Pub Date : 2025-01-25DOI: 10.1016/j.gca.2025.01.029
Giuseppe D. Saldi, Thierry Decrausaz, Vasileios Mavromatis, Pascale Bénézeth
The study of natural analogues of CO2 mineral sequestration combined with the experimental quantification of carbonation reactions constitutes a fundamental approach to understand the spatial and structural distribution of carbonated bodies and the time scales by which large amounts of CO2 can be stored in solid form into geologic formations. To better quantify the carbonation rates of ultramafic rocks and study the evolution of dissolved Mg isotope composition during their interaction with CO2-rich fluids, a series of batch carbonation experiments using a partially serpentinized harzburgite from the Semail ophiolite (Oman) was conducted at 90–180 °C and at constant CO2 partial pressures (∼ 15–20 bar). The yield of the carbonation reaction increased from ∼ 0 at 90 °C to a maximum of 31 mol % at 150 °C, decreasing to 12 mol % at 180 °C over a period of one month. Magnesites containing 3–9 wt% of Fe and silica polymorphs (SiO2(am) and chalcedony) were the main reaction products, with a fraction of secondary Mg-silicates that increased with increasing temperature, significantly reducing the carbonation extent at 180 °C. The aqueous fluid became progressively enriched in heavy isotopes with the progress of the carbonation reaction. The apparent Mg isotope fractionations between the rock and bulk fluid (Δ26Mg = δ26Mgsolid − δ26Mgfluid) varied from −1.6 ‰ at 120 °C to −0.9 ‰ at 180 °C, consistent with the preferential uptake of 24Mg by carbonate minerals and the decrease of isotope fractionation with increasing temperature. The average magnesite isotope compositions (−1.6 ‰ ≤ δ26Mg ≤ -0.3 ‰) derived from mass-balance calculations were found to be within the range of δ26Mg values reported for Oman listvenites, suggesting that the carbonation processes in this geological unit took place within the temperature range considered in this study (∼120–180 °C).
{"title":"Carbonation processes in Oman peridotite: temperature-dependent reactions and Mg isotope composition of reacting fluids","authors":"Giuseppe D. Saldi, Thierry Decrausaz, Vasileios Mavromatis, Pascale Bénézeth","doi":"10.1016/j.gca.2025.01.029","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.029","url":null,"abstract":"The study of natural analogues of CO<ce:inf loc=\"post\">2</ce:inf> mineral sequestration combined with the experimental quantification of carbonation reactions constitutes a fundamental approach to understand the spatial and structural distribution of carbonated bodies and the time scales by which large amounts of CO<ce:inf loc=\"post\">2</ce:inf> can be stored in solid form into geologic formations. To better quantify the carbonation rates of ultramafic rocks and study the evolution of dissolved Mg isotope composition during their interaction with CO<ce:inf loc=\"post\">2</ce:inf>-rich fluids, a series of batch carbonation experiments using a partially serpentinized harzburgite from the Semail ophiolite (Oman) was conducted at 90–180 °C and at constant CO<ce:inf loc=\"post\">2</ce:inf> partial pressures (∼ 15–20 bar). The yield of the carbonation reaction increased from ∼ 0 at 90 °C to a maximum of 31 mol % at 150 °C, decreasing to 12 mol % at 180 °C over a period of one month. Magnesites containing 3–9 wt% of Fe and silica polymorphs (SiO<ce:inf loc=\"post\">2(am)</ce:inf> and chalcedony) were the main reaction products, with a fraction of secondary Mg-silicates that increased with increasing temperature, significantly reducing the carbonation extent at 180 °C. The aqueous fluid became progressively enriched in heavy isotopes with the progress of the carbonation reaction. The apparent Mg isotope fractionations between the rock and bulk fluid (Δ<ce:sup loc=\"post\">26</ce:sup>Mg = δ<ce:sup loc=\"post\">26</ce:sup>Mg<ce:inf loc=\"post\">solid</ce:inf> − δ<ce:sup loc=\"post\">26</ce:sup>Mg<ce:inf loc=\"post\">fluid</ce:inf>) varied from −1.6 ‰ at 120 °C to −0.9 ‰ at 180 °C, consistent with the preferential uptake of <ce:sup loc=\"post\">24</ce:sup>Mg by carbonate minerals and the decrease of isotope fractionation with increasing temperature. The average magnesite isotope compositions (−1.6 ‰ ≤ δ<ce:sup loc=\"post\">26</ce:sup>Mg ≤ -0.3 ‰) derived from mass-balance calculations were found to be within the range of δ<ce:sup loc=\"post\">26</ce:sup>Mg values reported for Oman listvenites, suggesting that the carbonation processes in this geological unit took place within the temperature range considered in this study (∼120–180 °C).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"41 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125392","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 : 2025-01-23DOI: 10.1016/j.gca.2025.01.024
Daniel E. Harlov, Justin Casaus, Brian A. Konecke, Adam C. Simon
Here, we report results from hydrothermal alteration and crystallization experiments at 800 °C and 1 GPa that constrain the partitioning of S, Fe, Sr, and Ce (as a proxy for the REE) between fluorapatite and hydrothermal fluids of variable compositions. The data from these experiments demonstrate that S can be incorporated in apatite by the two known coupled substitutions S6+ + Na+ = P5+ + Ca2+ and S6+ + Si4+ = 2P5+. The data also demonstrate that the presence of Sr in hydrothermal fluids promotes the incorporation of Na and S in apatite via the coupled substitution S6+ + Na+ = P5+ + Sr2+. Our data also reveal a previously unknown intrinsic relationship between Fe and S, and Ce and S in metasomatized fluorapatite that can be explained by the coupled substitutions Ca2+ + P5+ = Fe3+ + S4+ and Ca2+ + P5+ = Ce3+ + S4+, respectively. The concentrations of Cl, OH, and S in run-product apatite are positively correlated with each other, which indicates that the presence of Cl and OH can play a determinative role in the incorporation of S in apatite. Overall, the data from these metasomatism experiments, involving S and apatite, demonstrate that incorporation of sulfate and sulfite into apatite during metasomatism depends on the abundance of charge-balancing cations in the fluid.
