Pub Date : 2025-03-12DOI: 10.1016/j.gca.2025.02.038
Yuan Liu , Hongyu Chen , Yizhi Sheng , Weiguo Hou , Wenhui Zhang , Wenhui Hu , Hailiang Dong
Geothermal systems are hot spots for interaction among minerals, microorganisms, and hydrocarbons. Coupled hydrocarbon transformation and redox cycling of iron in minerals is important to ecosystem functions but remains poorly understood. This work studied abiotic transformation of petroleum hydrocarbons by reactive oxygen species produced upon oxygenation of a reduced clay mineral (nontronite NAu-2). Subsequently, the impact of such abiotic petroleum-clay interactions on coupled reduction of structural Fe(III) in clay mineral and petroleum transformation was studied under anaerobic condition. In the abiotic phase, hydrocarbons in a crude oil sample were oxidized by hydroxyl radicals (OH) generated upon oxygenation of reduced NAu-2, forming partially oxygenated compounds with hydroxyl, carbonyl, and carboxyl groups. In the subsequent bio-reduction experiments, these more bioavailable compounds significantly enhanced Fe(III) bio-reduction by a thermophilic microbial community enriched from a terrestrial hot spring. In particular, Sphingomonas and Phyllobacterium were enriched, both of which possessed genes for anaerobic hydrocarbon activation and Fe(III) reduction. Notably, the thermophilic community possessed more genes for breaking down C, H, and O-containing compounds. In contrast, when the same thermophilic community was exposed to the original (unoxidized) petroleum hydrocarbons, they possessed more genes for degrading C and H compounds. These findings enhance our understanding of the important role of minerals in regulating hydrocarbon transformation and in shaping subsurface microbial community.
{"title":"Abiotic and biotic transformation of petroleum hydrocarbons coupled with redox cycling of structural iron in clay mineral","authors":"Yuan Liu , Hongyu Chen , Yizhi Sheng , Weiguo Hou , Wenhui Zhang , Wenhui Hu , Hailiang Dong","doi":"10.1016/j.gca.2025.02.038","DOIUrl":"10.1016/j.gca.2025.02.038","url":null,"abstract":"<div><div>Geothermal systems are hot spots for interaction among minerals, microorganisms, and hydrocarbons. Coupled hydrocarbon transformation and redox cycling of iron in minerals is important to ecosystem functions but remains poorly understood. This work studied abiotic transformation of petroleum hydrocarbons by reactive oxygen species produced upon oxygenation of a reduced clay mineral (nontronite NAu-2). Subsequently, the impact of such abiotic petroleum-clay interactions on coupled reduction of structural Fe(III) in clay mineral and petroleum transformation was studied under anaerobic condition. In the abiotic phase, hydrocarbons in a crude oil sample were oxidized by hydroxyl radicals (<sup><img></sup>OH) generated upon oxygenation of reduced NAu-2, forming partially oxygenated compounds with hydroxyl, carbonyl, and carboxyl groups. In the subsequent bio-reduction experiments, these more bioavailable compounds significantly enhanced Fe(III) bio-reduction by a thermophilic microbial community enriched from a terrestrial hot spring. In particular, <em>Sphingomonas</em> and <em>Phyllobacterium</em> were enriched, both of which possessed genes for anaerobic hydrocarbon activation and Fe(III) reduction. Notably, the thermophilic community possessed more genes for breaking down C, H, and O-containing compounds. In contrast, when the same thermophilic community was exposed to the original (unoxidized) petroleum hydrocarbons, they possessed more genes for degrading C and H compounds. These findings enhance our understanding of the important role of minerals in regulating hydrocarbon transformation and in shaping subsurface microbial community.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 44-63"},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666482","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}
Pub Date : 2025-03-12DOI: 10.1016/j.gca.2025.03.008
Shannon C. Doherty , Catherine V. Davis , Jennifer S. Fehrenbacher
Microenvironments inside marine organic particles can host anaerobic microbial respiration outside of ocean anoxic zones, but these environments are challenging to directly observe. We present evidence that the planktic foraminifer Globorotaloides hexagonus inhabits a particle microenvironment and suggest that their shell chemistry records anaerobic microbial metabolisms inside particles. We propose a novel interpretation of intrashell trends in Ba/Ca, Mn/Ca, and Zn/Ca ratios as signals of denitrification, Mn respiration, and sulfate reduction. We measure these trace elements in G. hexagonus collected from discrete depth horizons across a pelagic oxygen gradient in the Eastern Tropical North Pacific. Using this intrashell trace element framework, we find that denitrification may have occurred inside particles throughout the water column, and that Mn respiration and sulfate reduction may have occurred inside particles throughout the oxygen minimum zone. Our results have implications for budgets of nitrogen, sulfur, manganese, and other trace elements in regions with expanding oxygen minimum zones and suggest a new method of interpreting intrashell trends in trace element-to-calcium ratios in planktic foraminifera.
