Chemie Der Erde-Geochemistry最新文献

{"title":"Geology, mineralogy, geochemistry and Sr-Nd-Pb isotopic composition of the ultrapotassic rocks and associated shoshonites of Kef Hahouner (Northeastern Algeria): New data and geodynamic implications","authors":"Mohamed Yacine Laghouag , Moulley Charaf Chabou , Gaston Godard , Riccardo Avanzinelli , Martina Casalini , Rabah Laouar , Carlos J. Garrido","doi":"10.1016/j.chemer.2025.126313","DOIUrl":"10.1016/j.chemer.2025.126313","url":null,"abstract":"<div><div>The association of ultrapotassic rocks and shoshonites is common in the Alpine-Mediterranean region, with the exception of the Maghrebide Chain of Northern Africa, where only two small outcrops of ultrapotassic rocks have been documented. This study reports detailed field observations and new data on the petrology, mineral chemistry, whole-rock geochemistry and Sr-Nd-Pb isotopic compositions of the volcanic ultrapotassic rocks and shoshonites of the Kef Hahouner region (Northeastern Algeria). The results indicate that these rocks are composed of an association of ultrapotassic rocks that outcrop at the base of a lava flow sequence, and shoshonites that constitute shallow volcanic intrusions and the upper part of the abovementioned lava flow pile. The ultrapotassic rocks are K<sub>2</sub>O-rich, with K<sub>2</sub>O/Na<sub>2</sub>O > 2, high Mg# (Mg/(Mg + Fe<sup>2+</sup>) = 0.70–0.72), and high Ni (∼173 μg.g<sup>−1</sup> [ppm]) and Cr contents (∼392 μg.g<sup>−1</sup>). They are strongly enriched in LREE and extremely enriched in Th and LILE (Rb, Ba, Sr), with respect to High Field Strenght Elements (Ta, Nb, and Ti), showing an orogenic-type pattern. Shoshonites display lower K<sub>2</sub>O and higher Na<sub>2</sub>O and Al<sub>2</sub>O<sub>3</sub> contents compared to the ultrapotassic facies. However, these rocks have similar trace and rare earth element (REE) patterns to those observed in the ultrapotassic rocks, albeit with slightly lower LILE and MREE contents. The initial <sup>87</sup>Sr/<sup>86</sup>Sr values range from 0.706101 to 0.709500, and <sup>143</sup>Nd/<sup>144</sup>Nd from 0.512246 to 0.512438, while the lead isotope ratios vary between 18.538 and 18.571 for <sup>206</sup>Pb/<sup>204</sup>Pb, 15.649 to 15.657 for <sup>207</sup>Pb/<sup>204</sup>Pb, and 39.806 to 39.998 for <sup>208</sup>Pb/<sup>204</sup>Pb. Ultrapotassic rocks exhibit higher <sup>87</sup>Sr/<sup>86</sup>Sr, <sup>206</sup>Pb/<sup>204</sup>Pb, <sup>208</sup>Pb/<sup>204</sup>Pb and lower <sup>143</sup>Nd/<sup>144</sup>Nd than shoshonites. The two volcanic suites most likely result from the increasing partial melting of the metasomatised mantle source in which the ambient mantle component dilutes the alkaline-rich component derived from the partial melting of the sole vein, explaining the transition from ultrapotassic to shoshonite magma. Compared to the North-African Cenozoic magmatic belt, the Kef Hahouner ultrapotassic and shoshonitic lithologies are unique and have no equivalent among the entire belt. We, therefore, propose a geodynamic model in which the subduction of the African continental margin beneath the Kabylian domain and its break-off during the Tortonian times caused the strong metasomatic episode in the source region, resulting in the formation and emplacement of the ultrapotassic rocks and shoshonites in the region. The observed Kef Hahouner–Djebel Debar fault may represent the surface expression of the tear fault related to the southern ed","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126313"},"PeriodicalIF":2.