{"title":"Experimental metasomatic incorporation of sulfur into fluorapatite as a function of coupled substitutions involving sodium, silicon, iron, and cerium","authors":"Daniel E. Harlov, Justin Casaus, Brian A. Konecke, Adam C. Simon","doi":"10.1016/j.gca.2025.01.024","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.024","url":null,"abstract":"Here, we report results from hydrothermal alteration and crystallization experiments at 800 °C and 1 GPa that constrain the partitioning of S, Fe, Sr, and Ce (as a proxy for the REE) between fluorapatite and hydrothermal fluids of variable compositions. The data from these experiments demonstrate that S can be incorporated in apatite by the two known coupled substitutions S<ce:sup loc=\"post\">6+</ce:sup> + Na<ce:sup loc=\"post\">+</ce:sup> = P<ce:sup loc=\"post\">5+</ce:sup> + Ca<ce:sup loc=\"post\">2+</ce:sup> and S<ce:sup loc=\"post\">6+</ce:sup> + Si<ce:sup loc=\"post\">4+</ce:sup> = 2P<ce:sup loc=\"post\">5+</ce:sup>. The data also demonstrate that the presence of Sr in hydrothermal fluids promotes the incorporation of Na and S in apatite via the coupled substitution S<ce:sup loc=\"post\">6+</ce:sup> + Na<ce:sup loc=\"post\">+</ce:sup> = P<ce:sup loc=\"post\">5+</ce:sup> + Sr<ce:sup loc=\"post\">2+</ce:sup>. Our data also reveal a previously unknown intrinsic relationship between Fe and S, and Ce and S in metasomatized fluorapatite that can be explained by the coupled substitutions Ca<ce:sup loc=\"post\">2+</ce:sup> + P<ce:sup loc=\"post\">5+</ce:sup> = Fe<ce:sup loc=\"post\">3+</ce:sup> + S<ce:sup loc=\"post\">4+</ce:sup> and Ca<ce:sup loc=\"post\">2+</ce:sup> + P<ce:sup loc=\"post\">5+</ce:sup> = Ce<ce:sup loc=\"post\">3+</ce:sup> + S<ce:sup loc=\"post\">4+</ce:sup>, respectively. The concentrations of Cl, OH, and S in run-product apatite are positively correlated with each other, which indicates that the presence of Cl and OH can play a determinative role in the incorporation of S in apatite. Overall, the data from these metasomatism experiments, involving S and apatite, demonstrate that incorporation of sulfate and sulfite into apatite during metasomatism depends on the abundance of charge-balancing cations in the fluid.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125250","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 : 2025-01-23DOI: 10.1016/j.gca.2025.01.020
Monika K. Rusiecka, Bernard J. Wood
We have determined the solubility and behavior of chlorine in hydrous basaltic melts at high pressures (0.5–1.5 GPa) and temperatures (1200–1300 °C) using the chlorine fugacity control method of Thomas and Wood (2021). By systematically increasing the water content of the melt from 0 to 4 wt% at fixed chlorine and oxygen fugacities we find that addition of H2O leads to an increase in chlorine concentration under all conditions studied. In order to develop a comprehensive equation for chlorine solubility we combined our data with 60 results on anhydrous compositions from Thomas and Wood (2021,2023). We define chloride capacity CCl for each experiment as:
{"title":"Chlorine and NaCl in hydrous basaltic melts","authors":"Monika K. Rusiecka, Bernard J. Wood","doi":"10.1016/j.gca.2025.01.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.020","url":null,"abstract":"We have determined the solubility and behavior of chlorine in hydrous basaltic melts at high pressures (0.5–1.5 GPa) and temperatures (1200–1300 °C) using the chlorine fugacity control method of Thomas and Wood (2021). By systematically increasing the water content of the melt from 0 to 4 wt% at fixed chlorine and oxygen fugacities we find that addition of H<ce:inf loc=\"post\">2</ce:inf>O leads to an increase in chlorine concentration under all conditions studied. In order to develop a comprehensive equation for chlorine solubility we combined our data with 60 results on anhydrous compositions from Thomas and Wood (2021,2023). We define chloride capacity C<ce:inf loc=\"post\">Cl</ce:inf> for each experiment as:","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"8 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125045","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 : 2025-01-20DOI: 10.1016/j.gca.2025.01.028
V. Megevand, J.-C. Viennet, C. Le Guillou, F. Guyot, S. Bernard
The mineral assemblage referred to as “iddingsite” has been described in Martian meteorites. In Nakhlites, this assemblage is mainly composed of Fe/Mg-rich phyllosilicates (such as serpentine and smectites) associated in some cases with Fe-oxides (such as ferrihydrite, goethite or (titano)magnetite) and carbonates, and occurs either as patches and veinlets in the mesostasis or as veins infiltrating olivines and clinopyroxenes. So far, iddingsite has usually been interpreted as a product of low-temperature (<150 °C) alteration of pre-existing silicates by (sub)surface water. Here, we report results of the petrographic study of a section of NWA 817 revealing that the olivine-hosted iddingsite veins are symmetrically structured with an internal part exhibiting a mica-celadonite composition and an external part displaying a nontronite-saponite composition. These features are consistent with a progressive differentiation of a residual magmatic fluid having infiltrated decompression-induced cracks of olivines at the end of the cooling sequence. We propose that this residual liquid directly produced the ferric mica-celadonite phyllosilicates while triggering the deuteric alteration of the hosting olivine (i.e. oxidative alteration during magma cooling), thereby producing an alteration front made of Fe-nontronite-saponite at the contact with olivine. Altogether, without excluding the possibility that other Nakhlites (such as Lafayette) may have experienced secondary alteration by (sub)surface Martian water, the observations reported in the present study rather point to the tardi-magmatic production of iddingsite in NWA 817.
