A. Pham, Pierre Damien, Daniel McCoy, Matthew Mar, F. Kessouri, James C. McWilliams, James Moffett, Daniele Bianchi
Release of iron (Fe) from continental shelves is a major source of this limiting nutrient for phytoplankton in the open ocean, including productive Eastern Boundary Upwelling Systems. The mechanisms governing the transport and fate of Fe along continental margins remain poorly understood, reflecting interaction of physical and biogeochemical processes that are crudely represented by global ocean biogeochemical models. Here, we use a submesoscale‐permitting physical‐biogeochemical model to investigate processes governing the delivery of shelf‐derived Fe to the open ocean along the northern U.S. West Coast. We find that a significant fraction (∼20%) of the Fe released by sediments on the shelf is transported offshore, fertilizing the broader Northeast Pacific Ocean. This transport is governed by two main pathways that reflect interaction between the wind‐driven ocean circulation and Fe release by low‐oxygen sediments: the first in the surface boundary layer during upwelling events; the second in the bottom boundary layer, associated with pervasive interactions of the poleward California Undercurrent with bottom topography. In the water column interior, transient and standing eddies strengthen offshore transport, counteracting the onshore pull of the mean upwelling circulation. Several hot‐spots of intense Fe delivery to the open ocean are maintained by standing meanders in the mean current and enhanced by transient eddies and seasonal oxygen depletion. Our results highlight the importance of fine‐scale dynamics for the transport of Fe and shelf‐derived elements from continental margins to the open ocean, and the need to improve representation of these processes in biogeochemical models used for climate studies.
{"title":"The shelf-to-basin transport of iron from the Northern U.S West Coast to the Pacific Ocean","authors":"A. Pham, Pierre Damien, Daniel McCoy, Matthew Mar, F. Kessouri, James C. McWilliams, James Moffett, Daniele Bianchi","doi":"10.7185/gold2023.17142","DOIUrl":"https://doi.org/10.7185/gold2023.17142","url":null,"abstract":"Release of iron (Fe) from continental shelves is a major source of this limiting nutrient for phytoplankton in the open ocean, including productive Eastern Boundary Upwelling Systems. The mechanisms governing the transport and fate of Fe along continental margins remain poorly understood, reflecting interaction of physical and biogeochemical processes that are crudely represented by global ocean biogeochemical models. Here, we use a submesoscale‐permitting physical‐biogeochemical model to investigate processes governing the delivery of shelf‐derived Fe to the open ocean along the northern U.S. West Coast. We find that a significant fraction (∼20%) of the Fe released by sediments on the shelf is transported offshore, fertilizing the broader Northeast Pacific Ocean. This transport is governed by two main pathways that reflect interaction between the wind‐driven ocean circulation and Fe release by low‐oxygen sediments: the first in the surface boundary layer during upwelling events; the second in the bottom boundary layer, associated with pervasive interactions of the poleward California Undercurrent with bottom topography. In the water column interior, transient and standing eddies strengthen offshore transport, counteracting the onshore pull of the mean upwelling circulation. Several hot‐spots of intense Fe delivery to the open ocean are maintained by standing meanders in the mean current and enhanced by transient eddies and seasonal oxygen depletion. Our results highlight the importance of fine‐scale dynamics for the transport of Fe and shelf‐derived elements from continental margins to the open ocean, and the need to improve representation of these processes in biogeochemical models used for climate studies.","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141033687","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}
Xuanyu Liu, Ming Tang, Wenrong Cao, Wei-Qiang Ji, Hao Chen
