The northeastern Algeria hydrothermal system: gravimetric data and structural implication

Abstract The Tell Atlas of Algeria has a huge potential for hydrothermal energy from over 240 thermal springs with temperatures up to $$98^\circ$$ 98 ∘ C in the Guelma area. The most exciting region is situated in the northeastern part which is known to have the hottest hydrothermal systems. In this work, we use a high-resolution gravity study to identify the location and origin of the hot water, and how it reaches the surface. Gravimetric data analysis shows the shapes of the anomalies arising due to structures at different subsurface depths. The calculation of the energy spectrum for the data also showcases the depths of the bodies causing anomalies. 3D-Euler deconvolution is applied to estimate the depths of preexisting tectonic structures (faults). These preprocessing steps assist with assessing signal attenuation that impacts the Bouguer anomaly map. The residual anomaly is used in a three-dimensional inversion to provide a subsurface density distribution model that illustrates the locations of the origin of the dominant subsurface thermal systems. Overall, the combination of these standard processing steps applied to the measurements of gravity data at the surface provides new insights about the sources of the hydrothermal systems in the Hammam Debagh and Hammam Ouled Ali regions. Faults that are key to the water infiltrating from depth to the surface are also identified. These represent the pathway of the hot water in the study area

Late Panafrican evolution of the main Hoggar fault zones: Implications of magnetic fabric study in the In Telloukh pluton (Tin Serririne basin, Algeria)

International audienceThe Late Panafrican evolution of the Hoggar shield is characterized by emplacement of magmatic intrusions and by occurrence of major shear zones separating different terranes. In Telloukh granite is close to the In Guezzam faults (western border of the Tin Serririne basin). Analysis of its visible and magnetic fabrics suggests an emplacement mode and deformation that are not related to the In Guezzam faults, but most likely to a N-S compression, an event not yet identified. Dioritic dykes crosscutting the granite have a very different magnetic fabric, which is related on the contrary to dextral strike-slip movements along the In Guezzam faults. In both cases, no visible fabric can be correlated with the magnetic fabric, which has been likely acquired during late magmatic stages. This magnetic fabric was not significantly affected by the tectonic events that took place after entire crystallization of the magma. The In Guezzam faults and the major 7°30 and 4°50 shear zones are close to intrusions such as In Telloukh dykes and the Alous En Tides and Tesnou plutons where quite similar magnetic fabrics are observed, all related with dextral strike-slip movements along these structures

Âge 40K/40Ar, Carbonifère inférieur, du magmatisme basique filonien du synclinal paléozoïque de Tin Serririne, Sud-Est du Hoggar (Algérie) Lower Carboniferous 40K/40Ar dating of intrusive basic magmatism of the Paleozoic syncline of Tin Serririne, southeastern Hoggar (Algeria)

International audienceÂge 40K/40Ar, Carbonifère inférieur, du magmatisme basique filonien du synclinal paléozoïque de Tin Serririne, Sud-Est du Hoggar (Algérie) Lower Carboniferous 40K/40Ar dating of intrusive basic magmatism of the Paleozoic syncline of Tin Serririne, southeastern Hoggar (Algeria) Les séries primaires des Tassilis Oua-n-Ahaggar (Sud-Est du Hoggar) exposent, dans le synclinal de Tin Serririne, des passées magmatiques basiques alcalines. Le léger métamorphisme de contact qui affecte la couche les recouvrant et des études d'anisotropie de susceptibilité magnétique de ces dolérites ont permis de préciser que ces dernières correspondaient à des sills et à des dykes. Les datations 40K/40Ar d'un échantillon sur roche totale et sur feldspaths séparés et de deux autres échantillons sur roche totale se recoupent à Click to view the MathML source (pour Click to view the MathML source), indiquant de ce fait un âge qui correspond au Carbonifère inférieur (Tournaisien). La prise en compte de l'âge de ce magmatisme et des données stratigraphiques et structurales sur ce secteur suggèrent une mise en place de ces magmas au cours d'une distension liée au rejeu d'accidents tardi-panafricains. Pour citer cet article : H. Djellit et al., C. R. Geoscience 338 (2006)

“Neotectonics” in the northern African margin: new paleomagnetic constraints from northwestern Algeria