{"title":"Tardi-magmatic iddingsite in the Martian Nakhlite NWA 817","authors":"V. Megevand, J.-C. Viennet, C. Le Guillou, F. Guyot, S. Bernard","doi":"10.1016/j.gca.2025.01.028","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.028","url":null,"abstract":"The mineral assemblage referred to as “iddingsite” has been described in Martian meteorites. In Nakhlites, this assemblage is mainly composed of Fe/Mg-rich phyllosilicates (such as serpentine and smectites) associated in some cases with Fe-oxides (such as ferrihydrite, goethite or (titano)magnetite) and carbonates, and occurs either as patches and veinlets in the mesostasis or as veins infiltrating olivines and clinopyroxenes. So far, iddingsite has usually been interpreted as a product of low-temperature (<150 °C) alteration of pre-existing silicates by (sub)surface water. Here, we report results of the petrographic study of a section of NWA 817 revealing that the olivine-hosted iddingsite veins are symmetrically structured with an internal part exhibiting a mica-celadonite composition and an external part displaying a nontronite-saponite composition. These features are consistent with a progressive differentiation of a residual magmatic fluid having infiltrated decompression-induced cracks of olivines at the end of the cooling sequence. We propose that this residual liquid directly produced the ferric mica-celadonite phyllosilicates while triggering the deuteric alteration of the hosting olivine (i.e. oxidative alteration during magma cooling), thereby producing an alteration front made of Fe-nontronite-saponite at the contact with olivine. Altogether, without excluding the possibility that other Nakhlites (such as Lafayette) may have experienced secondary alteration by (sub)surface Martian water, the observations reported in the present study rather point to the tardi-magmatic production of iddingsite in NWA 817.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055420","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 : 2025-01-20DOI: 10.1016/j.gca.2025.01.022
Niels A.G.M. van Helmond, Olga M. Żygadłowska, Wytze K. Lenstra, Robin Klomp, Christoph Humborg, Daniel J. Conley, Mike S.M. Jetten, Caroline P. Slomp
Sedimentary concentrations of redox-sensitive trace metals are widely used to reconstruct past ocean redox conditions. Vanadium (V) has great potential as a (paleo)redox proxy, due to its strong redox-dependent speciation (+III, +IV, +V) and the increased sedimentary sequestration of its more reduced species. The geochemistry of V in sulfide-rich marine environments is not yet well understood, however, hampering the use of V as a (paleo)redox proxy. Here, we present V data for two coastal systems, with bottom water redox conditions ranging from oxic to euxinic, to further constrain V geochemistry. Our sedimentary record from a eutrophic coastal marine basin (Scharendijke basin, Lake Grevelingen, the Netherlands), covering the last decade, shows distinct enrichments in molybdenum (Mo) and organic carbon (Corg) but depletions in V during seasonal bottom water euxinia, which can be discerned due to the exceptionally high sedimentation rate at our study site (up to 20 cm yr−1). A seasonal study for the same coastal basin confirms this trend and reveals the accumulation of V, iron (Fe) and manganese (Mn) in the water column during summer euxinia. We conclude that the slow kinetics of V reduction to V(III) and subsequent precipitation as (oxy)hydroxide V(OH)3(s) likely provide the opportunity for V to escape sedimentary sequestration during summer euxinia, resulting in the observed sedimentary V depletion. Sediments from three sites with contrasting bottom water redox conditions (oxic, seasonally hypoxic, euxinic) in the eutrophic Stockholm Archipelago, show a similar trend as that of Lake Grevelingen, with decreasing V concentrations and increasing Mo and Corg concentrations as bottom water conditions become more reducing. This confirms that our findings for Lake Grevelingen are not site-specific and are likely a generic feature of euxinic coastal systems with high sulfide concentrations (> 0.5 mmol L−1) near the sediment surface and high rates of anaerobic degradation of organic matter. Our results show that co-occurring sedimentary Mo and Corg enrichments and V depletion (or absence or suppression of an enrichment) are indicators of strongly sulfidic conditions in such settings. Finally, we show that maxima in sedimentary molar V/Mn ratios correlate with strongly reducing conditions. This finding contrasts with prior work on V/Mn ratios as a (paleo)redox proxy, implying that further research is necessary.
