R. Turnbull, J. Schwartz, M. Fiorentini, K. Klepeis, R. Jongens, E. Miranda, N. Evans, T. Ludwig, T. Waight, K. Faure, B. McDonald
{"title":"Mapping the 4D Lithospheric Architecture of Zealandia Using Zircon O and Hf Isotopes in Plutonic Rocks","authors":"R. Turnbull, J. Schwartz, M. Fiorentini, K. Klepeis, R. Jongens, E. Miranda, N. Evans, T. Ludwig, T. Waight, K. Faure, B. McDonald","doi":"10.46427/gold2020.2637","DOIUrl":"https://doi.org/10.46427/gold2020.2637","url":null,"abstract":"","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80358783","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Compositional Variability of San Carlos Olivine","authors":"Sarah G. Hamilton, S. Lambart","doi":"10.46427/gold2020.937","DOIUrl":"https://doi.org/10.46427/gold2020.937","url":null,"abstract":"","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89365901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
MX80 bentonite has been selected as the buffer and backfill in a proposed method of long-term deep geological storage of nuclear waste. Extensive studies have been carried out on the geomechanical properties of MX80; however, it is not clear what effect microbes will have on its ability to function as an effective barrier. Specifically, in the UK, as carbon steel waste canisters will contribute iron oxides and rust products to the immediate environment, iron-reducing bacteria are of interest. Iron-reducing bacteria can reduce structural or external Fe (III) to Fe (II) and some species are adapted to high temperatures and low water availability, in keeping with conditions within the waste repository. Indigenous iron-interacting bacteria have been identified in compacted MX80 and microbially-influenced iron-reduction was observed in groundwater salinity up to 0.45M NaCl. Experiments investigating gas production, and silica-solubilising abilities of this community were carried out. Further experiments in pressurised test cells investigated microbial activities at the clay / steel interface. Significant increases in hydrogen production were observed when microbes were present, and biogenically influenced changes in structure and appearance of MX80 were seen in all experiments. Additionally, silica release occurred, likely coupled to metal / microbe interactions. Corrosion products differed depending on microbial presence following incubation in test cells. Biogenic transformation of clay minerals through iron reduction or release of silica to groundwater could significantly impact the geomechanical properties of MX80, as indicated by observed changes in clay plasticity, and ultimately this could affect the behavior of the material as a barrier.
{"title":"Microbial Community of MX80 Bentonite and their Interaction with Iron","authors":"Katie A. Gilmour, C. Davie, N. Gray","doi":"10.46427/gold2020.833","DOIUrl":"https://doi.org/10.46427/gold2020.833","url":null,"abstract":"MX80 bentonite has been selected as the buffer and backfill in a proposed method of long-term deep geological storage of nuclear waste. Extensive studies have been carried out on the geomechanical properties of MX80; however, it is not clear what effect microbes will have on its ability to function as an effective barrier. Specifically, in the UK, as carbon steel waste canisters will contribute iron oxides and rust products to the immediate environment, iron-reducing bacteria are of interest. Iron-reducing bacteria can reduce structural or external Fe (III) to Fe (II) and some species are adapted to high temperatures and low water availability, in keeping with conditions within the waste repository. Indigenous iron-interacting bacteria have been identified in compacted MX80 and microbially-influenced iron-reduction was observed in groundwater salinity up to 0.45M NaCl. Experiments investigating gas production, and silica-solubilising abilities of this community were carried out. Further experiments in pressurised test cells investigated microbial activities at the clay / steel interface. Significant increases in hydrogen production were observed when microbes were present, and biogenically influenced changes in structure and appearance of MX80 were seen in all experiments. Additionally, silica release occurred, likely coupled to metal / microbe interactions. Corrosion products differed depending on microbial presence following incubation in test cells. Biogenic transformation of clay minerals through iron reduction or release of silica to groundwater could significantly impact the geomechanical properties of MX80, as indicated by observed changes in clay plasticity, and ultimately this could affect the behavior of the material as a barrier.","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75865156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Q. Guan, Y. Mei, B. Etschmann, M. Louvel, J. Brugger
