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[Display omitted] • Zircon U-Pb-Hf isotope analyses and geochemistry on granitoides from Silet terrane. • Neoproterozoic geodynamic evolution of Silet-arc (Western Hoggar). • Disparities in magmatism ages explained in V-shaped Silet Ocean closure model. • Geochemical and isotopic data confirm that Silet is a continental arc. This study presents results of zircon U-Pb-Hf isotope analyses and whole-rock geochemistry applied to magmatic rocks of the Silet terrane in the Western Hoggar, forming a part of the Neoproterozoic arc exposed along the boundary between the LATEA metacraton and the Paleoproterozoic In Ouzzal terrane. According to zircon U-Pb geochronology four distinct pulses of Neoproterozoic granitoids magmatism are recognized in the Silet terrane: Tonian (c. 870–840 Ma), Late Tonian (c. 770 Ma), Latest Tonian (c. 730 Ma) and Late Cryogenian (c. 675 Ma). Geochemical and Hf isotope data indicate a progressive shift in geotectonic settings. The c. 870–840 Ma Tonian TTG pulses (Tonalite-Trondhjemite-Granodiorite) in the North Silet batholith, with superchondritic εHf values (+5.8 to + 7.2), suggest formation in a subduction zone. The subsequent c. 770 Ma Late Tonian magmatism, characterized by mafic compositions, reflects a back-arc tectonic setting, as evidenced by high Ti/V ratios, low V contents, and εHf values of + 6.12 to + 8.95. The c. 730 Ma Latest Tonian magmatism, with more evolved acidic pulses, indicates hybrid mantle–crustal involvement (εHf + 6.53 to + 8.08). The Late Cryogenian intrusions (c. 675 Ma), featuring the lowest εHf values (+1.84 to + 4.09) and inherited c. 870 Ma zircons, suggest formation from the melting of Tonian TTGs during continental collision. Integrating U-Pb dating with geochemical data provides a comprehensive view of the Silet terrane's tectonic evolution, supporting a continental arc origin. Disparities in magmatism ages between the northern (c. 870–675 Ma) and southern (c. 740–640 Ma) segments of the Silet arc correlate with the diachronous collision/subduction of a V-shaped "Silet Ocean", forming an introverted oceanic system (oceans that have formed by rifted continental blocks that were subsequently re‑joined in approximately the same position) within the broader West Gondwana context. Structural analysis indicates that the regional structures of the Silet arc were shaped in a WNW-ESE collisional transpressive regime during the Pan-African orogeny, offering new insights into the Neoproterozoic Silet arc's geodynamic evolution and its paleogeographical location in the West Gondwana orogeny. [ABSTRACT FROM AUTHOR]

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The present investigation embarks on understanding the spatial distribution of the microalgae population in the Hoggar and Tassili regions of the Central Sahara of Algeria. Thirty-eight sites were sampled between April 2016 and April 2017. Environmental parameters were measured at each station. A total of 77 taxa belonging to 7 classes were identified: Bacillariophyceae (27), Cyanophyceae (15), Chlorophyceae (14), Zygnematophyceae (13), Euglenophyceae (5), Dinophyceae (2), and Xanthophyceae (1). The highest values of the Shannon-Weaver and Equitability indexes were recorded at station H5S1 (H’ = 4.62, E = 0.95), respectively, in the region of Hoggar. In the Tassili region, the highest values were recorded at station T1S2 (H’ = 4.50, E = 0.88), respectively. Canonical correspondence analysis (CCA) was established between the environmental parameters and species in both regions. According to the results, pH, altitude, and depth were the most important environmental factors influencing the microalgae diversity. [ABSTRACT FROM AUTHOR]

In 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. [ABSTRACT FROM AUTHOR]

Nowadays, machine learning algorithms are considered a powerful tool for analyzing big and complex data due to their ability to deliver accurate and fast results. The main objective of the present study is to prove the effectiveness of the extreme gradient boosting (XGBoost) method as well as employed data types in the Saharan region mapping. To reveal the potential of the XGBoost, we conducted two experiments. The first was to use different combinations of: airborne gamma-ray spectrometry data, airborne magnetic data, Landsat 8 data and digital elevation model. The objective is to train 9 XGBoost models in order to determine each data type sensitivity in capturing the lithological rock classes. The second experiment was to compare the XGBoost to deep neural networks (DNN) to display its potential against other machine learning algorithms. Compared to the existing geological map, the application of XGBoost reveals a great potential for geological mapping as it was able to achieve a correlation score of (78%) where igneous and metamorphic rocks are easily identified compared to sedimentary rocks. In addition, using different data combinations reveals airborne magnetic data utility to discriminate some lithological units. It also reveals the potential of the apparent density, derived from airborne magnetic data, to improve the algorithm's accuracy up to 20%. Furthermore, the second experiment in this study indicates that the XGBoost is a better choice for the geological mapping task compared to the DNN. The obtained predicted map shows that the XGBoost method provides an efficient tool to update existing geological maps and to edit new geological maps in the region with well outcropped rocks. [ABSTRACT FROM AUTHOR]