{"title":"Sedimentary vanadium depletion under sulfidic conditions: Implications for (paleo)redox proxy applications","authors":"Niels A.G.M. van Helmond, Olga M. Żygadłowska, Wytze K. Lenstra, Robin Klomp, Christoph Humborg, Daniel J. Conley, Mike S.M. Jetten, Caroline P. Slomp","doi":"10.1016/j.gca.2025.01.022","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.022","url":null,"abstract":"Sedimentary concentrations of redox-sensitive trace metals are widely used to reconstruct past ocean redox conditions. Vanadium (V) has great potential as a (paleo)redox proxy, due to its strong redox-dependent speciation (+III, +IV, +V) and the increased sedimentary sequestration of its more reduced species. The geochemistry of V in sulfide-rich marine environments is not yet well understood, however, hampering the use of V as a (paleo)redox proxy. Here, we present V data for two coastal systems, with bottom water redox conditions ranging from oxic to euxinic, to further constrain V geochemistry. Our sedimentary record from a eutrophic coastal marine basin (Scharendijke basin, Lake Grevelingen, the Netherlands), covering the last decade, shows distinct enrichments in molybdenum (Mo) and organic carbon (C<ce:inf loc=\"post\">org</ce:inf>) but depletions in V during seasonal bottom water euxinia, which can be discerned due to the exceptionally high sedimentation rate at our study site (up to 20 cm yr<ce:sup loc=\"post\">−1</ce:sup>). A seasonal study for the same coastal basin confirms this trend and reveals the accumulation of V, iron (Fe) and manganese (Mn) in the water column during summer euxinia. We conclude that the slow kinetics of V reduction to V(III) and subsequent precipitation as (oxy)hydroxide V(OH)<ce:inf loc=\"post\">3(s)</ce:inf> likely provide the opportunity for V to escape sedimentary sequestration during summer euxinia, resulting in the observed sedimentary V depletion. Sediments from three sites with contrasting bottom water redox conditions (oxic, seasonally hypoxic, euxinic) in the eutrophic Stockholm Archipelago, show a similar trend as that of Lake Grevelingen, with decreasing V concentrations and increasing Mo and C<ce:inf loc=\"post\">org</ce:inf> concentrations as bottom water conditions become more reducing. This confirms that our findings for Lake Grevelingen are not site-specific and are likely a generic feature of euxinic coastal systems with high sulfide concentrations (> 0.5 mmol L<ce:sup loc=\"post\">−1</ce:sup>) near the sediment surface and high rates of anaerobic degradation of organic matter. Our results show that co-occurring sedimentary Mo and C<ce:inf loc=\"post\">org</ce:inf> enrichments and V depletion (or absence or suppression of an enrichment) are indicators of strongly sulfidic conditions in such settings. Finally, we show that maxima in sedimentary molar V/Mn ratios correlate with strongly reducing conditions. This finding contrasts with prior work on V/Mn ratios as a (paleo)redox proxy, implying that further research is necessary.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"50 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055425","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}
Most endogenic gold deposits are associated with H2O-rich magmatism or their associated hydrothermal systems. However, the role that H2O plays in the transfer and enrichment of gold remains elusive. Here we conducted piston cylinder experiments at 1 GPa and 850 or 950 °C on sulfur-bearing dacitic compositions with variable H2O contents and under different controlled oxygen fugacity. Our results show that increasing the H2O contents of the melts from 2 to 15 wt% enhances gold solubilities by up to 37-fold at moderate oxidizing conditions (approximately 2 log units above the fayalite-magnetite-quartz buffer). This dramatic increase results from H2O-induced elevation of melt FeO content, which increases reduced sulfur concentrations, thereby promoting Au-S complexation in the melt. Under these conditions, H2O-rich, near fluid-saturated melts exhibit gold partition coefficients between sulfide and silicate melt that are one order of magnitude lower than in H2O-poor melts. Thus, H2O content, combined with moderate oxygen fugacity, exerts substantial control on the gold fertility of primary magmas. These findings indicate that both partial melting of H2O-rich sources and crystallization of H2O-rich magmas can effectively mobilize and concentrate gold. The process is further enhanced when fluid exsolution occurs before gold sequestration into sulfides. In contrast, copper partitioning shows stronger dependence on oxygen fugacity than H2O content, explaining the differing behavior of gold and copper during magmatic-hydrothermal evolution. These results provide new insights into the formation of gold-rich magmatic-hydrothermal ore deposits.
