Pub Date : 2024-11-30DOI: 10.1016/j.gca.2024.11.029
Fengli Shao, Yaoling Niu, Haiquan Wei, Yu Zhang, Guodong Wang
Globally, granites and rhyolites with SiO<ce:inf loc="post">2</ce:inf> > 70 wt% show large Fe isotope variation (δ<ce:sup loc="post">56</ce:sup>Fe = −0.05 to +0.65 ‰) relative to less silicic igneous rocks in δ<ce:sup loc="post">56</ce:sup>Fe vs. SiO<ce:inf loc="post">2</ce:inf> space. The upper bound of the data tends to show δ<ce:sup loc="post">56</ce:sup>Fe increase with increasing SiO<ce:inf loc="post">2</ce:inf>. Granitic magma differentiation can be invoked to explain magma compositional variation, including Fe isotope variation, but clearly cannot explain the highly varied δ<ce:sup loc="post">56</ce:sup>Fe values. The latter may result from magma differentiation of varying liquidus phases, magma mixing, assimilation and magma source compositional variation. To decipher how each of these and altogether explain the large δ<ce:sup loc="post">56</ce:sup>Fe variation requires rigorous studies of varying well characterized sample suites. This paper is not to solve all these issues but demonstrates clearly using three sample suites with well-defined liquid lines of descent from alkaline basalts to peralkaline rhyolites to show that the δ<ce:sup loc="post">56</ce:sup>Fe increases with continued magma differentiation (increasing SiO<ce:inf loc="post">2</ce:inf>, SiO<ce:inf loc="post">2</ce:inf>/MgO and decreasing MgO). The rapid δ<ce:sup loc="post">56</ce:sup>Fe increase for samples with SiO<ce:inf loc="post">2</ce:inf> > 70 wt% results from ilmenite (vs. magnetite) fractionation. Among all the major liquidus phases, ilmenite has a distinctive affinity with light-Fe isotope, whose crystallization elevates δ<ce:sup loc="post">56</ce:sup>Fe in the residual melts. This result demonstrates the affinity of isotopically heavy Fe with Fe<ce:sup loc="post">3+</ce:sup> and the correlation of isotopically light Fe with Fe<ce:sup loc="post">2+</ce:sup> because δ<ce:sup loc="post">56</ce:sup>Fe values of ilmenite (TiFe<ce:sup loc="post">2+</ce:sup>O<ce:inf loc="post">3</ce:inf>) ≪ δ<ce:sup loc="post">56</ce:sup>Fe values of magnetite (<mml:math altimg="si1.svg"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">F</mml:mi><mml:mi mathvariant="normal">e</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mi mathvariant="normal">O</mml:mi><mml:mo>∙</mml:mo><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">F</mml:mi><mml:mi mathvariant="normal">e</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>). We can conclude that ilmenite solid solution is likely the major oxide liquidus phase at the late-stage felsic melt evolution for relatively dry magmas with low <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> such as peralkaline rhyolites we study here and mid-ocean ridge basalts. We further predict that magnetite (vs. ilmenite) sol
{"title":"Iron isotope fractionation in highly evolved magmas results from ilmenite crystallization","authors":"Fengli Shao, Yaoling Niu, Haiquan Wei, Yu Zhang, Guodong Wang","doi":"10.1016/j.gca.2024.11.029","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.029","url":null,"abstract":"Globally, granites and rhyolites with SiO<ce:inf loc=\"post\">2</ce:inf> > 70 wt% show large Fe isotope variation (δ<ce:sup loc=\"post\">56</ce:sup>Fe = −0.05 to +0.65 ‰) relative to less silicic igneous rocks in δ<ce:sup loc=\"post\">56</ce:sup>Fe vs. SiO<ce:inf loc=\"post\">2</ce:inf> space. The upper bound of the data tends to show δ<ce:sup loc=\"post\">56</ce:sup>Fe increase with increasing SiO<ce:inf loc=\"post\">2</ce:inf>. Granitic magma differentiation can be invoked to explain magma compositional variation, including Fe isotope variation, but clearly cannot explain the highly varied δ<ce:sup loc=\"post\">56</ce:sup>Fe values. The latter may result from magma differentiation of varying liquidus phases, magma mixing, assimilation and magma source compositional variation. To decipher how each of these and altogether explain the large δ<ce:sup loc=\"post\">56</ce:sup>Fe variation requires rigorous studies of varying well characterized sample suites. This paper is not to solve all these issues but demonstrates clearly using three sample suites with well-defined liquid lines of descent from alkaline basalts to peralkaline rhyolites to show that the δ<ce:sup loc=\"post\">56</ce:sup>Fe increases with continued magma differentiation (increasing SiO<ce:inf loc=\"post\">2</ce:inf>, SiO<ce:inf loc=\"post\">2</ce:inf>/MgO and decreasing MgO). The rapid δ<ce:sup loc=\"post\">56</ce:sup>Fe increase for samples with SiO<ce:inf loc=\"post\">2</ce:inf> > 70 wt% results from ilmenite (vs. magnetite) fractionation. Among all the major liquidus phases, ilmenite has a distinctive affinity with light-Fe isotope, whose crystallization elevates δ<ce:sup loc=\"post\">56</ce:sup>Fe in the residual melts. This result demonstrates the affinity of isotopically heavy Fe with Fe<ce:sup loc=\"post\">3+</ce:sup> and the correlation of isotopically light Fe with Fe<ce:sup loc=\"post\">2+</ce:sup> because δ<ce:sup loc=\"post\">56</ce:sup>Fe values of ilmenite (TiFe<ce:sup loc=\"post\">2+</ce:sup>O<ce:inf loc=\"post\">3</ce:inf>) ≪ δ<ce:sup loc=\"post\">56</ce:sup>Fe values of magnetite (<mml:math altimg=\"si1.svg\"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant=\"normal\">F</mml:mi><mml:mi