Myrtus nivellei Bath & Trab is a medicinal plant used in the Algerian traditional medicines to treat diabetes. This study was undertaken to evaluate the antioxidant effect of decoction from Saharan myrtle in rats made diabetic by injection of alloxan. Daily administration of this extract at two different doses of 100 mg/kg and 300 mg/kg to diabetic rats for 21 days caused a significant increase in the activity of antioxidant enzymes [superoxide dismutase and catalase and reduced glutathione (GSH), and decreased in malondialdehyde (MDA) as oxidative stress markers especially at 300 mg/kg. However, a decrease in activity of these enzymes (GSH) and increase in MDAwas observed in untreated diabetic rats. The objective of present study is to confirm the traditional use of Myrtus nivellei to minimize oxidative stress and prevent the installation of diabetic. [ABSTRACT FROM AUTHOR]

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 Neoproterozoic orogen. [ABSTRACT FROM AUTHOR]

Cowpea is among the most grain legumes consumed in Algeria. The Algerian Saharan is a hostile environment characterized by high temperatures, scarcity of water and salinity of water and soil. In these regions, the farmers have for generations cultivated landraces cowpeas which are probably adapted to these particular environments and which may have particular nutritional and functional characteristics. These cowpeas deserve to be known and exploited in breeding and improvement programs. This study aims to determine the nutritional value and functional properties of Saharan cowpea through their chemical composition and the analysis of biochemical variability between accessions taking into consideration the environments of origin. Eighteen cowpea landraces were harvested in an arid region of southern Algeria (Hoggar, Tamanrasset). The seeds composition was evaluated by the determination of certain chemical characteristics such as moisture ash, crude protein, fat, total carbohydrates, and energy value. The antioxidant activity was also evaluated which includes total non-enzymatic antioxidant capacity (CANET) and lipid peroxidation, which were determined by conventional methods. The results showed variability among the accessions studied (p ≥ 0.05), and that all the landraces had high crude protein and total carbohydrates. The total non-enzymatic antioxidant capacity (CANET) recorded is low, as well as lipid peroxidation. The moisture content, ash content and fat content were also low in these saharan cowpea accessions. The Functional properties of the flour were also evaluated. The water absorption capacity (WAC) varies with an average of 1.17 g/gMS, the oil absorption capacity (OAC) with an average of 0.4 g/gMs, and the swelling index (SI) with an average of 2.63. The accessions NEA7 and NEA13 are the richest in protein and they have the highest nutritional value. We report here for the first time that cowpea seeds grown in the Hoggar region have high biochemical variability and highly acceptable functional characteristics; however, they could be a good source of nutrients. [ABSTRACT FROM AUTHOR]

The 2 Ga-old Ihouhaouene alkaline complex (Western Hoggar, Algeria) is among the oldest known carbonatite occurrences on Earth. The carbonatites are calciocarbonatites hosted by syenites, the predominant rock type in the complex. Both rock types are characterized by medium-grained to pegmatitic textures and contain clinopyroxene, apatite, and wollastonite, associated with K-feldspar in syenites and a groundmass of calcite in carbonatites. The rock suite shows a continuous range of compositions from 57–65 wt.% SiO2 and 0.1–0.4 wt.% CO2 in red syenites to 52–58 wt.% SiO2 and 0.1–6.5 wt.% CO2 in white syenites, 20–35 wt.% SiO2 and 11–24 wt.% CO2 in Si-rich carbonatites (>10% silicate minerals), and 50), whereas clinopyroxene was precipitated from silicate liquids characterized by lower LREE/HREE (Ce/Lu = 49–234) and variable Nb/Ta ratios (Nb/Ta = 2–30). The Si-poor carbonatites resemble the Si-rich carbonatites and the white syenites with elevated REE contents in apatite equilibrium melts compared to clinopyroxene. However, apatite equilibrium melt in Si-poor carbonatite shows a majority of subchondritic values (Nb/Ta

