Zongqi Zou, Yi-Gang Xu, Zaicong Wang, Yu Wang, Ming Li, Meiling Wang, Yutian Lei
The low-velocity zone (LVZ) in shallow asthenosphere is crucial for Earth’s geodynamics and is widely linked to the presence of partial melts. Incipient melts from mantle peridotite melting are highly mobile and tend to quickly escape from their sources; however, it remains enigmatic how the LVZ can extend to the depths where partial melting initiates. Here, we identify a suite of primitive low-MgO basalts derived from an eclogitized oceanic crust at ∼200 km within the LVZ, providing a compelling scenario for the LVZ formation. These primitive basalts exhibit significantly heavier Fe isotopes and lighter Ca-Mo-O isotopes compared to mid-ocean-ridge basalts, indicating that they originated from eclogitized oceanic crust rather than peridotite. This highlights the fact that oceanic crust recycled into the mantle can melt to form primitive Mg-poor and Si-rich melts. Given their relatively high density and viscosity, these melts show low-mobility and accumulate at depths of ∼150−200 km, forming a low-velocity layer within the asthenosphere.
{"title":"Melting of eclogitic oceanic crust for the low-velocity zone within Earth’s upper asthenosphere","authors":"Zongqi Zou, Yi-Gang Xu, Zaicong Wang, Yu Wang, Ming Li, Meiling Wang, Yutian Lei","doi":"10.1130/g53540.1","DOIUrl":"https://doi.org/10.1130/g53540.1","url":null,"abstract":"The low-velocity zone (LVZ) in shallow asthenosphere is crucial for Earth’s geodynamics and is widely linked to the presence of partial melts. Incipient melts from mantle peridotite melting are highly mobile and tend to quickly escape from their sources; however, it remains enigmatic how the LVZ can extend to the depths where partial melting initiates. Here, we identify a suite of primitive low-MgO basalts derived from an eclogitized oceanic crust at ∼200 km within the LVZ, providing a compelling scenario for the LVZ formation. These primitive basalts exhibit significantly heavier Fe isotopes and lighter Ca-Mo-O isotopes compared to mid-ocean-ridge basalts, indicating that they originated from eclogitized oceanic crust rather than peridotite. This highlights the fact that oceanic crust recycled into the mantle can melt to form primitive Mg-poor and Si-rich melts. Given their relatively high density and viscosity, these melts show low-mobility and accumulate at depths of ∼150−200 km, forming a low-velocity layer within the asthenosphere.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"24 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145003072","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}
Elizabeth J. Trower, Miquela Ingalls, James R. Gutoski, Virginia T. Wala
Although it is difficult to reconstruct Earth surface temperatures during Neoproterozoic time, sedimentological and paleomagnetic evidence demonstrate a dynamic climate, featuring two global “Snowball Earth” glaciations. The recent observation of petrographic fingerprints of ikaite, a mineral that typically forms in near-freezing sedimentary environments, in late Tonian strata was interpreted as evidence that low-latitude shallow marine environments were cold millions of years prior to the Cryogenian Period. Meanwhile, other recent work has demonstrated that elevated phosphate concentration ([DIP]) can inhibit calcite nucleation (perhaps enabling ikaite to form and persist at warmer temperatures) and that late Tonian carbonates formed in phosphate-rich seawater. So, was late Tonian seawater cold, or was it phosphate-rich? To address this question, we combined measurements of carbonate-associated phosphate and ooid-size-based pH constraints to reconstruct seawater [DIP] values for one snapshot of time in the late Tonian Period. Our seawater [DIP] estimates range from 3.8 µM to 7.8 µM, substantially elevated relative to modern shallow seawater and consistent with inferences from previous approaches. Our estimates are below values at which calcite nucleation inhibition has been observed, suggesting that elevated phosphate is an insufficient explanation for the ikaite forming in warm conditions and supporting the hypothesis that late Tonian climate was cool.