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144338443","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":"Mixed fluid processes in FeMn dendrite formation and associated carbon and nickel isotope fractionation","authors":"Anna Neubeck ,&nbsp;Piotr Szymczak ,&nbsp;Vyllinniskii Cameron ,&nbsp;Daniel Buczko ,&nbsp;Magnus Ivarsson","doi":"10.1016/j.chemer.2025.126303","DOIUrl":"10.1016/j.chemer.2025.126303","url":null,"abstract":"<div><div>Dendritic iron- and/or manganese-rich microstructures, often referred to as “microstromatolites,” are commonly observed in carbonate veins in the deep subsurface. However, the mechanisms responsible for their formation, particularly the role of microbial processes, remain incompletely understood. One hypothesis suggests that Fe- and Mn-enriched fluids, sourced from submarine hydrothermal vents and circulating through mafic or ultramafic rocks, lead to the precipitation of manganese dendrites within open fractures. Microbial activity has been proposed as a contributing factor, particularly due to its ability to catalyze Mn²⁺ oxidation to Mn⁴⁺ at rates significantly faster than abiotic processes under ambient conditions. Such microbial mediation often results in the formation of poorly crystalline Mn oxide phases, which are commonly associated with biologically mediated oxidation. These disordered Mn oxides, frequently observed in natural settings, suggest a microbial contribution to mineral precipitation, particularly in environments where redox gradients and fluid-rock interactions are prominent. Because manganese oxides are an important sink for Ni in marine systems, stable Ni isotope analyses may offer valuable insights into their formation. Biological activity in laboratory systems is known to fractionate Ni isotopes, producing negative δ⁶⁰Ni values, while abiotic interactions with Mn oxides can result in a range of isotopic signatures. In this study, we show that manganese-rich dendrites likely formed through the interplay between organic matter, oxidizing fluids and viscous serpentine muds, resulting in the fractionation of both carbon and nickel isotopes. The moderately negative δ¹³C and δ⁶⁰Ni values, together with the presence of organic matter, suggest a mixed formation pathway involving both abiotic mineral precipitation and biologically mediated processes. One plausible mechanism involves the nucleation of Mn oxides on nanoparticulate “seeds,” which could include both abiotic particles, organic matter, microbial cells and their metabolic byproducts. Understanding the formation of Fe<img>Mn dendrites is key to interpreting the biogeochemical cycling of essential elements like iron, manganese, and nickel. Due to its redox flexibility, Mn forms highly reactive oxides that effectively scavenge trace metals such as Ni, Co, Fe, and Cu, facilitating their removal from seawater and incorporation into marine minerals. Our findings underscore the complexity of Fe<img>Mn oxide formation and point to the combined influence of abiotic fluid dynamics and microbial processes. This improves our ability to interpret geochemical signatures in both modern and ancient environments and enhances the utility of stable isotope systems in reconstructing past ocean conditions and elemental cycling.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126303"},"PeriodicalIF":2.6,"publicationDate":"2025-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144189512","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":"Cambrian mid-ocean ridge basalt-like mafic rocks and associated boninites in the Dachadaban ophiolite from the North Qilian Block, northwest China: Petrogenesis and implications for back-arc extension","authors":"De-Chao Li ,&nbsp;Xi-Jun Liu ,&nbsp;Xiao Liu ,&nbsp;Gang Chen ,&nbsp;Qi Song ,&nbsp;Hao Tian ,&nbsp;Zheng-Lin Li ,&nbsp;Peng-De Liu ,&nbsp;Rong-Guo Hu","doi":"10.1016/j.chemer.2025.126301","DOIUrl":"10.1016/j.chemer.2025.126301","url":null,"abstract":"<div><div>The early Paleozoic Qilian Orogen is ideal for investigating ancient plate tectonic processes and can be divided into the north, middle, and south Qilian blocks. There is a consensus that North Qilian oceanic lithosphere was subducted northward beneath the Alxa Block. However, the details of this subduction in the North Qilian Ocean (e.g., whether an intra-oceanic back-arc basin was developed) are poorly constrained. In this study, we undertook petrological observations, zircon U<img>Pb geochronological and Hf isotopic analyses, and whole–rock and mineral major and trace element, and Sr<img>Nd isotopic