{"title":"Planktic foraminifera record the succession of anaerobic metabolisms in particle microenvironments across a pelagic oxygen gradient","authors":"Shannon C. Doherty , Catherine V. Davis , Jennifer S. Fehrenbacher","doi":"10.1016/j.gca.2025.03.008","DOIUrl":"10.1016/j.gca.2025.03.008","url":null,"abstract":"<div><div>Microenvironments inside marine organic particles can host anaerobic microbial respiration outside of ocean anoxic zones, but these environments are challenging to directly observe. We present evidence that the planktic foraminifer <em>Globorotaloides hexagonus</em> inhabits a particle microenvironment and suggest that their shell chemistry records anaerobic microbial metabolisms inside particles. We propose a novel interpretation of intrashell trends in Ba/Ca, Mn/Ca, and Zn/Ca ratios as signals of denitrification, Mn respiration, and sulfate reduction. We measure these trace elements in <em>G. hexagonus</em> collected from discrete depth horizons across a pelagic oxygen gradient in the Eastern Tropical North Pacific. Using this intrashell trace element framework, we find that denitrification may have occurred inside particles throughout the water column, and that Mn respiration and sulfate reduction may have occurred inside particles throughout the oxygen minimum zone. Our results have implications for budgets of nitrogen, sulfur, manganese, and other trace elements in regions with expanding oxygen minimum zones and suggest a new method of interpreting intrashell trends in trace element-to-calcium ratios in planktic foraminifera.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 267-276"},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-08DOI: 10.1016/j.gca.2025.03.003
Michael Fettweis , Saumya Silori , Rieko Adriaens , Xavier Desmit
Particulate (POC) and dissolved organic carbon (DOC) concentration, clay mineral content and composition and the suspended particulate matter (SPM) concentration have been analyzed in water samples taken along transects from the high turbid nearshore to the low turbid offshore on the North Sea shelf. The suspended POC has been classified into a mineral-associated (POCmineral), a slowly degrading (POCslow) and a fresh fraction (POCfresh). The POCmineral has been estimated based on the clay mineral composition and on literature data of the mineral specific surface area per g and the OC content per specific surface area. It consists of organic molecules adsorbed onto mineral surfaces and is thereby the most refractory fraction. The POCfresh content (% of POCfresh in SPM) has been calculated using the semi-empirical POC-SPM model of Fettweis et al. (2022) and is intrinsically labile. The POCslow content is refractory with variable rates of degradation. The total POC content of the SPM was between 2 and 11%, from which about 0.3–6.6% (0.1–2.1%) was POCfresh in spring (resp., winter). The POCmineral content was between 0.4% and 1.1% and decreased towards the offshore, meaning that the POC offshore is less refractory than nearshore. The organic molecules adsorbed onto clay minerals, are dynamically exchanging with the DOC, and thus influencing its fate and concentration. However this process is not sufficient to explain the increasing POC/DOC ratio with increasing SPM concentration, which is further explained by primary production, advection and diffusion, density gradients and seabed erosion. Our results highlight the difficulty and the necessity of estimating the respective sample-POC and DOC concentrations, fluxes and fates along SPM concentration gradients in coastal zones. This is needed as organo-mineral interactions influence the vertical dynamics and horizontal transport of SPM and have an impact on particles and organic carbon fluxes.
{"title":"Clay minerals and the stability of organic carbon in suspension along coastal to offshore transects","authors":"Michael Fettweis , Saumya Silori , Rieko Adriaens , Xavier Desmit","doi":"10.1016/j.gca.2025.03.003","DOIUrl":"10.1016/j.gca.2025.03.003","url":null,"abstract":"<div><div>Particulate (POC) and dissolved organic carbon (DOC) concentration, clay mineral content and composition and the suspended particulate matter (SPM) concentration have been analyzed in water samples taken along transects from the high turbid nearshore to the low turbid offshore on the North Sea shelf. The suspended POC has been classified into a mineral-associated (POC<sub>mineral</sub>), a slowly degrading (POC<sub>slow</sub>) and a fresh fraction (POC<sub>fresh</sub>). The POC<sub>mineral</sub> has been estimated based on the clay mineral composition and on literature data of the mineral specific surface area per g and the OC content per specific surface area. It consists of organic molecules adsorbed onto mineral surfaces and is thereby the most refractory fraction. The POC<sub>fresh</sub> content (% of POC<sub>fresh</sub> in SPM) has been calculated using the semi-empirical POC-SPM model of Fettweis et al. (2022) and is intrinsically labile. The POC<sub>slow</sub> content is refractory with variable rates of degradation. The total POC content of the SPM was between 2 and 11%, from which about 0.3–6.6% (0.1–2.1%) was POC<sub>fresh</sub> in spring (resp., winter). The POC<sub>mineral</sub> content was between 0.4% and 1.1% and decreased towards the offshore, meaning that the POC offshore is less refractory than nearshore. The organic molecules adsorbed onto clay minerals, are dynamically exchanging with the DOC, and thus influencing its fate and concentration. However this process is not sufficient to explain the increasing POC/DOC ratio with increasing SPM concentration, which is further explained by primary production, advection and diffusion, density gradients and seabed erosion. Our results highlight the difficulty and the necessity of estimating the respective sample-POC and DOC concentrations, fluxes and fates along SPM concentration gradients in coastal zones. This is needed as organo-mineral interactions influence the vertical dynamics and horizontal transport of SPM and have an impact on particles and organic carbon fluxes.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 229-237"},"PeriodicalIF":4.5,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666341","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}
Pub Date : 2025-03-07DOI: 10.1016/j.gca.2025.03.004
Carolina Dantas Cardoso , Raphaël Pik , Antonio Caracausi , Sæmundur Ari Halldórsson , Andri Stefánsson , Laurent Zimmermann , Guillaume Paris , Andrea Ricci , Hreinn Hjartarson
<div><div>Iceland is a location of geological interest due to the combination of upwelling mantle plume and divergent plate boundary, which resulted in the formation of its extensive surface area (>100,000 km<sup>2</sup>) that rises above sea-level. This unique setting facilitates assessing the role of the underlying mantle plume and tectonic activity on crust-forming processes. Helium isotopes provide a useful tool in this regard, as they can identify physical processes and resolve deep and shallow fluid sources in the crust. In Iceland, the highest <sup>3</sup>He/<sup>4</sup>He for geothermal fluids are found in Vestfirðir with values up to 29 R<sub>a</sub> (where R<sub>a</sub> is the <sup>3</sup>He/<sup>4</sup>He of air), more than 110 km away from current active rift zones. Such locations are key to understand the extent of mantle degassing processes associated with the high buoyant Icelandic mantle plume. Other off-rift regions, such as most of North Iceland, have not been extensively investigated, despite the widespread presence of geothermal activity. Although North Iceland has been volcanically inactive for the past 0.8 Ma, severe earthquake hazards associated with mature and partially on-land transform zones have occurred, rendering the