{"title":"New constraints on phosphate concentration and temperature in shallow late Tonian seawater","authors":"Elizabeth J. Trower, Miquela Ingalls, James R. Gutoski, Virginia T. Wala","doi":"10.1130/g53532.1","DOIUrl":"https://doi.org/10.1130/g53532.1","url":null,"abstract":"Although it is difficult to reconstruct Earth surface temperatures during Neoproterozoic time, sedimentological and paleomagnetic evidence demonstrate a dynamic climate, featuring two global “Snowball Earth” glaciations. The recent observation of petrographic fingerprints of ikaite, a mineral that typically forms in near-freezing sedimentary environments, in late Tonian strata was interpreted as evidence that low-latitude shallow marine environments were cold millions of years prior to the Cryogenian Period. Meanwhile, other recent work has demonstrated that elevated phosphate concentration ([DIP]) can inhibit calcite nucleation (perhaps enabling ikaite to form and persist at warmer temperatures) and that late Tonian carbonates formed in phosphate-rich seawater. So, was late Tonian seawater cold, or was it phosphate-rich? To address this question, we combined measurements of carbonate-associated phosphate and ooid-size-based pH constraints to reconstruct seawater [DIP] values for one snapshot of time in the late Tonian Period. Our seawater [DIP] estimates range from 3.8 µM to 7.8 µM, substantially elevated relative to modern shallow seawater and consistent with inferences from previous approaches. Our estimates are below values at which calcite nucleation inhibition has been observed, suggesting that elevated phosphate is an insufficient explanation for the ikaite forming in warm conditions and supporting the hypothesis that late Tonian climate was cool.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"33 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145003073","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}
Trishit Ruj, Hanaya Okuda, Goro Komatsu, Hitoshi Hasegawa, James W. Head, Tomohiro Usui, Shun Mihira, Makito Kobayashi
Subsurface ice in the mid-latitudes of Mars represents one of the largest present-day water ice reservoirs. While atmospheric models predict Late Amazonian (during the past hundreds of millions of years) obliquity-driven ice accumulation, its long-term variations, and the factors influencing accumulation remain unclear. Using geomorphological evidence and numerical modeling, we reveal a southwestern depositional trend within northern mid-latitudinal crater walls and floors. Detailed crater-fill deposit analyses indicate multiple glaciation stages, including an earlier, high-intensity stage followed by a later, lower-intensity stage, both exhibiting this southwestern trend (ca. 640−98 Ma). We conclude that persistent multiple-stage Amazonian glaciations were governed by atmospheric water availability and obliquity-driven climate cycles.
{"title":"Long-term and multi-stage ice accumulation in the martian mid-latitudes during the Amazonian","authors":"Trishit Ruj, Hanaya Okuda, Goro Komatsu, Hitoshi Hasegawa, James W. Head, Tomohiro Usui, Shun Mihira, Makito Kobayashi","doi":"10.1130/g53418.1","DOIUrl":"https://doi.org/10.1130/g53418.1","url":null,"abstract":"Subsurface ice in the mid-latitudes of Mars represents one of the largest present-day water ice reservoirs. While atmospheric models predict Late Amazonian (during the past hundreds of millions of years) obliquity-driven ice accumulation, its long-term variations, and the factors influencing accumulation remain unclear. Using geomorphological evidence and numerical modeling, we reveal a southwestern depositional trend within northern mid-latitudinal crater walls and floors. Detailed crater-fill deposit analyses indicate multiple glaciation stages, including an earlier, high-intensity stage followed by a later, lower-intensity stage, both exhibiting this southwestern trend (ca. 640−98 Ma). We conclude that persistent multiple-stage Amazonian glaciations were governed by atmospheric water availability and obliquity-driven climate cycles.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"63 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144931026","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}
Cody L. Colleps, Peter van der Beek, Julien Amalberti, Edward R. Sobel, Marissa M. Tremblay, Maxime Bernard
Apatite 4He/3He thermochronology has the potential to provide high-resolution low-temperature thermal histories that bring valuable insight into near-surface crustal processes. However, this system has yet to be directly evaluated using single-grain 4He/3He analyses from a natural sample with an established thermal history. We present apatite 4He/3He spectra from the widely used Fish Canyon Tuff (FCT) age standard (San Juan volcanic field, southern Colorado, USA), collected at two localities with contrasting thermal histories: (1) a distal locality (FCT-D) where the early Oligocene eruptive age of the FCT is preserved in the apatite (U-Th)/He (AHe) system and the thermal history is well established; and (2) the classic FCT sampling locality (FCT-C) with younger, Early Miocene AHe dates and an unconstrained posteruptive thermal history. FCT-D apatite shows 4He/3He spectra indicative of no diffusive loss, with relative edge depletion of 4He induced by alpha ejection only, corroborating rapid eruptive cooling. In contrast, FCT-C apatite revealed notably diffusive 4He/3He spectra. Thermal-history inversions highlight the resolving power of apatite 4He/3He thermochronology, demonstrating its ability to (1) independently resolve rapid eruptive cooling at the FCT-D site, and (2) improve the resolution of postemplacement reheating and Early Miocene cooling at the FCT-C site. Refined FCT-C thermal histories reveal a distinctive onset of moderate cooling at ca. 20−19 Ma, likely reflecting footwall topographic development coinciding with regional Rio Grande rifting. This collective assessment of 4He/3He systematics further verifies its ability to substantially improve thermal history resolution, which is crucial to elucidating mechanisms driving crustal cooling.