Rare earth elements (REE) have gained importance due to their widening industrial applications and their use as geochemical tracers. REE sulfate complexes are some of the most stable REE aqueous species in hydrothermal fluids, and may be responsible for REE transport and deposition in a wide variety of geological environments, ranging from sedimentary basins to magmatic hydrothermal settings. However, the thermodynamic properties of most REE-sulfate complexes are derived from extrapolation of ambient temperature data, since direct information on REE-sulfate complexing under hydrothermal conditions is limited to a single study that derived formation constants for Nd, Sm and Er in sulfate solutions to 250 ˚C (Migdisov and William-Jones, 2008). In this study, we employ ab initio molecular dynamics (MD) simulations to calculate the speciation and thermodynamic properties of yttrium(III) in sulfate and chloride solutions at temperatures and pressures up to 500 ºC and 800 bar. The MD results were complemented by in situ X-ray absorption spectroscopy (XAS) measurements. Our results show that yttrium(III) forms complexes with sulfate with both monodentate and bidentate structures over the investigated temperature range (200 ˚C to 500 ˚C). In simulation boxes containing both chloride and sulfate, yttrium(III) bonds with less sulfate and forms mixed Y-Cl-SO 4 complexes. The thermodynamic properties for yttrium(III) sulfate complexes derived from MD enable a better modelling of REE transport in hydrothermal systems.
{"title":"Yttrium Speciation in Sulfate-Rich Hydrothermal Ore-Forming Fluids","authors":"Q. Guan, Y. Mei, B. Etschmann, M. Louvel, J. Brugger","doi":"10.46427/gold2020.894","DOIUrl":"https://doi.org/10.46427/gold2020.894","url":null,"abstract":"Rare earth elements (REE) have gained importance due to their widening industrial applications and their use as geochemical tracers. REE sulfate complexes are some of the most stable REE aqueous species in hydrothermal fluids, and may be responsible for REE transport and deposition in a wide variety of geological environments, ranging from sedimentary basins to magmatic hydrothermal settings. However, the thermodynamic properties of most REE-sulfate complexes are derived from extrapolation of ambient temperature data, since direct information on REE-sulfate complexing under hydrothermal conditions is limited to a single study that derived formation constants for Nd, Sm and Er in sulfate solutions to 250 ˚C (Migdisov and William-Jones, 2008). In this study, we employ ab initio molecular dynamics (MD) simulations to calculate the speciation and thermodynamic properties of yttrium(III) in sulfate and chloride solutions at temperatures and pressures up to 500 ºC and 800 bar. The MD results were complemented by in situ X-ray absorption spectroscopy (XAS) measurements. Our results show that yttrium(III) forms complexes with sulfate with both monodentate and bidentate structures over the investigated temperature range (200 ˚C to 500 ˚C). In simulation boxes containing both chloride and sulfate, yttrium(III) bonds with less sulfate and forms mixed Y-Cl-SO 4 complexes. The thermodynamic properties for yttrium(III) sulfate complexes derived from MD enable a better modelling of REE transport in hydrothermal systems.","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"2015 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86254123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiangdong Wang, Peter A. Cawood, Laishi Zhao, Zhong‐Qiang Chen, Lei Zhang, Zhengyi Lyu, F. Ye
Abstract The biotic recovery following the end Permian mass extinction (EPME) was unstable with repeated environmental crises, each of which was followed by a comparably more hospitable interval for life. The early Triassic Smithian-Spathian boundary (SSB) event represents a conspicuous turnover in the environment, climate, and biotic communities. To explore the causes and consequences of this event we measured zinc and carbon isotopes along with elemental paleoenvironment proxies through the West Pingdingshan section, Chaohu, South China. An abrupt decrease of δ66Zn values, along with the highly negative δ13C values occur in the latest Smithian in Beds 47–50 of the section, are coincident with the bio-crisis, and are ascribed to weak marine productivity and extremely hot climatic conditions. Rapid positive shifts in δ13Corg and δ13Ccarb values and high contents of TOC in Beds 51–52, demonstrate elevated marine productivity associated with a surface seawater cooling event, but also resulted in oxygen-starved conditions lethal to organisms. Marine and terrestrial ecosystems recovered in the early Spathian in Beds 53–57, as evidenced by high values of δ66Zn, δ13C and the absence of framboid pyrite, and low Al content. These characteristics indicate a return to normal marine productivity and oxygenated seawater, and decreased terrestrial sediment input. Our findings propose that marine productivity played an important role in affecting the marine Zn cycling across the SSB and provide a scenario of environmental perturbations in response to temperature changes during the SSB transition.