monitoring of the full tectonic-hydrogeochemical system of societal importance. Our study in North Iceland aimed to (i) assess temporal variations in helium isotopic signatures in low-T geothermal water and their relationship with regional earthquakes, (ii) diminish the helium isotope data gap in geothermal fluids of this region, and (iii) elucidate both local and regional processes controlling the He isotope systematics in this region as a case study for other off-rift contexts on Earth. In order to achieve these goals, we report helium isotope time series data collected from June 2020 to October 2022 from a borehole in Hafralækur, Aðaldalur valley (95 samples collected on a near-weekly basis), along with an isotope survey (δ<sup>2</sup>H-<sup>3</sup>He/<sup>4</sup>He-δ<sup>13</sup>C<sub>TDIC</sub>-δ<sup>18</sup>O-δ<sup>34</sup>S<sub>SO4</sub>) of North Iceland geothermal fluids (T < 130 °C, n = 36 samples). The results indicate a large regional variability in helium isotope ratios (4 to 27 R<sub>a</sub>) that is comparable to the entire range evident in geothermal fluids across Iceland (∼1 to 29 R<sub>a</sub>) where the maximum <sup>3</sup>He/<sup>4</sup>He signature is among the highest measured in geothermal fluids from oceanic and continental hotspots globally. Several processes, both on regional and local scales, are needed to account for this large range: (i) influence of a deeply-derived mantle flux evidenced by a high <sup>3</sup>He/<sup>4</sup>He mantle component, degassing via fault systems, (ii) release of local radiogenic helium components, potentially associated with seismic events along the Dalvík Lineament, and (iii) local groundwater mixing, for example evident at the Hafralækur sit
{"title":"Helium isotopes in geothermal fluids reveal off-rift plume degassing and localized seismicity-induced processes in North Iceland","authors":"Carolina Dantas Cardoso , Raphaël Pik , Antonio Caracausi , Sæmundur Ari Halldórsson , Andri Stefánsson , Laurent Zimmermann , Guillaume Paris , Andrea Ricci , Hreinn Hjartarson","doi":"10.1016/j.gca.2025.03.004","DOIUrl":"10.1016/j.gca.2025.03.004","url":null,"abstract":"<div><div>Iceland is a location of geological interest due to the combination of upwelling mantle plume and divergent plate boundary, which resulted in the formation of its extensive surface area (>100,000 km<sup>2</sup>) that rises above sea-level. This unique setting facilitates assessing the role of the underlying mantle plume and tectonic activity on crust-forming processes. Helium isotopes provide a useful tool in this regard, as they can identify physical processes and resolve deep and shallow fluid sources in the crust. In Iceland, the highest <sup>3</sup>He/<sup>4</sup>He for geothermal fluids are found in Vestfirðir with values up to 29 R<sub>a</sub> (where R<sub>a</sub> is the <sup>3</sup>He/<sup>4</sup>He of air), more than 110 km away from current active rift zones. Such locations are key to understand the extent of mantle degassing processes associated with the high buoyant Icelandic mantle plume. Other off-rift regions, such as most of North Iceland, have not been extensively investigated, despite the widespread presence of geothermal activity. Although North Iceland has been volcanically inactive for the past 0.8 Ma, severe earthquake hazards associated with mature and partially on-land transform zones have occurred, rendering the monitoring of the full tectonic-hydrogeochemical system of societal importance. Our study in North Iceland aimed to (i) assess temporal variations in helium isotopic signatures in low-T geothermal water and their relationship with regional earthquakes, (ii) diminish the helium isotope data gap in geothermal fluids of this region, and (iii) elucidate both local and regional processes controlling the He isotope systematics in this region as a case study for other off-rift contexts on Earth. In order to achieve these goals, we report helium isotope time series data collected from June 2020 to October 2022 from a borehole in Hafralækur, Aðaldalur valley (95 samples collected on a near-weekly basis), along with an isotope survey (δ<sup>2</sup>H-<sup>3</sup>He/<sup>4</sup>He-δ<sup>13</sup>C<sub>TDIC</sub>-δ<sup>18</sup>O-δ<sup>34</sup>S<sub>SO4</sub>) of North Iceland geothermal fluids (T < 130 °C, n = 36 samples). The results indicate a large regional variability in helium isotope ratios (4 to 27 R<sub>a</sub>) that is comparable to the entire range evident in geothermal fluids across Iceland (∼1 to 29 R<sub>a</sub>) where the maximum <sup>3</sup>He/<sup>4</sup>He signature is among the highest measured in geothermal fluids from oceanic and continental hotspots globally. Several processes, both on regional and local scales, are needed to account for this large range: (i) influence of a deeply-derived mantle flux evidenced by a high <sup>3</sup>He/<sup>4</sup>He mantle component, degassing via fault systems, (ii) release of local radiogenic helium components, potentially associated with seismic events along the Dalvík Lineament, and (iii) local groundwater mixing, for example evident at the Hafralækur sit","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 12-31"},"PeriodicalIF":4.5,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629448","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}
Pub Date : 2025-03-06DOI: 10.1016/j.gca.2025.02.032
Yonghui Li , Justin Hardin , Wenzhong Wang , Zhongqing Wu , Shichun Huang
To better constrain the Ca isotope effect during partial melting of Earth’s mantle, we used ab initio molecular dynamic simulations to calculate the equilibrium mineral-silicate melt Ca isotope fractionation factors for the major Ca-bearing minerals of the upper mantle (orthopyroxene, clinopyroxene, olivine, and garnet), as well as plagioclase. We found that mineral-melt Ca isotope fractionation factors are dependent on pressure, temperature, and mineral major element compositions, but not the silicate melt composition. Specifically, our calculations show that under equilibrium, clinopyroxene has a slightly heavier Ca isotope composition compared to silicate melt, consistent with the inference of published research that studied the Ca isotope effects during basaltic magma evolution.
We then utilized the calculated mineral-melt Ca isotope fractionation factors to model the Ca isotope effects on both silicate melts and residues during partial melting of spinel peridotite at 1–2 GPa, garnet peridotite at 3–7 GPa, and garnet pyroxenite/eclogite at 2–5 GPa. Our model predicts that silicate melts only have δ44/40Ca up to 0.12 lower than their source value, consistent with previous estimates. Importantly, partial melts of spinel peridotite, garnet peridotite, and garnet pyroxenite/eclogite exhibit overlapping δ44/40Ca values, if their mantle sources have the same δ44/40Ca. Partial melting alone cannot explain the full range of δ44/40Ca values observed in natural basalts, and at least part of this variation must reflect δ44/40Ca variation of their mantle sources and/or other processes such as crystal fractionation.
Our calculations show that melting residues always have δ44/40Ca higher than their mantle source, with the highest δ44/40Ca at 0.40 higher than their source value. This range is much smaller than that observed in natural ultramafic rocks that might represent melting residues. In addition, the range and direction of inter-mineral Ca isotope fractionation factors predicted in our modeled residues for the mineral pairs orthopyroxene-clinopyroxene and garnet-clinopyroxene are much more restricted than those observed in natural ultramafic rocks, including peridotites and pyroxenites/eclogites. Therefore, most natural ultramafic rocks have likely experienced more complicated petrogeneses than partial melting.
