Chemie Der Erde-Geochemistry最新文献

{"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}

{"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}