analyses of the Cambrian (513–506 Ma) lower series mid-ocean ridge basalt (MORB)-like mafic rocks and upper series (503–490 Ma) boninites in the Dachadaban ophiolite in the North Qilian Block, northwest China. The lower series mafic rocks can be further divided into two types. Type 1 mafic rocks have uniform SiO₂ contents of 45.1–49.8 wt% and slightly enriched light rare earth element (REE) and relatively flat heavy REE patterns, similar to enriched-type MORBs. The type 2 mafic rocks and boninites have a wider range of SiO₂ contents of 49.3–59.2 and 48.1–56.6 wt%, respectively, and are depleted in light REEs and have relatively flat heavy REE patterns, similar to normal-type MORBs. In primitive-mantle-normalized element diagrams, the type 1 and 2 mafic rocks exhibit no or negligible Nb<img>Ta depletion, while the boninites exhibit obvious Nb<img>Ta depletion. The lower series type 1 and 2 mafic rocks have depleted whole-rock Nd (ε_Nd[t] = +2.6 to +6.5) and zircon Hf (ε_Hf[t] = +2.8 to +14.8) isotopic compositions, while the upper series boninites have relatively enriched Nd<img>Hf (ε_Nd[t] = +2.8 to +4.7; ε_Hf[t] = +3.4 to +13.6) isotopic compositions. We suggest that the lower series type 1 and 2 mafic rocks were formed by partial melting of garnet lherzolite (&gt;70 km depth; type 1) and spinel harzburgite (&lt;70 km; type 2) mantle sources, respectively. The upper series boninites were derived from a refractory harzburgitic mantle source that had been metasomatized by subducted-sediment-derived melts and minor slab-derived fluids. Based on these results and regional geological data, we suggest that the North Qilian Ocean experienced three stages of expansion, in the Precambrian–early Cambrian (550–520 Ma), middle–late Cambrian (513–497 Ma), and Middle–Late Ordovician (458–449 Ma). In addition, intra-oceanic subduction beneath the North Qilian Ocean and subsequent back-arc extension occurred during the middle–late Cambrian (513–490 Ma).</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126301"},"PeriodicalIF":2.6,"publicationDate":"2025-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144154683","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 process of a newly explored ion-adsorption type REE deposit in Pingtian, Guangdong, South China: A detailed profile analysis","authors":"Jianjun Liu ,&nbsp;Huan Li ,&nbsp;Ruilin Wang ,&nbsp;Yue Hou ,&nbsp;Shaban Godang","doi":"10.1016/j.chemer.2025.126302","DOIUrl":"10.1016/j.chemer.2025.126302","url":null,"abstract":"<div><div>Recently, ion-adsorption-type rare earth element (REE) deposits have been explored in Nanxiong Basin (South China), with an estimated total reserve of &gt;100 million tons. The formation of ion-adsorption-type deposits is closely linked to the weathered crust of their parent granitic rocks. To better understand how the weathered crust influences the formation of ion-adsorption type REE deposits, this study presents detailed research on the relationship between the characteristics of the weathered crust and parent rock in Pingtian Town, Nanxiong Basin, Guangdong Province, through a detailed profile analysis. The U<img>Pb dating of zircon and apatite indicates that the parent rock (biotite monzogranite) was formed at ca. 220 Ma, which provides favorable metallogenic conditions for the formation of the weathered crust. Minerals such as monazite, zircon, apatite, and plagioclase play critical roles in the formation of the weathered crust. Monazite and plagioclase are the main controlling minerals for REE enrichment in the weathered crust. Monazite, influenced by apatite, determines the REE distribution pattern in the crust, with a particular emphasis on light rare earth elements (LREE). Zircon, being resistant to weathering, leads to the preferential enrichment of LREE in the weathered crust and limits the accumulation of heavy rare earth elements (HREE). Plagioclase, through weathering into kaolinite, provides an adsorption medium for ionized REE. In addition, trace element analysis of zircon and apatite, as well as geochemical studies on the parent rock, indicate that the parent rock belongs to a moderately differentiated granite. The degree of granite differentiation impacts REE enrichment in the weathered crust. The higher the degree of differentiation, the more ionized REE elements and adsorption media are provided, facilitating the formation of ion-adsorption type REE deposits. This highlights the importance of detailed profile geochemical analysis in revealing the genesis of ion-adsorption-type REE deposits.