{"title":"Mineral-melt calcium isotope fractionation factors constrained using ab initio molecular dynamics simulations and their implications to calcium isotope effects during partial melting in the upper mantle","authors":"Yonghui Li , Justin Hardin , Wenzhong Wang , Zhongqing Wu , Shichun Huang","doi":"10.1016/j.gca.2025.02.032","DOIUrl":"10.1016/j.gca.2025.02.032","url":null,"abstract":"<div><div>To better constrain the Ca isotope effect during partial melting of Earth’s mantle, we used <em>ab initio</em> molecular dynamic simulations to calculate the equilibrium mineral-silicate melt Ca isotope fractionation factors for the major Ca-bearing minerals of the upper mantle (orthopyroxene, clinopyroxene, olivine, and garnet), as well as plagioclase. We found that mineral-melt Ca isotope fractionation factors are dependent on pressure, temperature, and mineral major element compositions, but not the silicate melt composition. Specifically, our calculations show that under equilibrium, clinopyroxene has a slightly heavier Ca isotope composition compared to silicate melt, consistent with the inference of published research that studied the Ca isotope effects during basaltic magma evolution.</div><div>We then utilized the calculated mineral-melt Ca isotope fractionation factors to model the Ca isotope effects on both silicate melts and residues during partial melting of spinel peridotite at 1–2 GPa, garnet peridotite at 3–7 GPa, and garnet pyroxenite/eclogite at 2–5 GPa. Our model predicts that silicate melts only have <em>δ</em><sup>44/40</sup>Ca up to 0.12 lower than their source value, consistent with previous estimates. Importantly, partial melts of spinel peridotite, garnet peridotite, and garnet pyroxenite/eclogite exhibit overlapping <em>δ</em><sup>44/40</sup>Ca values, if their mantle sources have the same <em>δ</em><sup>44/40</sup>Ca. Partial melting alone cannot explain the full range of <em>δ</em><sup>44/40</sup>Ca values observed in natural basalts, and at least part of this variation must reflect <em>δ</em><sup>44/40</sup>Ca variation of their mantle sources and/or other processes such as crystal fractionation.</div><div>Our calculations show that melting residues always have <em>δ</em><sup>44/40</sup>Ca higher than their mantle source, with the highest <em>δ</em><sup>44/40</sup>Ca at 0.40 higher than their source value. This range is much smaller than that observed in natural ultramafic rocks that might represent melting residues. In addition, the range and direction of inter-mineral Ca isotope fractionation factors predicted in our modeled residues for the mineral pairs orthopyroxene-clinopyroxene and garnet-clinopyroxene are much more restricted than those observed in natural ultramafic rocks, including peridotites and pyroxenites/eclogites. Therefore, most natural ultramafic rocks have likely experienced more complicated petrogeneses than partial melting.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 51-70"},"PeriodicalIF":4.5,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666342","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}
Pub Date : 2025-03-05DOI: 10.1016/j.gca.2025.02.020
Ekanshu Mallick , Kelsey Prissel , Kevin Righter , Colin R.M. Jackson
Nitrogen is important in planetary evolution because it is essential to life and the most abundant element in Earth’s atmosphere. Here, we investigate how core formation affects the distribution of N within accreting terrestrial planets. We conducted laser-heated diamond anvil cell experiments (LH-DAC) over a wide range of high pressure–temperature-compositional (PTX) conditions (38–103 GPa, 2728–5609 K, −1.95 to −1.03 ΔIW, 0.5–3.7 NBO/T) to study nitrogen partitioning in metal-silicate systems. Combining our data with existing low and high PT results, we developed a nitrogen partitioning model applicable from early accretion to extreme PT stages associated with giant impacts. We test the robustness of our model by accurately predicting nitrogen partitioning in a multi-anvil experiment conducted independently at 15 GPa, 2573 K with oxygen fugacity of −2.5 ΔIW. Our model shows that increasing pressure, oxygen fugacity, and N concentration in the alloy make nitrogen more siderophile, while increasing temperature, oxygen and silicon contents in the alloy, and the SiO2 content of the silicate melt make nitrogen less siderophile. Application of our model to core formation conditions under oxidized and reduced scenarios suggest that nitrogen can be siderophile or lithophile under low PT conditions but exhibits a neutral partitioning at high PT conditions (> 100 GPa, 5000 K) over a wide range of bulk planet compositions. Using our model, along with partitioning models for S and C, we examine how core formation scenarios can fractionate C/N and S/N ratios in the BSE. Our model suggests that backreaction of volatile rich cores from reduced, smaller impactors (sub-Mars-sized) within deep magma oceans can impart a wide range of C/N and S/N ratios on the magma ocean. We find that the amount of silicate entrainment has a strong control on elemental fractionations imparted to the magma oceans. Elevated C/N and S/N ratios are associated with larger degrees of silicate entrainment, and vice versa. Thus, Earth’s apparent depletion of N may relate to its volatiles being reprocessed within deep magma oceans, possibly during the end stages of accretion.