mathvariant=\"normal\">e</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mo>∙</mml:mo><mml:msubsup><mml:mrow><mml:mi mathvariant=\"normal\">F</mml:mi><mml:mi mathvariant=\"normal\">e</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup><mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>). We can conclude that ilmenite solid solution is likely the major oxide liquidus phase at the late-stage felsic melt evolution for relatively dry magmas with low <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> such as peralkaline rhyolites we study here and mid-ocean ridge basalts. We further predict that magnetite (vs. ilmenite) sol","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"52 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841591","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 : 2024-11-30DOI: 10.1016/j.gca.2024.11.028
Hugues Leroux, Pierre-Marie Zanetta, Corentin Le Guillou, Maya Marinova
The study of pristine chondrites provides insight into nebular processes that occurred prior to the accretion of small-sized parent bodies. The interchondrule matrix of the primitive chondrite Acfer 094 is characterized by the presence of submicron-sized anhydrous crystalline aggregates embedded in a silicate groundmass that is mostly amorphous. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDXS) were employed to investigate the matrix of Acfer 094 and its components.
{"title":"Submicron-sized anhydrous crystalline silicates and their relation to amorphous silicate in the matrix of Acfer 094","authors":"Hugues Leroux, Pierre-Marie Zanetta, Corentin Le Guillou, Maya Marinova","doi":"10.1016/j.gca.2024.11.028","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.028","url":null,"abstract":"The study of pristine chondrites provides insight into nebular processes that occurred prior to the accretion of small-sized parent bodies. The interchondrule matrix of the primitive chondrite Acfer 094 is characterized by the presence of submicron-sized anhydrous crystalline aggregates embedded in a silicate groundmass that is mostly amorphous. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDXS) were employed to investigate the matrix of Acfer 094 and its components.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"97 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142804468","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 : 2024-11-28DOI: 10.1016/j.gca.2024.11.024
Carmela Federica Faranda, Gaëlle Prouteau, Bruno Scaillet, Joan Andújar
Bromine, although a minor component in volcanic gases, has received increasing interest in recent studies due to its high atmospheric ozone depletion potential, but its behaviour in alkali-rich felsic hydrous magmas remains unexplored. In this study, fluid-melt partitioning experiments were carried out using natural, Cl- and F-bearing silicate glasses with phonolitic, comenditic and pantelleritic compositions. For each composition, experiments were performed with a range of Br concentrations, at P-T conditions simulating isothermal decompression degassing or isobaric equilibrium cooling at shallow crustal depth (800–1000 °C, 10–200 MPa, oxidising and reducing conditions). The major element, Cl and F concentrations of the run-product glasses were determined by electron microprobe and the Br concentrations by LA-ICPMS. Volatile concentrations in the fluid were determined by mass balance calculations. The experimental results show that more Br partitions into the fluid phase with increasing bulk halogen concentration. The most Br-doped experiments are typically saturated with a vapor phase and a hydrosaline liquid. Experiments at the lowest Br concentrations, closest to natural systems, show that the pressure dependence of vapor-melt Br partitioning is complex, with a minimum vapor-melt partition coefficient observed at 50 MPa in the phonolitic composition (1.8 ± 0.9 at 1000 °C and oxidising conditions). Our results indicate that the eruptive degassing of Br from peralkaline felsic magmas is restricted to the shallowest levels of the magmatic plumbing system and is likely to occur at much lower pressures than in metaluminous magmas. This observation is consistent with the composition of melt inclusions preserved in alkaline silicic magmas. An important finding is that the vapor-melt partitioning of Br and Cl decreases with increasing temperature. In phonolite, at 200 MPa and oxidising conditions, the Br vapor-melt partition coefficient decreases from 18.5 ± 3.6 at 900 °C to 3.8 ± 1.5 at 1000 °C. As the ratio between the Br and Cl vapor-melt partition coefficients is not conservative, the Br/Cl ratio in the vapor phase is likely to increase during isobaric cooling and degassing. The vapor-melt partition coefficients of Br and, to a lesser extent Cl also increase with decreasing fO2 in the phonolitic system, and the Br vapor-melt partition coefficient for a reduced alkaline magma is close to that for an oxidised calc-alkaline magma. Our results also show that during protracted storage at shallow levels, oxidised alkali- and F-rich rhyolites coexist with vapor and brine. This suggests that high F concentration promotes unmixing of the halogen-bearing phase coexisting with such melts. The exsolution of immiscible vapor and brine efficiently removes Br from peralkaline magmas and probably limits the flux of Br to the atmosphere from such magmas.