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126302"},"PeriodicalIF":2.6,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144154684","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":"Sedimentary records of tectonic background transition in the eastern Guangdong Basin in the Late Early Jurassic of the South China continental margin","authors":"Yanshen Liu ,&nbsp;Zhongjie Xu ,&nbsp;Hong Zhu ,&nbsp;Rihui Cheng","doi":"10.1016/j.chemer.2025.126297","DOIUrl":"10.1016/j.chemer.2025.126297","url":null,"abstract":"<div><div>The southeastern margin of the South China Block preserves sedimentary records of tectonic evolution controlled by Paleo-Pacific subduction. This study integrates sedimentological and detrital zircon U-Pb geochronological analyses of the Lower Jurassic Qiaoyuan Formation in the eastern Guangdong Basin. One Late Early Jurassic sample exhibits detrital zircon U-Pb ages ranging from 2317 to 187 Ma, with dominant age groups at 260–240 Ma and 1900–1800 Ma. In contrast, a terminal Early Jurassic sample shows age spectra of 2827–180 Ma dominated by a 200–180 Ma group, reflecting a transition from multi-peak to unimodal age distributions. Provenance analysis indicates that late Early Jurassic sediments (Member 1) were primarily sourced from the Jiangnan Orogen, Yunkai Terrane, and Hainan Island, while terminal Early Jurassic deposits (Member 3) originated predominantly from the Nanling Tectonic Belt. Comparative analysis of detrital zircon age characteristics in Mesozoic strata across the South China Block, incorporating similarity assessments, visualization methods, and crustal thickness estimations, demonstrates that the southeastern margin completed the transition from a compressional to extensional tectonic setting by approximately 180 Ma. This shift is chronologically constrained by provenance reorganization, basin structural transformation, and progressive crustal thinning, documenting the dynamic interplay between Paleo-Pacific subduction and intracontinental deformation.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126297"},"PeriodicalIF":2.6,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143931566","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":"Late Neoarchean multi-stage granitoid rocks in the Dengfeng terrane, North China Craton: Petrogenesis and implications for geodynamic processes","authors":"Heng Liu ,&nbsp;Lei Liu ,&nbsp;Shuhab D. Khan ,&nbsp;Yongjun Gao ,&nbsp;Lijuan Xu ,&nbsp;Tianyang Hu ,&nbsp;Inkyeong Moon","doi":"10.1016/j.chemer.2025.126300","DOIUrl":"10.1016/j.chemer.2025.126300","url":null,"abstract":"<div><div>During the late Neoarchean era, the rise of K-rich granitoid rocks marked a significant geological event indicative of the maturation and stabilization of continental crust. These granitoids, emerging after tonalite-trondhjemite-granodiorite (TTG) magmatism, stirred debates over the interrelations and geodynamic implications. In this study, diverse granitoid rocks were identified in the Dengfeng terrane of the North China Craton (NCC), dating as approximately 2.63–2.50 Ga. The 2.5 Ga meta-dioritic rocks exhibit elevated MgO (2.2–7.7 wt%) and Mg^# (45–69). Geochemical simulation reveals sanukitoid-like pattern, featuring highly fractionated REE compositions and depleted zircon Hf isotopes (Ɛ_Hf(t) values range from +3.9 to +6.5). Apatite Nd isotopes of ε_Nd(t) values ranging from −0.1 to 4.69. Meta-dioritic rocks were interpreted to be formed by partial melting of a depleted mantle source influenced by subducted slab-derived fluids. The TTG gneiss (2.63–2.52 