Chemie Der Erde-Geochemistry最新文献

{"title":"Integrated remote sensing and geophysical studies of the Silet-Tin Felki area: Insights into the Pan-African tectonics and magmatic evolution of the Hoggar Shield, Southern Algeria","authors":"Narimene Berrahmane ,&nbsp;Abderrahmane Bendaoud ,&nbsp;El-Hocine Fettous ,&nbsp;Sid Ali Doukkari ,&nbsp;Takfarinas Lamri ,&nbsp;Basem Zoheir ,&nbsp;Mohamed Hamoudi","doi":"10.1016/j.chemer.2024.126242","DOIUrl":"10.1016/j.chemer.2024.126242","url":null,"abstract":"<div><div>The Silet-Tin Felki area, located within the Tuareg Shield, represents a key area for understanding the Pan-African orogeny and associated magmatic processes. This study employs a comprehensive approach, integrating remote sensing, airborne geophysics, and the previously available geochemical data to produce an enhanced lithological and structural map of the area. Remote sensing methods, including optimal RGB band combinations and principal component analysis (PCA), effectively distinguish between volcanic, granitoid, and metamorphic units. High-resolution magnetic and gamma-ray spectrometry further elucidate lithological boundaries and tectonic features, including significant shear zones. The study identifies two distinct lithological blocks, separated by the 4°50′E lithospheric shear zone: the LATEA-Aouilène block to the east, featuring Neoproterozoic high-grade metamorphic rocks, and the Pharusien Belt to the west, characterized by Neoproterozoic volcanic arc and accretionary wedge complexes. The Tonian TTG batholiths in the northern Silet region display moderate radioactivity and magnetic signatures, contrasting with the highly radiogenic post-orogenic granites.</div><div>Key geodynamic features, such as mafic-ultramafic intrusions associated with a back-arc basin, were delineated, refining the regional geological model and enhancing the understanding of magmatic evolution and tectonic interactions. The integration of gamma-ray spectrometry and aeromagnetic data enabled the detailed mapping of pre-, <em>syn</em>-, and post-collisional granitoids, including transitional TTG suites, and revealed complex tectonic history with significant shear zones and lineaments. This updated geological framework provides critical insights for future exploration and underscores the need for further geochronological and petrological research to fully comprehend the tectono-magmatic evolution of this part of the Tuareg Shield.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126242"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineralogical and geochemical characteristics of AlFe granulites and banded iron formations in the Archean supracrustal unit of the In Ouzzal terrane (NW Hoggar, Algeria)","authors":"Assia Badani ,&nbsp;Saïda Aït Djafer ,&nbsp;Zouhir Adjerid ,&nbsp;Khadidja Ouzegane ,&nbsp;Jean-Robert Kienast ,&nbsp;Nadia Boureghda","doi":"10.1016/j.chemer.2025.126261","DOIUrl":"10.1016/j.chemer.2025.126261","url":null,"abstract":"<div><div>In the northern In Ouzzal terrane, Al<img>Fe granulites and banded iron formations (BIFs) constitute a supracrustal unit, locally associated with Al<img>Mg granulites, marbles, calc-silicate granulites, and mafic or ultramafic rocks. The Al<img>Fe granulites display variable SiO₂ content (55.62 to 79.26 wt%) and X_Mg ratio (0.11–0.48) and are characterised by spinel–quartz parageneses, locally retrograded to garnet-sillimanite coronas. Cordierite is absent in some Al<img>Fe granulite samples, while others contain cordierite-spinel or cordierite-spinel-orthopyroxene symplectites that are a breakdown product of spinel-garnet-sillimanite-quartz assemblages. The BIFs display a unique corundum-quartz-magnetite paragenesis, characteristic of ultra-high-temperature (UHT) metamorphic conditions. Another exceptionally