With the most prominent topography on Earth, the Tibetan Plateau has profound influences on the hydrologic cycle and climate dynamics in Asia. However, the regional uplift history of the Tibetan Plateau remains highly uncertain. Here, we use Eu anomaly in detrital zircon from modern rivers to constrain the crustal thickness evolution along the Gangdese mountain belt in southern Tibet. Our results reveal contrasting crustal thickening histories of the eastern (east of 88°E) and western (west of 88°E) parts of the Gangdese. In the Late Cretaceous, prior to the India-Eurasia collision (~60-55 Ma), the crust of the eastern Gangdese thickened continuously from ~40 km to nearly 60 km, while the western Gangdese maintained a mildly thickened crust of ~50 km. Although both the eastern and western Gangdese underwent substantial crustal thinning (to 40-45 km) immediately before the India-Eurasia collision, the eastern Gangdese rethickened rapidly after the continental collision, whereas in the western Gangdese, post-collisional thickening was delayed until 20 Myr later. On the other hand, the LREE/HREE ratio of detrital zircon and the whole-rock La/Yb ratio over time show similar trends to that of our Eu/Eu* in zircon, supporting our results to a first order. We propose the contrasting post-collisional thickening patterns may reflect the distinct nature between the western and eastern Gangdese lithosphere prior to the India-Eurasia collision. The delayed thickening of the vast western Gangdese may have resulted in a mild elevation of < 2 km for most areas of southern Tibet until the late Oligocene
青藏高原是地球上地形最突出的地区，对亚洲的水文循环和气候动态有着深远的影响。然而，青藏高原的区域隆升史仍极不确定。在这里，我们利用现代河流出产的锆英石中的Eu异常来制约西藏南部冈底斯山地带的地壳厚度演化。我们的研究结果揭示了冈底斯山脉东部（88°E以东）和西部（88°E以西）截然不同的地壳增厚历史。在晚白垩世，即印度-欧亚大陆碰撞之前（约 60-55 Ma），冈底斯东部地壳持续增厚，从约 40 km 增厚到近 60 km，而冈底斯西部地壳保持了约 50 km 的轻度增厚。尽管在印度-欧亚大陆碰撞之前，冈底斯东部和西部的地壳都发生了大幅度的减薄（减薄到40-45千米），但在大陆碰撞之后，冈底斯东部的地壳迅速增厚，而冈底斯西部的地壳增厚则推迟到20兆年之后。另一方面，碎屑锆石的LREE/HREE比值和全岩的La/Yb比值随时间变化的趋势与锆石的Eu/Eu*比值的趋势相似，这在一阶上支持了我们的结果。我们认为，碰撞后不同的增厚模式可能反映了印度-欧亚大陆碰撞之前冈底斯西部和东部岩石圈的不同性质。广阔的冈底斯西部的延迟增厚可能导致西藏南部大部分地区直到渐新世晚期才出现小于2千米的温和抬升。
{"title":"Sluggish Rise of the Western Gangdese Mountains after India-Eurasia Collision","authors":"Xuanyu Liu, Ming Tang, Wenrong Cao, Wei-Qiang Ji, Hao Chen","doi":"10.7185/gold2023.15730","DOIUrl":"https://doi.org/10.7185/gold2023.15730","url":null,"abstract":"With the most prominent topography on Earth, the Tibetan Plateau has profound influences on the hydrologic cycle and climate dynamics in Asia. However, the regional uplift history of the Tibetan Plateau remains highly uncertain. Here, we use Eu anomaly in detrital zircon from modern rivers to constrain the crustal thickness evolution along the Gangdese mountain belt in southern Tibet. Our results reveal contrasting crustal thickening histories of the eastern (east of 88°E) and western (west of 88°E) parts of the Gangdese. In the Late Cretaceous, prior to the India-Eurasia collision (~60-55 Ma), the crust of the eastern Gangdese thickened continuously from ~40 km to nearly 60 km, while the western Gangdese maintained a mildly thickened crust of ~50 km. Although both the eastern and western Gangdese underwent substantial crustal thinning (to 40-45 km) immediately before the India-Eurasia collision, the eastern Gangdese rethickened rapidly after the continental collision, whereas in the western Gangdese, post-collisional thickening was delayed until 20 Myr later. On the other hand, the LREE/HREE ratio of detrital zircon and the whole-rock La/Yb ratio over time show similar trends to that of our Eu/Eu* in zircon, supporting our results to a first order. We propose the contrasting post-collisional thickening patterns may reflect the distinct nature between the western and eastern Gangdese lithosphere prior to the India-Eurasia collision. The delayed thickening of the vast western Gangdese may have resulted in a mild elevation of < 2 km for most areas of southern Tibet until the late Oligocene","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141042410","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}
Tahar Hammouda, Paul Frossard, Maud Boyet, Audrey Bouvier, Matthew Newville, A. Lanzirotti