{"title":"Evaluating the resolving power of apatite 4He/3He thermochronology: Insights from the Fish Canyon Tuff","authors":"Cody L. Colleps, Peter van der Beek, Julien Amalberti, Edward R. Sobel, Marissa M. Tremblay, Maxime Bernard","doi":"10.1130/g53000.1","DOIUrl":"https://doi.org/10.1130/g53000.1","url":null,"abstract":"Apatite 4He/3He thermochronology has the potential to provide high-resolution low-temperature thermal histories that bring valuable insight into near-surface crustal processes. However, this system has yet to be directly evaluated using single-grain 4He/3He analyses from a natural sample with an established thermal history. We present apatite 4He/3He spectra from the widely used Fish Canyon Tuff (FCT) age standard (San Juan volcanic field, southern Colorado, USA), collected at two localities with contrasting thermal histories: (1) a distal locality (FCT-D) where the early Oligocene eruptive age of the FCT is preserved in the apatite (U-Th)/He (AHe) system and the thermal history is well established; and (2) the classic FCT sampling locality (FCT-C) with younger, Early Miocene AHe dates and an unconstrained posteruptive thermal history. FCT-D apatite shows 4He/3He spectra indicative of no diffusive loss, with relative edge depletion of 4He induced by alpha ejection only, corroborating rapid eruptive cooling. In contrast, FCT-C apatite revealed notably diffusive 4He/3He spectra. Thermal-history inversions highlight the resolving power of apatite 4He/3He thermochronology, demonstrating its ability to (1) independently resolve rapid eruptive cooling at the FCT-D site, and (2) improve the resolution of postemplacement reheating and Early Miocene cooling at the FCT-C site. Refined FCT-C thermal histories reveal a distinctive onset of moderate cooling at ca. 20−19 Ma, likely reflecting footwall topographic development coinciding with regional Rio Grande rifting. This collective assessment of 4He/3He systematics further verifies its ability to substantially improve thermal history resolution, which is crucial to elucidating mechanisms driving crustal cooling.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"10 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144919587","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}
Yanzhe Fu, Chong Dong, Dolev Fabrikant, Chenyang Cai, Carolin Haug, Joachim T. Haug, Diying Huang
Animals have evolved diverse defensive strategies under selective pressures, with mimicry being a crucial survival strategy for insects. Leaf mimicry is widespread in modern ecosystems, yet its fossil record remains sparse, often lacking direct evidence of target plant or clear morphological adaptations. We report three novel cases of leaf mimicry in Jurassic orthopterans (grasshoppers and crickets, including katydids) (Prophalangopsidae) from the Daohugou biota (ca. 163.5 Ma, northeastern China), in which the forewings exhibit highly specialized contrasting color patterns that closely resemble the abundantly co-occurring bennettitalean (extinct seed-bearing, cycad-like group) leaves. These cases provide the first unambiguous evidence in which both the mimicking insects and their plant models are preserved in the same bedding plane. It represents the first known instance of orthopteran mimicry in the Jurassic, fills a gap in the fossil record, and suggests that leaf mimicry has been a long-standing adaptive strategy in Orthoptera, independently evolving across different lineages throughout geological history. This finding highlights the dynamic interplay between plant community succession, predation pressures, and insect defensive strategies, expanding our understanding of the ecological significance and evolution of leaf mimicry in orthopterans.