rare type of BIF in the region consists of orthoferrosilite (X_Mg = 0.14–0.29) in equilibrium with high chlorine-rich (3.88 to 5.12 wt%) hastingsite, surpassing values reported in international literature. The Al<img>Fe granulites exhibit geochemical characteristics comparable to post-Archean shales and are interpreted as the products of mixed protoliths. These protoliths consist of mature detrital material, primarily quartz, derived from trondhjemite and tonalite sources emplaced between 3300 and 2700 Ma. Additionally, they include immature predominantly chloritic components enriched in Al, Cr (100–300 ppm) and V (100–200 ppm). Banded iron formations (BIFs) are mainly composed of three key components: SiO₂, FeO, and Fe₂O₃, with their combined content ranging from 91.51 to 99.23 wt%. The concentrations of Al₂O₃, TiO₂, CaO, and rare earth elements (REEs) are notably low, consistent with those of classic Archean BIFs. This composition implies that their formation resulted from the direct precipitation of Fe-rich minerals in oxidizing marine exhalative environments, while silica-rich layers (mainly chert) formed during periods of low oxygen concentration, and with the absence of detrital materials.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126261"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reactions in UHT calc-silicate granulites from the In Ouzzal terrane (Western Hoggar, South Algeria): Implication for pressure-temperature-fluid evolution","authors":"Nadia Boureghda ,&nbsp;Khadidja Ouzegane ,&nbsp;Saïda Aït-Djafer ,&nbsp;Jean-Robert Kienast ,&nbsp;Abderrahmane Bendaoud ,&nbsp;Amar Arab ,&nbsp;Zouhir Adjerid","doi":"10.1016/j.chemer.2024.126079","DOIUrl":"10.1016/j.chemer.2024.126079","url":null,"abstract":"<div><div><span>Calc-silicate granulites<span> constitute a relatively small part of the whole granulitic material outcrops characterizing the In Ouzzal terrane (NW Hoggar, South Algeria). However, these rocks preserve a number of spectacular reaction textures that could be effectively used to infer their pressure-temperature-fluid history. These textures are interpreted using P-T and T-X</span></span>_CO2 grids in the simplified CaO-Al₂O₃-SiO₂<span>-Vapor system. In this process, sequences of reactions have been subdivided into two distinct stages: (i) the early prograde stage that was accompanied by significant rise of temperature from about 800 °C up to 1050 °C at around10 kbar followed by (ii) the decompression stage from about 9 to 6 kbar. During the prograde stage, coarse grained wollastonites were produced according to the reaction calcite<span> + quartz → wollastonite + CO</span></span>₂<span>. Furthermore, in the peak pressure temperature stage, the reaction producing wollastonite + scapolite<span> from coarse primary garnet consumes CO</span></span>₂ with temperature increasing from 850 °C to 1000 °C according to the reaction 3grossular + 3CO₂ → 3wollastonite + 2calcite + scapolite. The latest reactions have been occurred during the decompression stage from about 10 kbar to 5 kbar and cooling from 1000 °C to 800 °C. The growth of calcite + quartz around wollastonite besides to garnet coronas between wollastonite, calcite and scapolite are explained by the reaction: calcite + quartz → wollastonite + CO₂ and 3wollastonite + scapolite +2calcite → 3grossular + 3CO₂. The appearance of anorthite around scapolite occurs following a decrease of temperature independently to the fluids according to the reaction scapolite → 3anorthite + calcite. All reactions took place at CO₂ low pressure which was estimated between 0.04 and 0.55.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126079"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139469519","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Formation of pseudotachylytes under granulite facies conditions in the UHT In Ouzzal terrane (Western Hoggar, Algeria): Witnesses of paleoseism in the Paleoproterozoic lower continental crust at 0.82 Ga","authors":"E.