Rare-earth elements (REE, restricted here to the lanthanides) usually form 3+ cations in terrestrial rocks, although Eu 2+ and Ce 4+ are often found. In enstatite chondrite (EC), elemental anomalies in Eu and Yb have been reported in calcium sulfide (oldhamite) [1-3] and in leaching experiments on whole rocks [4]. The presence of Yb 2+ in sulfides synthesized experimentally in highly reduced conditions corresponding to those of EC formation has been identified by X-ray absorption near-edge spectroscopy (XANES) [5]. In order to gain further insight on the redox formation conditions of Solar System objects, we have determined the valence state of Yb in a collection of meteorites covering 4 to 5 orders of magnitude in oxygen fugacity (fO 2 ) by XANES at sector 13 of the Advanced Photon Source. In the studied meteorite minerals, Yb abundance ranges from 1 to 30 ppm. The data were collected on merrillite grains from two equilibrated ordinary chondrites (H6 and LL6), oldhamite grains from three EH (EH3 to EH5) and four EL (EL3 to EL6) EC, one merrilite grain and one stanfieldite grain in a pallasite (Seymchan), on merrillite grains from a eucrite, and phosphates of an ungrouped primitive achondrite (NWA 11119). The obtained Yb XANES spectra were compared to those measured in terrestrial apatites
{"title":"Mapping the redox state of the young Solar System using ytterbium valence state","authors":"Tahar Hammouda, Paul Frossard, Maud Boyet, Audrey Bouvier, Matthew Newville, A. Lanzirotti","doi":"10.7185/gold2023.16477","DOIUrl":"https://doi.org/10.7185/gold2023.16477","url":null,"abstract":"Rare-earth elements (REE, restricted here to the lanthanides) usually form 3+ cations in terrestrial rocks, although Eu 2+ and Ce 4+ are often found. In enstatite chondrite (EC), elemental anomalies in Eu and Yb have been reported in calcium sulfide (oldhamite) [1-3] and in leaching experiments on whole rocks [4]. The presence of Yb 2+ in sulfides synthesized experimentally in highly reduced conditions corresponding to those of EC formation has been identified by X-ray absorption near-edge spectroscopy (XANES) [5]. In order to gain further insight on the redox formation conditions of Solar System objects, we have determined the valence state of Yb in a collection of meteorites covering 4 to 5 orders of magnitude in oxygen fugacity (fO 2 ) by XANES at sector 13 of the Advanced Photon Source. In the studied meteorite minerals, Yb abundance ranges from 1 to 30 ppm. The data were collected on merrillite grains from two equilibrated ordinary chondrites (H6 and LL6), oldhamite grains from three EH (EH3 to EH5) and four EL (EL3 to EL6) EC, one merrilite grain and one stanfieldite grain in a pallasite (Seymchan), on merrillite grains from a eucrite, and phosphates of an ungrouped primitive achondrite (NWA 11119). The obtained Yb XANES spectra were compared to those measured in terrestrial apatites","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141039868","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}
Jean Mura, M. Ranchou-Peyruse, Marion Guignard, Perla G Haddad, M. Ducousso, Franck Casteran, Pascale Sénéchal, M. Larregieu, M. Isaure, Peter Moonen, I. Le Hécho, G. Hoareau, Alice Baldy, Antoine Lafont, Anélia Petit, P. Chiquet, Guilhem Caumette, Pierre Cézac, Anthony Ranchou-Peyruse
In the context of climate change and resource depletion, an adaptation in the energy mix towards decarbonation and renewable energy is crucial. Dihydrogen (H2) is a promising alternative to traditional carbonated energy sources. Besides being storable, it also has the potential to be produced using renewable and low carbon processes. In order to use H2 on a large scale, it will be necessary to store massive quantities by means of, for example, Underground Gas Storage (UGS) in deep aquifers. H2’s behavior in deep aquifer is related to its geochemical reactivity and to the microbial activity. Also, it is an electron donor as well as an energy source for numerous indigenous microorganisms. In this study, H2 injection in three different UGS, with different formation waters, rocks and microbial communities, were simulated in a high-pressure reactor following a previously defined protocol [1]. To better understand the intricate phenomena at work, extent of reaction equations based on microbial diversities were solved to identify the main reactions taking place in the reactor. The broadly used geochemical modeling software PHREEQC was used to calculate gases solubilities, resulting pH and redox potential inside the reactor.