氮在行星演化过程中非常重要，因为它是生命的必需元素，也是地球大气中最丰富的元素。在这里，我们研究了内核的形成如何影响氮在吸积陆地行星中的分布。我们在广泛的高压-高温-成分（PTX）条件（38-103 GPa, 2728-5609 K, -1.95 to -1.03 ΔIW, 0.5-3.7 NBO/T）下进行了激光加热金刚石砧单元实验（LH-DAC），以研究金属硅酸盐系统中的氮分配。结合我们的数据和现有的低PT和高PT结果，我们建立了一个适用于从早期吸积到与巨型撞击相关的极端PT阶段的氮分配模型。我们通过准确预测在 15 GPa、2573 K 条件下独立进行的氧富集度为 -2.5 ΔIW 的多砧实验中的氮分配情况，检验了模型的稳健性。我们的模型表明，合金中的压力、氧富集度和氮浓度的增加会使氮的亲络合度增加，而温度、合金中的氧和硅含量以及硅酸盐熔体中的二氧化硅含量的增加会使氮的亲络合度降低。将我们的模型应用于氧化和还原情况下的地核形成条件表明，在低PT条件下，氮可能是亲铁或亲石的，但在高PT条件下（> 100 GPa, 5000 K），在广泛的大块行星成分范围内，氮表现出中性分配。利用我们的模型以及 S 和 C 的分配模型，我们研究了内核形成情景如何在 BSE 中分馏 C/N 和 S/N 比率。我们的模型表明，在深层岩浆洋中，来自减小的、较小的撞击器（亚火星大小）的富含挥发性的岩心的反作用会给岩浆洋带来广泛的 C/N 和 S/N 比率。我们发现，硅酸盐的夹带量对岩浆洋的元素分馏有很强的控制作用。C/N和S/N比值的升高与硅酸盐夹带量的增加有关，反之亦然。因此，地球表面上的氮耗竭可能与其挥发物在深层岩浆海洋中的再加工有关，可能是在增生的末期阶段。
{"title":"The fate of nitrogen in deep magma oceans","authors":"Ekanshu Mallick , Kelsey Prissel , Kevin Righter , Colin R.M. Jackson","doi":"10.1016/j.gca.2025.02.020","DOIUrl":"10.1016/j.gca.2025.02.020","url":null,"abstract":"<div><div>Nitrogen is important in planetary evolution because it is essential to life and the most abundant element in Earth’s atmosphere. Here, we investigate how core formation affects the distribution of N within accreting terrestrial planets. We conducted laser-heated diamond anvil cell experiments (LH-DAC) over a wide range of high pressure–temperature-compositional (PTX) conditions (38–103 GPa, 2728–5609 K, −1.95 to −1.03 ΔIW, 0.5–3.7 NBO/T) to study nitrogen partitioning in metal-silicate systems. Combining our data with existing low and high PT results, we developed a nitrogen partitioning model applicable from early accretion to extreme PT stages associated with giant impacts. We test the robustness of our model by accurately predicting nitrogen partitioning in a multi-anvil experiment conducted independently at 15 GPa, 2573 K with oxygen fugacity of −2.5 ΔIW. Our model shows that increasing pressure, oxygen fugacity, and N concentration in the alloy make nitrogen more siderophile, while increasing temperature, oxygen and silicon contents in the alloy, and the SiO<sub>2</sub> content of the silicate melt make nitrogen less siderophile. Application of our model to core formation conditions under oxidized and reduced scenarios suggest that nitrogen can be siderophile or lithophile under low PT conditions but exhibits a neutral partitioning at high PT conditions (> 100 GPa, 5000 K) over a wide range of bulk planet compositions. Using our model, along with partitioning models for S and C, we examine how core formation scenarios can fractionate C/N and S/N ratios in the BSE. Our model suggests that backreaction of volatile rich cores from reduced, smaller impactors (sub-Mars-sized) within deep magma oceans can impart a wide range of C/N and S/N ratios on the magma ocean. We find that the amount of silicate entrainment has a strong control on elemental fractionations imparted to the magma oceans. Elevated C/N and S/N ratios are associated with larger degrees of silicate entrainment, and vice versa. Thus, Earth’s apparent depletion of N may relate to its volatiles being reprocessed within deep magma oceans, possibly during the end stages of accretion.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 298-318"},"PeriodicalIF":4.5,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-04DOI: 10.1016/j.gca.2025.03.001
Pratigya J. Polissar , A.Tyler Karp , William J. D’Andrea
Plant leaf waxes and their isotopic composition are important tracers of ecological, environmental, and climate variability, with strong preservation potential in sedimentary archives. However, they represent an integrated, and often complicated, signal of vegetation and hydrology within a watershed. Here, we report a new approach for examining complex mixtures of n-alkanes in sediments and their isotope values: non-negative matrix factorization (NMF). NMF identifies the endmembers in a mixture from the integrated n-alkane data and provides quantitative information on the relative importance of those endmembers across samples. We apply this approach to a synthetic dataset and two previously published datasets to illustrate its uses. Our application of NMF to re-analyse previously published data reveals new insights into past climate and ecological change. We demonstrate that NMF allows a user to 1) identify potential mixing problems, 2) evaluate which specific compounds in a mixture carry the isotope signal that can best address a given scientific objective, 3) determine compound concentrations after excluding contributions from particular endmember sources, and 4) calculate isotope values of different sources. NMF provides a quantitative approach for evaluating the influence of endmember mixing on molecular concentrations and isotope values within a dataset. The re-analysis of two published datasets reveals new quantitative insight into Holocene Arctic climate and Neogene vegetation change.
