Quentin Bollaert, Mathieu Chassé, Nicolas Menguy, Corentin Le Guillou, Artur Bastos Neto, David Troadec, Laurence Galoisy, Georges Calas
The origin of the mobility of low-solubility elements such as niobium during supergene weathering remains elusive, despite growing evidence, especially in strongly weathered regolith. In the critical zone, the low mobility of these high field strength elements (HFSEs) is assigned to the resistance of their mineral hosts. This property led to their use as geochemical invariants to quantify mass transfer during alteration. Pyrochlore is a quintessential weathering-resistant mineral accommodating most HFSEs. Here, we investigate the surface alteration layers of pyrochlore using a nanoscale approach within a well-characterized regolith subject to intense weathering over millions of years. In the profile, porous pyrochlore rims exhibit distinct chemistry with higher Th contents. Sharp chemical and textural nanometer-scale interfaces between Pb-rich and Th-rich pyrochlore provide compelling evidence for interface-coupled dissolution-reprecipitation. This demonstrates the alterability of the Nb octahedral framework in pyrochlore and the relative stability of its Th-rich counterpart during tropical weathering. Nanoscale analyses of Ce-rich pyrochlores in two additional lateritic horizons confirm the generality of this mechanism across the deposit. The presence of Nb in secondary nano-cerianite found in manganiferous veins establishes its transport during weathering. These nanomineralogical studies of secondary assemblages provide the first direct evidence of Nb mobility during weathering at the deposit scale, underscoring the need to reappraise HFSE geochemical cycles at Earth’s surface, especially in light of growing mining volumes. This paves the way for further investigations into the alteration of weathering-resistant minerals at the nanoscale, providing new models of mobilization and sequestration through previously undocumented processes.
{"title":"Pyrochlore nanomineralogy questions the immobility of niobium during tropical weathering","authors":"Quentin Bollaert, Mathieu Chassé, Nicolas Menguy, Corentin Le Guillou, Artur Bastos Neto, David Troadec, Laurence Galoisy, Georges Calas","doi":"10.1130/g53465.1","DOIUrl":"https://doi.org/10.1130/g53465.1","url":null,"abstract":"The origin of the mobility of low-solubility elements such as niobium during supergene weathering remains elusive, despite growing evidence, especially in strongly weathered regolith. In the critical zone, the low mobility of these high field strength elements (HFSEs) is assigned to the resistance of their mineral hosts. This property led to their use as geochemical invariants to quantify mass transfer during alteration. Pyrochlore is a quintessential weathering-resistant mineral accommodating most HFSEs. Here, we investigate the surface alteration layers of pyrochlore using a nanoscale approach within a well-characterized regolith subject to intense weathering over millions of years. In the profile, porous pyrochlore rims exhibit distinct chemistry with higher Th contents. Sharp chemical and textural nanometer-scale interfaces between Pb-rich and Th-rich pyrochlore provide compelling evidence for interface-coupled dissolution-reprecipitation. This demonstrates the alterability of the Nb octahedral framework in pyrochlore and the relative stability of its Th-rich counterpart during tropical weathering. Nanoscale analyses of Ce-rich pyrochlores in two additional lateritic horizons confirm the generality of this mechanism across the deposit. The presence of Nb in secondary nano-cerianite found in manganiferous veins establishes its transport during weathering. These nanomineralogical studies of secondary assemblages provide the first direct evidence of Nb mobility during weathering at the deposit scale, underscoring the need to reappraise HFSE geochemical cycles at Earth’s surface, especially in light of growing mining volumes. This paves the way for further investigations into the alteration of weathering-resistant minerals at the nanoscale, providing new models of mobilization and sequestration through previously undocumented processes.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"5 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Chetan Nathwani, Emanuel Giovanini, Olivier Bachmann, Paolo Sossi, Julien Allaz, Marine Cotte, Lorenzo Candioti, Cyril Chelle-Michou
Sulfide saturation during arc magma evolution depletes ascending magmas in chalcophile elements (e.g., Cu) and promotes metal recycling into the mantle. Although sulfide saturation is posited to be delayed by high oxygen fugacity (ƒO2) in the deep crust of arcs, the timing and controls on sulfide saturation in arcs remain disputed. Here, we report new constraints on S speciation in the deep crust of arcs using measurements of the relative abundance of S species (S2−, S4+, and S6+) in apatite in deep crustal arc cumulates from the Sierra Valle Fértil−La Huerta (Argentina). Sulfide is rare in primitive cumulates (<0.01%), only becoming abundant in evolved cumulates (Mg# <0.65), indicating that sulfide saturation was delayed in the magmatic evolution. Apatite yields consistently high S6+/ΣS (0.8−1.0), giving an fO2 of 1.4 ± 0.4 log units above the fayalite-magnetite-quartz (FMQ) redox buffer. Delayed sulfide saturation was therefore the result of the parental magma having elevated fO2 acquired from its mantle source. We use modeling to show that magma differentiation at FMQ+1.4 would be sufficient to delay sulfide saturation and produce mafic to intermediate melts with elevated Cu concentrations. Oxidized, hydrous intermediate magmas may therefore play a key role in delivering elevated sulfur and Cu fluxes to magmatic-hydrothermal systems and the atmosphere, contributing to the Cu deficit of modern continental crust.