{"title":"Marine Productivity Variations and Environmental Perturbations Across the Early Triassic Smithian-Spathian Boundary: Insights from Zinc and Carbon Isotopes","authors":"Xiangdong Wang, Peter A. Cawood, Laishi Zhao, Zhong‐Qiang Chen, Lei Zhang, Zhengyi Lyu, F. Ye","doi":"10.46427/gold2020.2777","DOIUrl":"https://doi.org/10.46427/gold2020.2777","url":null,"abstract":"Abstract The biotic recovery following the end Permian mass extinction (EPME) was unstable with repeated environmental crises, each of which was followed by a comparably more hospitable interval for life. The early Triassic Smithian-Spathian boundary (SSB) event represents a conspicuous turnover in the environment, climate, and biotic communities. To explore the causes and consequences of this event we measured zinc and carbon isotopes along with elemental paleoenvironment proxies through the West Pingdingshan section, Chaohu, South China. An abrupt decrease of δ66Zn values, along with the highly negative δ13C values occur in the latest Smithian in Beds 47–50 of the section, are coincident with the bio-crisis, and are ascribed to weak marine productivity and extremely hot climatic conditions. Rapid positive shifts in δ13Corg and δ13Ccarb values and high contents of TOC in Beds 51–52, demonstrate elevated marine productivity associated with a surface seawater cooling event, but also resulted in oxygen-starved conditions lethal to organisms. Marine and terrestrial ecosystems recovered in the early Spathian in Beds 53–57, as evidenced by high values of δ66Zn, δ13C and the absence of framboid pyrite, and low Al content. These characteristics indicate a return to normal marine productivity and oxygenated seawater, and decreased terrestrial sediment input. Our findings propose that marine productivity played an important role in affecting the marine Zn cycling across the SSB and provide a scenario of environmental perturbations in response to temperature changes during the SSB transition.","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"108 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75860887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jinshu Yan, N. Sharma, Elaine D. Flynn, D. Giammar, G. Schwartz, Scott Brook, P. Weisenhorn, K. Kemner, E. O’Loughlin, D. Kaplan, J. Catalano
Trace metal are essential for microbially-mediated biogeochemical processes occurring in anoxic wetland soils and stream bed sediments, but low availability of these elements may inhibit anaerobic element cycling and transformations. Solid-phase speciation is likely a critical control on trace metal availability but has seen limited study in anoxic systems having concentrations similar to geological background levels, where metal limitations may be most prevalent. We have investigated trace metal concentrations and solid-phase speciation in three freshwater subsurface aquatic systems: marsh wetland soils, riparian wetland soils, and the sediments of a streambed. These systems displayed low solid-phase trace metal concentrations, generally at or below geological background levels, which generally followed the trend Zn > Cu ≈ Ni > Co and showed no correlation with major element compositions. All soils and sediments were dominated by quartz but varied in clay mineralogy as well as the organic matter, total sulfur, and total iron contents. X-ray absorption near-edge structure (XANES) spectroscopy shows that sulfur speciation in both wetlands is dominated by organic sulfur. Elemental sulfur and iron sulfides together made up <25% of the sulfur in the wetland soils, but the distribution between inorganic and organic forms was reversed in the stream sediments. Ferrous and ferric iron in clay minerals were common species identified by both XANES and extended X-ray absorption fine structure (EXAFS) spectroscopies at all sites. Iron(III) oxides were substantial components in all but the marsh wetland soils. Quantitative analysis of copper, nickel, and zinc XANES spectra revealed similar metal speciation across all sites. Copper speciation was dominated by sulfides, adsorbed species, and minor amounts of copper bound to organic matter; no metallic copper was detected. Nickel speciation also varied little and was dominated by nickel in clay mineral octahedral sheets and nickel sulfide, with adsorbed species also present. Zinc speciation was slightly more varied, with the marsh wetland soils and stream bed sediments containing adsorbed species, zinc associated with clay mineral structures, and zinc bound