-H. Fettous ,&nbsp;Y. Mahdjoub ,&nbsp;P. Monie","doi":"10.1016/j.chemer.2025.126253","DOIUrl":"10.1016/j.chemer.2025.126253","url":null,"abstract":"<div><div>Archaean charnockitic orthogneisses transected by 2.0 Ga high-grade exhumed ductile shear zones form part of the ultra-high temperature In Ouzzal Terrane, located in the western Hoggar, within the Neoproterozoic Pan-African Trans-Saharan belt of north-west Africa. Faults and injection veins of pseudotachylytes exhibit sharp contacts with their host charnockitic orthogneisses and are composed of a dark, and sometimes banded matrix, containing numerous clasts of pyroxene, feldspar, quartz, and rarely biotite. Recrystallized mineral assemblages in the matrix are indicative of granulitic facies conditions and consist of very fine-grained crystals of hypersthene, phlogopite, oligoclase, orthoclase, quartz, and accessory Mn-ilmenite and Cr-magnetite. This assemblage differs from that of the charnockitic orthogneiss host notably by the absence of the mesoperthitic K-feldspar. The chemical compositions of the pseudotachylytes are in general similar to those of the charnockitic orthogneisses suggesting a non-selective melting process consistent with in situ and total recrystallization. The chemical variations are observed in Tin Tchik Tchik pseudotachylytes and shear planes, including slight enrichments of calcium in orthopyroxene, plagioclase, and K-feldspar, as well as iron in biotite. These variations are attributed to recrystallization under decreasing temperature during faster cooling. The newly formed granulitic-facies mineral phases within the pseudotachylytes are synchronous with brittle deformation, lining fractures parallel to major shear zones and occupying spaces created by T-fractures, or those between Riedel R and T fractures, or P and R'. This Riedel fracture network indicates NW-SE to WNW-ESE shortening.</div><div>The ⁴⁰Ar/³⁹Ar dating of the pseudotachylyte matrix indicates its formation at 820.5 ± 6.6 Ma, providing the first evidence of early Neoproterozoic tectonism in the In Ouzzal terrane. Regionally, this event corresponds to the convergence period between the West African Craton and East Saharan Craton leading to subduction and the development of oceanic/continental arcs in western Hoggar. Earlier polyphase dehydration of charnockitic orthogneiss, during Archaean partial melting events (2.65 and 2.5 Ga) and Eburnean (2.0 Ga) ultra-high temperature metamorphism, suggests a reactivation under brittle coseismic conditions of Paleoproterozoic ductile main shear zones at 0.82 Ga in a nearly anhydrous lower crust and provides a natural example of earthquakes in the lower continental crust, controlled by a brittle rheology.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126253"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evidence of an Archean-Paleoproterozoic micro-continent remobilized during the Neoproterozoic from the western Hoggar (Tuareg Shield, Algeria): Geodynamic evolution and implication on gold mineralization","authors":"Abderrahmane Bendaoud ,&nbsp;Renaud Caby ,&nbsp;Safouane Djemaï ,&nbsp;Olivier Bruguier ,&nbsp;Djamal-Eddine Aissa ,&nbsp;Aboubakr Deramchi ,&nbsp;Sid Ali Doukkari ,&nbsp;Khadidja Ouzegane ,&nbsp;Fatna Kourim ,&nbsp;Jean-Robert Kienast","doi":"10.1016/j.chemer.2024.126213","DOIUrl":"10.1016/j.chemer.2024.126213","url":null,"abstract":"<div><div>The western boundary of the Tirek terrane in the Hoggar contains the two largest gold deposits in Algeria, namely the Amesmessa and Tirek gold fields. New geological mapping of this area and results of a combined