Ga) exhibit mildly fractionated REE patterns, weakly positive Eu anomalies, lack of magmatic fractionation evidence, and high (La/Yb)_N (6.94–114.9) and Sr/Y (28.6–294) ratios, indicating their formation derived from partial melting of pre-existing low-K mafic crust. The K-rich granitoids (2.56 Ga) are characterized by high K₂O/Na₂O ratios (0.67–1.89), low MgO content and Mg^# (&lt; 1.2 wt% and &lt; 55, respectively). A chain of evidence including geochemical modeling, constant aluminum saturation index (ASI) values of 1.00–1.35, and zircon ε_Hf(t) values ranging from +8.2 to +11.2 suggest their derivation through partial melting of tonalitic rocks. Further analysis suggests that the source for K-rich granitoids are enriched by subducted slab melts or metasedimentary rocks at various crustal depths. In terms of petrogenesis, late Neoarchean granitoid magmatism in Dengfeng terrane likely relates to subduction and accretionary orogeny. Archean active continental margins are vital for early crustal maturation and granitoid diversification during subduction and collision.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126300"},"PeriodicalIF":2.6,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144068553","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":"Positive Matrix Factorization (PMF) based on geochemical data for revising geological map in semi-desert covered terrains: A case study from a map sheer of Urat Rear Banner, Inner Mongolia, China","authors":"Yanling Sun,&nbsp;Xueqiu Wang,&nbsp;Hanliang Liu,&nbsp;Jian Zhou,&nbsp;Mingjun Xie","doi":"10.1016/j.chemer.2025.126299","DOIUrl":"10.1016/j.chemer.2025.126299","url":null,"abstract":"<div><div>There is a significant deficiency for geological mapping in the Gobi Desert terrain covered by wind-blown sands with limited exposure of bedrock. Major and minor element data of stream sediments using Positive Matrix Factorization (PMF) analysis were employed to interpret the geological signatures from the Urat Rear Banner, a representative area of the Gobi Desert terrains. Six primary geochemical factors (M1, M2, M3, T1, T2, T3), corresponding to geological units were extracted from 8 major elements and 18 minor elements. Notably, the SiO₂-Al₂O₃-K₂O-and Pb-Ba-Th-Be-Y-Li-U combinations (primarily M1 and T1) are associated with felsic intrusive rocks, complex metamorphic rocks, and sandstones. The MgO-Fe₂O₃-TiO₂, Cu-Mn-Zn-Co combinations (primarily M2 and T2) indicate basic intrusive rocks, complexes. The Al₂O₃-Na₂O-CaO, Sr-Co-Mn-P-Cu-Zn-Ba (primarily M3 and T3) are related to neutral intrusive bodies (or complexes) and marble (or limestone). Additionally, the study utilizes standardized M1, M2, and M3 factor scores to refine the delineation of lithological boundaries of magmatic rocks. The findings highlight the effectiveness of the PMF method coupled with stream sediment geochemistry, as a powerful tool for extracting geological signatures. This approach offers valuable insights into geological information extraction in Gobi Desert terrains, particularly for identifying and delineating lithological boundaries within magmatic rock formations.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126299"},"PeriodicalIF":2.6,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911632","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":"Anticlockwise metamorphic evolution of the Tin Hallen area (Ahnet Terrane, NW Hoggar, Algeria): Evidence for granulitic and blueschist-facies metamorphism in Fe-Ti metagabbros","authors":"Malika Mokri ,&nbsp;Khadidja Ouzegane ,&nbsp;Sid Ali Doukkari ,&nbsp;Saida Ait Djafer ,&nbsp;Jean-Robert Kienast ,&nbsp;Zouhir Adjerid ,&nbsp;Nadia Boureghda ,&nbsp;Hamid Haddoum","doi":"10.1016/j.chemer.2024.126245","DOIUrl":"10.1016/j.chemer.2024.126245","url":null,"abstract":"<div><div>The Tin Hallen area (Ahnet terrane, NW Hoggar, Algeria) represents one of the most well-preserved examples of blueschist-facies metamorphism in West Gondwana, associated with Fe<img>Ti garnet-bearing metagabbros. The textural analysis reveals four distinct