to reduced sulfur groups on organic matter, whereas the riparian wetland soils lacked clay-associated zinc but contained zinc sulfide. Trace metals bound to reduced sulfur occurred at every site, with a greater sulfur-bound fraction for copper. The fractional abundance of sulfur-bound species showed no relationship with soil or sediment total sulfur content, which varied by two orders of magnitude. More broadly, the observations in this study suggest that trace metal speciation in freshwater wetland soils and stream sediments is consistently dominated by a small set of recurring components which are distinct for each metal. This may represent a general geochemical phenomenon in anoxic soils and sediments containing trace metals at background concentrations (a
{"title":"Consistent Controls on Trace Metal Micronutrient Speciation in Wetland Soils and Stream Sediments","authors":"Jinshu Yan, N. Sharma, Elaine D. Flynn, D. Giammar, G. Schwartz, Scott Brook, P. Weisenhorn, K. Kemner, E. O’Loughlin, D. Kaplan, J. Catalano","doi":"10.46427/gold2020.337","DOIUrl":"https://doi.org/10.46427/gold2020.337","url":null,"abstract":"Trace metal are essential for microbially-mediated biogeochemical processes occurring in anoxic wetland soils and stream bed sediments, but low availability of these elements may inhibit anaerobic element cycling and transformations. Solid-phase speciation is likely a critical control on trace metal availability but has seen limited study in anoxic systems having concentrations similar to geological background levels, where metal limitations may be most prevalent. We have investigated trace metal concentrations and solid-phase speciation in three freshwater subsurface aquatic systems: marsh wetland soils, riparian wetland soils, and the sediments of a streambed. These systems displayed low solid-phase trace metal concentrations, generally at or below geological background levels, which generally followed the trend Zn > Cu ≈ Ni > Co and showed no correlation with major element compositions. All soils and sediments were dominated by quartz but varied in clay mineralogy as well as the organic matter, total sulfur, and total iron contents. X-ray absorption near-edge structure (XANES) spectroscopy shows that sulfur speciation in both wetlands is dominated by organic sulfur. Elemental sulfur and iron sulfides together made up <25% of the sulfur in the wetland soils, but the distribution between inorganic and organic forms was reversed in the stream sediments. Ferrous and ferric iron in clay minerals were common species identified by both XANES and extended X-ray absorption fine structure (EXAFS) spectroscopies at all sites. Iron(III) oxides were substantial components in all but the marsh wetland soils. Quantitative analysis of copper, nickel, and zinc XANES spectra revealed similar metal speciation across all sites. Copper speciation was dominated by sulfides, adsorbed species, and minor amounts of copper bound to organic matter; no metallic copper was detected. Nickel speciation also varied little and was dominated by nickel in clay mineral octahedral sheets and nickel sulfide, with adsorbed species also present. Zinc speciation was slightly more varied, with the marsh wetland soils and stream bed sediments containing adsorbed species, zinc associated with clay mineral structures, and zinc bound to reduced sulfur groups on organic matter, whereas the riparian wetland soils lacked clay-associated zinc but contained zinc sulfide. Trace metals bound to reduced sulfur occurred at every site, with a greater sulfur-bound fraction for copper. The fractional abundance of sulfur-bound species showed no relationship with soil or sediment total sulfur content, which varied by two orders of magnitude. More broadly, the observations in this study suggest that trace metal speciation in freshwater wetland soils and stream sediments is consistently dominated by a small set of recurring components which are distinct for each metal. This may represent a general geochemical phenomenon in anoxic soils and sediments containing trace metals at background concentrations (a","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80844500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Guo, W. Mao, Ru Y. Zhang, J. Liou, W. Ernst, Jingsui Yang, Xiao-dong Liu, Xiangzhen Xu, Yong Zhang, Bin Wu