The In Allarene mafic-ultramafic complex is located at the southern part of the In Ouzzal terrane and was known as the unique Pan-African mafic-ultramafic intrusion in this terrane. The complex shows a ring-shaped intrusion of about 20 km2 and concentric structures. Petrological observations and mineralogical analyses show that the core of the intrusion is composed of harzburgites and dunites surrounded by lherzolites, whereas the outer part consists of fine- to coarse-grained gabbros that are crosscut by dolerite dykes. The mineralogy and geochemistry of these rocks show that they are mainly cumulates, but some gabbros and dolerites have characteristics indicating that they correspond to magmatic liquids or they have trapped a variable amount of magmatic liquid. They correspond to the least magnesian and the most alkaline-rich gabbros and dolerites. The geochemistry of the gabbros and dolerites is very similar to the mafic-ultramafic complexes linked to arc zones and they exhibit all the features of the subduction zones magmatism as showing in the N-MORB normalization, with LILE enrichment relatively to HFSE, and Nb-Ta and Ti negative anomalies. The chemical compositions of clinopyroxene and spinel support this hypothesis. This is also the case for all geodynamic setting discrimination diagrams, both those using major elements and trace elements. Several of these diagrams also show that the studied rocks can be distinguished from intracontinental plate tholeiites, which can be very close geochemically to continental arc tholeiites. These results support the hypothesis of the existence of an arc-type metasomatized mantle under the In Ouzzal terrane during Pan-African orogeny. [ABSTRACT FROM AUTHOR]

Many of today's advanced materials depend on quartz as a raw material. Quartz usually contains abundant inclusions, both solid and liquid, and due to the number of these inclusions and their small size, complete separation is most difficult. Typical properties of raw quartz that must be characterized are: Size and Chemical composition of inclusions, their spatial distribution, localization of isomorphic substitutional elements (e.g. Al, Fe). The aim of this study has been to test experimental methods for investigating some inclusions (impurities) present in the Tihimatine quartz from El Hoggar region deposits (southern Algeria) using X Ray Fluorescence, scanning electron microscopy, optical Microscopy with reflected and transmitted lights, infra-red spectrometer, Raman spectrometer. Despite the high concentration of SiO 2 in studied quartz reaching 98%, several harmful inclusions were found and identified as hematite, anatase, muscovite, graphite, it contains: Fe, Ti, Al, K, Ca. Some fluid inclusions were found. We detect the presence of carbon dioxide and water using raman spectroscopy. The repartition of solid impurities is aleatory and not homogeneous with maximum size of 10 μm. Concerning the fluid impurities, their diameter vary between 5 and 20 μm and their repartition is aleatory. [ABSTRACT FROM AUTHOR]

The Ahnet and Tin Zaouatine terranes are located in the southern sector of the Algerian Desert and are part of the Tuareg Shield, which was built up during east-west shortening (Pan-African orogeny). This paper presents a new 1/200,000 geological and tectonic map of the Tin Tanet Firt sheet map (mainly of the Ahnet terrane and the northwestern part of the Tin Zaouatine terrane). Enhancement and processing of multispectral satellite data (Landsat 7 ETM+) combined with field campaign and airborne geophysics was used to discriminate geological lithologies and tectonic structures. We define six geological domains: (i) Palaeozoic formation and Cambrian continental facies and plutonic rocks, (ii) Late- to post-orogenic plutonic rocks, (iii) synchronous orogenic plutonic rocks, (iv) Neoproterozoic formation, (v) Mesoproterozoic volcanics, metasedimentary rocks, and associated plutonic rocks, and (vi) Late Paleoproterozoic metasedimentary rocks. Airborne magnetic data and textural features derived from remote sensing and fieldwork allow us to identify faults and shear zones that affect the whole studied terrane. Interpreted tectonic lines and foliation paths leads us to suggest a deformation model which involves two deformation pahses: an older N-S to NNE-SSW shortening D1 and a younger D2 defined by the N-S trend and a compressional character revealed in the Ahnet terrane and Camp Zohra Complex domain which is considered a continuum deformation split into three phases that affect and form structures of the whole Ahnet and the northwestern part of Tin Zaouatine terranes at the Pan-African orogeny. The most recent stress field recorded in this region is expressed as NE-SW strike-slip faults. [ABSTRACT FROM AUTHOR]