{"title":"Comparative study of three H2 geological storages in deep aquifers simulated in high pressure reactors.","authors":"Jean Mura, M. Ranchou-Peyruse, Marion Guignard, Perla G Haddad, M. Ducousso, Franck Casteran, Pascale Sénéchal, M. Larregieu, M. Isaure, Peter Moonen, I. Le Hécho, G. Hoareau, Alice Baldy, Antoine Lafont, Anélia Petit, P. Chiquet, Guilhem Caumette, Pierre Cézac, Anthony Ranchou-Peyruse","doi":"10.7185/gold2023.18303","DOIUrl":"https://doi.org/10.7185/gold2023.18303","url":null,"abstract":"In the context of climate change and resource depletion, an adaptation in the energy mix towards decarbonation and renewable energy is crucial. Dihydrogen (H2) is a promising alternative to traditional carbonated energy sources. Besides being storable, it also has the potential to be produced using renewable and low carbon processes. In order to use H2 on a large scale, it will be necessary to store massive quantities by means of, for example, Underground Gas Storage (UGS) in deep aquifers. H2’s behavior in deep aquifer is related to its geochemical reactivity and to the microbial activity. Also, it is an electron donor as well as an energy source for numerous indigenous microorganisms. In this study, H2 injection in three different UGS, with different formation waters, rocks and microbial communities, were simulated in a high-pressure reactor following a previously defined protocol [1]. To better understand the intricate phenomena at work, extent of reaction equations based on microbial diversities were solved to identify the main reactions taking place in the reactor. The broadly used geochemical modeling software PHREEQC was used to calculate gases solubilities, resulting pH and redox potential inside the reactor.","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140353531","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}
Investigating mineral/melt Sn partitioning at high temperatures and pressures is a difficult task because Sn is a redox-sensitive multivalent element and easily alloys with noble metal sample capsules. To obtain accurate Sn partition coefficients between titanite, ilmenite, and granitic melts, we developed single capsule Pt or Au and double capsule Pt95Rh5 (or Au)–Re designs to avoid significant Sn loss at a controlled oxygen fugacity (ƒO2). With these new capsule designs, we performed piston-cylinder experiments of Sn partitioning between titanite, ilmenite, and granitic melts. The experimental P–T–ƒO2 conditions were 0.5–1.0 GPa, 850–1000 °C and ~QFM+8 to ~QFM–4 (QFM: Quartz–Fayalite–Magnetite buffer), with ƒO2 controlled by the solid buffers of Ru–RuO2, Re–ReO2, Co–CoO, graphite, and Fe–FeO. The obtained mineral/melt Sn partition coefficients (DSnmin/melt) are 0.48–184.75 for titanite and 0.03–69.45 for ilmenite at the experimental conditions. The DSnmin/melt values are largely dependent on ƒO2 although the effects of temperature and melt composition are also observed. DSnTtn/melt strongly decreases with decreasing ƒO2, from ~46–185 at the most oxidizing conditions (Ru–RuO2 buffer), to ~2–16 at moderately oxidizing to moderately reducing conditions (Re–ReO2 to Co–CoO and graphite buffers), to < 1 at the most reducing conditions (Fe–FeO buffer). DSnIlm/melt exhibits a variation trend similar to DSnTtn/melt, but is always lower than DSnTtn/melt at a given ƒO2. These DSnmin/melt values can be applied to quantitatively assess the mineralization potential of granitic magmas. Using DSnTtn/melt, we estimate that Sn contents are ~150–400 ppm in the premineralization magmas of the tin-mineralized Qitianling plutons (South China).