{"title":"Behaviour of bromine in Cl- and F-bearing alkali-rich felsic magmas at crustal depth: An experimental study at 800–1100 °C, 10–200 MPa","authors":"Carmela Federica Faranda, Gaëlle Prouteau, Bruno Scaillet, Joan Andújar","doi":"10.1016/j.gca.2024.11.024","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.024","url":null,"abstract":"Bromine, although a minor component in volcanic gases, has received increasing interest in recent studies due to its high atmospheric ozone depletion potential, but its behaviour in alkali-rich felsic hydrous magmas remains unexplored. In this study, fluid-melt partitioning experiments were carried out using natural, Cl- and F-bearing silicate glasses with phonolitic, comenditic and pantelleritic compositions. For each composition, experiments were performed with a range of Br concentrations, at <ce:italic>P-T</ce:italic> conditions simulating isothermal decompression degassing or isobaric equilibrium cooling at shallow crustal depth (800–1000 °C, 10–200 MPa, oxidising and reducing conditions). The major element, Cl and F concentrations of the run-product glasses were determined by electron microprobe and the Br concentrations by LA-ICPMS. Volatile concentrations in the fluid were determined by mass balance calculations. The experimental results show that more Br partitions into the fluid phase with increasing bulk halogen concentration. The most Br-doped experiments are typically saturated with a vapor phase and a hydrosaline liquid. Experiments at the lowest Br concentrations, closest to natural systems, show that the pressure dependence of vapor-melt Br partitioning is complex, with a minimum vapor-melt partition coefficient observed at 50 MPa in the phonolitic composition (1.8 ± 0.9 at 1000 °C and oxidising conditions). Our results indicate that the eruptive degassing of Br from peralkaline felsic magmas is restricted to the shallowest levels of the magmatic plumbing system and is likely to occur at much lower pressures than in metaluminous magmas. This observation is consistent with the composition of melt inclusions preserved in alkaline silicic magmas. An important finding is that the vapor-melt partitioning of Br and Cl decreases with increasing temperature. In phonolite, at 200 MPa and oxidising conditions, the Br vapor-melt partition coefficient decreases from 18.5 ± 3.6 at 900 °C to 3.8 ± 1.5 at 1000 °C. As the ratio between the Br and Cl vapor-melt partition coefficients is not conservative, the Br/Cl ratio in the vapor phase is likely to increase during isobaric cooling and degassing. The vapor-melt partition coefficients of Br and, to a lesser extent Cl also increase with decreasing <ce:italic>fO<ce:inf loc=\"post\">2</ce:inf></ce:italic> in the phonolitic system, and the Br vapor-melt partition coefficient for a reduced alkaline magma is close to that for an oxidised calc-alkaline magma. Our results also show that during protracted storage at shallow levels, oxidised alkali- and F-rich rhyolites coexist with vapor and brine. This suggests that high F concentration promotes unmixing of the halogen-bearing phase coexisting with such melts. The exsolution of immiscible vapor and brine efficiently removes Br from peralkaline magmas and probably limits the flux of Br to the atmosphere from such magmas.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"57 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142884588","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 : 2024-11-27DOI: 10.1016/j.gca.2024.11.026
Mara Miranda, Zoltán Zajacz, Alexandra Tsay, Anne-Sophie Bouvier
The release of fluids from magmas at crustal depths is an essential process for the formation of magmatic-hydrothermal ore deposits. However, assessing the extent of volatile loss by magma degassing or volatile gain by fluid fluxing from deeper magmas remains challenging. To develop a new tool to quantitatively track these processes, we experimentally determined the partition coefficients of Cl, Br, and I between aqueous fluids and haplogranitic melts (<mml:math altimg="si7.svg"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math>) as a function of fluid salinity and the aluminum saturation index [ASI = Al<ce:inf loc="post">2</ce:inf>O<ce:inf loc="post">3</ce:inf>/(Na<ce:inf loc="post">2</ce:inf>O + K<ce:inf loc="post">2</ce:inf>O)] of the silicate melt. The experiments were conducted in externally heated rapid-quench René 41 cold-seal pressure vessel apparatus at 200 MPa and 790 ± 10 °C. The Br and I concentrations in the run product glasses were determined by laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry, whereas the concentration of Cl was determined by electron probe microanalysis. The results show that the partition coefficients of the three halogens in a system with chloride-dominated fluids increase with fluid salinity increasing from 1.49 to 60.6 wt% total NaCl equivalent. Specifically, <mml:math altimg="si3.svg"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Cl</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> increases from 23 ± 5 to 168 ± 7 (1σ), <mml:math altimg="si1.svg"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Br</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> increases from 57 ± 13 to 271 ± 14, and <mml:math altimg="si2.svg"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>I</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> increases from 198 ± 61 to 736 ± 159. As for the influence of melt composition, <mml:math altimg="si3.svg"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Cl</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> and <mml:math altimg="si1.svg"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Br</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> attain maximum values at ASI = 1, whereas <mml:math altimg="si2.svg"><mml:mrow><mml:msubsup><mm