{"title":"Mixed messages: Unmixing sedimentary molecular distributions reveals source contributions and isotopic values","authors":"Pratigya J. Polissar , A.Tyler Karp , William J. D’Andrea","doi":"10.1016/j.gca.2025.03.001","DOIUrl":"10.1016/j.gca.2025.03.001","url":null,"abstract":"<div><div>Plant leaf waxes and their isotopic composition are important tracers of ecological, environmental, and climate variability, with strong preservation potential in sedimentary archives. However, they represent an integrated, and often complicated, signal of vegetation and hydrology within a watershed. Here, we report a new approach for examining complex mixtures of <em>n</em>-alkanes in sediments and their isotope values: non-negative matrix factorization (NMF). NMF identifies the endmembers in a mixture from the integrated <em>n</em>-alkane data and provides quantitative information on the relative importance of those endmembers across samples. We apply this approach to a synthetic dataset and two previously published datasets to illustrate its uses. Our application of NMF to re-analyse previously published data reveals new insights into past climate and ecological change. We demonstrate that NMF allows a user to 1) identify potential mixing problems, 2) evaluate which specific compounds in a mixture carry the isotope signal that can best address a given scientific objective, 3) determine compound concentrations after excluding contributions from particular endmember sources, and 4) calculate isotope values of different sources. NMF provides a quantitative approach for evaluating the influence of endmember mixing on molecular concentrations and isotope values within a dataset. The re-analysis of two published datasets reveals new quantitative insight into Holocene Arctic climate and Neogene vegetation change.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 122-134"},"PeriodicalIF":4.5,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666344","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}
Pub Date : 2025-03-04DOI: 10.1016/j.gca.2025.03.002
Maria A. Dias , Ralf Dohmen , Harald Behrens
<div><div>Knowledge of Fe-Mg interdiffusion coefficients (<em>D</em><sub>Fe-Mg</sub>) in orthopyroxene (opx) is relevant for diffusion chronometry as well as for thermometers based on Fe-Mg exchange between opx and other common mafic minerals. We extended the existing data set for <em>D</em><sub>Fe-Mg</sub> to quantify the effect of the molar fraction of Fe, <em>X</em><sub>Fe</sub> = Fe/(Fe + Mg) = 0.1 to 0.4, and oxygen fugacity, <em>f</em>O<sub>2</sub> = 10<sup>-7</sup> to 10<sup>-11</sup> Pa, in the temperature range, <em>T</em> = 950–1100 °C, where we build up on our recently developed experimental and analytical approach. Thin film diffusion couples using different natural opx with different trace element contents were annealed in vertical gas mixing furnaces. The diffusion profiles were extracted by acquiring backscattered electron images on foils cut from the samples using a focused ion beam-scanning electron microscope. We found complex interplays between the effect of <em>T</em>, <em>X</em><sub>Fe</sub> and <em>f</em>O<sub>2</sub> on <em>D</em><sub>Fe-Mg</sub>. The effect of <em>X</em><sub>Fe</sub> increases with <em>T</em> for <em>f</em>O<sub>2</sub> = 10<sup>-7</sup> to 10<sup>-9</sup> Pa but decreases with <em>T</em> for more reducing conditions. For <em>T</em> > 1000 °C and <em>f</em>O<sub>2</sub> > 10<sup>-10</sup> Pa, <em>D</em><sub>Fe-Mg</sub> depends on <em>f</em>O<sub>2</sub> and <em>X</em><sub>Fe</sub>. For these conditions <em>D</em><sub>Fe-Mg</sub> is described by an activation energy of 284 ± 19 kJ/mol. For <em>T</em> = 950 °C to 1000 °C and for <em>f</em>O<sub>2</sub> < 10<sup>-10</sup> Pa, <em>D</em><sub>Fe-Mg</sub> seemingly ceases to depend on <em>f</em>O<sub>2</sub>, indicating a change of the diffusion mechanism, and is described by an activation energy of 246 ± 78 kJ/mol. Based on these diffusion data, we propose a qualitative point defect model for opx where the majority point defects changes over the explored Fe content, <em>f</em>O<sub>2</sub> and <em>T</em> conditions from vacancies on the metal site/electron holes to vacancies on the metal site/Fe<sup>3+</sup> to Mg interstitials/electrons, each one responsible for a different effect of <em>f</em>O<sub>2</sub> on <em>D</em><sub>Fe-Mg</sub>. Based on the re-evaluation of kinetic data of order–disorder in orthopyroxene we propose that for <em>T</em> < 950 °C <em>D</em><sub>Fe-Mg</sub> becomes insensitive to <em>f</em>O<sub>2</sub> and the effect of Fe is relatively constant and smaller than at higher <em>T</em>. We derived two parameterizations valid for temperatures between 950 and 1100 °C and <em>f</em>O<sub>2</sub> > 10<sup>-10</sup> Pa and for the same temperature range but for log <em>f</em>O<sub>2</sub> ≤ 10<sup>-10</sup> Pa. In addition, we explore how the new diffusion data would affect the re-equilibration of Fe-Mg during cooling between opx and spinel as well as opx and clinopyroxene. Based on our results, it is likely that the peak composi
了解正辉石（opx）中的铁镁相互扩散系数（DFe-Mg）与扩散时间测定法以及基于opx和其他常见岩浆矿物之间的铁镁交换的温度计有关。我们扩展了现有的 DFe-Mg 数据集，以量化铁摩尔分数 XFe = Fe/(Fe + Mg) = 0.1 至 0.4 和氧富集度 fO2 = 10-7 至 10-11 Pa 在温度范围 T = 950 至 1100 °C（我们最近开发的实验和分析方法）中的影响。使用不同痕量元素含量的不同天然氧化物的薄膜扩散偶在垂直气体混合炉中退火。通过使用聚焦离子束扫描电子显微镜在从样品上切割下来的箔片上获取反向散射电子图像来提取扩散曲线。我们发现 T、XFe 和 fO2 对 DFe-Mg 的影响之间存在复杂的相互作用。在 fO2 = 10-7 到 10-9 Pa 的条件下，XFe 的影响随温度的升高而增大，但在更具还原性的条件下，XFe 的影响随温度的升高而减小。在 T > 1000 °C 和 fO2 > 10-10 Pa 条件下，DFe-Mg 取决于 fO2 和 XFe。在这些条件下，DFe-Mg 的活化能为 284 ± 19 kJ/mol。在 T = 950 °C 至 1000 °C 和 fO2 < 10-10 Pa 条件下，DFe-Mg 似乎不再取决于 fO2，这表明扩散机制发生了变化，其活化能为 246 ± 78 kJ/mol。根据这些扩散数据，我们提出了 opx 的定性点缺陷模型，在该模型中，大多数点缺陷会随着所探讨的铁含量、fO2 和 T 条件的变化而变化，从金属位上的空位/电子空穴到金属位上的空位/Fe3+，再到 Mg 间隙/电子，每一种点缺陷都会造成 fO2 对 DFe-Mg 的不同影响。基于对正长石中有序-无序动力学数据的重新评估，我们提出在温度为 950 °C时，DFe-Mg 对 fO2 不敏感，而 Fe 的影响相对恒定，且小于较高温度时的影响。此外，我们还探讨了新的扩散数据将如何影响蛋白石与尖晶石以及蛋白石与霞石在冷却过程中的铁镁再平衡。根据我们的研究结果，在峰值 T > 1100 °C、更氧化的条件、更高的铁含量和更慢的冷却速率（例如 10 °C/Myr）下，opx 核心的峰值成分很可能很容易发生改变，这对利用opx 与交换伙伴之间的铁镁分布来评估地温数据具有影响。