petrological, geochemical and geochronological study (U-Pb zircon geochronological (LA-)ICP-MS method) reveals a Paleoproterozoic TTG basement, dated at 1965 ± 18 Ma (inherited zircons from 2771 to 2006 Ma), overlain by a supracrustal unit made up of quartzites and metapelites. Detrital zircons from metapelites yielded ages ranging from Archaean to Paleoproterozoic (2710 Ma–2050 Ma). Furthermore, sills and dykes of sub-alkaline orthogneisses that intrude the previous lithologies have been dated at 1843 ± 19 Ma. On the other hand, the migmatitic granitic-granodioritic batholith, which covers 50 % of the studied area and intrudes all units, has a subduction magmatism affinity and is dated at 663 ± 4 Ma.</div><div>The study area was affected by a HT-LP metamorphic overprint during a clockwise P-T evolution with a peak conditions around 800–850 °C at 5 kbar followed by a decompression, then a cooling reaching the P-T conditions of 600 °C and 3 kbar. Uranium-Pb dating of monazite yields an age of 578 ± 5 Ma, which is interpreted to reflect the time of peak metamorphic overprint synchronous with the emplacement of synkinematic granites along shear zones with transcurrent movement. During this event, the western border of the studied area, the East Ouzzalian Shear zone, was the site of magmatic intrusions as well as the circulation of various fluids. This promoted an important fluid/rock interaction event, leading to extraction of gold by fluid percolation through the rocks and its deposition along N-S/NE-SW quartz vein ore shoots. The comparison with the western terranes of the Tuareg Shield (In Ouzzal, Iforas, Tassendjanet, and Kidal terranes) suggests that Tirek and these terranes represent relics of a single Archean-Paleoproterozoic continent. Currently, the Archean lower crust cross out in the central part of this micro-continent. The latter is mainly affected by Paleoproterozoic granulite facies metamorphism, unlike the Paleoproterozoic middle crust, which is exposed on either side and was strongly remobilized during the Pan-African orogeny (850–570 Ma), allowing gold mineralization during the later stages of this event.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126213"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pan-African eclogite-facies tectonic mélange in the Egéré area, Tuareg Shield (Algeria): Integrated approaches for lithological and structural mapping","authors":"Yasser Laichaoui ,&nbsp;Mohamed Hamoudi ,&nbsp;Khadidja Ouzegane ,&nbsp;Jean-Paul Liégeois ,&nbsp;Walid Farhi ,&nbsp;Takfarinas Lamri ,&nbsp;Sidali Doukkari ,&nbsp;Alain Vauchez ,&nbsp;Amar Arab ,&nbsp;Massinissa Amara","doi":"10.1016/j.chemer.2024.126217","DOIUrl":"10.1016/j.chemer.2024.126217","url":null,"abstract":"<div><div>The Tuareg Shield is made up of 25 terranes separated by extensive shear zones that are several hundred km-long, which have been attributed to a northward post-collisional tectonic escape during the Pan-African orogeny. The development of these shear zones was accompanied by abundant high-K calc-alkaline batholiths and plutons (~630–580 Ma). In the northern Egéré-Aleksod terrane of Central Hoggar (LATEA metacraton), the Egéré area exhibits minimal Pan-African magmatism, preserving earlier tectonic events such as subduction, collision, and terrane exhumation. The Egéré region consists of a parautochthonous amphibolite-facies unit (Arechchoum Group) and three eclogite-facies nappe units (Lower Egéré, Upper Egéré, and Oneral groups). These were thrust over the Archean Amadror cratonic core after the subduction of the LATEA passive margin superstructure to which they belong. These units have Paleoproterozoic protoliths, predominantly magmatic in the Arechchoum Group, or mixed magmatic and sedimentary in the Egéré Group, while the Oneral Group, which forms the uppermost nappe, comprise Neoproterozoic sediments.