The Saghro Group (SG) is a folded, low-grade volcano-sedimentary series up to 8 km thick that crops out within and to the north of the Pan-African suture zone in the central and eastern Anti-Atlas. Here we describe the SG of the Ougnat inliers that are exposed in the easternmost Anti-Atlas beneath the unconformable, Late Ediacaran Ouarzazate Group (OZG) volcanic rocks. The Ougnat SG mostly consists of volcaniclastic greywackes accumulated in a peritidal-to-shallow basin. The basin infilling was deformed by NNE-trending, mostly upright folds with axial-planar slaty cleavage and low-grade metamorphism. The deformed SG rocks were intruded by the ∼550 Ma Mellab hypovolcanic granodiorite. The latter also crosscuts the lowest OZG rocks that are dated to 574–571 Ma in the western Saghro region. The SG rocks that form the Siroua and Saghro inliers have an oldest age of 620–610 Ma and were folded at ∼610–580 Ma at the onset of the Cadomian orogenic events. We show that the SG rocks are similar to the “Série verte” (SV) rocks that are exposed in the Ougarta and western Hoggar east of the Pan-African suture. We infer that the SG and SV rocks accumulated in a same, continuous basin that was bounding the West African Craton to the north and the east. This strongly subsiding basin formed close to a volcanic arc and was folded during the last Pan-African synmetamorphic events. Fold orientation and age of folding differ however along the edge of the West African Craton. The orogenic greywackes that form the remnants of the SG-SV basin thus constitute a precious record of the diachronic Cadomian event s.l. along the West African Craton northern margin. [ABSTRACT FROM AUTHOR]

The Azrou volcanic district, located to the south-east to the Atakor district in the Hoggar, has a landscape is governed by a number of felsic volcanic highs and dissected mafic plateau lavas. Our new Rb-Sr age (i.e. 23.1 ± 1.6 Ma) indicates that the Azrou felsic lavas are contemporaneous with the Achkal ring complexes (Anahef region). The Azrou felsic lavas (mainly trachyte and phonolite) show remarkably homogeneous compositions both in major elements (57.5 ≤ SiO 2 ≤ 63.1 wt%; 10.8 ≤(Na 2 O + K 2 O)≤12.4 wt%), trace elements (33.2 ≤ Th ≤ 107 ppm; 170 ≤ La≤472 ppm; 8.7<(La/Yb)N < 27.3) and radiogenic isotopes (0.703359 < 87 Sr/ 86 Sr < 0.706539; 0.512727 < 143 Nd/ 144 Nd < 0.512925; 2< ε Nd <5.84. These data indicate that the lavas have been only very weakly contaminated by the Precambrian basement. Geodynamically, this genesis coupled with the low volume of both trachytic and phonolitic trends implies the reworking of pre-existing shear-zones allowing the rapid ascent of these small batches of magmas. This is in agreement with the general model of linear delamination along these shear zones due to the Africa-Europe convergence developed by Liégeois et al. (2005) and recently imaged by the magneto-telluric investigation of Bouzid et al. (2015). [ABSTRACT FROM AUTHOR]

This study presents a multidisciplinary approach to discriminate and map different types and generations of Pan-African granitoids in the Hoggar, southern Algeria, using remote sensing and airborne geophysics in close correlation with previous works and established geological maps. RGB (Red, Green, Blue) combinations of band ratios; principal component analysis (PCA) and image classification for Landsat 7 ETM+ (Enhanced Thematic Mapper Plus), allow spatial discrimination and mapping of granitoid rocks of the studied area (200*350 km). This area extend over four contrasted Pan-African terranes (In Tedeini, Iskel, Tefedest and Laouni terranes, the two latter belong to the LATEA (Laouni-Azrou-n-Fad-Tefedest-Egéré-Aleksod-Assodé-Issalane) metacraton. The airborne magnetic intensity provides a wide range of responses from high values (youngest granitoids) to low values (volcano-sedimentary and gneissic country-rocks). Radiometric data, displaying radioelements concentration, discriminate efficiently the late alkaline granitoids (high values), the calk-alkaline granitoids (intermediate values) and the Tonalite-Trondhjemite-Granodiorite series (low values). This study led to the establishment of a more accurate geological map where the geochemical characteristics of the Pan-African granitoids are determined, including plutons not yet studied, especially in the poorly known In Tedeini terrane, and brings new constraints for the geodynamic development of the Tuareg Shield, which includes the Hoggar. [ABSTRACT FROM AUTHOR]