{"title":"Fe-Mg interdiffusion in orthopyroxene: Complex interdependencies of temperature, composition and oxygen fugacity","authors":"Maria A. Dias , Ralf Dohmen , Harald Behrens","doi":"10.1016/j.gca.2025.03.002","DOIUrl":"10.1016/j.gca.2025.03.002","url":null,"abstract":"<div><div>Knowledge of Fe-Mg interdiffusion coefficients (<em>D</em><sub>Fe-Mg</sub>) in orthopyroxene (opx) is relevant for diffusion chronometry as well as for thermometers based on Fe-Mg exchange between opx and other common mafic minerals. We extended the existing data set for <em>D</em><sub>Fe-Mg</sub> to quantify the effect of the molar fraction of Fe, <em>X</em><sub>Fe</sub> = Fe/(Fe + Mg) = 0.1 to 0.4, and oxygen fugacity, <em>f</em>O<sub>2</sub> = 10<sup>-7</sup> to 10<sup>-11</sup> Pa, in the temperature range, <em>T</em> = 950–1100 °C, where we build up on our recently developed experimental and analytical approach. Thin film diffusion couples using different natural opx with different trace element contents were annealed in vertical gas mixing furnaces. The diffusion profiles were extracted by acquiring backscattered electron images on foils cut from the samples using a focused ion beam-scanning electron microscope. We found complex interplays between the effect of <em>T</em>, <em>X</em><sub>Fe</sub> and <em>f</em>O<sub>2</sub> on <em>D</em><sub>Fe-Mg</sub>. The effect of <em>X</em><sub>Fe</sub> increases with <em>T</em> for <em>f</em>O<sub>2</sub> = 10<sup>-7</sup> to 10<sup>-9</sup> Pa but decreases with <em>T</em> for more reducing conditions. For <em>T</em> > 1000 °C and <em>f</em>O<sub>2</sub> > 10<sup>-10</sup> Pa, <em>D</em><sub>Fe-Mg</sub> depends on <em>f</em>O<sub>2</sub> and <em>X</em><sub>Fe</sub>. For these conditions <em>D</em><sub>Fe-Mg</sub> is described by an activation energy of 284 ± 19 kJ/mol. For <em>T</em> = 950 °C to 1000 °C and for <em>f</em>O<sub>2</sub> < 10<sup>-10</sup> Pa, <em>D</em><sub>Fe-Mg</sub> seemingly ceases to depend on <em>f</em>O<sub>2</sub>, indicating a change of the diffusion mechanism, and is described by an activation energy of 246 ± 78 kJ/mol. Based on these diffusion data, we propose a qualitative point defect model for opx where the majority point defects changes over the explored Fe content, <em>f</em>O<sub>2</sub> and <em>T</em> conditions from vacancies on the metal site/electron holes to vacancies on the metal site/Fe<sup>3+</sup> to Mg interstitials/electrons, each one responsible for a different effect of <em>f</em>O<sub>2</sub> on <em>D</em><sub>Fe-Mg</sub>. Based on the re-evaluation of kinetic data of order–disorder in orthopyroxene we propose that for <em>T</em> < 950 °C <em>D</em><sub>Fe-Mg</sub> becomes insensitive to <em>f</em>O<sub>2</sub> and the effect of Fe is relatively constant and smaller than at higher <em>T</em>. We derived two parameterizations valid for temperatures between 950 and 1100 °C and <em>f</em>O<sub>2</sub> > 10<sup>-10</sup> Pa and for the same temperature range but for log <em>f</em>O<sub>2</sub> ≤ 10<sup>-10</sup> Pa. In addition, we explore how the new diffusion data would affect the re-equilibration of Fe-Mg during cooling between opx and spinel as well as opx and clinopyroxene. Based on our results, it is likely that the peak composi","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 195-211"},"PeriodicalIF":4.5,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-03DOI: 10.1016/j.gca.2025.02.037
Antonio Lanzirotti , Michelle Muth , Elisabet Head , Matthew Newville , Molly McCanta , Paul J. Wallace , Zoltan Zajacz
This study evaluates changes in copper (Cu) speciation that occur in sulfate-dominated basaltic and andesitic magmas equilibrated at oxygen fugacities (fO2′s) above the nickel-nickel oxide (NNO) buffer. Cu K-edge microfocused X-ray absorption fine structure spectroscopy (XAFS) data are presented from both natural and synthetic silicate glasses. Natural samples analyzed include olivine-hosted melt inclusions from tephra of mafic cinder cones in the Lassen segment of the Cascade arc (USA) and from the Michoacán-Guanajuato volcanic field (Mexico) as representative samples from melts equilibrated at fO2 > NNO. A comparison with melts equilibrated at fO2 < NNO is provided by analysis of olivine-hosted melt inclusions from Kīlauea Volcano. Data are also presented from copper- and sulfur-bearing synthetic hydrous andesitic glasses synthesized over a range of fO2, from roughly NNO-2 to NNO+2. The Cu spectroscopy data from the natural and synthetic glasses show two dominant Cu species, Cu1+ oxides (referred to here as Cu–O) and Cu1+ sulfides (referred to here broadly as Cu-S, but not precluding Cu-Fe-S species). The relative proportion of each species present correlates with the relative concentration of dissolved sulfide in the melt. Synthetic sulfur-bearing glasses equilibrated at NNO-1.2 were found to contain exclusively Cu-S species. Sulfur-bearing experimental glasses equilibrated at NNO-0.5 give calculated Cu–O/(Cu–O + Cu-S), defined here as the “Cu–O fraction”, of < 0.10, whereas sulfur-bearing glasses synthesized at NNO+0.6 and NNO+1.8 give calculated Cu–O fraction > 0.96. Natural melt inclusions from Lassen and Kīlauea show a bimodal distribution in Cu–O fraction, with overlapping ranges, of 0.14–0.77 for Lassen and 0.18––0.78 for Kīlauea. Michoacán-Guanajuato inclusions yield Cu–O fractions of 0.68–0.91. The difference in the calculated proportions of Cu–O to Cu-S species appear correlated with available sulfide in the melt. As relative S2- concentrations decrease, the dissolved Cu species in the melt evolves from dominantly Cu-S to Cu–O. This includes melts equilibrated at fO2’s where S6+ is the dominant S species. At intermediate sulfide abundances both species appear to coexist. Thermodynamic modeling of the Cu speciation in these silicate glasses suggests that speciation of Cu as a CuFeS2 melt species (akin to chalcopyrite or intermediate solid solution) most accurately predicts the measured Cu species. The modeling suggests that aFeO in the silicate melt, fO2 and melt S2- (expressed as fS2) are the most important parameters controlling the proportions of Cu–O vs. Cu-S species. Our results provide a new perspective for understanding Cu solubility, transport, and partitioning in magmatic systems.