</div><div>Space-borne imagery data are used to map the eclogitic layers, integrated with magnetic and gravity surveys to delineate major shear and thrust zones. In addition, 2D modelling of magnetic and gravity data was used to investigate the upper crust, revealing a Pan-African granitic batholith and a large ultramafic-mafic bod at depth. The results allowed detailed geological mapping of such a complex tectonic mélange belonging to both lower and upper plate segments. Integrated with the published geochronological data, this mélange includes rocks with Rhyacian to Statherian, Calymmian, and Early Cryogenian ages, all of which underwent Late Cryogenian high-pressure metamorphism, followed by Ediacaran high-temperature metamorphism and tectonic escape processes.</div><div>Our results reveal the complex tectonic evolution of a former passive margin that was subducted to great depths during the Pan-African orogeny. The preservation of early subduction and exhumation events provides key insights into tectonometamorphic processes and deep crustal evolution in this high-pressure metamorphic terrane.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126217"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical comparison of biotite from TTG batholiths and A-type complexes on either side of the Tin-Dahar fault: Geodynamic considerations (Silet region, Western Hoggar, Algeria)","authors":"Sarra Mokaddem ,&nbsp;Fatene Bechiri-Benmerzoug ,&nbsp;Hamid Bechiri ,&nbsp;Halima Chaa ,&nbsp;Latifa Remki ,&nbsp;Rekia Kheloui ,&nbsp;Yousra Kara ,&nbsp;Sara Miloudi ,&nbsp;Khadidja Bouzid ,&nbsp;Nicolas Rividi ,&nbsp;Bernard Bonin","doi":"10.1016/j.chemer.2025.126269","DOIUrl":"10.1016/j.chemer.2025.126269","url":null,"abstract":"&lt;div&gt;&lt;div&gt;We studied the chemical composition of primary biotite (n = 265 chemical analyses, performed by electron microprobe) from some acidic plutonic rocks in the central part of the Silet terrane (Hoggar, Algeria). Which is considered an island arc accreted onto the metacraton LATEA during the climax of the Pan-African orogeny at around 650 Ma, accompanied by northward migration of LATEA, following final clamping between the West African craton and the Saharan metacraton. The plutonic acidic rocks constitute nearly 70 % from study area, essentially represented by Tonian-Cryogenian TTG batholiths and Ediacaran-Fortunian A-type granitic complexes. They cross-cut Neoproterozoic volcano-sedimentary series and are organized into two narrow stripes with opposite isotopic signatures, separated by the N-S Tin-Dahar fault: the Juvenile Western Stripe (J-WS) and the Contaminated Eastern Stripe (C-ES). We compared biotite of the western stripe (TTG + type A granitic batholiths) with that of the same rocks of the eastern stripe (C-ES). So, we selected three TTG batholiths (Tin-Tekadiouit, Ahambatou and Silet) + two A-type granite complexes (Tin-Erit and Tioueïne) from the J-WS and one TTG type (Eheli) + two A-type granite (Teg-Orak and Inedjaren) from the C-ES. The petrographic observation shows in all studied rocks of the western stripe (J-WS) that biotite is often associated with amphibole, whereas in the eastern stripe rocks (C-ES), biotite is only. Consequently, biotite from both TTG and A-type granitoids from J-WS differ in chemical compositions from biotite from C-ES. Three biotite types were determined in the studied felsic rocks: 1- Mg-biotite in TTG batholiths of the two stripes (Tin-Tekadiouit, Ahambatou, Silet and Eheli) and in the A-type granite complex of Inedjaren, located in the C-ES; 2- Fe-biotite–annite of A-type Tioueine and Tin-Erit complexes (J-WS) and 3- Fe-biotite–siderophyllite of A-type Teg-Orak (C-ES). In detail, Mg-biotite in TTG of the J-WS reflects calc-alkaline, orogenic and peraluminous host rocks, whereas, in the Eheli TTG and the Inedjaren A-type of C-ES, it reflects calc-alkaline, orogenic host rocks. Fe-biotite–annite of the A-type granite of J-WS reflects alkali-calcic to alkaline anorogenic host rocks when Fe-biotite–siderophyllite from Teg-Orak complex, located to the north of C-ES, reflects calc-alkaline to alkali-calcic rocks.