弧岩浆演化过程中的硫化物饱和耗尽上升岩浆中的亲铜元素（如Cu），促进金属再循环进入地幔。虽然在弧深地壳中，高氧逸度（ƒO2）延迟了硫化物的饱和，但弧中硫化物饱和的时间和控制仍然存在争议。本文通过对阿根廷Sierra Valle f - La Huerta地区深地壳弧堆积中磷灰石中S元素（S2−、S4+和S6+）相对丰度的测量，报道了弧深地壳中S物种形成的新限制。硫化物在原始堆积物中含量较低（<0.01%），在演化堆积物中含量较丰富（Mg# <0.65），表明岩浆演化过程中硫化物饱和度延迟。磷灰石的产率一直很高，S6+/ΣS(0.8−1.0)，在费雅石-磁铁矿-石英（FMQ）氧化还原缓冲液上的fO2为1.4±0.4 log单位。因此，延迟的硫化物饱和是母岩浆从地幔源获得的fO2升高的结果。我们利用模型表明，FMQ+1.4的岩浆分异足以延迟硫化物饱和，并产生镁基到中间的高铜浓度熔体。因此，氧化、含水的中间岩浆可能在向岩浆-热液系统和大气输送硫和铜通量的过程中发挥了关键作用，从而导致现代大陆地壳的铜亏缺。
{"title":"Sulfate-dominant apatite in the deep arc crust indicates that high oxidation state promotes copper fluxing in arcs","authors":"Chetan Nathwani, Emanuel Giovanini, Olivier Bachmann, Paolo Sossi, Julien Allaz, Marine Cotte, Lorenzo Candioti, Cyril Chelle-Michou","doi":"10.1130/g53549.1","DOIUrl":"https://doi.org/10.1130/g53549.1","url":null,"abstract":"Sulfide saturation during arc magma evolution depletes ascending magmas in chalcophile elements (e.g., Cu) and promotes metal recycling into the mantle. Although sulfide saturation is posited to be delayed by high oxygen fugacity (ƒO2) in the deep crust of arcs, the timing and controls on sulfide saturation in arcs remain disputed. Here, we report new constraints on S speciation in the deep crust of arcs using measurements of the relative abundance of S species (S2−, S4+, and S6+) in apatite in deep crustal arc cumulates from the Sierra Valle Fértil−La Huerta (Argentina). Sulfide is rare in primitive cumulates (&lt;0.01%), only becoming abundant in evolved cumulates (Mg# &lt;0.65), indicating that sulfide saturation was delayed in the magmatic evolution. Apatite yields consistently high S6+/ΣS (0.8−1.0), giving an fO2 of 1.4 ± 0.4 log units above the fayalite-magnetite-quartz (FMQ) redox buffer. Delayed sulfide saturation was therefore the result of the parental magma having elevated fO2 acquired from its mantle source. We use modeling to show that magma differentiation at FMQ+1.4 would be sufficient to delay sulfide saturation and produce mafic to intermediate melts with elevated Cu concentrations. Oxidized, hydrous intermediate magmas may therefore play a key role in delivering elevated sulfur and Cu fluxes to magmatic-hydrothermal systems and the atmosphere, contributing to the Cu deficit of modern continental crust.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"24 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145508808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Diogo Ribeiro, Bertrand Rottier, Antoine Godet, Georges Beaudoin, Clifford G.C. Patten, Carl Guilmette, Adrian G. Rehm, Isaac S. Malta, Jochen Kolb, Douglas K. Tinkham, Iain Pitcairn
The southern Superior Province (Canada) comprises large metasedimentary belts, such as the Pontiac and Quetico subprovinces, adjacent to Au-endowed greenstone belts. The Pontiac sedimentary rocks have been proposed as a source of Au for the highly endowed southern Abitibi greenstone belt. However, a comparison with sedimentary rocks adjacent to poorly endowed greenstone belts is lacking. Here we examine a suite of metasedimentary and minor volcanic rocks collected from three transects in the Pontiac and Quetico metasedimentary belts adjacent to greenstone belts with variable Au endowments. We combine in situ Au data of sulfides in metasedimentary rocks with whole-rock ultra-low-detection Au data. Gold concentrations decrease across metamorphic isograds in the well- and moderately endowed transects, while limited Au mobility is observed in the poorly endowed transect. The release of Au from metasedimentary rocks is linked to the pyrite-pyrrhotite transition. This reaction is incomplete in the poorly endowed transect, explaining the limited Au mobility observed. Our data reveal a spatial correlation between Au mobility in metasedimentary belts and Au endowment in the adjacent greenstone belts.