{"title":"Unique leaf mimicry in Jurassic insects","authors":"Yanzhe Fu, Chong Dong, Dolev Fabrikant, Chenyang Cai, Carolin Haug, Joachim T. Haug, Diying Huang","doi":"10.1130/g53399.1","DOIUrl":"https://doi.org/10.1130/g53399.1","url":null,"abstract":"Animals have evolved diverse defensive strategies under selective pressures, with mimicry being a crucial survival strategy for insects. Leaf mimicry is widespread in modern ecosystems, yet its fossil record remains sparse, often lacking direct evidence of target plant or clear morphological adaptations. We report three novel cases of leaf mimicry in Jurassic orthopterans (grasshoppers and crickets, including katydids) (Prophalangopsidae) from the Daohugou biota (ca. 163.5 Ma, northeastern China), in which the forewings exhibit highly specialized contrasting color patterns that closely resemble the abundantly co-occurring bennettitalean (extinct seed-bearing, cycad-like group) leaves. These cases provide the first unambiguous evidence in which both the mimicking insects and their plant models are preserved in the same bedding plane. It represents the first known instance of orthopteran mimicry in the Jurassic, fills a gap in the fossil record, and suggests that leaf mimicry has been a long-standing adaptive strategy in Orthoptera, independently evolving across different lineages throughout geological history. This finding highlights the dynamic interplay between plant community succession, predation pressures, and insect defensive strategies, expanding our understanding of the ecological significance and evolution of leaf mimicry in orthopterans.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"11 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144916093","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}
Ana Anzulović, Anne H. Davis, Carmen Gaina, Razvan Caracas
Kimberlite melts are primary carriers of mantle-derived carbon and hydrogen, playing an important role in Earth’s deep carbon cycle and diamond transport. Their low densities, viscosities, and vapor exsolution enable fast ascent rates. Ascending from the upper mantle, kimberlite melts incorporate xenoliths and xenocrysts and exsolve volatiles. These processes alter their initial composition, increasing the discrepancy between the proto-kimberlite magma and the magma that reaches the surface. To explain kimberlite volcanism, we examine atomic diffusivities and densities of kimberlite melts with varying volatile contents. We show that water makes the melts more diffusive, which should also lower their viscosity. All our kimberlite melts are positively buoyant below the lower continental crust (the MOHO discontinuity). They require ∼8.2 wt% CO2 to cross and rise through the MOHO. Above the MOHO, the most volatile-rich kimberlite melts can carry up to ∼44% xenolithic fragments of depleted peridotite type.
{"title":"Buoyancy of volatile-rich kimberlite melts, magma ascent, and xenolith transport","authors":"Ana Anzulović, Anne H. Davis, Carmen Gaina, Razvan Caracas","doi":"10.1130/g53387.1","DOIUrl":"https://doi.org/10.1130/g53387.1","url":null,"abstract":"Kimberlite melts are primary carriers of mantle-derived carbon and hydrogen, playing an important role in Earth’s deep carbon cycle and diamond transport. Their low densities, viscosities, and vapor exsolution enable fast ascent rates. Ascending from the upper mantle, kimberlite melts incorporate xenoliths and xenocrysts and exsolve volatiles. These processes alter their initial composition, increasing the discrepancy between the proto-kimberlite magma and the magma that reaches the surface. To explain kimberlite volcanism, we examine atomic diffusivities and densities of kimberlite melts with varying volatile contents. We show that water makes the melts more diffusive, which should also lower their viscosity. All our kimberlite melts are positively buoyant below the lower continental crust (the MOHO discontinuity). They require ∼8.2 wt% CO2 to cross and rise through the MOHO. Above the MOHO, the most volatile-rich kimberlite melts can carry up to ∼44% xenolithic fragments of depleted peridotite type.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"31 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900812","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}
Fluid-present melting and fluid-absent melting are two primary mechanisms for the chemical differentiation of continental crust. However, it is still challenging to decode these processes with conventional geochemical methods. In this study, we present systematic Fe isotope data of anatectic migmatites and gneisses from the Dabie orogen, China, which were formed by different mechanisms of crustal anatexis. Fluid-present melting of biotite generates migmatites with restricted Fe3+/ΣFe (0.31−0.44) and homogeneous δ56Fe values (0.06‰−0.17‰). In contrast, fluid-absent melting of phengite produces migmatites and migmatitic gneisses with dramatic Fe3+/ΣFe (0.26−0.94) and δ56Fe (0.04‰−0.61‰) variations. Quantitative modeling of Fe distribution during partial melting reveals that Fe isotope fractionation is governed by source mineral assemblages under varying melting regimes. During fluid-absent melting, the reactant phengite has much higher Fe3+/ΣFe and δ56Fe values than the peritectic biotite, resulting in high and heterogeneous δ56Fe values in the complementary melt. In contrast, during fluid-present melting, the reactant biotite and peritectic amphibole have similarly low Fe3+/ΣFe and δ56Fe values, leading to low and homogeneous δ56Fe values in the complementary melt. This establishes Fe isotopes as a novel tracer for crustal anatexis, critical for understanding continental reworking and intracrustal differentiation.