{"title":"Gold solubility enhanced by H2O in sulfur-bearing magma: Implications for gold partitioning and mineralization","authors":"Xingcheng Liu, Lanqin Li, Ting Xu, Xiaolin Xiong, Jintuan Wang, Zaicong Wang, Hugh St.C. O’Neill","doi":"10.1016/j.gca.2025.01.017","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.017","url":null,"abstract":"Most endogenic gold deposits are associated with H<ce:inf loc=\"post\">2</ce:inf>O-rich magmatism or their associated hydrothermal systems. However, the role that H<ce:inf loc=\"post\">2</ce:inf>O plays in the transfer and enrichment of gold remains elusive. Here we conducted piston cylinder experiments at 1 GPa and 850 or 950 °C on sulfur-bearing dacitic compositions with variable H<ce:inf loc=\"post\">2</ce:inf>O contents and under different controlled oxygen fugacity. Our results show that increasing the H<ce:inf loc=\"post\">2</ce:inf>O contents of the melts from 2 to 15 wt% enhances gold solubilities by up to 37-fold at moderate oxidizing conditions (approximately 2 log units above the fayalite-magnetite-quartz buffer). This dramatic increase results from H<ce:inf loc=\"post\">2</ce:inf>O-induced elevation of melt FeO content, which increases reduced sulfur concentrations, thereby promoting Au-S complexation in the melt. Under these conditions, H<ce:inf loc=\"post\">2</ce:inf>O-rich, near fluid-saturated melts exhibit gold partition coefficients between sulfide and silicate melt that are one order of magnitude lower than in H<ce:inf loc=\"post\">2</ce:inf>O-poor melts. Thus, H<ce:inf loc=\"post\">2</ce:inf>O content, combined with moderate oxygen fugacity, exerts substantial control on the gold fertility of primary magmas. These findings indicate that both partial melting of H<ce:inf loc=\"post\">2</ce:inf>O-rich sources and crystallization of H<ce:inf loc=\"post\">2</ce:inf>O-rich magmas can effectively mobilize and concentrate gold. The process is further enhanced when fluid exsolution occurs before gold sequestration into sulfides. In contrast, copper partitioning shows stronger dependence on oxygen fugacity than H<ce:inf loc=\"post\">2</ce:inf>O content, explaining the differing behavior of gold and copper during magmatic-hydrothermal evolution. These results provide new insights into the formation of gold-rich magmatic-hydrothermal ore deposits.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"29 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055250","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 : 2025-01-19DOI: 10.1016/j.gca.2025.01.025
Rudolf I. Mashkovtsev, Sanda M. Botis, Jinru Lin, Reza Deevsalar, Leo Ka Long Cheung, Eli Wiens, Ayetullah Tunc, Ning Chen, Roman Chernikov, Yuanming Pan
The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and ab initio theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi2]0 and [GeHH2]0 centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge2+ state. Ge K-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge2+. Theoretical calculations reproduce the experimental 1H and 7Li hyperfine constants of the [GeHLi2]0 center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant c-axis channel, again supporting the Ge2+ state. The presence of Ge2+ in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge4+ is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge2+ in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.
{"title":"Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics","authors":"Rudolf I. Mashkovtsev, Sanda M. Botis, Jinru Lin, Reza Deevsalar, Leo Ka Long Cheung, Eli Wiens, Ayetullah Tunc, Ning Chen, Roman Chernikov, Yuanming Pan","doi":"10.1016/j.gca.2025.01.025","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.025","url":null,"abstract":"The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and <ce:italic>ab initio</ce:italic> theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi<ce:inf loc=\"post\">2</ce:inf>]<ce:sup loc=\"post\">0</ce:sup> and [GeHH<ce:inf loc=\"post\">2</ce:inf>]<ce:sup loc=\"post\">0</ce:sup> centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge<ce:sup loc=\"post\">2+</ce:sup> state. Ge <ce:italic>K</ce:italic>-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge<ce:sup loc=\"post\">2+</ce:sup>. Theoretical calculations reproduce the experimental <ce:sup loc=\"post\">1</ce:sup>H and <ce:sup loc=\"post\">7</ce:sup>Li hyperfine constants of the [GeHLi<ce:inf loc=\"post\">2</ce:inf>]<ce:sup loc=\"post\">0</ce:sup> center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant <ce:italic>c</ce:italic>-axis channel, again supporting the Ge<ce:sup loc=\"post\">2+</ce:sup> state. The presence of Ge<ce:sup loc=\"post\">2+</ce:sup> in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge<ce:sup loc=\"post\">4+</ce:sup> is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge<ce:sup loc=\"post\">2+</ce:sup> in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"59 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055426","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 : 2025-01-19DOI: 10.1016/j.gca.2025.01.016
Sarah Fleischmann , Florian Scholz , Jianghui Du , Jan Scholten , Derek Vance
Nickel (Ni) is a biologically active metal whose reactivity and isotope fractionation in the marine realm are strongly influenced by biological and redox-related processes, giving the stable isotope system potential for studying past ocean environments. Reducing, organic-rich, sediments constitute an important sink of Ni from the modern ocean. Importantly, at open ocean upwelling margins, these kinds of sediment record the isotope composition of the modern deep ocean. Thus, records of their Ni isotope composition in the past have the potential to record the past deep ocean isotope composition and the oceanic isotope mass balance. However, the detailed processes controlling the upwelling sink are not fully understood. Here, we address this issue through data for sediments, porewaters and the water column of Kiel Bight in the Western Baltic Sea. This setting preserves sediments that have similar characteristics to those of open ocean upwelling margins, allowing us to study specific controlling processes in a well constrained setting.