&lt;/div&gt;&lt;div&gt;Crystallization temperatures and pressures of Mg-biotite in TTG batholiths of J-WS are lower (750–800 °C, 3–6 kbar) than those recorded in the Eheli TTG batholith (850–900 °C, 4–8 kbar) of C-ES. Mg-biotite of the Inedjaren A-type complex (800–900 °C, 3–6 kbar) of C-ES shows higher temperature than biotite of the other A-type complexes (Fe-biotite–annite trend; Fe-biotite–siderophyllite trend), yielding variable pressure values (700–750 °C, 3–10 kbar).&lt;/div&gt;&lt;div&gt;The three different types of biotite are emphasized by estimates of thermodynamic conditions (T, P, &lt;em&gt;f&lt;/em&gt;O&lt;sub&gt;2&lt;/sub&gt;)","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126269"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical and geochronological characterization of the Tamanrasset W-Sn-(±Ta-Nb-Li) granites: Prolonged rare metal magmatism in the Laouni terrane (Central Hoggar, Algeria)","authors":"B. Zoheir ,&nbsp;A. Holzheid ,&nbsp;T. Graupner ,&nbsp;A. Zeh ,&nbsp;B. Lehmann ,&nbsp;S. Goldmann ,&nbsp;M. Steele-MacInnis ,&nbsp;K. Ali ,&nbsp;M. Kesraoui ,&nbsp;A. Bendaoud ,&nbsp;E. Fettous ,&nbsp;T. Lamri ,&nbsp;B. Ayad","doi":"10.1016/j.chemer.2025.126267","DOIUrl":"10.1016/j.chemer.2025.126267","url":null,"abstract":"<div><div>The origin of topaz-mica granites within the central Hoggar massif, along with their associated rare metal mineralization, remains a compelling subject despite extensive geochemical and geochronological research. This study presents new bulk-rock geochemical data and zircon U<img>Pb ages and Hf isotopic composition for the Tamanrasset W-Sn-(±Ta-Nb-Li) granites in the Laouni terrane, supplemented by Nd<img>Sm isotope analyses. These data enhance the understanding of the formation and tectonic setting of the investigated granites.</div><div>Petrographic and geochemical analyses identify four granite varieties: fine-grained monzogranite, fluorite-bearing two-mica granite, porphyritic topaz-alkali feldspar granite, and topaz-mica-albite granite. Generally, these rocks are low-P (P₂O₅ &lt; 0.14 wt%) and range from weakly metaluminous to strongly peraluminous (A/CNK = 0.94–1.83), with high degrees of fractional crystallization (50–90 %) evidenced by enrichment in F, Rb, W, Sn, Cs, Y, Zr, and Ta. The studied rocks feature distinct REE patterns, including strong negative Eu anomalies (Eu/Eu* ≤ 0.1) and M-type tetrad effects in topaz- and fluorite-bearing granites, while monzogranite shows weaker anomalies. Zircon saturation thermometry and <em>P</em>_<em>H2O</em> barometry suggest crystallization under low-temperature, water-rich conditions (11–15 MPa, &lt; 800 °C), with high fluorine activity and volatile-rich phases, suggesting shallow, evolved magmas. Zircon U<img>Pb dating defined ages of 605.4 ± 3.7 Ma for Aleméda monzogranite, 603.2 ± 2.6 Ma for topaz-alkali feldspar granite, and 592.9 ± 3.9 Ma for topaz-mica-albite granite, with younger ages (∼575–572 Ma) in two-mica granites from Tin Amzi-El Karoussa. Conversely, the Hanana-Hananère topaz-mica-albite granite has a distinctly older age of 638.0 ± 3.1 Ma.