{"title":"The fluid/melt partitioning of chlorine, bromine and iodine in felsic magmas and the utility of halogen ratios to track the devolatilization and fluid fluxing of magma reservoirs","authors":"Mara Miranda, Zoltán Zajacz, Alexandra Tsay, Anne-Sophie Bouvier","doi":"10.1016/j.gca.2024.11.026","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.026","url":null,"abstract":"The release of fluids from magmas at crustal depths is an essential process for the formation of magmatic-hydrothermal ore deposits. However, assessing the extent of volatile loss by magma degassing or volatile gain by fluid fluxing from deeper magmas remains challenging. To develop a new tool to quantitatively track these processes, we experimentally determined the partition coefficients of Cl, Br, and I between aqueous fluids and haplogranitic melts (<mml:math altimg=\"si7.svg\"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy=\"false\">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math>) as a function of fluid salinity and the aluminum saturation index [ASI = Al<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf>/(Na<ce:inf loc=\"post\">2</ce:inf>O + K<ce:inf loc=\"post\">2</ce:inf>O)] of the silicate melt. The experiments were conducted in externally heated rapid-quench René 41 cold-seal pressure vessel apparatus at 200 MPa and 790 ± 10 °C. The Br and I concentrations in the run product glasses were determined by laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry, whereas the concentration of Cl was determined by electron probe microanalysis. The results show that the partition coefficients of the three halogens in a system with chloride-dominated fluids increase with fluid salinity increasing from 1.49 to 60.6 wt% total NaCl equivalent. Specifically, <mml:math altimg=\"si3.svg\"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Cl</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy=\"false\">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> increases from 23 ± 5 to 168 ± 7 (1σ), <mml:math altimg=\"si1.svg\"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Br</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy=\"false\">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> increases from 57 ± 13 to 271 ± 14, and <mml:math altimg=\"si2.svg\"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>I</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy=\"false\">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> increases from 198 ± 61 to 736 ± 159. As for the influence of melt composition, <mml:math altimg=\"si3.svg\"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Cl</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy=\"false\">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> and <mml:math altimg=\"si1.svg\"><mml:mrow><mml:msubsup><mml:mi>D</mml:mi><mml:mrow><mml:mtext>Br</mml:mtext></mml:mrow><mml:mrow><mml:mi>f</mml:mi><mml:mo stretchy=\"false\">/</mml:mo><mml:mi>m</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> attain maximum values at ASI = 1, whereas <mml:math altimg=\"si2.svg\"><mml:mrow><mml:msubsup><mm","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"30 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841527","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}
Type 7 chondrites, which record a higher degree of heating process than typical type 3 to type 6 chondrites, are characterized with textures and petrography of partial melting. Understanding the timing and cooling history of incipient melting event for type 7 chondrites could provide insights into the complex thermal process of the early solar system. Here, we studied two chondrites NWA 12272 and NWA 11021. Both samples display partial melting characteristics of LL chondrites, including interconnected plagioclase/high-Ca pyroxene network, zoned plagioclase and lack of chondrules, which concurs with their classification of LL7 chondrites in the Meteoritical Bulletin Database. The 53Mn-53Cr isotopic data of NWA 12272, determined by mineral separates and bulk samples, yielded an isochron with a 53Mn/55Mn ratio of (1.40 ± 0.59) × 10-6 and a corresponding absolute age of 4558.8 ± 2.3 Ma (anchored to D’Orbigny angrite). Combined with the cooling rate estimated by the integration of REE-in-two-pyroxene thermometry and two-pyroxene thermometry, Mn-Cr isochron age of 4558.8 ± 2.3 Ma and Ca-phosphate Pb-Pb age of 4517 ± 6 Ma, we suggest that NWA 12272 experienced a two-stage cooling process after the incipient melting: it exposed to a relatively cold environment with a rapid cooling rate of ∼ 30-100°C/yr at 1150–1000 °C, and soon reburied with a slower cooling rate of ∼ 13 °C/Ma at 1000–475 °C. Although the Mn-Cr isotopic study was not conducted for NWA 11021, the average Ca-phosphate Pb-Pb age of 4509 ± 7 Ma and high-temperature cooling rate (∼1-30°C/yr) of NWA 11021 are indistinguishable from or slightly lower than those of NWA 12272. Assuming NWA 11021 cooled from the same incipient melting event as NWA 12272, it could have recorded a similar two-stage cooling process. We suggest that the studied LL7 chondrites were most likely formed in the early solar system when additional impact heat overlapped on the “heated” type 5–6 chondrites. Integrated with the previous cooling rates of LL6-7 chondrites, the prevailing two-stage cooling rates of LL chondrites provide compelling evidence for the fragmentation-re-accretion process in the early history of LL chondrite parent body. This early impact event also happened in other ordinary chondrite groups and some iron meteorites.