In common with sediments from open-ocean upwelling settings, Ni is well-correlated with carbon in solid sediment, suggesting delivery of Ni via rain of organic carbon from the water column. Overall, porewaters at all sites studied show increasing Ni concentrations from around 10 nM near the sediment–water interface to as high as 50 nM at 25 cm depth. This increase is correlated with increases in ammonia concentrations, suggesting release of Ni from anaerobic respiration of organic matter. However, porewater Ni/NH4 ratios are always lower than Ni:N of water column suspended particulate matter, suggesting an additional process that removes Ni from the porewater. Porewater sulphide also increases with depth, from as low as zero at the sediment–water interface to levels as high as 3 mM at 25 cm. Overall, porewater Ni isotopes become heavier with depth, from bottom water δ60Ni around +0.5 to +1‰, to values as high as +2.3‰ at depth. All these observations strongly suggest that Ni is removed from porewater into a solid sulphide. Mass balance indicates that over 90% of the Ni delivered in organic material to the sediment–water interface is transferred from organic matter into solid sulphide. Upward diffusive fluxes lead to the loss of a small amount back to the water column via a benthic flux. Given the large proportion of Ni retained within the sediment, the loss of such Ni does not strongly impact the isotope composition of the buried pool. These data are crucial in clarifying the processes controlling the size and isotope composition of organic-rich sediments on upwelling margins.
{"title":"Processes controlling nickel and its isotopes in anoxic sediments of a seasonally hypoxic bay","authors":"Sarah Fleischmann , Florian Scholz , Jianghui Du , Jan Scholten , Derek Vance","doi":"10.1016/j.gca.2025.01.016","DOIUrl":"10.1016/j.gca.2025.01.016","url":null,"abstract":"<div><div>Nickel (Ni) is a biologically active metal whose reactivity and isotope fractionation in the marine realm are strongly influenced by biological and redox-related processes, giving the stable isotope system potential for studying past ocean environments. Reducing, organic-rich, sediments constitute an important sink of Ni from the modern ocean. Importantly, at open ocean upwelling margins, these kinds of sediment record the isotope composition of the modern deep ocean. Thus, records of their Ni isotope composition in the past have the potential to record the past deep ocean isotope composition and the oceanic isotope mass balance. However, the detailed processes controlling the upwelling sink are not fully understood. Here, we address this issue through data for sediments, porewaters and the water column of Kiel Bight in the Western Baltic Sea. This setting preserves sediments that have similar characteristics to those of open ocean upwelling margins, allowing us to study specific controlling processes in a well constrained setting.</div><div>In common with sediments from open-ocean upwelling settings, Ni is well-correlated with carbon in solid sediment, suggesting delivery of Ni via rain of organic carbon from the water column. Overall, porewaters at all sites studied show increasing Ni concentrations from around 10 nM near the sediment–water interface to as high as 50 nM at 25 cm depth. This increase is correlated with increases in ammonia concentrations, suggesting release of Ni from anaerobic respiration of organic matter. However, porewater Ni/NH<sub>4</sub> ratios are always lower than Ni:N of water column suspended particulate matter, suggesting an additional process that removes Ni from the porewater. Porewater sulphide also increases with depth, from as low as zero at the sediment–water interface to levels as high as 3 mM at 25 cm. Overall, porewater Ni isotopes become heavier with depth, from bottom water δ<sup>60</sup>Ni around +0.5 to +1‰, to values as high as +2.3‰ at depth. All these observations strongly suggest that Ni is removed from porewater into a solid sulphide. Mass balance indicates that over 90% of the Ni delivered in organic material to the sediment–water interface is transferred from organic matter into solid sulphide. Upward diffusive fluxes lead to the loss of a small amount back to the water column via a benthic flux. Given the large proportion of Ni retained within the sediment, the loss of such Ni does not strongly impact the isotope composition of the buried pool. These data are crucial in clarifying the processes controlling the size and isotope composition of organic-rich sediments on upwelling margins.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"391 ","pages":"Pages 1-15"},"PeriodicalIF":4.5,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055247","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 : 2025-01-19DOI: 10.1016/j.gca.2025.01.026
