Geophys. J. Int. (2020) 223, 1973–1986 doi: 10.1093/gji/ggaa432 Advance Access publication 2020 September 12 GJI Geomagnetism, Rock Magnetism and Palaeomagnetism Magnetotelluric investigation of the Precambrian crust and intraplate Cenozoic volcanism in the Gour Oumelalen area, Central Hoggar, South Algeria Zakaria Boukhalfa, 1,2,3 Abderrezak Bouzid, 2 Yixian Xu , 1 Abderrahmane Bendaoud, 3 Bo Yang, 1 Mohamed Hamoudi, 3 Said Sofiane Bougchiche, 2 Aboubakr Deramchi, 2 Massinissa Amara, 3 Khadidja Ouzegane, 3 Walid Boukhlouf, 4 Abdeslam Abtout, 2 Abdelhamid Bendekken 4 and Mohamed Djeddi 3 1 School of Earth science, Zhejiang University, Hangzhou 310027, China. E-mail: xyxian@zju.edu.cn 2 Centre de Recherche en Astronomie, Astrophysique et Geophysique (CRAAG), B1P 63, Route de l’Observatoire, Bouzareah, Algiers, 16340, Algeria 3 Facult´ e des Sciences de la Terre, de G´ eographie et de l’Am´ enagement du Territoire, Universit´ e des Sciences et Technologie Houari Boumedien (USTHB), Algiers. Algeria 4 Unit´ e de Recherche de Tamanrasset, CRAAG, Tamanrassat, Algeria Accepted 2020 September 10. Received 2020 September 5; in original form 2019 May 17 SUMMARY The Tuareg Shield was assembled by oceanic closures and horizontal movements along mega-shear zones between approximately 20 terranes during the Pan-African Orogeny (750– 550 Ma). Although there is an ongoing debate about its origin, the exhumation of the Tuareg Shield is assumed to be related to Cenozoic intraplate volcanism. The Gour Oumelalen is a key region of the Tuareg Shield and is located in the northeastern part of the Eg´ er´ e-Aleksod terrane, corresponding to the eastern boundary of the Archean–Palaeoproterozoic microcon- tinent LATEA (Central Hoggar). The eastern boundary of the study area corresponds to a Neoproterozoic suture zone separating two old microcontinents, LATEA and the Orosirian Stripe. We deployed two magnetotelluric (MT) profiles consisting of 33 broad-band MT sta- tions and combined these with aeromagnetic data, aiming to define the crustal structure in detail. The resistivity cross-sections obtained from the 3-D inversion of full impedance tensor and tipper data from stations along the profiles, confirm the main Precambrian faults, some of which are covered by Quaternary sediments and hence, have not yet been deciphered. The cross-sections also highlight the Cretaceous–Quaternary sedimentary basins represented by low resistivities. The upper crust is typically cratonic with a high electrical resistivity. On the contrary, the lower crust shows a drastic drop in resistivity (<10 m). The most plausible hypothesis is that the study area corresponds to a Cretaceous rifting zone. The Cretaceous magmatic event and its related fluids and mineralization as well as the recent fluids associated with Cenozoic volcanism, are plausible causes of a very conductive lower crust. However, we cannot exclude other reasons such as: (i) a high-temperature and strongly sheared mobile belt or (ii) a contribution of inheritance involving Pan-African events that affected this former suture area. Key words: Magnetotellurics; Cratons; Crustal structure. 1 INTRODUCTION The Tuareg Shield (Fig. 1), situated in Northwest Africa, comprises 25 terranes (Li´ egeois 2019). A major part of the shield is located in Hoggar in Algeria, and extends southward in the ‘Iforas Massif’ and the ‘A¨ ır Massif’, which are situated in Mali and Niger, respectively. The Hoggar was formed during the Pan-African orogeny by colli- sion, accretion, and transcurrent movements between some juvenile terranes and the Archean and/or Palaeoproterozoic terranes. These processes were part of the formation of central Gondwana (870–520 Ma; Meert & Lieberman 2008). The Hoggar also witnessed a series of collisions between several microcontinents and the accretion of C  The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com 1973 Downloaded from https://academic.oup.com/gji/article/223/3/1973/5904761 by guest on 24 November 2023