{"title":"The geochronology and cooling history of type 7 chondrites: Insights into the early impact events on chondritic parent body","authors":"Ye Li, Yuting Wang, Haoxuan Jiang, Jia Liu, Liping Qin, Qiu-Li Li, Yu Liu, Zhenfei Wang, Weibiao Hsu","doi":"10.1016/j.gca.2024.11.020","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.020","url":null,"abstract":"Type 7 chondrites, which record a higher degree of heating process than typical type 3 to type 6 chondrites, are characterized with textures and petrography of partial melting. Understanding the timing and cooling history of incipient melting event for type 7 chondrites could provide insights into the complex thermal process of the early solar system. Here, we studied two chondrites NWA 12272 and NWA 11021. Both samples display partial melting characteristics of LL chondrites, including interconnected plagioclase/high-Ca pyroxene network, zoned plagioclase and lack of chondrules, which concurs with their classification of LL7 chondrites in the Meteoritical Bulletin Database. The <ce:sup loc=\"post\">53</ce:sup>Mn-<ce:sup loc=\"post\">53</ce:sup>Cr isotopic data of NWA 12272, determined by mineral separates and bulk samples, yielded an isochron with a <ce:sup loc=\"post\">53</ce:sup>Mn/<ce:sup loc=\"post\">55</ce:sup>Mn ratio of (1.40 ± 0.59) × 10<ce:sup loc=\"post\">-6</ce:sup> and a corresponding absolute age of 4558.8 ± 2.3 Ma (anchored to D’Orbigny angrite). Combined with the cooling rate estimated by the integration of REE-in-two-pyroxene thermometry and two-pyroxene thermometry, Mn-Cr isochron age of 4558.8 ± 2.3 Ma and Ca-phosphate Pb-Pb age of 4517 ± 6 Ma, we suggest that NWA 12272 experienced a two-stage cooling process after the incipient melting: it exposed to a relatively cold environment with a rapid cooling rate of ∼ 30-100°C/yr at 1150–1000 °C, and soon reburied with a slower cooling rate of ∼ 13 °C/Ma at 1000–475 °C. Although the Mn-Cr isotopic study was not conducted for NWA 11021, the average Ca-phosphate Pb-Pb age of 4509 ± 7 Ma and high-temperature cooling rate (∼1-30°C/yr) of NWA 11021 are indistinguishable from or slightly lower than those of NWA 12272. Assuming NWA 11021 cooled from the same incipient melting event as NWA 12272, it could have recorded a similar two-stage cooling process. We suggest that the studied LL7 chondrites were most likely formed in the early solar system when additional impact heat overlapped on the “heated” type 5–6 chondrites. Integrated with the previous cooling rates of LL6-7 chondrites, the prevailing two-stage cooling rates of LL chondrites provide compelling evidence for the fragmentation-re-accretion process in the early history of LL chondrite parent body. This early impact event also happened in other ordinary chondrite groups and some iron meteorites.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"116 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142763010","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 : 2024-11-26DOI: 10.1016/j.gca.2024.11.018
Ryan Mathur , Linda Godfrey , Hartwig E. Frimmel , Nathan Yee , David Mossman , Peter Baran , Victor A. Valencia
A comparison of the copper isotope composition of sedimentary rock strata spanning in age across the Great Oxidation Event (GOE) and that of pyrite, carbon, and native gold from the Mesoarchean Witwatersrand Basin reveal that an oxidative gradient triggered gold precipitation on biologic material, now present in the form of gold-rich carbon seams in the latter. Oxidative redox reactions are known to favor the heavier 65Cu isotope. A sequence of sedimentary rock strata on the Kaapvaal Craton records higher Cu isotope values before the start of the oxidation of the Proterozoic atmosphere in comparison to that of younger transitional-GOE strata. A similar increase in Cu isotope ratios was found in gold within carbon seams in comparison to the Cu isotope ratios in rounded pyrite in auriferous metaconglomerates of the ca. 2.9 Ga basal Central Rand Group. However, the Cu isotope ratios in the post-GOE sedimentary rocks of the Kaapvaal Craton and the pre-GOE native gold in the ca. 2.9 Ga carbon seams record different causes of oxidation. The gold in the carbon seams was not uniformly deposited across the lower Central Rand Basin but in isolated depositional environments. Changes in large-scale atmospheric oxidation, evident by the increase in δ65Cu in the pre and transitional-GOE sedimentary strata in the Kaapvaal Craton, cannot be tied to the elevated Cu isotope values in the carbon seams. Instead, the latter, which are higher than all other measured values (δ65Cu = +2.41 ± 0.24 ‰), mimics Cu isotope fractionation associated with acidophilic bacterial activity. Therefore, the significant difference in Cu isotope values of the carbon seams compared to those of detrital pyrite in the Witwatersrand metaconglomerates could be interpreted as a fingerprint of a microbial redox gradient that might have induced the precipitation of gold, thus having formed the richest known gold province in the world.