Haochen Duan, Fang Huang
Aqueous indium (In) speciation and isotope fractionation factors are important to understand the origin and transport of indium during magmatic-hydrothermal and atmosphere-hydrosphere processes. Here, we investigate indium speciation in chloride-rich aqueous solutions and explore their reduced partition function ratios (10<ce:sup loc="post">3</ce:sup><ce:italic>lnβ</ce:italic>) using first-principles calculations. The simulations with initial configurations of InCl(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">5</ce:inf><ce:sup loc="post">2+</ce:sup>, InCl<ce:inf loc="post">2</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">4</ce:inf><ce:sup loc="post">+</ce:sup>, InCl<ce:inf loc="post">3</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">3</ce:inf>, InCl<ce:inf loc="post">4</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">2</ce:inf><ce:sup loc="post">−</ce:sup> and InCl<ce:inf loc="post">5</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:sup loc="post">2−</ce:sup> were performed at 400 and 600 K, respectively. The results show that InCl(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">5</ce:inf><ce:sup loc="post">2+</ce:sup>, InCl<ce:inf loc="post">2</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">4</ce:inf><ce:sup loc="post">+</ce:sup>, InCl<ce:inf loc="post">3</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">2.4</ce:inf>, InCl<ce:inf loc="post">4</ce:inf><ce:sup loc="post">−</ce:sup> and InCl<ce:inf loc="post">5</ce:inf><ce:sup loc="post">2−</ce:sup> are the stable In<ce:sup loc="post">3+</ce:sup> species at 400 K, and their 10<ce:sup loc="post">3</ce:sup><ce:italic>lnβ</ce:italic> decreases from 1.00 ‰, 0.89 ‰, 0.83 ‰, 0.75 ‰ to 0.66 ‰. At 600 K, the stable In<ce:sup loc="post">3+</ce:sup> species are composed of InCl(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">5</ce:inf><ce:sup loc="post">2+</ce:sup>, InCl<ce:inf loc="post">2</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">3.7</ce:inf><ce:sup loc="post">+</ce:sup>, InCl<ce:inf loc="post">3</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">1.7</ce:inf>, InCl<ce:inf loc="post">4</ce:inf><ce:sup loc="post">−</ce:sup> and InCl<ce:inf loc="post">5</ce:inf><ce:sup loc="post">2−</ce:sup> with their 10<ce:sup loc="post">3</ce:sup><ce:italic>lnβ</ce:italic> decreasing from 0.46 ‰, 0.42 ‰, 0.39 ‰, 0.35 ‰ to 0.31 ‰. These results indicate that 10<ce:sup loc="post">3</ce:sup><ce:italic>lnβ</ce:italic> is negatively correlated with the coordination number and bond length of chlorine ligands in aqueous In<ce:sup loc="post">3+</ce:sup> species. Meanwhile, water molecules are gradually removed from the first hydration shell gradually with increasing temperature, such as InCl<ce:inf loc="post">2</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">4</ce:inf><ce:sup loc="post">+</ce:sup> and InCl<ce:inf loc="post">4</ce:inf>(H<ce:inf loc="post">2</ce:inf>O)<ce:inf loc="post">2</ce:inf><ce:sup loc="post">−</ce:sup> to
{"title":"Equilibrium indium isotope fractionation in chloride-rich aqueous solutions using first-principles calculations","authors":"Haochen Duan, Fang Huang","doi":"10.1016/j.gca.2025.01.026","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.026","url":null,"abstract":"Aqueous indium (In) speciation and isotope fractionation factors are important to understand the origin and transport of indium during magmatic-hydrothermal and atmosphere-hydrosphere processes. Here, we investigate indium speciation in chloride-rich aqueous solutions and explore their reduced partition function ratios (10<ce:sup loc=\"post\">3</ce:sup><ce:italic>lnβ</ce:italic>) using first-principles calculations. The simulations with initial configurations of InCl(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">5</ce:inf><ce:sup loc=\"post\">2+</ce:sup>, InCl<ce:inf loc=\"post\">2</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup>, InCl<ce:inf loc=\"post\">3</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">3</ce:inf>, InCl<ce:inf loc=\"post\">4</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">−</ce:sup> and InCl<ce:inf loc=\"post\">5</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:sup loc=\"post\">2−</ce:sup> were performed at 400 and 600 K, respectively. The results show that InCl(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">5</ce:inf><ce:sup loc=\"post\">2+</ce:sup>, InCl<ce:inf loc=\"post\">2</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup>, InCl<ce:inf loc=\"post\">3</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">2.4</ce:inf>, InCl<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">−</ce:sup> and InCl<ce:inf