International audiencePrevious paleomagnetic studies performed in the central North-Algeria (Chellif and Mitidja basins) on Neogene formations pointed out tectonic clockwise blocks rotations. This deformation pattern was interpreted as resulting from a bookshelf neotectonics, consequence of the Africa-Eurasia plates convergence. A new paleomagnetic study was conducted on the Neogene volcanic rocks outcropping in the northwestern Algeria (Marset Ben Mhidi, Aïn Temouchent, Tifaraouine area). The obtained stable remanent magnetization is mainly carried by Ti-poor titanomagnetite. The paleomagnetic data show that, since the lava emplacement, the northwestern Algeria underwent a mean moderate clockwise block rotation of 9.3° ± 4.5°. For the Algerian margin, this confirms a context of transpression and blocks rotations in a strike-slip tectonic setting. A decreasing deformation gradient from the E to the W affected the different basins of this margin, from strong rotations within the Mitidja, to the moderate ones in the Chellif and to Marset Ben Mhidi, Aïn Temouchent, Tifaraouine area, where rotation magnitudes are significantly lower

Upper Cretaceous-Cenozoic uplifts and tectonics within a Precambrian shield — insight from the Hoggar (Algeria) local sedimentary cover

International audienceIn order to better constrain the Mesozoic-Cenozoic evolution of the Precambrian Hoggar shield, a paleomagnetic study, combined with detailed fieldwork, was carried out to date its detrital local cover, the Serouenout Formation. Thermal demagnetization yields, only in a few samples, the characteristic remanent magnetization carried by hematite. Post-tilting remagnetization was obtained in sites located along a fault affected by intense fluids circulation. The paleomagnetic directions recorded at seven widespread other sites are on the contrary associated with a positive fold test. It provides a relatively well-defined paleomagnetic pole (A95 = 4.1°), sufficient to estimate the age of the Serouenout Formation. The comparison of this pole with the reference curve of Africa suggests two possible age windows, Triassic and Upper Cretaceous-Lower Paleocene, while the discovery in the uppermost levels of the Serouenout Formation of a fern-rich level with Weichselia reticulata (Bathonian to Cenomanian; Blanco-Moreno et al., 2018) imposes a deposition during the Cenomanian. The presence of a detrital formation at least 350 m thick, with a basal conglomerate containing large pebbles, implies the existence, during this time period, of a tectonic event that generated differential uplift. In addition, structural observations indicate that the Serouenout Formation recorded later brittle tectonics, dominated by a network of vertical N–S dextral faults. The horizontal displacement generated by one well-developed fault has been estimated to be at least 1 km. This activity is related to the known Alpine reactivations of the N–S Pan-African mega-structures, which are still at the origin of the current intraplate seismicity

Soil metal pollution from former Zn–Pb mining assessed by geochemical and magnetic investigations: case study of the Bou Caid area (Tissemsilt, Algeria)

International audienceAbstractFormer zinc and lead mines that have beenoperating for half a century are located in the massif of BouCaid (Tissemsilt, Algeria). Hazardous heavy metals emit-ted from the mines are abundant in the surrounding soil andcause strong metal pollution in the region. This paperinvestigates the extent of lead and zinc mine activityderived pollution by characterizing both magnetic andgeochemical properties of samples collected in the vicinityof the mines. The results of the magnetic study show thecoexistence of magnetic minerals such as magnetite,hematite and goethite. Analyses on surface soils andweathered rocks suggest that hematite and goethite haveore-related lithogenic origins. Magnetic susceptibilityshows a positive correlation with lead content when presentin low-to-medium concentrations (\*500 mg/kg). Athigher lead concentrations, there is no correlation withmagnetic susceptibility. The relationship between magneticsusceptibility and zinc content is not straightforward. Theseobservations are explained by the higher affinity of Pb toiron oxides at lower pollution levels and their preferentialbonding to carbonates when Pb and Zn contents areextremely high, as demonstrated by Iavazzo et al. (J Geo-chem Explor 113:56–67,2012) in a study of former Zn–Pbmine in Morocco. Based on the general features of thespatial maps of field-measured magnetic susceptibility,mass-specific magnetic susceptibility, Pb and Zn contents,it is concluded that field magnetic measurements provide agood qualitative proxy of pollution spread out of themining galleries, while laboratory measurements afford amore detailed investigation of the links between iron oxi-des and the main heavy metals in the ore