{"title":"Copper isotopic evidence of microbial gold fixation in the Mesoarchean Witwatersrand Basin","authors":"Ryan Mathur , Linda Godfrey , Hartwig E. Frimmel , Nathan Yee , David Mossman , Peter Baran , Victor A. Valencia","doi":"10.1016/j.gca.2024.11.018","DOIUrl":"10.1016/j.gca.2024.11.018","url":null,"abstract":"<div><div>A comparison of the copper isotope composition of sedimentary rock strata spanning in age across the Great Oxidation Event (GOE) and that of pyrite, carbon, and native gold from the Mesoarchean Witwatersrand Basin reveal that an oxidative gradient triggered gold precipitation on biologic material, now present in the form of gold-rich carbon seams in the latter. Oxidative redox reactions are known to favor the heavier <sup>65</sup>Cu isotope. A sequence of sedimentary rock strata on the Kaapvaal Craton records higher Cu isotope values before the start of the oxidation of the Proterozoic atmosphere in comparison to that of younger transitional-GOE strata. A similar increase in Cu isotope ratios was found in gold within carbon seams in comparison to the Cu isotope ratios in rounded pyrite in auriferous metaconglomerates of the ca. 2.9 Ga basal Central Rand Group. However, the Cu isotope ratios in the post-GOE sedimentary rocks of the Kaapvaal Craton and the pre-GOE native gold in the ca. 2.9 Ga carbon seams record different causes of oxidation. The gold in the carbon seams was not uniformly deposited across the lower Central Rand Basin but in isolated depositional environments. Changes in large-scale atmospheric oxidation, evident by the increase in δ<sup>65</sup>Cu in the pre and transitional-GOE sedimentary strata in the Kaapvaal Craton, cannot be tied to the elevated Cu isotope values in the carbon seams. Instead, the latter, which are higher than all other measured values (δ<sup>65</sup>Cu = +2.41 ± 0.24 ‰), mimics Cu isotope fractionation associated with acidophilic bacterial activity. Therefore, the significant difference in Cu isotope values of the carbon seams compared to those of detrital pyrite in the Witwatersrand metaconglomerates could be interpreted as a fingerprint of a microbial redox gradient that might have induced the precipitation of gold, thus having formed the richest known gold province in the world.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 114-126"},"PeriodicalIF":4.5,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142748009","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 : 2024-11-26DOI: 10.1016/j.gca.2024.11.017
Dachuan Wang , Tong Hou , Roman Botcharnikov , Stefan Weyer , Sarah-Lynn Haselbach , Zhaochong Zhang , Meng Wang , Ingo Horn , Francois Holtz
The genesis of high-grade Fe-Ti-V oxide ores (up to >90 vol%) in layered intrusions remains highly debated. Here, on example of Hongge layered intrusion in China, we show that hydrothermal dissolution and precipitation of Fe-Ti-V oxides played a critical role in forming high-grade massive ore deposits as demonstrated by textural-compositional evidence and in-situ iron isotope data (δ56Fe), analyzed with femtosecond laser ablation multicollector (LA-MC-) ICP-MS. Hongge is a mafic layered intrusion composed of a Lower olivine clinopyroxenite Zone (LZ), a Middle clinopyroxenite Zone (MZ), where thick massive ore layers (with up to 90 % Fe-Ti-V oxides) formed, and an Upper gabbro Zone (UZ). Magnetite in Hongge exhibits two contrasting generations: 1) Mag1, observed in all lithological zones and formed at the magmatic stage, has extensive ilmenite exsolution lamellae and high Ti and Cr content. The δ56Fe of Mag1 shows considerable variations from −0.23 to 0.63 ‰ and strikingly an offset of ∼0.3 ‰ towards lower values in the massive ore zone compared to the zones below and above; 2) Mag2, concentrated mainly in thick massive ore layers in MZ without exsolution lamellae, is almost pure magnetite (with low Ti, Al content) and has extremely low δ56Fe values (−1.24 to −0.09 ‰), indicating precipitation from Fe-enriched hydrothermal fluids. Similarly, the δ56Fe of ilmenite shows significant variations from −1.08 to −0.27 ‰ and is significantly lower than typical values for igneous ilmenite (−0.4–0 ‰). Ilmenite displays a similar Fe isotope variation pattern to Mag1 along the stratigraphic position, i.e., with significantly lower δ56Fe in the massive ore zone. As magnetite and ilmenite together contain essentially all Fe, the isotopic shift of these minerals in the ore zone translates to a bulk isotopic offset of ∼−0.3 ‰ compared to the zones below and above. This requires a bulk flux of isotopically light Fe resulting in Fe enrichment in this zone to form massive or even monomineralic ores. The very light isotopic values, particularly hydrothermal magnetite (Mag2) and petrologic evidence, strongly indicate that the Fe flux into the massive ore layers occurred during hydrothermal reworking. This scenario is furthermore supported by magnetite-ilmenite elemental and isotopic thermometry, according to which Fe-Ti oxides experienced hydrothermal re-equilibration in a temperature range of 400–300 °C. Iron isotopic mass balance calculations imply that ∼20–30 % of the Fe in the thick massive ore layers may result from secondary enrichment through hydrothermal precipitation, significantly increasing the ore tonnages and grades. Potentially, other layered intrusions experienced similar mechanisms of hydrothermal Fe enrichment, which will have to be proven in future investigations.