Abstract The Zedang ophiolite, containing pods of massive chromitite, crops out in the eastern segment of the Yarlung-Zangbo suture zone, Southern Tibet. Chromite grains in the Zedang chromitite bodies have high Cr# [Cr/(Cr + Al)] (0.73–0.82) and Mg# [Mg/(Mg + Fe)] (0.73–0.79), and low TiO2 content (0.13–0.25 wt%); they contain diopside (Di) exsolution lamellae and abundant inclusions of diopside, enstatite, hydrous silicates (e.q., Cr-bearing amphibole), and serpentine. The inclusions occur as isolated single-phase or multiphase (clinopyroxene + amphibole ± platinum group mineral) grains. Diopside lamellae-bearing chromite was probably a precursor CaFe2O4-phase (CF phase) forming at >12.5 GPa. Individual octahedral serpentine inclusions are likely pseudomorphs after isometric ringwoodite. Both the CF phase and ringwoodite crystallized within the mantle transition zone (MTZ). Equilibrium pressure-temperature (P-T) conditions of coexisting clinopyroxene-orthopyroxene (Cpx-Opx) inclusions are 8.5–21.5 ± 1.5 kbar, and 996–1097 ± 30 °C. These P-T conditions suggest that the inferred parental melts of the Zedang chromitites were boninitic. The boninitic liquid in turn was generated from depleted, metasomatized mantle in a supra-subduction zone (SSZ) environment. Linear alignment of hydrous silicate inclusions in chromitites imply fluid infiltration along fracture zones at shallow depths during consolidation of the ophiolite. Based on our new data, we propose a new three-stage model to explain the formation and evolution of the Zedang chromitites. It experienced a long journey from (i) the MTZ forming high-P chromite (containing ultrahigh-pressure minerals), (ii) to the upper mantle attending to the formation of the major part of the chromite, whereas it's host chromitites formed at melt-rock reaction process, and (iii) where high-P chromite was incorporated in low-P neoblastic chromite during subducting slab rollback-induced channel return flow to shallow depths (involving fluid input and alteration).
{"title":"Characteristics and Implications of Podiform-Chromite Hosted Silicate Inclusions in the Zedang Ophiolite, Southern Tibet","authors":"G. Guo, W. Mao, Ru Y. Zhang, J. Liou, W. Ernst, Jingsui Yang, Xiao-dong Liu, Xiangzhen Xu, Yong Zhang, Bin Wu","doi":"10.46427/gold2020.904","DOIUrl":"https://doi.org/10.46427/gold2020.904","url":null,"abstract":"Abstract The Zedang ophiolite, containing pods of massive chromitite, crops out in the eastern segment of the Yarlung-Zangbo suture zone, Southern Tibet. Chromite grains in the Zedang chromitite bodies have high Cr# [Cr/(Cr + Al)] (0.73–0.82) and Mg# [Mg/(Mg + Fe)] (0.73–0.79), and low TiO2 content (0.13–0.25 wt%); they contain diopside (Di) exsolution lamellae and abundant inclusions of diopside, enstatite, hydrous silicates (e.q., Cr-bearing amphibole), and serpentine. The inclusions occur as isolated single-phase or multiphase (clinopyroxene + amphibole ± platinum group mineral) grains. Diopside lamellae-bearing chromite was probably a precursor CaFe2O4-phase (CF phase) forming at >12.5 GPa. Individual octahedral serpentine inclusions are likely pseudomorphs after isometric ringwoodite. Both the CF phase and ringwoodite crystallized within the mantle transition zone (MTZ). Equilibrium pressure-temperature (P-T) conditions of coexisting clinopyroxene-orthopyroxene (Cpx-Opx) inclusions are 8.5–21.5 ± 1.5 kbar, and 996–1097 ± 30 °C. These P-T conditions suggest that the inferred parental melts of the Zedang chromitites were boninitic. The boninitic liquid in turn was generated from depleted, metasomatized mantle in a supra-subduction zone (SSZ) environment. Linear alignment of hydrous silicate inclusions in chromitites imply fluid infiltration along fracture zones at shallow depths during consolidation of the ophiolite. Based on our new data, we propose a new three-stage model to explain the formation and evolution of the Zedang chromitites. It experienced a long journey from (i) the MTZ forming high-P chromite (containing ultrahigh-pressure minerals), (ii) to the upper mantle attending to the formation of the major part of the chromite, whereas it's host chromitites formed at melt-rock reaction process, and (iii) where high-P chromite was incorporated in low-P neoblastic chromite during subducting slab rollback-induced channel return flow to shallow depths (involving fluid input and alteration).","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"60 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88999694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Haiyang Liu, Ying-Yu Xue, Guoliang Zhang, Weidongsun Sun, Z. Tian, Brenna Tuller-Ross, Kun Wang