{"title":"Gold mobility in Archean metasedimentary belts: Implications for orogenic gold deposits","authors":"Diogo Ribeiro, Bertrand Rottier, Antoine Godet, Georges Beaudoin, Clifford G.C. Patten, Carl Guilmette, Adrian G. Rehm, Isaac S. Malta, Jochen Kolb, Douglas K. Tinkham, Iain Pitcairn","doi":"10.1130/g53574.1","DOIUrl":"https://doi.org/10.1130/g53574.1","url":null,"abstract":"The southern Superior Province (Canada) comprises large metasedimentary belts, such as the Pontiac and Quetico subprovinces, adjacent to Au-endowed greenstone belts. The Pontiac sedimentary rocks have been proposed as a source of Au for the highly endowed southern Abitibi greenstone belt. However, a comparison with sedimentary rocks adjacent to poorly endowed greenstone belts is lacking. Here we examine a suite of metasedimentary and minor volcanic rocks collected from three transects in the Pontiac and Quetico metasedimentary belts adjacent to greenstone belts with variable Au endowments. We combine in situ Au data of sulfides in metasedimentary rocks with whole-rock ultra-low-detection Au data. Gold concentrations decrease across metamorphic isograds in the well- and moderately endowed transects, while limited Au mobility is observed in the poorly endowed transect. The release of Au from metasedimentary rocks is linked to the pyrite-pyrrhotite transition. This reaction is incomplete in the poorly endowed transect, explaining the limited Au mobility observed. Our data reveal a spatial correlation between Au mobility in metasedimentary belts and Au endowment in the adjacent greenstone belts.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"29 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145485391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hongxiang Guan, Steffen Kiel, Xiaoyan Xu, Jiachen Fan, Yi Zhang, Xiaoming Miao, Hangyu Nan, Nengyou Wu, Sanzhong Li
Chemosymbiosis-based invertebrate communities dominate deep-sea hydrothermal vents and methane seeps, but reliable methods for detecting chemosymbiosis in the fossil record and tracing its evolution into the geologic past are still lacking. Here, we investigate the lipid inventory of shells of four seep-dwelling bivalve species (from both live specimens and empty shells) hosting either methanotrophic or thiotrophic symbionts. All species share a common suite of lipids that are mostly derived from external heterotrophic sources, except for cholesterol and cholestanols in bathymodiolin mussels. The δ13C values of these sterols as low as −83‰ indicate an origin of these compounds from the animal. The transfer was independent of the symbionts being methanotrophic or thiotrophic and thus of the distinct biosynthetic pathways for cholesterol and cholestanol of these animals. This finding opens a new prospect for molecular paleontology by taking advantage of the source specificity and diagenetic stability of these compounds. It could allow tracing chemosymbiosis and its evolution into the fossil record, in particular in bathymodiolin mussels, and potentially also in other metazoan groups.