The In Ouzzal terrane in western Hoggar (Southern Algeria) preserves evidence of ultrahigh temperature (UHT) crustal metamorphism. It consists in Archean crustal units, composed of orthogneissic domes and greenstone belts, strongly remobilized during the Paleoproterozoic orogeny which was recognized as an UHT event (peak T > 1000 °C and P ≈ 9–12 kbar). This metamorphism was essentially defined locally in Al-Mg granulites, Al-Fe granulites and quartzites outcropping in the Northern part of the In Ouzzal terrane (IOT). In order to test and verify the regional spread of the UHT metamorphism in this terrane, ternary feldspar thermometry on varied rock types (Metanorite, Granulite Al-Mg and Orthogneiss) and samples that crop out in different zones of the In Ouzzal terrane. These rocks contain either perthitic, antiperthitic or mesoperthitic parageneses. Ternary feldspars used in this study have clearly a metamorphic origin. The obtained results combined with previous works show that this UHT metamorphism (>900 °C) affected the whole In Ouzzal crustal block. This is of major importance as for future discussion on the geodynamic context responsible for this regional UHT metamorphism. [ABSTRACT FROM AUTHOR]

• Microstructural observations and EBSD measurements were applied to nine mylonites from the 4°50′ shear zone. • Zircon U-Pb ages provide Pan-African ages and are related to dextral deformation accommodated with fluids. • Partial melting of lower crust/upper mantle triggered granitic intrusions from 661 ± 2.8 to 639 ± 2 Ma. • Successive magma batches during migmatization from 623 ± 4 Ma to 609 ± 2 Ma. • Local sinistral reactivation of the 4°50′ shear zone occurred posteriorly to 609 ± 2 Ma. • The 4°50′ shear zone remained active under high-temperature over ≥ 20 My. The 4°50′Shear zone (SZ), one of the major structures of western Gondwana, formed in Hoggar during the Pan-African orogeny is still poorly studied; especially ages and deformation characteristics are lacking. We performed microstructural analysis and EBSD measurements on nine selected mylonites from the 4°50′SZ, and zircon U-Pb dating on two granitoid samples. The protolith of these mylonites are granitoids. Most samples display segregation of dominant feldspar and minor quartz in separate layers that underline the N-S subvertical mylonitic foliation. Feldspar grains display evidence of intracrystalline deformation, supporting dextral shear-sense. Plagioclase and K-feldspar are frequently corroded with embayments infilled by secondary K-feldspar and plagioclase respectively. Interstitial quartz grains disseminated in feldspar aggregates may infill fractures in feldspar grains. Quartz ribbons, usually parallel to the foliation, locally crosscut feldspar layers. Quartz is partially recrystallized and elongate crystals form a secondary foliation at ∼ 30° to the main foliation, supporting a later sinistral shearing. In some samples, amphibole is associated with quartz and oriented parallel to the foliation. In all samples, quartz CPO suggests a dominant prism- slip-system, activated at medium/high temperature (∼500-700°c), but stress-induced oriented crystallization may have contributed to this CPO. K-feldspar CPO supports the activation of the [1 0 0](0 1 0) slip system while the plagioclase CPO points to activation of [1 0 0](0 0 1) system. These CPO support dislocation creep under amphibolite facies conditions. These new data, in addition to U-Pb dating, suggest the following evolution: 1) successive intrusions of granitoids in the SZ (∼661-∼639 Ma) due to partial-melting of the lower-crust and, possibly also of the lithospheric-mantle, 2) the 4°5 0′SZ was rooted in the lower-crust or the upper-mantle, and 3) dextral shearing lasted over ≥ 20My. This was followed by successive magma batches that intruded these rocks during a late migmatitic episode (∼623-∼609 Ma). After ∼ 609 Ma, a moderate sinistral reactivation of the 4°50′SZ occurred and was accommodated through dislocation creep mainly localized in quartz ribbons. During accretion of the Western Gondwana, the 4°50′SZ was active during subduction. During ≥ 20My, it was successively intruded by granitoids that cooled down slowly, and have been deformed in the submagmatic state then in the solid-state. [ABSTRACT FROM AUTHOR]

The study area is located in the western Hoggar Shield (southern Algeria). It includes the In Ouzzal terrane, which consists of Archaean metamorphic rocks. By contrast to other rocks of the Hoggar Shield, the In Ouzzal terrane represents an exception of being neither deformed nor metamorphosed during the Pan-African event, remaining as a rigid block since 2 Ga. Although, previous geophysical works in the area include an airborne magnetometer and gamma-ray spectrometric survey as well as ground gravity and magnetotelluric survey structurally, the study area has not been very well understood. In this paper, we present the interpretation results of the airborne magnetic data by using the 3D Euler deconvolution and the improved Tilt-angle methods. These results reveal the existing of fault systems (FS) occurring within the center of the study area and along the latitude of 22°; the results also suggested that the deepest fault system is oriented NE-SW and is represented by parallel major faults splitting the In Ouzzal terrane into two different parts: northern and southern. The northern part moved northwards, whereas the southern part moved southwards colliding with the Iforas unit. The interpretation confirms that the In Ouzzal terrane and the surrounding Pan-African structures are bound two by two sub-vertical lithospheric faults with the existence of dextral and sinistral faults in the west and east of the terrane, respectively. [ABSTRACT FROM AUTHOR]