{"title":"Fe-isotopic evidence for hydrothermal reworking as a mechanism to form high-grade Fe-Ti-V oxide ores in layered intrusions","authors":"Dachuan Wang , Tong Hou , Roman Botcharnikov , Stefan Weyer , Sarah-Lynn Haselbach , Zhaochong Zhang , Meng Wang , Ingo Horn , Francois Holtz","doi":"10.1016/j.gca.2024.11.017","DOIUrl":"10.1016/j.gca.2024.11.017","url":null,"abstract":"<div><div>The genesis of high-grade Fe-Ti-V oxide ores (up to >90 vol%) in layered intrusions remains highly debated. Here, on example of Hongge layered intrusion in China, we show that hydrothermal dissolution and precipitation of Fe-Ti-V oxides played a critical role in forming high-grade massive ore deposits as demonstrated by textural-compositional evidence and <em>in-situ</em> iron isotope data (δ<sup>56</sup>Fe), analyzed with femtosecond laser ablation multicollector (LA-MC-) ICP-MS. Hongge is a mafic layered intrusion composed of a Lower olivine clinopyroxenite Zone (LZ), a Middle clinopyroxenite Zone (MZ), where thick massive ore layers (with up to 90 % Fe-Ti-V oxides) formed, and an Upper gabbro Zone (UZ). Magnetite in Hongge exhibits two contrasting generations: 1) Mag1, observed in all lithological zones and formed at the magmatic stage, has extensive ilmenite exsolution lamellae and high Ti and Cr content. The δ<sup>56</sup>Fe of Mag1 shows considerable variations from −0.23 to 0.63 ‰ and strikingly an offset of ∼0.3 ‰ towards lower values in the massive ore zone compared to the zones below and above; 2) Mag2, concentrated mainly in thick massive ore layers in MZ without exsolution lamellae, is almost pure magnetite (with low Ti, Al content) and has extremely low δ<sup>56</sup>Fe values (−1.24 to −0.09 ‰), indicating precipitation from Fe-enriched hydrothermal fluids. Similarly, the δ<sup>56</sup>Fe of ilmenite shows significant variations from −1.08 to −0.27 ‰ and is significantly lower than typical values for igneous ilmenite (−0.4–0 ‰). Ilmenite displays a similar Fe isotope variation pattern to Mag1 along the stratigraphic position, i.e., with significantly lower δ<sup>56</sup>Fe in the massive ore zone. As magnetite and ilmenite together contain essentially all Fe, the isotopic shift of these minerals in the ore zone translates to a bulk isotopic offset of ∼−0.3 ‰ compared to the zones below and above. This requires a bulk flux of isotopically light Fe resulting in Fe enrichment in this zone to form massive or even monomineralic ores. The very light isotopic values, particularly hydrothermal magnetite (Mag2) and petrologic evidence, strongly indicate that the Fe flux into the massive ore layers occurred during hydrothermal reworking. This scenario is furthermore supported by magnetite-ilmenite elemental and isotopic thermometry, according to which Fe-Ti oxides experienced hydrothermal re-equilibration in a temperature range of 400–300 °C. Iron isotopic mass balance calculations imply that ∼20–30 % of the Fe in the thick massive ore layers may result from secondary enrichment through hydrothermal precipitation, significantly increasing the ore tonnages and grades. Potentially, other layered intrusions experienced similar mechanisms of hydrothermal Fe enrichment, which will have to be proven in future investigations.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 78-93"},"PeriodicalIF":4.5,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142718845","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 : 2024-11-26DOI: 10.1016/j.gca.2024.11.022
Hagar Hauzer, David Evans, Wolfgang Müller, Yair Rosenthal, Jonathan Erez
The sodium-to-calcium ratio (Na/Ca) of biogenic CaCO3 has recently been introduced as a proxy for past seawater Ca2+ concentrations ([Ca2+sw]) as demonstrated by a positive correlation between seawater and shell Na/Ca with a minor influence of salinity. In the present study, we investigate the effect of carbonate chemistry on the Na/Ca proxy by conducting a set of experiments in which pH and the concentration of dissolved inorganic carbon (DIC) were independently varied. In addition to Na+, the incorporation of Li+, Mg2+, and Sr2+ into the shells of the large benthic high-Mg calcitic foraminifer Operculina ammonoides was assessed by culturing under constant DIC (∼2170 µmol kg−1) with varying pH (7.5–8.4 NBS scale), and under varying DIC (830–2470 µmol kg−1) with constant pH (∼7.9). Foraminiferal growth rate correlates linearly with calcite saturation state (Ω) of the experimental seawater (SW). The lowest pH and DIC experiments were characterized by low population growth rates, and some of these specimens died and their shells partially dissolved.