{"title":"Sterols transferred from soft tissues to bivalve shells: A new tracer of molecular paleontology","authors":"Hongxiang Guan, Steffen Kiel, Xiaoyan Xu, Jiachen Fan, Yi Zhang, Xiaoming Miao, Hangyu Nan, Nengyou Wu, Sanzhong Li","doi":"10.1130/g53933.1","DOIUrl":"https://doi.org/10.1130/g53933.1","url":null,"abstract":"Chemosymbiosis-based invertebrate communities dominate deep-sea hydrothermal vents and methane seeps, but reliable methods for detecting chemosymbiosis in the fossil record and tracing its evolution into the geologic past are still lacking. Here, we investigate the lipid inventory of shells of four seep-dwelling bivalve species (from both live specimens and empty shells) hosting either methanotrophic or thiotrophic symbionts. All species share a common suite of lipids that are mostly derived from external heterotrophic sources, except for cholesterol and cholestanols in bathymodiolin mussels. The δ13C values of these sterols as low as −83‰ indicate an origin of these compounds from the animal. The transfer was independent of the symbionts being methanotrophic or thiotrophic and thus of the distinct biosynthetic pathways for cholesterol and cholestanol of these animals. This finding opens a new prospect for molecular paleontology by taking advantage of the source specificity and diagenetic stability of these compounds. It could allow tracing chemosymbiosis and its evolution into the fossil record, in particular in bathymodiolin mussels, and potentially also in other metazoan groups.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"183 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145454983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Large, shallow earthquakes typically produce surface ruptures, whereas aftershocks rarely do. Here, we document a rare case in which the 2024 Mw 7.0 Wushi earthquake (western China) did not rupture the surface, but a Mw 5.7 aftershock did. Integrated field observations, satellite imagery, interferometric synthetic aperture radar (InSAR) data, and relocated seismicity reveal that the aftershock reactivated shallow back- and fore-thrusts, forming a pop-up structure with clear surface breaks. This event demonstrates that aftershocks can generate significant surface deformation by reactivating pre-existing shallow faults—a process not commonly accounted for in seismic hazard assessments. Our findings emphasize the need to incorporate secondary shallow faults into hazard models, especially in complex fold-and-thrust systems.
{"title":"Aftershock-induced surface ruptures overshadow the 2024 Mw 7.0 Wushi mainshock, China","authors":"Haibing Li, Jiawei Pan, Marie-Luce Chevalier, Dongliang Liu, Shiguang Wang, Heng Luo, Long Zhang, Lihua Fang, Teng Wang, Fucai Liu, Shenqiang Chen, Xiaohui He, Xunzhang Zhu, Yihu Zhang, Qiong Wu, Chunrui Li","doi":"10.1130/g54078.1","DOIUrl":"https://doi.org/10.1130/g54078.1","url":null,"abstract":"Large, shallow earthquakes typically produce surface ruptures, whereas aftershocks rarely do. Here, we document a rare case in which the 2024 Mw 7.0 Wushi earthquake (western China) did not rupture the surface, but a Mw 5.7 aftershock did. Integrated field observations, satellite imagery, interferometric synthetic aperture radar (InSAR) data, and relocated seismicity reveal that the aftershock reactivated shallow back- and fore-thrusts, forming a pop-up structure with clear surface breaks. This event demonstrates that aftershocks can generate significant surface deformation by reactivating pre-existing shallow faults—a process not commonly accounted for in seismic hazard assessments. Our findings emphasize the need to incorporate secondary shallow faults into hazard models, especially in complex fold-and-thrust systems.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"2 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145448349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bolin Zhang, Xianguo Lang, Thomas J. Algeo, Wei Shi, Paul B. Wignall, Jian Cao, Chao Li, Suping Yao, Yiquan Ma, Chen Zhang, Runsheng Yin
The Middle Permian was characterized by a major climatic warming trend that heralded the end of the late Paleozoic Ice Age, as well as by widespread marine anoxia during the Capitanian biotic crisis. Although the Emeishan large igneous province (ELIP) has been implicated as a potential driver of this warming, its role remains contentious. We present a comprehensive analysis of mercury abundance and isotopes, along with zircon geochemistry, from tuffs interbedded in a Middle Permian deep-water succession from South China. Our data reveal sustained continental arc volcanism (CAV) prior to the ELIP eruptions that coincided with the Middle Permian warming, suggesting a potential causal relationship between them. Supported by Carbon-Oxygen-Phosphorus-Sulfur-Evolution modeling, we propose that globally increased CAV may have released sufficiently large quantities of CO2 to the atmosphere to trigger climate warming, ultimately leading to marine anoxia and biotic crisis. Our findings challenge the prevailing view of the ELIP as the sole cause of the Middle Permian warming and highlight the potential importance of CAV in Earth’s climate history.