{"title":"Experimental determination of tin partitioning between titanite, ilmenite and granitic melts using improved capsule designs.","authors":"Jintuan Wang, Fangfang Huang, Xiaolin Xiong, Mingdi Gao, Li Li, Chunxia Wei","doi":"10.7185/gold2023.19768","DOIUrl":"https://doi.org/10.7185/gold2023.19768","url":null,"abstract":"\u0000 Investigating mineral/melt Sn partitioning at high temperatures and pressures is a difficult task because Sn is a redox-sensitive multivalent element and easily alloys with noble metal sample capsules. To obtain accurate Sn partition coefficients between titanite, ilmenite, and granitic melts, we developed single capsule Pt or Au and double capsule Pt95Rh5 (or Au)–Re designs to avoid significant Sn loss at a controlled oxygen fugacity (ƒO2). With these new capsule designs, we performed piston-cylinder experiments of Sn partitioning between titanite, ilmenite, and granitic melts. The experimental P–T–ƒO2 conditions were 0.5–1.0 GPa, 850–1000 °C and ~QFM+8 to ~QFM–4 (QFM: Quartz–Fayalite–Magnetite buffer), with ƒO2 controlled by the solid buffers of Ru–RuO2, Re–ReO2, Co–CoO, graphite, and Fe–FeO. The obtained mineral/melt Sn partition coefficients (DSnmin/melt) are 0.48–184.75 for titanite and 0.03–69.45 for ilmenite at the experimental conditions. The DSnmin/melt values are largely dependent on ƒO2 although the effects of temperature and melt composition are also observed. DSnTtn/melt strongly decreases with decreasing ƒO2, from ~46–185 at the most oxidizing conditions (Ru–RuO2 buffer), to ~2–16 at moderately oxidizing to moderately reducing conditions (Re–ReO2 to Co–CoO and graphite buffers), to < 1 at the most reducing conditions (Fe–FeO buffer). DSnIlm/melt exhibits a variation trend similar to DSnTtn/melt, but is always lower than DSnTtn/melt at a given ƒO2. These DSnmin/melt values can be applied to quantitatively assess the mineralization potential of granitic magmas. Using DSnTtn/melt, we estimate that Sn contents are ~150–400 ppm in the premineralization magmas of the tin-mineralized Qitianling plutons (South China).","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140219775","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}
Morgane Léon, P. van Beek, V. Sanial, Corentin Baudet, Matthew Charette, M. Souhaut, Frédéric Vivier, Elodie Kestenare, Catherine Jeandel, Helene Planquette
Hydrothermal vents have been shown to be important vectors for various chemical elements into the ocean. In particular, radium is a naturally occurring radionuclide present in low concentrations in the ocean but is significantly enriched in hydrothermal fluids. Additionally, radium is only slightly impacted by scavenging or biological removal, which makes it a valuable tracer to evaluate the fate of the chemical elements released by hydrothermal vents
{"title":"Investigation of hydrothermal activity in the South West Indian Ridge region using Ra isotopes and 227Ac as tracers","authors":"Morgane Léon, P. van Beek, V. Sanial, Corentin Baudet, Matthew Charette, M. Souhaut, Frédéric Vivier, Elodie Kestenare, Catherine Jeandel, Helene Planquette","doi":"10.7185/gold2023.19331","DOIUrl":"https://doi.org/10.7185/gold2023.19331","url":null,"abstract":"Hydrothermal vents have been shown to be important vectors for various chemical elements into the ocean. In particular, radium is a naturally occurring radionuclide present in low concentrations in the ocean but is significantly enriched in hydrothermal fluids. Additionally, radium is only slightly impacted by scavenging or biological removal, which makes it a valuable tracer to evaluate the fate of the chemical elements released by hydrothermal vents","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139189703","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}
Earth likely acquired much of its inventory of volatile elements during the main stage of its formation. Some of Earth's proto-atmosphere must therefore have survived the giant impacts, collisions between planet-sized bodies, that dominate the latter phases of accretion. Here we use a suite of 1D hydrodynamic simulations and impedance match calculations to quantify the effect that pre-impact surface conditions (such as atmospheric pressure and presence of an ocean) have on the efficiency of atmospheric and ocean loss from proto-planets during giant impacts. We find that -- in the absence of an ocean -- lighter, hotter, and lower-pressure atmospheres are more easily lost. The presence of an ocean can significantly increase the efficiency of atmospheric loss compared to the no-ocean case, with a rapid transition between low and high loss regimes as the mass ratio of atmosphere to ocean decreases. However, contrary to previous thinking, the presence of an ocean can also reduce atmospheric loss if the ocean is not sufficiently massive, typically less than a few times the atmospheric mass. Volatile loss due to giant impacts is thus highly sensitive to the surface conditions on the colliding bodies. To allow our results to be combined with 3D impact simulations, we have developed scaling laws that relate loss to the ground velocity and surface conditions. Our results demonstrate that the final volatile budgets of planets are critically dependent on the exact timing and sequence of impacts experienced by their precursor planetary embryos, making atmospheric properties a highly stochastic outcome of accretion.
