Chemie Der Erde-Geochemistry最新文献

{"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}

{"title":"Nb-Ta-Sn oxides as markers of magmatic fractionation and magmatic-hydrothermal evolution: The example of the Nuweibi granite intrusion, Eastern Desert, Egypt","authors":"Simon Goldmann ,&nbsp;Julie Anne-Sophie Michaud ,&nbsp;Torge Krummacker ,&nbsp;Chao Zhang ,&nbsp;François Holtz ,&nbsp;Ali A. Khudeir ,&nbsp;Sadeq Hamid ,&nbsp;Mohamed Abu El-Rus","doi":"10.1016/j.chemer.2024.126215","DOIUrl":"10.1016/j.chemer.2024.126215","url":null,"abstract":"<div><div>The Nuweibi rare-metal granite is located in the Central Eastern Desert of Egypt and represents a highly evolved leucogranite pluton that intruded into Neoproterozoic basement rocks of the Arabian-Nubian Shield. It is separated by the NNE-SSW trending oblique sinistral Dabr fault into two principal granite facies: a medium-grained albite granite in the western block and a porphyritic albite granite in the eastern block. The major ore minerals among the disseminated Nb-Ta-Sn mineralization are columbite-group minerals (CGM), wodginite, microlite, and cassiterite, which follow a distinct crystallization sequence including partial dissolution and late recrystallization. These ore minerals are usually strongly zoned, exhibiting a wide range of chemical compositions. As peculiarity, cm-sized euhedral columbite crystals with thin Ta-rich rims are found in the massive quartz cap of the eastern block of the intrusion. On the basis of mineral textures and microanalysis of mineral chemistry of the Nb-Ta-Sn oxides, we propose a genetic model for the evolution of the Nuweibi granitic intrusion involving magmatic, magmatic-hydrothermal, and subsolidus ore-forming processes: 1) upward migration of a granitic melt to the level of emplacement and fractional crystallization resulting in enrichment of the residual melt in incompatible elements (e.g., Ta, Nb, Sn) and volatiles (H₂O and F); 2) incipient magmatic crystallization of early Nb-rich CGM-1, albite, and snowball quartz and Ta enrichment in the melt (more incompatible than Nb); 3) onset of fluid exsolution (fluid saturation in the melt at the magmatic-hydrothermal transition), magmatic crystallization of CGM-2 with increasingly higher #Ta with co-existing fluid; 4) solidification of the quartz cap due to undercooling saturation with precipitation of columbite under hydrothermal conditions from magmatic fluids; 5) late magmatic fluid circulation, dissolution of the CGM and re-precipitation of CGM-3, followed by late-stage wodginite and microlite; 6) oblique sinistral and normal faulting after solidification of the Nuweibi granite, leading to the western block of the intrusion to move diagonally upwards resulting in today's opposing levels of exposure. As a result, the mineral paragenesis, texture, and mineral chemistry of Nb-Ta-Sn minerals prove to be remarkable tracers of the evolution from magmatic to hydrothermal conditions in rare-metal granites.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126215"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290643","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":"Petrogenetic and dynamic links between felsic and mafic magmas: Insights from the Devonian post-collisional magmatism in the North Qaidam terrane, western China","authors":"Denghui Chen ,&nbsp;Hao Wu ,&nbsp;Dongdong Yan ,&nbsp;Chengxiang Li ,&nbsp;Huajun Wen ,&nbsp;Fuhao Xiong","doi":"10.1016/j.chemer.2025.126298","DOIUrl":"10.1016/j.chemer.2025.126298","url":null,"abstract":"<div><div>Felsic-mafic magmatism in post-collisional settings provides valuable insights into the growth and evolution of continental crust, but the interaction processes between felsic and mafic magmatism and their implications for the diversity of igneous rocks remain controversial. This study presents petrological, geochronological, geochemical, and Sr-Nd-Hf isotopic analyses of the Mohe felsic-mafic complex, a rare post-collisional composite pluton in the North Qaidam terrane (western China), to investigate the petrogenetic and dynamic links between felsic and mafic magmas. The results reveal that the Mohe complex, consisting of granite, granodiorite, diorite, and appinites, is genetically related and formed between ca. 408–400 Ma. The granites and granodiorites are classified as I-type and are characterized by enriched isotopic signatures, including whole-rock (⁸⁷Sr/⁸⁶Sr)ᵢ values of 0.714584–0.728765, εNd_{(400 Ma)} values of −7.75 to −5.56, and zircon εHf(t) values of −3.04 to −0.28. These rocks were primarily derived from partial melting of Mesoproterozoic to Paleoproterozoic crustal materials, with minor input from a mantle source. The appinites display depleted zircon Hf isotopic compositions (εHf(t) = +4.10 to +5.71), indicating derivation from an OIB-like depleted mantle source that was metasomatized by subducted slab-derived melts. The diorites show weakly enriched isotopes ((⁸⁷Sr/⁸⁶Sr)_<em>i</em> = 0.709358–0.713210, εNd_{(400 Ma)} = −2.99 to −2.73, εHf(t) = −1.35 to +3.54), and were formed by the mixing of 80–90 % appinitic magma with 10–20 % crustal-derived granitic magma. Our findings suggest that the Early Devonian magmatism in the North Qaidam terrane was likely driven by slab break-off-related geodynamic processes, where crust-mantle magma mixing, along with mineral accumulation and fractional crystallization, played a key role in the petrological diversity of the continental crust in a post-collisional extensional setting.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126298"},"PeriodicalIF":2.6,"publicationDate":"2025-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911631","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":"Enhanced analysis of hydrothermal alteration and mineral prospecting through integration of ASTER and aeroradiometric data: A case study from the Ouarzazate region, Morocco","authors":"Ilham El Hakimi,&nbsp;Lahsen Achkouch,&nbsp;Younesse El Cheikh,&nbsp;Mohammad Taadid,&nbsp;Houda Bourouda,&nbsp;Ahmed Rachid,&nbsp;Ahmed Attou","doi":"10.1016/j.chemer.2025.126296","DOIUrl":"10.1016/j.chemer.2025.126296","url":null,"abstract":"<div><div>The study area, situated in the western segment of the Saghro Massif within the Anti-Atlas belt, is characterized by mineralized deposits, intricate lithological formations, and distinctive tectonic features. This research integrates ASTER imagery analysis with gamma-ray spectrometry data to map alteration zones and examine the geochemical and mineralogical processes that influence radioactive element distribution. Specific analytical techniques are applied to investigate relationships among argillic, phyllic, propylitic alterations, iron oxides, and regions with elevated concentrations of radiometric elements. Gamma-ray spectrometry data, including mono-elemental maps of radiometric components (potassium in %, equivalent uranium in ppm, and equivalent thorium in ppm), are analyzed alongside interpreted ASTER images to identify potential mineralization zones. Ratios of K/eU and K/eTh, along with the F parameter, are processed within a fuzzy model framework, which combines these datasets into a comprehensive mineral prospectivity map that serves as a tool for guiding exploration. This analysis identifies four hydrothermal alteration zones as highly promising for mineral exploration, suggesting a likely association between magmatic processes and spatially correlated hydrothermal alteration, thereby supporting further detailed exploration initiatives.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126296"},"PeriodicalIF":2.6,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143883029","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}