{"title":"Continental arc volcanism fueled Middle Permian warming","authors":"Bolin Zhang, Xianguo Lang, Thomas J. Algeo, Wei Shi, Paul B. Wignall, Jian Cao, Chao Li, Suping Yao, Yiquan Ma, Chen Zhang, Runsheng Yin","doi":"10.1130/g54053.1","DOIUrl":"https://doi.org/10.1130/g54053.1","url":null,"abstract":"The Middle Permian was characterized by a major climatic warming trend that heralded the end of the late Paleozoic Ice Age, as well as by widespread marine anoxia during the Capitanian biotic crisis. Although the Emeishan large igneous province (ELIP) has been implicated as a potential driver of this warming, its role remains contentious. We present a comprehensive analysis of mercury abundance and isotopes, along with zircon geochemistry, from tuffs interbedded in a Middle Permian deep-water succession from South China. Our data reveal sustained continental arc volcanism (CAV) prior to the ELIP eruptions that coincided with the Middle Permian warming, suggesting a potential causal relationship between them. Supported by Carbon-Oxygen-Phosphorus-Sulfur-Evolution modeling, we propose that globally increased CAV may have released sufficiently large quantities of CO2 to the atmosphere to trigger climate warming, ultimately leading to marine anoxia and biotic crisis. Our findings challenge the prevailing view of the ELIP as the sole cause of the Middle Permian warming and highlight the potential importance of CAV in Earth’s climate history.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"39 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145441346","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Maxim Portnyagin, Roman Botcharnikov, Gene Yogodzinski, Dieter Garbe-Schönberg, Kaj Hoernle
Partial melts subducting oceanic crust (slab melts) have been proposed to play an important role in ore-forming processes and in the generation of continental crust, but the scarcity of erupted slab melts hampers direct evaluation of their role. Primitive Mg-rhyodacites with molar Mg/Mg+FeT >0.60 from the Western Aleutians represent nearly unmodified melts from eclogitized mid-ocean-ridge basalt (MORB) of the subducting Pacific plate. Here, we show that the presence of anhydrite phenocrysts and hornblende compositions indicate highly oxidizing conditions (ΔNNO ≥+1) of crystallization. Despite these conditions and the absence of sulfides in the mineral assemblage, the rocks exhibit strongly fractionated chalcophile element ratios (Ag/Cu ∼10 × MORB and Bi/Cu ∼100 × MORB), suggesting their geochemical signatures were imposed by the presence of monosulfide solid solution (MSS) phase during slab melting. The chalcophile element abundances in the Mg-rhyodacites can be quantitatively explained by partial melting of MORB eclogite at 2 GPa and 900 °C in the presence of MSS. With the exception of Ag and Bi, slab melts have low contents of strongly chalcophile elements, such as Cu, Se, Pt, and Au, and therefore a limited capacity to transport these elements under upper mantle conditions. The distinctively high Ag/Cu and Bi/Cu ratios in the Mg-rhyodacites further suggest that slab-derived magmas may have been significant contributors to the chalcophile element signatures of the continental crust throughout Earth’s history.
{"title":"Melting of sulfide-bearing slab beneath the Western Aleutian Arc: Implications for chalcophile element abundances in slab-derived melts and the origin of continental crust","authors":"Maxim Portnyagin, Roman Botcharnikov, Gene Yogodzinski, Dieter Garbe-Schönberg, Kaj Hoernle","doi":"10.1130/g53585.1","DOIUrl":"https://doi.org/10.1130/g53585.1","url":null,"abstract":"Partial melts subducting oceanic crust (slab melts) have been proposed to play an important role in ore-forming processes and in the generation of continental crust, but the scarcity of erupted slab melts hampers direct evaluation of their role. Primitive Mg-rhyodacites with molar Mg/Mg+FeT &gt;0.60 from the Western Aleutians represent nearly unmodified melts from eclogitized mid-ocean-ridge basalt (MORB) of the subducting Pacific plate. Here, we show that the presence of anhydrite phenocrysts and hornblende compositions indicate highly oxidizing conditions (ΔNNO ≥+1) of crystallization. Despite these conditions and the absence of sulfides in the mineral assemblage, the rocks exhibit strongly fractionated chalcophile element ratios (Ag/Cu ∼10 × MORB and Bi/Cu ∼100 × MORB), suggesting their geochemical signatures were imposed