{"title":"Fe isotope decoding of fluid-absent versus fluid-present melting of deeply subducted continental crust","authors":"Er-Lin Zhu, Qiong-Xia Xia, Yi-Xiang Chen, Ren-Xu Chen, Hao-Hong Shu, Zhao-Ya Li, Yong-Fei Zheng","doi":"10.1130/g52997.1","DOIUrl":"https://doi.org/10.1130/g52997.1","url":null,"abstract":"Fluid-present melting and fluid-absent melting are two primary mechanisms for the chemical differentiation of continental crust. However, it is still challenging to decode these processes with conventional geochemical methods. In this study, we present systematic Fe isotope data of anatectic migmatites and gneisses from the Dabie orogen, China, which were formed by different mechanisms of crustal anatexis. Fluid-present melting of biotite generates migmatites with restricted Fe3+/ΣFe (0.31−0.44) and homogeneous δ56Fe values (0.06‰−0.17‰). In contrast, fluid-absent melting of phengite produces migmatites and migmatitic gneisses with dramatic Fe3+/ΣFe (0.26−0.94) and δ56Fe (0.04‰−0.61‰) variations. Quantitative modeling of Fe distribution during partial melting reveals that Fe isotope fractionation is governed by source mineral assemblages under varying melting regimes. During fluid-absent melting, the reactant phengite has much higher Fe3+/ΣFe and δ56Fe values than the peritectic biotite, resulting in high and heterogeneous δ56Fe values in the complementary melt. In contrast, during fluid-present melting, the reactant biotite and peritectic amphibole have similarly low Fe3+/ΣFe and δ56Fe values, leading to low and homogeneous δ56Fe values in the complementary melt. This establishes Fe isotopes as a novel tracer for crustal anatexis, critical for understanding continental reworking and intracrustal differentiation.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"27 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900811","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}
Maija J. Raudsepp, Sasha Wilson, Benjamin M. Tutolo
The silicate−carbonate cycle controls atmospheric CO2 concentrations and moderates Earth’s climate over geologic time scales. Chemical weathering of silicate minerals by CO2 results in the release of cations and the neutralization of CO2 to HCO3− or CO32−. The precipitation of Ca- and Mg-carbonate minerals is expected once waters are supersaturated. However, quantifying the magnitude of supersaturation required, particularly for Mg-carbonates, has remained challenging. Here we present a database of 854 water samples from the Central Plateau, British Columbia, Canada, representing a wide range of salinities, including both Na−(SO4)−HCO3−CO3 and Mg−Na−SO4 hypersaline lakes, to determine the geochemical thresholds for Ca- and Mg-carbonate formation. For HCO3-dominated waters, the data indicate maximum alkalinity thresholds of ∼5 mEq/kg for Ca-carbonates and ∼40 mEq/kg for Mg-carbonates. Activity plots of Ca−CO32− and Mg−CO32− suggest that maximum saturation thresholds for both Ca-carbonates and Mg-carbonates are applicable to HCO3-dominated, SO4-dominated, and CO2-rich waters. These geochemical thresholds may be used to optimize geochemical carbon dioxide removal (geoCDR) technologies, such as enhanced rock weathering, as HCO3− has up to double the CDR efficiency of carbonate minerals.