</div><div>The studied granites show diverse REE profiles, zircon εHf^(t) (−3.6 to −13.3), bulk-rock εNd^(t) (0.3 to −16.3), and model ages (1.3–2.4 Ga), indicating crustal reworking, mantle delamination, and partial melting. Orogenic collapse and mantle delamination triggered magmatic activity, leading to volatile-rich, evolved ferroan A2-type granites with rare-metal mineralization potential. Their isotopic variability suggests a transcrustal MASH system driven by mantle-crust interactions, with strong spatial association to mega shear zones, highlighting tectonic control on magma ascent and crustal reworking, and incorporation of ancient crustal materials.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126267"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrology and P-T evolution of high-grade garnet metabasites from the Tin Begane area (Laouni terrane, South Algeria)","authors":"Amar Arab ,&nbsp;Amel Bitam-Derridj ,&nbsp;Khadidja Ouzegane ,&nbsp;Gaston Godard ,&nbsp;Sidali Doukkari","doi":"10.1016/j.chemer.2025.126260","DOIUrl":"10.1016/j.chemer.2025.126260","url":null,"abstract":"<div><div>The south of the Tin Begane region (Laouni terrane, Central Hoggar, southern Algeria) has been subjected to high grade metamorphism and shows well-preserved relicts of garnet-bearing metabasites boudinaged within metapelites and migmatites. These rocks have preserved a number of spectacular mineral assemblages and reaction microstructures. Two successive metamorphic stages have been recognised, on the basis of metamorphic microstructures and mineral compositions: (i) the main primary paragenesis consists of garnet porphyroblasts, amphibole, clinopyroxene, titanite and quartz; (ii) the retrograde stage is evidenced by clinopyroxene-amphibole-plagioclase symplectites, which developed mainly at the expense of garnet, as well as peculiar clinopyroxene-ilmenite symplectites after titanite. Garnet porphyroblasts are almandine-grossular (Alm_46–58 Prp_7–14 Grs_28–42 Sps_1–5) and show a smooth zoning pattern from the core to the outer rim. The clinopyroxene is diopside but shows slight chemical variations depending on its microstructural position in the rock (inclusion in garnet: <em>X</em>_<em>Fe</em> = 0.39; Al_total = 0.06 apfu; Ca = 0.90 apfu; ameboid crystals in the matrix: <em>X</em>_<em>Fe</em> = 0.42–0.47; Al_total = 0.15–0.16 apfu; Ca = 0.90–0.93 apfu; clinopyroxene in symplectite: <em>X</em>_<em>Fe</em> = 0.37–0.52; Al_total = 0.06–0.11 apfu; Ca = 0.91–0.95 apfu). The amphibole is (ferro-)tchermackite to (ferro/magnesio)-hornblende, with some grains exhibiting a smooth chemical zoning profile from core to rim. Plagioclase, either from the main paragenesis or from the Cpx + Pl symplectites, is anorthite (<em>X</em>_<em>An</em> = 0.92–0.97). To reconstruct the pressure-temperature evolution of a selected sample, two <em>P-T</em> pseudosections were calculated in the NCKFMASHTO system. The first pseudosection was modelled using the bulk-rock composition of the sample, whereas the second was calculated for the overall composition of the late symplectites, estimated by balancing the reaction that produced them. The results indicate that the studied metabasites have experienced a clockwise <em>P-T</em> path, with a decompression from peak conditions estimated at 13–15 kbar and 750 ± 50 °C down to 7–4.5 kbar and 810 ± 50 °C. The clockwise <em>P-T</em> path can be interpreted in terms of crustal thickening followed by exhumation, most likely during the Pan-African orogenesis.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126260"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preface: “Geodynamic evolution and metallogeny of the Hoggar massif”","authors":"Torsten Graupner ,&nbsp;Abderrahmane Bendaoud ,&nbsp;Mohamed Hamoudi ,&nbsp;Astrid Holzheid ,&nbsp;Basem Zoheir ,&nbsp;El-Hocine Fettous ,&nbsp;Simon Goldmann","doi":"10.1016/j.chemer.2025.126291","DOIUrl":"10.1016/j.chemer.2025.126291","url":null,"abstract":"","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126291"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}