by the presence of monosulfide solid solution (MSS) phase during slab melting. The chalcophile element abundances in the Mg-rhyodacites can be quantitatively explained by partial melting of MORB eclogite at 2 GPa and 900 °C in the presence of MSS. With the exception of Ag and Bi, slab melts have low contents of strongly chalcophile elements, such as Cu, Se, Pt, and Au, and therefore a limited capacity to transport these elements under upper mantle conditions. The distinctively high Ag/Cu and Bi/Cu ratios in the Mg-rhyodacites further suggest that slab-derived magmas may have been significant contributors to the chalcophile element signatures of the continental crust throughout Earth’s history.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"3 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145441347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We sampled modern sand from small (0.4−16.0 km2) catchments within the western Yarlung suture zone of southern Tibet. Many (29%−45%) of the zircon ages are Eocene to Miocene, younger than the Paleozoic to Paleogene bedrock but consistent with zircon ages in local modern river sands. Eolian dunes and sand sheets in part of the study area, and a widespread <21 ka loessic soil mantle, suggest that sediment was transported upslope out of the riverbeds by eolian processes since the Last Glacial Maximum. Loessic soil is ubiquitous on the Tibetan Plateau, and its preservation and dominance in small catchments suggests that loess deposition outpaces erosion of the underlying bedrock. Small (<50 km2) catchments may better identify when wind plays a significant role in sediment transport. Our case study highlights the efficacy of uphill sediment transport by wind and the detrital significance of loess in southern Tibet.
{"title":"The Tibetan Plateau is covered in wind-blown sand: Implications for detrital provenance studies","authors":"Kathryn Metcalf, Paul Kapp","doi":"10.1130/g53981.1","DOIUrl":"https://doi.org/10.1130/g53981.1","url":null,"abstract":"We sampled modern sand from small (0.4−16.0 km2) catchments within the western Yarlung suture zone of southern Tibet. Many (29%−45%) of the zircon ages are Eocene to Miocene, younger than the Paleozoic to Paleogene bedrock but consistent with zircon ages in local modern river sands. Eolian dunes and sand sheets in part of the study area, and a widespread &lt;21 ka loessic soil mantle, suggest that sediment was transported upslope out of the riverbeds by eolian processes since the Last Glacial Maximum. Loessic soil is ubiquitous on the Tibetan Plateau, and its preservation and dominance in small catchments suggests that loess deposition outpaces erosion of the underlying bedrock. Small (&lt;50 km2) catchments may better identify when wind plays a significant role in sediment transport. Our case study highlights the efficacy of uphill sediment transport by wind and the detrital significance of loess in southern Tibet.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"27 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145434703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tao Wu, Liang Liu, Wen Zhang, Simon A. Wilde, Guoliang Zhang, Xiaochao Che, Chun-Feng Li, Liyan Tian, Taoran Song, Yidi Hong, Hengrui Zhu, Hayden Dalton, Qiuli Li, Uwe Kirscher
The Challenger Deep is the deepest part of the world’s ocean at ∼10.9 km. It constitutes the southern part of the Isu-Bonin-Mariana system, formed by intra-oceanic subduction of the Pacific plate. However, instead of consisting of Jurassic Pacific mid-ocean-ridge basalt (∼150 m.y. old), samples collected in situ using the submersible Fendouzhe from the bottom of the Challenger Deep, and five other nearby sites on the subducting plate, reveal that the basalt is much younger, with U-Pb zircon and plagioclase 40Ar/39Ar crystallization ages of ca. 34−17 Ma. These are coeval with tholeiitic basalt on the nearby Caroline Plateau, with which they share a similar chemistry. The subducting plate has therefore been resurfaced by Cenozoic basalts generated by the Caroline hotspot, with only a thin veneer of overlying sediments. Numerical modeling indicates that subduction of an old plate with these characteristics may possibly account for the features exhibited by the Challenger Deep, including its slow convergence rate and induced slab rollback due to increased friction between the subducting and overriding plates, thereby producing the deepest trench on Earth.
