Neoproterozoic amalgamation and Phanerozoic reactivation of Central/Western Hoggar (Southern Algeria, Tuareg Shield) lithosphere imaging using Magnetotelluric data

Abstract

Hoggar, as part of the Tuareg shield, is a key area in the assembly of Western Gondwana during the Neoproterozoic. To better understand the tectonic process, 61 broadband magnetotelluric (MT) stations were acquired in Central/Western Hoggar to image the underlying lithosphere. We performed 2-D and 3-D inversions of the impedance tensor and the vertical magnetic field transfer function using data from three profiles. The resistive crust is interrupted by several conductors related to the known shear zones of the area. Some conductors can be associated with Cretaceous-Cenozoic fluid flow combined with mineralization (graphite, magnetite or more locally gold). MT models suggest three distinct blocks. (1) An oriental block composed of Tefedest, Laouni, Aouilène and Silet juvenile terrane characterized by a moderately conductive lithospheric mantle (LM). (2) A central block formed by the In Tedëini and Tin Zaouatene terranes, previously considered as Neoproterozoic juvenile, exhibit resistive characteristics typical of an old continental LM. Finally, (3) an occidental block corresponding to the In Ouzzal terrane with a highly conductive LM. The oriental and occidental blocks were strongly remobilized during the Neoproterozoic, and perhaps even locally during the Cretaceous and Cenozoic. The main shear zones of the study area are (1) the Iskel shear zone, a major suture zone separating the oriental and central blocks. The MT model suggests that the geometry of this lithospheric shear zone is characterized by an eastward dipping angle, according to the central block a passive margin character where Silet arc was accreted. Consequently, east from Silet a collision with the oriental block may have been in an active margin environment. (2) The Adrar fault and the West Ouzzalian shear zone correspond to terrane boundaries of the In Ouzzal. They are associated with deep-reaching high conductivity, consistent with large scale suture zones. The resistivity models provide new geometric constraints for the terranes and highlight new Pan-African and Phanerozoic tectonic features.