loc=\"post\">5</ce:inf><ce:sup loc=\"post\">2−</ce:sup> are the stable In<ce:sup loc=\"post\">3+</ce:sup> species at 400 K, and their 10<ce:sup loc=\"post\">3</ce:sup><ce:italic>lnβ</ce:italic> decreases from 1.00 ‰, 0.89 ‰, 0.83 ‰, 0.75 ‰ to 0.66 ‰. At 600 K, the stable In<ce:sup loc=\"post\">3+</ce:sup> species are composed of InCl(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">5</ce:inf><ce:sup loc=\"post\">2+</ce:sup>, InCl<ce:inf loc=\"post\">2</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">3.7</ce:inf><ce:sup loc=\"post\">+</ce:sup>, InCl<ce:inf loc=\"post\">3</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">1.7</ce:inf>, InCl<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">−</ce:sup> and InCl<ce:inf loc=\"post\">5</ce:inf><ce:sup loc=\"post\">2−</ce:sup> with their 10<ce:sup loc=\"post\">3</ce:sup><ce:italic>lnβ</ce:italic> decreasing from 0.46 ‰, 0.42 ‰, 0.39 ‰, 0.35 ‰ to 0.31 ‰. These results indicate that 10<ce:sup loc=\"post\">3</ce:sup><ce:italic>lnβ</ce:italic> is negatively correlated with the coordination number and bond length of chlorine ligands in aqueous In<ce:sup loc=\"post\">3+</ce:sup> species. Meanwhile, water molecules are gradually removed from the first hydration shell gradually with increasing temperature, such as InCl<ce:inf loc=\"post\">2</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup> and InCl<ce:inf loc=\"post\">4</ce:inf>(H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">−</ce:sup> to ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"36 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055370","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 : 2025-01-17DOI: 10.1016/j.gca.2025.01.013
I.S. Puchtel, J.L. Hellmann, H. Rizo, J. Blichert-Toft, A.V. Stepanova, A.V. Samsonov, R.J. Walker
In order to further evaluate the timing and possible mechanisms responsible for the transition from both positive and negative to no 142Nd and 182W anomalies in the Archean mantle, we obtained 142,143Nd, 176Hf, 186,187Os, 182W isotope and lithophile trace and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data for mantle plume-derived ∼2.0 Ga picrites and an associated differentiated mafic–ultramafic sill from the Onega Basin on the Fennoscandian Shield. The Onega Basin picrites share striking chemical similarities with the modern Kilauea picrites, featuring enrichments in light rare earth elements (LREE; La/SmN = 1.5 ± 0.2), depletions in heavy rare earth elements (HREE; Gd/YbN = 2.2 ± 0.1), positive high field strength element (HFSE) anomalies (Hf/Hf* = 1.2 ± 0.1, Nb/Nb* = 1.6 ± 0.1), and modern bulk silicate Earth (BSE)-like average W/Th = 0.20 ± 0.08 (2SD). Model calculations indicate that the parental picritic magmas were likely derived from 3 % equilibrium batch melting of a LREE-depleted garnet lherzolite PREMA-type mantle source containing a component of recycled oceanic crust.
{"title":"Bulk silicate Earth-like 142Nd and 182W mantle component sampled by 2.0 Ga Onega Basin picrites, Fennoscandia","authors":"I.S. Puchtel, J.L. Hellmann, H. Rizo, J. Blichert-Toft, A.V. Stepanova, A.V. Samsonov, R.J. Walker","doi":"10.1016/j.gca.2025.01.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.013","url":null,"abstract":"In order to further evaluate the timing and possible mechanisms responsible for the transition from both positive and negative to no <ce:sup loc=\"post\">142</ce:sup>Nd and <ce:sup loc=\"post\">182</ce:sup>W anomalies in the Archean mantle, we obtained <ce:sup loc=\"post\">142,143</ce:sup>Nd, <ce:sup loc=\"post\">176</ce:sup>Hf, <ce:sup loc=\"post\">186,187</ce:sup>Os, <ce:sup loc=\"post\">182</ce:sup>W isotope and lithophile trace and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data for mantle plume-derived ∼2.0 Ga picrites and an associated differentiated mafic–ultramafic sill from the Onega Basin on the Fennoscandian Shield. The Onega Basin picrites share striking chemical similarities with the modern Kilauea picrites, featuring enrichments in light rare earth elements (LREE; La/Sm<ce:inf loc=\"post\">N</ce:inf> = 1.5 ± 0.2), depletions in heavy rare earth elements (HREE; Gd/Yb<ce:inf loc=\"post\">N</ce:inf> = 2.2 ± 0.1), positive high field strength element (HFSE) anomalies (Hf/Hf* = 1.2 ± 0.1, Nb/Nb* = 1.6 ± 0.1), and modern bulk silicate Earth (BSE)-like average W/Th = 0.20 ± 0.08 (2SD). Model calculations indicate that the parental picritic magmas were likely derived from 3 % equilibrium batch melting of a LREE-depleted garnet lherzolite PREMA-type mantle source containing a component of recycled oceanic crust.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"59 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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