{"title":"Implications of unexpectedly young seafloor in the Challenger Deep","authors":"Tao Wu, Liang Liu, Wen Zhang, Simon A. Wilde, Guoliang Zhang, Xiaochao Che, Chun-Feng Li, Liyan Tian, Taoran Song, Yidi Hong, Hengrui Zhu, Hayden Dalton, Qiuli Li, Uwe Kirscher","doi":"10.1130/g53728.1","DOIUrl":"https://doi.org/10.1130/g53728.1","url":null,"abstract":"The Challenger Deep is the deepest part of the world’s ocean at &#8764;10.9 km. It constitutes the southern part of the Isu-Bonin-Mariana system, formed by intra-oceanic subduction of the Pacific plate. However, instead of consisting of Jurassic Pacific mid-ocean-ridge basalt (&#8764;150 m.y. old), samples collected in situ using the submersible Fendouzhe from the bottom of the Challenger Deep, and five other nearby sites on the subducting plate, reveal that the basalt is much younger, with U-Pb zircon and plagioclase 40Ar/39Ar crystallization ages of ca. 34−17 Ma. These are coeval with tholeiitic basalt on the nearby Caroline Plateau, with which they share a similar chemistry. The subducting plate has therefore been resurfaced by Cenozoic basalts generated by the Caroline hotspot, with only a thin veneer of overlying sediments. Numerical modeling indicates that subduction of an old plate with these characteristics may possibly account for the features exhibited by the Challenger Deep, including its slow convergence rate and induced slab rollback due to increased friction between the subducting and overriding plates, thereby producing the deepest trench on Earth.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"13 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145404168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yan Yang, Wenyuan Fan, Mark D. Behn, Sarah B. Das, Jeffrey J. McGuire
Ice loss from the Greenland Ice Sheet contributes significantly to global sea-level rise; however, its magnitude and sensitivity to future climate change remain uncertain in large part due to questions regarding how basal processes influence ice-sheet dynamics. Specifically, the role of subglacial sediments in regulating Greenland Ice Sheet dynamics is not well understood. Thawed and saturated subglacial sediments enhance ice-sheet basal sliding, making it essential to quantify their distribution and properties beneath the Greenland Ice Sheet. Here, we apply high-frequency receiver function (RF) analysis to investigate subglacial sediments using seismic data collected across the Greenland Ice Sheet over recent decades. We find that the observed RFs consistently exhibit arrival-time delays relative to synthetic predictions from ice−over−hard bed models, indicating widespread low-velocity layers at the ice-bed interface. This low-velocity layer can be best explained by subglacial sediments with thicknesses up to ∼200 m. The mapped results suggest that deformable sediments are more extensive than previously recognized but are distributed heterogeneously in space. Sediment thickness broadly correlates with modeled basal thermal state, with thicker and weaker sediments generally found beneath thawed regions. The presence of such sediments—even beneath regions not currently undergoing basal thaw—may precondition parts of the Greenland Ice Sheet for future dynamic change. Our findings highlight the importance of incorporating subglacial sediment properties into projections of ice-sheet behavior under a warming climate.
{"title":"Seismic evidence of widespread sediments beneath the Greenland Ice Sheet","authors":"Yan Yang, Wenyuan Fan, Mark D. Behn, Sarah B. Das, Jeffrey J. McGuire","doi":"10.1130/g53653.1","DOIUrl":"https://doi.org/10.1130/g53653.1","url":null,"abstract":"Ice loss from the Greenland Ice Sheet contributes significantly to global sea-level rise; however, its magnitude and sensitivity to future climate change remain uncertain in large part due to questions regarding how basal processes influence ice-sheet dynamics. Specifically, the role of subglacial sediments in regulating Greenland Ice Sheet dynamics is not well understood. Thawed and saturated subglacial sediments enhance ice-sheet basal sliding, making it essential to quantify their distribution and properties beneath the Greenland Ice Sheet. Here, we apply high-frequency receiver function (RF) analysis to investigate subglacial sediments using seismic data collected across the Greenland Ice Sheet over recent decades. We find that the observed RFs consistently exhibit arrival-time delays relative to synthetic predictions from ice−over−hard bed models, indicating widespread low-velocity layers at the ice-bed interface. This low-velocity layer can be best explained by subglacial sediments with thicknesses up to ∼200 m. The mapped results suggest that deformable sediments are more extensive than previously recognized but are distributed heterogeneously in space. Sediment thickness broadly correlates with modeled basal thermal state, with thicker and weaker sediments generally found beneath thawed regions. The presence of such sediments—even beneath regions not currently undergoing basal thaw—may precondition parts of the Greenland Ice Sheet for future dynamic change. Our findings highlight the importance of incorporating subglacial sediment properties into projections of ice-sheet behavior under a warming climate.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"8 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145396641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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