The Gour Oumelalen area exposes Paleoproterozoic (1.9 Ga) marbles and calc-silicate granulites. Some marbles show a specific mineralogy characterized by the presence of a highly aluminous clinopyroxene with AlO content exceeding16 wt%. This clinopyroxene shows a marked zoning with a hedenbergitic core rimmed by fassaite. Phase relations are expressed by spectacular reaction textures in calc-silicate granulites as Opx + Cpx + Pl + HO == > Grt + Qtz ± Am and Cpx + Ilm + Pl ± Mt = > Grt + Qtz + Spn. In olivine-bearing marbles, clinopyroxene and dolomite occur around olivine and calcite. According to thermodynamic modeling in the NaO-CaO-FeO-MgO-AlO-SiO-HO-TiO-FeO (NCFMASHTO) system, the first stage of metamorphism is located at 800 °C and 6-7 kbar, which is followed by an increase in pressure at 9-10 kbar and 800 °C and an isobaric cooling at 680 °C. The deduced anticlockwise P-T path is consistent with a granulitic metamorphism occurring in an active continental margin context. [ABSTRACT FROM AUTHOR]

The development in the emerging technologies of information and communications requires more rare metals. The existing resources, insufficient to assume this progress, require further investigations to discover new rare metal deposits. The traditional methods, based on manual overlay, are unsuitable and expensive. Thus, mineral exploration requires updated methods to easily, quickly, and cost effectively delineate new promising exploration zones. Geographical Information System (GIS) and applied geomatics provide and perfect various modeling techniques implemented in GIS software. In recent years, two spatial modeling techniques were developed and widely applied in mineral exploration, data-driven methods, and knowledge methods. Weight of evidence (WofE) is a data-driven method based on the Bayesian theorem and its fundamental concept of prior and posterior probabilities. The method combines statistically diverse geodata that represent ore-controlling factors by weighting their evidence using 'control points' to create a 'posterior probability map.' Our study area, located at the southern part of Hoggar in the south of Algeria, is potential for Sn, W, and rare metals and encloses several deposits related to peraluminous post-orogenic rare metal granitoïds (RMGs). In this work, 'weights of evidence' modeling is applied to map mineral potential of this style of mineralization. Seventeen predictor maps, representing the deposit recognition criterion model, were generated from multi-source geodata (lithology, geochemistry, tectonic, magmatism, and geophysics). These data were used as 'input data' and the known deposits (48 mineral occurrences) as 'training sites.' The WofE modeling gets the following results: (1) generate an output map called 'mineral potential map' (MPM), where potential zones are reduced to small areas; (2) the MPM efficiently predicts the well-known deposits of Nahda, Sedis, Rechla, and Tit N'Enir; and (3) highlights some unrecognized areas such as Tedjrine, Monts de Tessalit, and Gara Akeboum. (4) The control model demonstrates the possibility to extend the WofE method to the adjacent regions enclosing a small number of known mineral deposits. [ABSTRACT FROM AUTHOR]

