Magnetotelluric Investigation of the Underlying Structure of Manzaz Volcanic District (Hoggar, Southern Algeria)

Abstract

The main objective of this study was to model the lithospheric structure of the Manzaz volcanic district (Hoggar) using the magnetotelluric (MT) method. For this purpose, eleven MT stations forming a 70-km long NW-SE profile, intersecting the Manzaz, were modeled. The 2D resistivity model shows an anomalously conductive crust resting on a lithospheric mantle of normal resistivity. The anomalously high conductivity of the middle and lower crust results probably from magma ascent from the asthenosphere to the surface. It could correspond to the presence of partial melting, trapped fluids released by the magma and/or precipitation of mineralization. The conductive structures underlying the Manzaz could correspond to intracrustal magmatic chambers or to magmatic underplating zones at the Moho or at lower/upper crust discontinuities. located some tens km to the south [2]. Thus, to highlight its lithospheric structure, a Magnetotelluric (MT) field survey has been conducted recently. MT is a passive electromagnetic geophysical method, that infers the distribution of the electrical conductivity in the lithosphere by recording the natural telluric current fluctuations and the magnetic field variations [6]. Electrical conductivity is a geological marker that can reflect geodynamic conditions in the Earth. It can also be strongly affected by the presence of fluid, mineralization or partial melting in the crust. MT is thus a suitable method for the investigation of the underlying structure of the Manzaz volcanic district. In this work, we presented the preliminary 2D modeling of a NW-SE MT profile.