stages. The first stage (M1) is magmatic, characterized by an orthopyroxene, plagioclase ± clinopyroxene, and ilmenite assemblage, primarily observed in areas distant from shear zones. The second stage (M2) involves the development of granulite-facies coronae and symplectites composed of garnet, clinopyroxene2, quartz, rutile, and brown amphibole. The third stage (M3) is defined by the appearance of green amphibole, sphene and epidote. Finally, the fourth stage (M4) is marked by the formation of glaucophane-bearing schists, indicating an advanced retrograde evolution within shear zones. Through the integration of thermodynamic modeling (P-T-M_H2O pseudosections), petrology, mineral chemistry, and reaction textures, a counterclockwise P-T path has been established for the area. The Tin Hallen metagabbros display a prominent granulitic imprint surrounding magmatic relicts in H₂O-undersaturated conditions. This evolution reflects a pressure increase at nearly constant temperature, progressing from c. 6 kbar and c. 900 °C (M1) to 9–10.5 kbar and 850–900 °C (M2), likely linked to the thickening of the magmatic arc root, as suggested by other international studies. The granulitization is followed by further pressure increases and temperature decreases, leading to the mylonitic garnet amphibolite stage (M3) at ~14 kbar and 740 °C, along with a significant rise in M_H2O. Moreover, the presence of an original blueschist-facies stage (M4) with high-pressure, low-temperature (HP-LT) conditions (c. 8 kbar and 470 °C) is characteristic of cold subduction gradients (10–15 °C/km).</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126245"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290640","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":"Tourmaline associated with orogenic gold occurrences in the Silet terrane, South Algeria: Evolution of composition and redox state during hydrothermal crystallization","authors":"Ismahen Chaouche ,&nbsp;Jan Cempírek ,&nbsp;Mohamed Talbi ,&nbsp;Riad Ben El Khaznadji ,&nbsp;Nadjet Ait Taleb ,&nbsp;Yves Fuchs","doi":"10.1016/j.chemer.2025.126259","DOIUrl":"10.1016/j.chemer.2025.126259","url":null,"abstract":"<div><div>In the Silet terrane (western Hoggar, southern Algeria), gold occurs in association with tourmaline in quartz veins. In the Assouf Mellen, Seldrar, and Idreksi occurrences, gold-bearing veins cut diorite and granodiorite complexes of the pre-orogenic Tonalite-Trondhjemite-Granodiorite group (868–840 Ma). These veins trend dominantly in the N-S, NE-SW, and NW-SE directions, and are preferentially developed at the intersection zones of secondary NE-SW and NW-SE fault splays off the main 4°30′ fault zone (Iskel Shear Zone). Free gold is present as inclusions disseminated in quartz and tourmaline, and as fissure-fillings in deformed tourmaline crystals. Gold was also found as inclusions in chalcopyrite and in iron oxides.</div><div>Based on the mineral chemistry, the tourmaline belongs to the alkali group and represents the schorl–dravite and foitite–oxy-foitite series and shows evolution trends to bosiite/povondraite; tourmaline components from the calcic group (lucchesiite, magnesio-lucchesiite) are minor only. Tourmaline in Silet was likely formed as Al-deficient Fe³⁺-enriched schorl (Tur I), later recrystallized (Tur II) and enriched in Mg and Al with higher X-site vacancy (Mg-rich schorl to Fe-rich dravite). In the Seldrar occurrences (middle part of Silet terrane), gold is associated with tourmaline with high initial Fe³⁺-contents (Tur I) while the assemblage of the later Tur II is barren. The evolution towards Fe³⁺-rich schorl may be explained as a result of more oxidizing conditions in the late stage of formation of the mineralized quartz veins. Part of gold was remobilized by low-temperature weathering processes.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 2","pages":"Article 126259"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144290642","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":"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}