{"title":"Atmospheric loss in giant impacts depends on pre-impact surface conditions","authors":"S. Lock, Sarah T. Stewart","doi":"10.7185/gold2023.19972","DOIUrl":"https://doi.org/10.7185/gold2023.19972","url":null,"abstract":"Earth likely acquired much of its inventory of volatile elements during the main stage of its formation. Some of Earth's proto-atmosphere must therefore have survived the giant impacts, collisions between planet-sized bodies, that dominate the latter phases of accretion. Here we use a suite of 1D hydrodynamic simulations and impedance match calculations to quantify the effect that pre-impact surface conditions (such as atmospheric pressure and presence of an ocean) have on the efficiency of atmospheric and ocean loss from proto-planets during giant impacts. We find that -- in the absence of an ocean -- lighter, hotter, and lower-pressure atmospheres are more easily lost. The presence of an ocean can significantly increase the efficiency of atmospheric loss compared to the no-ocean case, with a rapid transition between low and high loss regimes as the mass ratio of atmosphere to ocean decreases. However, contrary to previous thinking, the presence of an ocean can also reduce atmospheric loss if the ocean is not sufficiently massive, typically less than a few times the atmospheric mass. Volatile loss due to giant impacts is thus highly sensitive to the surface conditions on the colliding bodies. To allow our results to be combined with 3D impact simulations, we have developed scaling laws that relate loss to the ground velocity and surface conditions. Our results demonstrate that the final volatile budgets of planets are critically dependent on the exact timing and sequence of impacts experienced by their precursor planetary embryos, making atmospheric properties a highly stochastic outcome of accretion.","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139334831","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}
Hydrous minerals contribute largely to the transport and distribution of water into the mantle of earth to regulate the process of deep-water cycle. Brucite is one of the simplest layered dense hydrous mineral belonging to MgO-SiO2-H2O ternary system, which contains significant amount of water in the form of OH- groups, spanning a wide range of pressure stability. Simultaneously, the pressure (p) and temperature (T) induced mobility of protons within the layered structure of brucite is crucial for consequences on electrical conductivity of the mantle. Using ab initio molecular dynamics (AIMD) simulations, we investigate the diffusion of H in high-pressure trigonal P-3 polymorph of brucite in a combined p-T range of 10-85 GPa and 1250-2000K, relevant to the mantle of earth. The AIMD simulations reveal an unusual pressure-dependence of the proton migration in brucite characterized by maximum H-diffusion in the pressure range of 72-76 GPa along different isotherms. We predict that in the P-3 brucite the H mobility is onset only when a critical hydrostatic pressure is attained. The onset pressure is observed to drop with increasing temperature. The H-diffusion in brucite phase at elevated p-T takes place in such a manner that the process results in the amorphization of the H-sublattice, without disturbing the Mg- and O-sublattices. This selective amorphization yields a pool of highly mobile protons causing a subsequent increment in the electrical conductivity in P-3 brucite. Our calculated values of conductivity are compared with ex-situ geophysical magnetic satellite data indicating that brucite can be present in larger quantities in the lower mantle than previously observed. This hydroxide phase can occur as segregated patches between the dominant constituents e.g., silicates and oxides of the lower mantle and thus can explain the origin of high electrical conductivity therein.