Abstract To constrain the behavior of K isotopes during the low-temperature alteration of oceanic crust and reveal its impact on the global K cycle, we measured the K isotopic compositions of 49 fresh and altered basalts recovered from the Integrated Ocean Drilling Program (IODP) Sites U1365 (∼100 Ma) and U1368 (∼13.5 Ma) in the South Pacific Ocean. The measured basalts representing the uppermost oceanic crust have been subjected to low-temperature (
{"title":"Potassium Isotopic Composition of Low-Temperature Altered Oceanic Crust and its Impact on the Global K Cycle","authors":"Haiyang Liu, Ying-Yu Xue, Guoliang Zhang, Weidongsun Sun, Z. Tian, Brenna Tuller-Ross, Kun Wang","doi":"10.46427/gold2020.1585","DOIUrl":"https://doi.org/10.46427/gold2020.1585","url":null,"abstract":"Abstract To constrain the behavior of K isotopes during the low-temperature alteration of oceanic crust and reveal its impact on the global K cycle, we measured the K isotopic compositions of 49 fresh and altered basalts recovered from the Integrated Ocean Drilling Program (IODP) Sites U1365 (∼100 Ma) and U1368 (∼13.5 Ma) in the South Pacific Ocean. The measured basalts representing the uppermost oceanic crust have been subjected to low-temperature (","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"116 1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84222773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Eruption onset, style and duration are governed, in part, by the movement and interaction of distinct magma bodies at depth. High-resolution investigation of erupted products can retrospectively inform our understanding of such processes and improve future interpretation of real-time monitoring signals. In 2002-03, Mount Etna (Italy) erupted two elementally and isotopically distinct magmas simultaneously, providing a unique opportunity to explore magma transport and evolution through complex, well-documented and monitored volcanic activity. In this study, melt chemistry (groundmass fraction as opposed to whole-rock) and mineral zoning (X-ray fluorescence mapping and electron microprobe) are treated as separate recorders of magma history tracking syn- and pre-eruptive processes, respectively. Elemental mapping of entire thin sections revealed a largely antecrystic, hybrid crystal cargo hosting reverse-zoned clinopyroxene and olivine, supporting extensive magma mixing in southern flank conduits. Antecryst-free groundmass chemo-stratigraphies reveal melt compositional variations on timescales of days to weeks. In agreement with previous whole-rock studies, we find that during the early-middle stages of activity, melt erupted on the southern flank was rich in MgO, CaO, Cr, Ni, and radiogenic-Sr, and depleted in Al2O3, Na2O, La, Zr, relative to its north-eastern counterpart. In addition, high resolution tracking of melt composition reveals a progressive shift to increasingly evolved compositions over the course of the S-rift eruption. A corresponding shift in 87Sr/86Sr isotope ratios (0.70366 to 0.70358) across the same period implies progressive mixing of isotopically distinct magmas as the main driver of the observed compositional change. In contrast, NE-rift products lack evidence of mixing in both melt and mineral records, in agreement with previous work suggesting geodynamically controlled draining of shallow, isolated magma pockets. Comparing recharge-to-eruption timescales derived from mineral zonation with real-time monitoring data and groundmass compositional data, we show that the onset of magma mixing in the S-rift coincided with a deep seismic event (8-18 km) and was followed by the ascent of undegassed magma approximately 2 months before eruption onset. Finally, we demonstrate that high-resolution temporal changes in melt composition, approached through melt geochemistry, are closely linked to eruption intensity and SO2 emission. We suggest that composition and explosivity on the southern rift fluctuated in response to multiple phases of recharge-mixing-hybridisation between undegassed ‘eccentric’ magma and a degassed resident magma at 3-5 km depth. Our results highlight that high-resolution geochemistry can improve our understanding of deep magmatic processes driving eruption onset, duration and intensity. Rapid analysis of melt composition integrated with traditional monitoring approaches could improve future hazard response at