The Egéré domain belongs to the Egéré-Aleksod terrane (LATEA metacraton), which has the peculiarity in the Tuareg Shield of being practically devoid of Pan-African batholiths allowing the preservation of pre-Neoproterozoic and early Pan-African events. It is composed of amphibolitic to eclogitic facies metamorphic rocks with the mostly metamagmatic Arechchoum Group, the mostly metasedimentary Egéré Supergroup and the here defined metasedimentary Oneral Group. Petrological P-T-t study, U-Pb on zircon dating, geochemical composition and Sr-Nd isotopic compositions decipher largely unsuspected Paleoproterozoic, Mesoproterozoic and Neoproterozoic evolution for the Tuareg Shield in addition to an Archean cratonic nucleus. We show here that (1) the Arechchoum Group, now composed mainly of garnet orthogneiss, is an alkaline silicic large igneous province (SLIP) of early Rhyacian age (c. 2.28 Ga) underlain by the Archean Amadror craton, defined here. Additional alkaline pulses occurred during the Siderian (c. 2.37 Ga), the late Orosirian (c. 1.89 Ga, gabbro) and the Statherian (c. 1.74 Ga, rhyolitic dykes). (2) The Lower Egéré Group is made of marbles and quartzites interlayered with a large volume of bimodal magmatic rocks during the late Rhyacian (c. 2.1Ga) and the Orosirian (c. 2.0 Ga) reminiscent of the Karoo LIP and emplaced during an extensional continental setting. (3) The Upper Egéré Group consists of paragneiss, quartzite and marble deposited at the end of the Orosirian (c. 1.8 Ga) with a majority of Archean zircon grains (Amadror craton) and a complete record from Arechchoum and Egéré groups. It houses also a Calymmian high-Fe intraplate tholeiitic basaltic event (c. 1.55 Ga) marking a rifting event. (4) The newly defined Oneral Group deposited at c. 0.7 Ga comprising sediments whose source was located to the west of LATEA named Tin Hinan terrane, a continental arc made of a Stenian basement and Tonian subduction-related rocks. At c. 0.68 Ga, all these groups were subducted (continental subduction) generating an eclogitic facies (c. 650 °C/20 kbar) in the Egéré Supergroup and the Oneral Group. The exhumation, triggered by slab breakoff (c. 800 °C/14 kbar) at c. 0.65 Ga, put these groups back on the Arechchoum Group at c. 0.63 Ga, the whole package recording c. 690 °C and 8 kbar. During the long post-collisional transpressive period (630–580 Ma), corresponding to the general northward Tuareg tectonic escape, they were slowly exhumed up to c. 610°/6 kbar, during which time the rigid Amadror craton generated the spectacular NW-verging thrust structure of the Egéré region while the Tuareg Shield is dominated by NE verging structures. [ABSTRACT FROM AUTHOR]

In front of the fast development of information technology and increasing requests for digital or analog geological data in the Hoggar region, GIS has become now a full-fledged technology in the field of digital management of geological information to ensure effectively the organization, storage, and retrieval of useful information. In this context, the work we present is part of a methodological approach for data analyzing and processing on the gold mineralization geology and metallogeny of the Hoggar. The resulting geographic information system has allowed us to develop a base of 'Or-Hoggar-Geodatabase' data, structured according to several categories and classes of information (fields, indexes, and mineralized points, geological formations, tectonic, hydrographic network, and topography). This structured set of information using Arcgis support allows the design and combination of thematic maps at different scales levels of Hoggar, including structural map, geological map (with all showings optional representation), and hydrographic chart. This system offers also an editing possibility of several cartographic materials at different scales and a better option for analyzing the Hoggar geological data. It also allows an exceptional view for the gold mineralization distribution of the Hoggar. Thus, GIS applied to the Hoggar region shows that even if the showings of this region have different characteristics and morphology, they are all controlled by tectonic structures related to major events that have affected the Hoggar. [ABSTRACT FROM AUTHOR]

A natural process can be described as a mixture of several components of different scales. The two-dimensional anisotropic wavelet transform is shown to be appropriate to study such processes and to focus on details at a given analyzing scale. In this paper, we apply the normalized optimized anisotropic wavelet coefficient (NOAWC) method on airborne gamma ray recorded over the Hoggar area (Algeria) to characterize anisotropies of orientation, shape and spatial distributions of the radioactive sources at different scales. This technique may provide additional significant information to the conventional analysis. [ABSTRACT FROM AUTHOR]

Adrar Izzilatène in the Egéré-Aleksod terrane of the LATEA metacraton (Hoggar, Algeria) exposes one of the best preserved examples of eclogite facies metamorphism in Hoggar. Three distinct stages of metamorphic development are recognised, namely, the pre-peak stage (M1), characterised by garnet, amphibole, epidote, quartz and rutile, the peak eclogite facies stage (M2), consisting of omphacite, garnet, edenite, epidote, quartz and rutile, and the retrograde stage (M3), where initial decompression resulted in the appearance of plagioclase, the development of pargasite + plagioclase kelyphites and finally the formation of anhydrous plagioclase + diopside coronas. Porphyroblastic omphacite has a jadeite content of up to X Jd = 0.36, which is the highest yet observed for eclogite facies rocks from the Tuareg Shield. Garnet growth zoning patterns are characterised by flat profiles in the cores ( X Alm = 0.55–0.60; X Prp = 0.12–0.16; X Grs = 0.26–0.30) before showing a decrease in almandine to X Alm = 0.45, coupled to an increase in pyrope to X Prp = 0.29 and decrease in grossular to X Grs = 0.26 at the rims. Calculated P–T–M H2O pseudosections show that the prograde M1 assemblage equilibrated at 13–14 kbar and 580 °C, before pressure and temperature increased to 19 kbar and 650–700 °C at fluid-saturated conditions during peak metamorphism. Retrogression involved near-isothermal decompression to 8–9 kbar and 700–750 °C at fluid-undersaturated conditions. Prograde-to-peak metamorphism of the Izzilatène eclogite could have involved either oceanic or continental subduction, followed by exhumation as the area was obducted towards the LATEA metacraton during the Pan-African orogeny and the assembly of Western Gondwana. [ABSTRACT FROM AUTHOR]