{"title":"The role of dissolved sulfide in controlling copper speciation in basaltic melts","authors":"Antonio Lanzirotti , Michelle Muth , Elisabet Head , Matthew Newville , Molly McCanta , Paul J. Wallace , Zoltan Zajacz","doi":"10.1016/j.gca.2025.02.037","DOIUrl":"10.1016/j.gca.2025.02.037","url":null,"abstract":"<div><div>This study evaluates changes in copper (Cu) speciation that occur in sulfate-dominated basaltic and andesitic magmas equilibrated at oxygen fugacities (<em>f</em>O<sub>2</sub>′s) above the nickel-nickel oxide (NNO) buffer. Cu K-edge microfocused X-ray absorption fine structure spectroscopy (XAFS) data are presented from both natural and synthetic silicate glasses. Natural samples analyzed include olivine-hosted melt inclusions from tephra of mafic cinder cones in the Lassen segment of the Cascade arc (USA) and from the Michoacán-Guanajuato volcanic field (Mexico) as representative samples from melts equilibrated at <em>f</em>O<sub>2</sub> > NNO. A comparison with melts equilibrated at <em>f</em>O<sub>2</sub> < NNO is provided by analysis of olivine-hosted melt inclusions from Kīlauea Volcano. Data are also presented from copper- and sulfur-bearing synthetic hydrous andesitic glasses synthesized over a range of <em>f</em>O<sub>2</sub>, from roughly NNO-2 to NNO+2. The Cu spectroscopy data from the natural and synthetic glasses show two dominant Cu species, Cu<sup>1+</sup> oxides (referred to here as Cu–O) and Cu<sup>1+</sup> sulfides (referred to here broadly as Cu-S, but not precluding Cu-Fe-S species). The relative proportion of each species present correlates with the relative concentration of dissolved sulfide in the melt. Synthetic sulfur-bearing glasses equilibrated at NNO-1.2 were found to contain exclusively Cu-S species. Sulfur-bearing experimental glasses equilibrated at NNO-0.5 give calculated Cu–O/(Cu–O + Cu-S), defined here as the “Cu–O fraction”, of < 0.10, whereas sulfur-bearing glasses synthesized at NNO+0.6 and NNO+1.8 give calculated Cu–O fraction > 0.96. Natural melt inclusions from Lassen and Kīlauea show a bimodal distribution in Cu–O fraction, with overlapping ranges, of 0.14–0.77 for Lassen and 0.18––0.78 for Kīlauea. Michoacán-Guanajuato inclusions yield Cu–O fractions of 0.68–0.91. The difference in the calculated proportions of Cu–O to Cu-S species appear correlated with available sulfide in the melt. As relative S<sup>2-</sup> concentrations decrease, the dissolved Cu species in the melt evolves from dominantly Cu-S to Cu–O. This includes melts equilibrated at <em>f</em>O<sub>2</sub>’s where S<sup>6+</sup> is the dominant S species. At intermediate sulfide abundances both species appear to coexist. Thermodynamic modeling of the Cu speciation in these silicate glasses suggests that speciation of Cu as a CuFeS<sub>2</sub> melt species (akin to chalcopyrite or intermediate solid solution) most accurately predicts the measured Cu species. The modeling suggests that a<sub>FeO</sub> in the silicate melt, <em>f</em>O<sub>2</sub> and melt S<sup>2-</sup> (expressed as <em>f</em>S<sub>2</sub>) are the most important parameters controlling the proportions of Cu–O vs. Cu-S species. Our results provide a new perspective for understanding Cu solubility, transport, and partitioning in magmatic systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 181-194"},"PeriodicalIF":4.5,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-03DOI: 10.1016/j.gca.2025.02.033
Andrew C. Turner , Roman Korol , Markus Bill , Daniel A. Stolper
The stable isotopic compositions of light n-alkanes, including methane, ethane, and propane, are often used to identify the sources and thermal maturity of natural gas samples. Though stable isotopic compositions of these molecules are commonly assumed to be controlled by kinetic isotope effects, recent studies have proposed both carbon and hydrogen isotopic equilibrium may also occur in some samples. Assessing whether samples are in isotopic equilibrium requires knowledge of light alkane equilibrium fractionation factors over geologically relevant temperatures for formation and storage (up to ∼300 °C). In this study, we report experimental results of hydrogen isotopic equilibrium between ethane and H2 from 30 to 200 °C and propane and H2 from 75 to 200 °C. We compare these results with high-level theoretical calculations and provide a preferred polynomial fit to describe equilibrium fractionation factors. Comparison of these fractionation factors with a compilation of ∼500 compiled environmental gas samples supports the proposal that many (∼50%) of these natural gas samples exhibit hydrogen isotopic compositions consistent with having formed in or attained methane-ethane-propane hydrogen isotopic equilibrium over geologically relevant temperatures for formation and storage (50–300 °C).
{"title":"Stable isotope equilibria in the dihydrogen-water-methane-ethane-propane system. Part 2: Experimental determination of hydrogen isotopic equilibrium for ethane-H2 from 30 to 200 °C and propane-H2 from 75 to 200 °C","authors":"Andrew C. Turner , Roman Korol , Markus Bill , Daniel A. Stolper","doi":"10.1016/j.gca.2025.02.033","DOIUrl":"10.1016/j.gca.2025.02.033","url":null,"abstract":"<div><div>The stable isotopic compositions of light <em>n</em>-alkanes, including methane, ethane, and propane, are often used to identify the sources and thermal maturity of natural gas samples. Though stable isotopic compositions of these molecules are commonly assumed to be controlled by kinetic isotope effects, recent studies have proposed both carbon and hydrogen isotopic equilibrium may also occur in some samples. Assessing whether samples are in isotopic equilibrium requires knowledge of light alkane equilibrium fractionation factors over geologically relevant temperatures for formation and storage (up to ∼300 °C). In this study, we report experimental results of hydrogen isotopic equilibrium between ethane and H<sub>2</sub> from 30 to 200 °C and propane and H<sub>2</sub> from 75 to 200 °C. We compare these results with high-level theoretical calculations and provide a preferred polynomial fit to describe equilibrium fractionation factors. Comparison of these fractionation factors with a compilation of ∼500 compiled environmental gas samples supports the proposal that many (∼50%) of these natural gas samples exhibit hydrogen isotopic compositions consistent with having formed in or attained methane-ethane-propane hydrogen isotopic equilibrium over geologically relevant temperatures for formation and storage (50–300 °C).</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 91-106"},"PeriodicalIF":4.5,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666346","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}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号