{"title":"Days to Weeks of Syn-Eruptive Magma Interaction: High-Resolution Geochemistry of the 2002-03 Branched Eruption at Mount Etna","authors":"Ruadhan Magee, T. Ubide, J. Caulfield","doi":"10.46427/gold2020.1698","DOIUrl":"https://doi.org/10.46427/gold2020.1698","url":null,"abstract":"Abstract Eruption onset, style and duration are governed, in part, by the movement and interaction of distinct magma bodies at depth. High-resolution investigation of erupted products can retrospectively inform our understanding of such processes and improve future interpretation of real-time monitoring signals. In 2002-03, Mount Etna (Italy) erupted two elementally and isotopically distinct magmas simultaneously, providing a unique opportunity to explore magma transport and evolution through complex, well-documented and monitored volcanic activity. In this study, melt chemistry (groundmass fraction as opposed to whole-rock) and mineral zoning (X-ray fluorescence mapping and electron microprobe) are treated as separate recorders of magma history tracking syn- and pre-eruptive processes, respectively. Elemental mapping of entire thin sections revealed a largely antecrystic, hybrid crystal cargo hosting reverse-zoned clinopyroxene and olivine, supporting extensive magma mixing in southern flank conduits. Antecryst-free groundmass chemo-stratigraphies reveal melt compositional variations on timescales of days to weeks. In agreement with previous whole-rock studies, we find that during the early-middle stages of activity, melt erupted on the southern flank was rich in MgO, CaO, Cr, Ni, and radiogenic-Sr, and depleted in Al2O3, Na2O, La, Zr, relative to its north-eastern counterpart. In addition, high resolution tracking of melt composition reveals a progressive shift to increasingly evolved compositions over the course of the S-rift eruption. A corresponding shift in 87Sr/86Sr isotope ratios (0.70366 to 0.70358) across the same period implies progressive mixing of isotopically distinct magmas as the main driver of the observed compositional change. In contrast, NE-rift products lack evidence of mixing in both melt and mineral records, in agreement with previous work suggesting geodynamically controlled draining of shallow, isolated magma pockets. Comparing recharge-to-eruption timescales derived from mineral zonation with real-time monitoring data and groundmass compositional data, we show that the onset of magma mixing in the S-rift coincided with a deep seismic event (8-18 km) and was followed by the ascent of undegassed magma approximately 2 months before eruption onset. Finally, we demonstrate that high-resolution temporal changes in melt composition, approached through melt geochemistry, are closely linked to eruption intensity and SO2 emission. We suggest that composition and explosivity on the southern rift fluctuated in response to multiple phases of recharge-mixing-hybridisation between undegassed ‘eccentric’ magma and a degassed resident magma at 3-5 km depth. Our results highlight that high-resolution geochemistry can improve our understanding of deep magmatic processes driving eruption onset, duration and intensity. Rapid analysis of melt composition integrated with traditional monitoring approaches could improve future hazard response at","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87098371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sediment pore waters in the depositional areas of the Baltic Sea are enriched with the dissolved organic carbon (DOC), which results in a diffusive flux of DOC to the water column. It was found that up to 30% of OM deposited in the sediments returns to the water column and may alter processes occurring there e.g. increase the oxygen demand in the bottom waters. Still little is known about the bioavailability of sediment-derived DOC and its remineralization dynamics. Thus, the aim of this study was to assess the bioavailability, degradation rate constant and half-life time of sediment-derived DOC.
Bottom water and pore water, collected during r/v Oceania cruise in March 2018 in the Gdańsk Deep, have been mixed in a volume ratio of 4:1. To ensure oxic conditions in the experiment, the mixture was bubbled with the ambient air to reach 100% O2 saturation. Incubation of such prepared samples was conducted in 23±0.1°C for 126 days. At the beginning (t=0) and after 1, 2, 6, 18, 35, 73 and 126 days of the incubation the individual samples were analyzed for total dissolved organic carbon DOC. In parallel, untreated bottom water was incubated as a control, while the obtained results have been used to decouple the remineralization dynamics in the mixture.