Kyanite-bearing metapelites from the Egere terrane (Central Hoggar, South Algeria) have a high-pressure eclogitic facies paragenesis; furthermore, they preserve evidence of partial melting with the development of metamorphic textures involving garnet-kyanite-biotite-white mica-plagioclase-K-feldspar-quartz-rutile and ilmenite. Garnet porphyroblasts in these rocks display a calcium zonation formed during high-P metamorphism followed by decompression. Moreover, the large garnet poikiloblasts reflect complex mineral-melt relationships, and their growth was strongly linked to melt production. In order to give an account of the various textures and explain the evolution of the different parageneses in relation with pressure and temperature, thermodynamic modeling in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 (NCKFMASHTO) system is a powerful approach. The intersection of isopleths of grossular content and Fe⁄(Fe + Mg) of core of garnet provides constraints on the P-T conditions of the metamorphic peak. Kyanite-bearing metapelites experienced a clockwise P-T path culminating at about 850 °C and 17-19 kbar. Peak conditions were followed by decompression to about 9 kbar and 750 °C. [ABSTRACT FROM AUTHOR]

Here, we suggest a new algorithm to study the local fractal properties of airborne spectrometric data considered as 2D-mBm paths. This algorithm is first validated on synthetic two-dimensional multifractional Brownian motion (2D-mBm) paths, and then implemented on natural Gamma rays measurements recorded in Hoggar (Algeria). The regularity (Hölder exponent) maps obtained from the different channels (K, Th and U) show a strong correlation. Besides, these maps allow depicting the location of some faults affecting the studied area, especially the main 4°50’ fault. Our findings show that the Hölder exponent can then be used as a tool for the geological characterization. [ABSTRACT FROM AUTHOR]

The Tighsi area is situated in the northern part of the Egere-Aleksod terrane (Central Hoggar, South of Algeria). The eclogites and the garnet-amphibolites occur as lenses in marble, metapelite and quartzite. The petrological study shows that the high pressure paragenesis is characterized by the assemblage omphacite–garnet–rutile–quartz and epidote. Omphacite contains epidote, rutile and quartz inclusions. Due to the decompression, omphacite is the first mineral to destabilize into very thin symplectites of albite and clinopyroxene poorer of the jadeitic component. The paragenese of the lower pressure is represented by kelyphites and symplectites of amphibole–plagioclase separating garnet from omphacite and quartz. During this evolution, rutile transforms into ilmenite then, in the latest stage sphene replaces ilmenite. The thermodynamic modeling using THERMOCALC has confirmed these textural observations and suggests that the eclogites have experienced three stages of metamorphism. Stage I is the high pressure association, an H 2 O under-saturated pseudosection adapted to this stage has been constructed in NCFMASHTO system. The association of high pressure corresponds to the field where garnet is in equilibrium with omphacite including epidote-rutile and quartz; The P – T conditions of 19.6 kbar and 694 °C have been estimated using the garnet core compositions. Stage II is the isothermal decompression where the amphibole–plagioclase kelyphites occur at the expense of garnet, omphacite and quartz at 15.5 kbar and 774 °C (conditions estimated using the garnet rim and the plagioclase–amphibole kelyphites compositions). Stage III is the late retrograde evolution; a second pseudosection with H 2 O in excess has been constructed to model this stage and show the transformation of eclogites into garnet-bearing amphibolites and explains the occurrence of sphene. The P – T conditions of 9.3 kbar and 695 °C have been estimated using the compositions of the plagioclase with the maximum X an and the amphibole with the minimum concentration of Al VI . Both pseudosections show a clockwise path for eclogite evolution to garnet-amphibolites. This path characterizes the exhumation that succeeded a subduction event; therefore, the P – T path shows an isothermal decompression. Then, the geothermic gradients became normal so the decrease of pressure is accompanied with a decrease in temperature. [ABSTRACT FROM AUTHOR]