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Continental intraplate volcanic systems, with their location far from plate tectonic boundaries, are not well understood: the crustal and lithospheric mantle structure of these systems remain enigmatic and there is no consensus on the mechanisms that cause melt generation and ascent. The Cenozoic saw the development of numerous volcanic provinces on the African plate. This includes the Hoggar volcanic province, located in Northwest Africa, part of the Tuareg shield. It is composed of several massifs with contrasting ages and eruptive styles. The magmatic activity began at around 34 Ma and continued throughout the Neogene-Quaternary. Phonolite and trachyte domes as well as scoria cones and necks are found in the Manzaz and Atakor volcanic districts. In order to image the crustal and lithospheric mantle structure of this region, and to understand the origins and potential mechanisms of the continental intraplate volcanic activity in the Central Hoggar and specifically the Atakor/Manzaz area, we acquired magnetotelluric (MT) measurements from 40 locations and generated a 3-D electrical resistivity model. The model covers an area of about 100 km by 200 km. Images of the subsurface architecture, in terms of electrical resistivity, from the near-surface to the lithospheric mantle, allow us image the deep plumbing system of the volcanic system. Low resistivity features (i.e., conductors) in the crust that are narrow, linear structures trending approximately north-south, are revealed along the two boundaries of the Azrou N’Fad terrane, in the Manzaz area. They likely reflect the Pan-African mega-shear zones, which were reactivated throughout the tectonic evolution of the region. The model reveals that these faults are lithospheric-scale. In addition, the low-resistivity features likely represent the signatures of past fluid flow. The location of the recent Cenozoic volcanic activity was likely influenced by the pre-existing structure. A deep feature of moderate conductivity, Applied Geophysics and Petrophysics

The Egéré terrane (Central Hoggar, South Algeria) includes mafic eclogite lenses boudinaged in metapelitic rocks with high-pressure relicts. These metapelites show textural records of partial melting, mainly primary melt inclusions enclosed in garnet crystals and later crystallized as "nanogranitoids."Garnet porphyroblasts also contain inclusions of quartz, kyanite, phengite, biotite, staurolite, and rutile and show a smoothed prograde zoning with a Mn bell-shaped profile. The peak high-pressure metamorphic assemblage consists of garnet, kyanite, phengite (Si up to 6.36), quartz, rutile, ±ilmenite, ±feldspars, and melt. Phengite has partially transformed into fine-grained aggregates of biotite, plagioclase, and K-feldspar, a microstructure interpreted as resulting from a dehydration melting during exhumation. Phengite breakdown, along with other retrograde reactions, produced a late paragenesis with biotite, plagioclase, K-feldspar, quartz, almandine-rich garnet, ±sillimanite, ±staurolite, ±muscovite, and ilmenite. The thermodynamic modeling of P-T pseudosections allows us to constrain various steps of the metamorphic history: beginning of the garnet growth at 4.0 kbar and ~600 °C during prograde metamorphism; pressure peak at 14-20 kbar; temperature peak at 800-820 °C; formation of the last assemblage at 6.0-5.5 kbar and 725-685 °C. Partial melting likely started during the prograde path when crossing the H2O-saturated solidus, at T ≥ 650-670 °C and P ≥ 10 kbar, continued upon heating, up to the peak conditions, as well as during decompression. This evolution is interpreted in terms of subduction of the continental crust to mantle depths, followed by an exhumation through a clockwise P-T path during the Pan-African orogeny. The Egéré metapelites are relatively well-preserved eclogite-facies rocks, contain inclusions of "nanogranitoids"hitherto very little known in eclogite-facies metamorphic rocks, and represent an unusual trace of subduction within a Neoproterozoi

The East-Ouzzal shear zone is a dextral transcurrent N-S ductile fault separating a granulite complex, the In Ouzzal block, from a Middle Proterozoic unit comprising orthogneisses. The shear zone hosts numerous quartz veins, many containing significant gold mineralisation. These are either N-S along an ultramylonite belt close to the In Ouzzal block (Amesmessa), or along oblique dextral shear zones overprinting the East-Ouzzal shear zone (Tirek). In the late Panafrican, gold was leached from the In Ouzzal granulites and deposited in quartz veins along the inactive East-Ouzzal shear zone, under deep geothermal conditions triggered by acid magmatism., The East-Ouzzal shear zone is a dextral transcurrent N-S ductile fault separating a granulite complex, the In Ouzzal block, from a Middle Proterozoic unit comprising orthogneisses. The shear zone hosts numerous quartz veins, many containing significant gold mineralisation. These are either N-S along an ultramylonite belt close to the In Ouzzal block (Amesmessa), or along oblique dextral shear zones overprinting the East-Ouzzal shear zone (Tirek). In the late Panafrican, gold was leached from the In Ouzzal granulites and deposited in quartz veins along the inactive East-Ouzzal shear zone, under deep geothermal conditions triggered by acid magmatism.

There are two exploration scenarios for gold and base metals in the late Proterozoic Pan-African orogenic belts: ground that has already been explored but merits re-evaluation, such as the copperbelt-hosting Katangan belt and the Damara belt, and ground that has been subjected to little previous investigation, such as the Mozambique belt and Hoggar. It is predicted that genetic modelling, based on the source-migration-trap paradigm used in oil exploration and following a progression from geodynamic domain scale through terranes and mineral play types to prospect scale, will play an important part in future exploration in Africa. The greatest immediate potential of this methodology lies in its application to the copperbelt, the Damaran mobile belt, the West Congolian belt and, possibly, the exposed parts of the North African Altaid-style orogen from Hoggar to the Red Sea., There are two exploration scenarios for gold and base metals in the late Proterozoic Pan-African orogenic belts: ground that has already been explored but merits re-evaluation, such as the copperbelt-hosting Katangan belt and the Damara belt, and ground that has been subjected to little previous investigation, such as the Mozambique belt and Hoggar. It is predicted that genetic modelling, based on the source-migration-trap paradigm used in oil exploration and following a progression from geodynamic domain scale through terranes and mineral play types to prospect scale, will play an important part in future exploration in Africa. The greatest immediate potential of this methodology lies in its application to the copperbelt, the Damaran mobile belt, the West Congolian belt and, possibly, the exposed parts of the North African Altaid-style orogen from Hoggar to the Red Sea.