含水矿物在很大程度上有助于水向地幔的输送和分布，从而调节深层水循环过程。黑云母是属于 MgO-SiO2-H2O 三元系统的最简单的层状致密含水矿物之一，其中含有大量以 OH- 基团形式存在的水，其压力稳定性跨度很大。同时，压力（p）和温度（T）引起的质子在青金石层状结构中的流动性对地幔导电性的影响至关重要。通过使用 ab initio 分子动力学（AIMD）模拟，我们研究了与地幔相关的 10-85 GPa 和 1250-2000K 的组合 p-T 范围内 H 在高压三棱 P-3 多晶体青金石中的扩散情况。AIMD 模拟揭示了青金石中质子迁移的异常压力依赖性，其特点是在 72-76 GPa 压力范围内沿着不同的等温线进行最大 H 扩散。我们预测，在 P-3 青金石中，只有当达到临界静水压力时，H 迁移才会开始。据观察，随着温度的升高，起始压力会下降。在 p-T 升高时，H 在青金石相中的扩散是以这样一种方式进行的：这一过程导致 H 亚晶格的非晶化，而不会干扰镁亚晶格和 O 亚晶格。这种选择性的非晶化产生了高流动性质子池，从而导致 P-3 青金石的电导率增加。我们计算出的电导率值与原位地球物理磁卫星数据进行了比较，结果表明青金石在下地幔中的含量可能比以前观测到的要高。这种氢氧化物相可能在下地幔的主要成分（如硅酸盐和氧化物）之间以分离斑块的形式存在，因此可以解释其中高导电率的来源。
{"title":"High pressure-temperature proton migration in P-3 brucite [Mg(OH)2]: Implication for electrical conductivity in deep mantle","authors":"S. Mondal, Pratik Kumar Das, Nibir Mandal","doi":"10.7185/gold2023.14068","DOIUrl":"https://doi.org/10.7185/gold2023.14068","url":null,"abstract":"Hydrous minerals contribute largely to the transport and distribution of water into the mantle of earth to regulate the process of deep-water cycle. Brucite is one of the simplest layered dense hydrous mineral belonging to MgO-SiO2-H2O ternary system, which contains significant amount of water in the form of OH- groups, spanning a wide range of pressure stability. Simultaneously, the pressure (p) and temperature (T) induced mobility of protons within the layered structure of brucite is crucial for consequences on electrical conductivity of the mantle. Using ab initio molecular dynamics (AIMD) simulations, we investigate the diffusion of H in high-pressure trigonal P-3 polymorph of brucite in a combined p-T range of 10-85 GPa and 1250-2000K, relevant to the mantle of earth. The AIMD simulations reveal an unusual pressure-dependence of the proton migration in brucite characterized by maximum H-diffusion in the pressure range of 72-76 GPa along different isotherms. We predict that in the P-3 brucite the H mobility is onset only when a critical hydrostatic pressure is attained. The onset pressure is observed to drop with increasing temperature. The H-diffusion in brucite phase at elevated p-T takes place in such a manner that the process results in the amorphization of the H-sublattice, without disturbing the Mg- and O-sublattices. This selective amorphization yields a pool of highly mobile protons causing a subsequent increment in the electrical conductivity in P-3 brucite. Our calculated values of conductivity are compared with ex-situ geophysical magnetic satellite data indicating that brucite can be present in larger quantities in the lower mantle than previously observed. This hydroxide phase can occur as segregated patches between the dominant constituents e.g., silicates and oxides of the lower mantle and thus can explain the origin of high electrical conductivity therein.","PeriodicalId":507710,"journal":{"name":"Goldschmidt2023 abstracts","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139341501","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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