The DOC decay had an exponential character. The highest dynamics of DOC remineralization was at the beginning of the experiment and it gradually decreased over time. During the incubation period pore water DOC concentration decreased from 1408 to 850 µmol l-1, which corresponds to almost 40% loss. In the control samples (bottom water) DOC concentration decreased from 304 to 260 µmol l-1 i.e. by ~14%.
In the experiment three different DOC fractions have been identified: labile DOC (DOCL), semi-labile DOC (DOCSL) and refractory DOC (DOCR). To quantify the DOC remineralization rate constants (k) and half-life times (t1/2) the first order kinetics was used. The total bioavailable fraction of pore water DOC (DOCL+DOCSL) amounted to 54%, while k and t1/2 were 0.0958 d-1 and 7.24 d for DOCL and 0.0082 d-1 and 84.53 d for DOCSL, respectively.
This study shows that about half of sediment-derived DOC is bioavailable, which gives a new insight on the Baltic Sea carbon cycle and O2 consumption in deeper water layers.
{"title":"Bioavailability and remineralization of sediment-derived dissolved organic carbon from the Baltic Sea depositional area","authors":"Monika Lengier, B. Szymczycha, K. Kuliński","doi":"10.46427/gold2020.1458","DOIUrl":"https://doi.org/10.46427/gold2020.1458","url":null,"abstract":"<p>Sediment pore waters in the depositional areas of the Baltic Sea are enriched with the dissolved organic carbon (DOC), which results in a diffusive flux of DOC to the water column. It was found that up to 30% of OM deposited in the sediments returns to the water column and may alter processes occurring there e.g. increase the oxygen demand in the bottom waters. Still little is known about the bioavailability of sediment-derived DOC and its remineralization dynamics. Thus, the aim of this study was to assess the bioavailability, degradation rate constant and half-life time of sediment-derived DOC.</p><p>Bottom water and pore water, collected during r/v Oceania cruise in March 2018 in the Gdańsk Deep, have been mixed in a volume ratio of 4:1. To ensure oxic conditions in the experiment, the mixture was bubbled with the ambient air to reach 100% O<sub>2</sub> saturation. Incubation of such prepared samples was conducted in 23±0.1°C for 126 days. At the beginning (t=0) and after 1, 2, 6, 18, 35, 73 and 126 days of the incubation the individual samples were analyzed for total dissolved organic carbon DOC. In parallel, untreated bottom water was incubated as a control, while the obtained results have been used to decouple the remineralization dynamics in the mixture.</p><p>The DOC decay had an exponential character. The highest dynamics of DOC remineralization was at the beginning of the experiment and it gradually decreased over time. During the incubation period pore water DOC concentration decreased from 1408 to 850 µmol l-<sup>1</sup><sub>,</sub> which corresponds to almost 40% loss. In the control samples (bottom water) DOC concentration decreased from 304 to 260 µmol l<sup>-1</sup> i.e. by ~14%.</p><p>In the experiment three different DOC fractions have been identified: labile DOC (DOC<sub>L</sub>), semi-labile DOC (DOC<sub>SL</sub>) and refractory DOC (DOC<sub>R</sub>). To quantify the DOC remineralization rate constants (k) and half-life times (t<sub>1/2</sub>) the first order kinetics was used. The total bioavailable fraction of pore water DOC (DOC<sub>L</sub>+DOC<sub>SL</sub>) amounted to 54%, while k and t<sub>1/2</sub> were 0.0958 d<sup>-1</sup> and 7.24 d for DOC<sub>L</sub> and 0.0082 d<sup>-1</sup> and 84.53 d for DOC<sub>SL</sub>, respectively.</p><p>This study shows that about half of sediment-derived DOC is bioavailable, which gives a new insight on the Baltic Sea carbon cycle and O­<sub>2</sub> consumption in deeper water layers.</p>","PeriodicalId":12817,"journal":{"name":"Goldschmidt Abstracts","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75542582","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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