abstract

The Tuareg Shield, to which Hoggar belongs, has a swell-shaped morphology of lithospheric scale of c. 1,000 km in diameter linked to Cenozoic volcanism occurring in several regions, including Atakor, the center of the swell, up to nearly 3,000 m in altitude. The lack of highresolution geophysical data for constraining its deep structure is at the origin of a controversy about its innermost nature and about the origin of the Cenozoic volcanism. During the course of this study, magnetotelluric (MT) broadband data were collected at 18 sites forming a NE-SW profile 170 km long, within the Atakor region. The electrical resistivity model obtained by inverting the magnetotelluric data reveals lithospheric structure down to a depth of about 100 km. From this depth to the surface, the model does not show any regional anomaly that may result from a metasomatized lithosphere or from an asthenospheric upwelling, including a mantle plume. MT data reveal rather a lithosphere affected by a set of rather thin subvertical conductors that can be attributed to the electrical signature of some known shear zones resulting from the Pan-African evolution of the LATEA metacraton, which globally corresponds to the uplifted Central Hoggar swell. The main anomaly is deeply rooted in the lithosphere and underlies remarkably the Atakor/Manzaz volcanic districts. As a whole, MT data are therefore properly integrated within the hypothesis of the reactivation of shear zones due the intraplate deformation related to the collision between Africa and Europe since the Eocene applied on a metacratonic region.

Discovery of a Devonian mafic magmatism on the western border of the Murzuq basin (Saharan metacraton): Paleomagnetic dating and geodynamical implications

“…These reactivations, even induced by the rather low stress propagating in remote intracontinental regions, must affect the whole lithospheric thickness allowing for small mantle melt volumes to reach the surface. This is the case of the megashear zones within metacratonic areas that are rigid but fractured (Liégeois et al, 2003(Liégeois et al, , 2005(Liégeois et al, , 2013Bardintzeff et al, 2011) through vertical planar delamination as recently evidenced by magnetotelluric studies in Hoggar (Bouzid et al, 2015).…”

Geodynamics

“…On the other hand, in ancient stable shields due to mylonitization in fossil shear zones and low porosity of highly metamorphic rocks, fluid loss occurs during deformation, and the existence of lowresistivity structures in the earth's crust and upper mantle of crystalline terranes is more likely associated with the sulphite-graphite content in metasediments and metavolcanites of high metamorphic stages and in basic and ultrabasic rocks (e.g. [Korja et al, 2002;Bouzid et al, 2015;Yin et al, 2014;Kaplun 2018;Sarafian et al, 2018;Malleswari et al, 2019]).…”

Detection of Ring Structures and Their Surrounding Tectonic Pattern in South-Algeria, North-Mali and North- Niger based on Satellite Data

“…Although a large amount of research has been carried out related to the geologic history and structural and tectonic inventory in Southern Algeria and adjacent areas (Lié geois et al, 2005;Azzouni-Sekkal et al, 2007;Fezaa et al, 2010;Yahiaoui et al, 2014;Bouzid et al, 2015) combined evaluations of different satellite data integrated into a GeoInformation System (GIS) are investigated, whether they can contribute to further additional geologic knowledge Especially the combination of Landsat 8 and 9 thermal band-, and Sentinel 2 optical images, and Sentinel 1-, ALOS PALSAR-and SIR-C-radar images allows the detection of surface-near structures (Paillou et al, 2006).…”