{"title":"The fate of CO2, Ca, and Mg after terrestrial rock weathering","authors":"Maija J. Raudsepp, Sasha Wilson, Benjamin M. Tutolo","doi":"10.1130/g53354.1","DOIUrl":"https://doi.org/10.1130/g53354.1","url":null,"abstract":"The silicate−carbonate cycle controls atmospheric CO2 concentrations and moderates Earth’s climate over geologic time scales. Chemical weathering of silicate minerals by CO2 results in the release of cations and the neutralization of CO2 to HCO3− or CO32−. The precipitation of Ca- and Mg-carbonate minerals is expected once waters are supersaturated. However, quantifying the magnitude of supersaturation required, particularly for Mg-carbonates, has remained challenging. Here we present a database of 854 water samples from the Central Plateau, British Columbia, Canada, representing a wide range of salinities, including both Na−(SO4)−HCO3−CO3 and Mg−Na−SO4 hypersaline lakes, to determine the geochemical thresholds for Ca- and Mg-carbonate formation. For HCO3-dominated waters, the data indicate maximum alkalinity thresholds of ∼5 mEq/kg for Ca-carbonates and ∼40 mEq/kg for Mg-carbonates. Activity plots of Ca−CO32− and Mg−CO32− suggest that maximum saturation thresholds for both Ca-carbonates and Mg-carbonates are applicable to HCO3-dominated, SO4-dominated, and CO2-rich waters. These geochemical thresholds may be used to optimize geochemical carbon dioxide removal (geoCDR) technologies, such as enhanced rock weathering, as HCO3− has up to double the CDR efficiency of carbonate minerals.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"7 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900813","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}
Nicholas L. Swanson-Hysell, Yiming Zhang, Francis A. Macdonald, Isabel Koran, Adrian R. Tasistro-Hart, Annabel F. Jay
The closure of the Mozambique Ocean defines the final assembly of the megacontinent Gondwana and is associated with a vast region of crustal growth in the Arabian-Nubian Shield. Despite this central paleogeographic position, there are few constraints on the position of terranes within and bounding the Mozambique Ocean. We report paleomagnetic data from ca. 726 Ma dikes exposed in southern Oman. Well-resolved magnetite magnetization is constrained to be primary by a conglomerate test on mafic clasts within overlying Cryogenian diamictite. The resulting paleomagnetic pole indicates that Oman was at a paleolatitude of 37 ± 2.5°N and was rotated ∼80° counterclockwise from its present-day orientation. This position is consistent with Oman forming a contiguous plate with the India and South China cratons on the northern margin of the Mozambique Ocean in a distinct tectonic domain from Arabian-Nubian arcs to the south. This position reveals an ∼5500-km-wide oceanic realm prior to subsequent closure that resulted in a major zone of Neoproterozoic crustal growth.
{"title":"Oman was on the northern margin of a wide late Tonian Mozambique Ocean","authors":"Nicholas L. Swanson-Hysell, Yiming Zhang, Francis A. Macdonald, Isabel Koran, Adrian R. Tasistro-Hart, Annabel F. Jay","doi":"10.1130/g53450.1","DOIUrl":"https://doi.org/10.1130/g53450.1","url":null,"abstract":"The closure of the Mozambique Ocean defines the final assembly of the megacontinent Gondwana and is associated with a vast region of crustal growth in the Arabian-Nubian Shield. Despite this central paleogeographic position, there are few constraints on the position of terranes within and bounding the Mozambique Ocean. We report paleomagnetic data from ca. 726 Ma dikes exposed in southern Oman. Well-resolved magnetite magnetization is constrained to be primary by a conglomerate test on mafic clasts within overlying Cryogenian diamictite. The resulting paleomagnetic pole indicates that Oman was at a paleolatitude of 37 ± 2.5°N and was rotated ∼80° counterclockwise from its present-day orientation. This position is consistent with Oman forming a contiguous plate with the India and South China cratons on the northern margin of the Mozambique Ocean in a distinct tectonic domain from Arabian-Nubian arcs to the south. This position reveals an ∼5500-km-wide oceanic realm prior to subsequent closure that resulted in a major zone of Neoproterozoic crustal growth.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"24 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144901768","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}
James G. Saulsbury, Anna Piwoni-Piórewicz, Piotr Kukliński, Emanuela Di Martino, Lee Hsiang Liow
Under the calcite-aragonite seas hypothesis, the evolutionary history of calcifying marine organisms reflects changes in global seawater chemistry, alternately favoring precipitation of skeletons made of calcite or aragonite. Most calcifying groups including corals, coccolithophores, and stromatoporoids do not switch mineralogies in response to these changes; instead, they expand and dwindle as their favored seawater conditions come and go. Cheilostome bryozoans have been suggested as an exception to this rule, apparently transitioning between aragonite and calcite many times. These changes have never been surveyed in detail, but have important consequences for material properties, fossil preservation, and the capacity of marine organisms to adapt to environmental change. We used new large-scale phylogenetic, paleontological, and mineralogical data sets to analyze the evolution of skeletal mineralogy in cheilostomes as they diversified across the early Cenozoic calcite-aragonite seas transition. Ancestral state reconstructions and stochastic character maps indicate at least 50 independent acquisitions of partly or fully aragonitic skeletons from calcitic ancestors, with many more transitions toward the aragonitic state than away from it. Fossil faunas are dominated almost entirely by calcitic species in the Cretaceous, but bimineralic species become common by the Oligocene, and aragonitic species by the Pliocene−Pleistocene. Phylogenetic and fossil analyses reveal a coherent timeline consistent with the shift to aragonite seas. Cheilostome skeletal development may be predisposed to mineralogical flexibility, with adaptive consequences for colony construction and modularity.
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