{"title":"The effect of carbonate chemistry on trace element incorporation in high-Mg calcitic foraminifera","authors":"Hagar Hauzer, David Evans, Wolfgang Müller, Yair Rosenthal, Jonathan Erez","doi":"10.1016/j.gca.2024.11.022","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.022","url":null,"abstract":"The sodium-to-calcium ratio (Na/Ca) of biogenic CaCO<ce:inf loc=\"post\">3</ce:inf> has recently been introduced as a proxy for past seawater Ca<ce:sup loc=\"post\">2+</ce:sup> concentrations ([Ca<ce:sup loc=\"post\">2+</ce:sup><ce:inf loc=\"post\">sw</ce:inf>]) as demonstrated by a positive correlation between seawater and shell Na/Ca with a minor influence of salinity. In the present study, we investigate the effect of carbonate chemistry on the Na/Ca proxy by conducting a set of experiments in which pH and the concentration of dissolved inorganic carbon (DIC) were independently varied. In addition to Na<ce:sup loc=\"post\">+</ce:sup>, the incorporation of Li<ce:sup loc=\"post\">+</ce:sup>, Mg<ce:sup loc=\"post\">2+</ce:sup>, and Sr<ce:sup loc=\"post\">2+</ce:sup> into the shells of the large benthic high-Mg calcitic foraminifer <ce:italic>Operculina ammonoides</ce:italic> was assessed by culturing under constant DIC (∼2170 µmol kg<ce:sup loc=\"post\">−1</ce:sup>) with varying pH (7.5–8.4 NBS scale), and under varying DIC (830–2470 µmol kg<ce:sup loc=\"post\">−1</ce:sup>) with constant pH (∼7.9). Foraminiferal growth rate correlates linearly with calcite saturation state (Ω) of the experimental seawater (SW). The lowest pH and DIC experiments were characterized by low population growth rates, and some of these specimens died and their shells partially dissolved.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"19 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142804470","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 : 2024-11-26DOI: 10.1016/j.gca.2024.11.023
Christian R. Singer, Harald Behrens, Ingo Horn, Michael Fechtelkord, Stefan Weyer
In this study, we experimentally investigate the diffusion of B in flux-rich (1.7 % Li2O, 2.5 % B2O3, 2.7 % P2O5 and 3.5 % F) pegmatite forming melts in order to assess the transport mechanisms of B in rare-element pegmatite deposits. Glasses were synthesized with either different B isotope compositions or with different B concentrations (up to 2.45 wt% B2O3). In order to explore the effect of water on transport properties, nominally dry and hydrous glasses (3.1–3.9 wt% H2O) were investigated. The produced glasses were combined to diffusion couples to study self-diffusion and chemical diffusion of B in the same chemical system. Experiments were conducted using an internally heated pressure vessel and a rapid-heat and rapid-quench cold-seal pressure vessel at 100 MPa Ar pressure in the temperature range of 850–1250 °C for 1.6–97.3 h. In chemical diffusion experiments, the flow of B is compensated by a combined opposing flow of all other cations and F, without changing their element ratios. Thus, effective binary diffusion coefficients are obtained. Similar activation energies were determined for B self-diffusion and chemical diffusion under nominally dry conditions (196 ± 6 kJ/mol and 200 ± 17kJ/mol, respectively). Many hydrous experiments show a tilted to strongly deformed interface after the run, which was probably formed by advective flow of the low-viscosity melts during heating under pressure. Based on the successful experiments, an activation energy of 138 ± 8 kJ/mol was estimated for chemical diffusion of B in hydrous melts. We show that B diffusivity correlates with the Eyring diffusivity and, therefore, with the melt viscosity. The stable isotopes of B fractionate kinetically along the diffusion profiles due to the faster diffusivity of 10B over 11B. This isotope fractionation can be quantified with an empirical isotope fractionation factor (β) of 0.032 ± 0.002. This effect is small, but significant and was previously not observed in experimental studies. While it is insensitive to the water contents used in our study, it seems to be strongly dependent on the experimental boundary conditions, such as the ratios of B between the diffusion couple halves and the B enrichment in the melt. Solid-state NMR experiments reveal that the majority of B is in trigonal coordination in our melts, which effectively weakens the melt structure. This further suggests that coordination differences are unlikely to be the driving force for B isotope fractionation between melt and fluid during late-stage fluid exsolution in pegmatitic systems.
{"title":"Boron diffusion, related isotope fractionation and the structural role of B in pegmatite forming melts","authors":"Christian R. Singer, Harald Behrens, Ingo Horn, Michael Fechtelkord, Stefan Weyer","doi":"10.1016/j.gca.2024.11.023","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.023","url":null,"abstract":"In this study, we experimentally investigate the diffusion of B in flux-rich (1.7 % Li<ce:inf loc=\"post\">2</ce:inf>O, 2.5 % B<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf>, 2.7 % P<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">5</ce:inf> and 3.5 % F) pegmatite forming melts in order to assess the transport mechanisms of B in rare-element pegmatite deposits. Glasses were synthesized with either different B isotope compositions or with different B concentrations (up to 2.45 wt% B<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf>). In order to explore the effect of water on transport properties, nominally dry and hydrous glasses (3.1–3.9 wt% H<ce:inf loc=\"post\">2</ce:inf>O) were investigated. The produced glasses were combined to diffusion couples to study self-diffusion and chemical diffusion of B in the same chemical system. Experiments were conducted using an internally heated pressure vessel and a rapid-heat and rapid-quench cold-seal pressure vessel at 100 MPa Ar pressure in the temperature range of 850–1250 °C for 1.6–97.3 h. In chemical diffusion experiments, the flow of B is compensated by a combined opposing flow of all other cations and F, without changing their element ratios. Thus, effective binary diffusion coefficients are obtained. Similar activation energies were determined for B self-diffusion and chemical diffusion under nominally dry conditions (196 ± 6 kJ/mol and 200 ± 17kJ/mol, respectively). Many hydrous experiments show a tilted to strongly deformed interface after the run, which was probably formed by advective flow of the low-viscosity melts during heating under pressure. Based on the successful experiments, an activation energy of 138 ± 8 kJ/mol was estimated for chemical diffusion of B in hydrous melts. We show that B diffusivity correlates with the Eyring diffusivity and, therefore, with the melt viscosity. The stable isotopes of B fractionate kinetically along the diffusion profiles due to the faster diffusivity of <ce:sup loc=\"post\">10</ce:sup>B over <ce:sup loc=\"post\">11</ce:sup>B. This isotope fractionation can be quantified with an empirical isotope fractionation factor (<ce:italic>β</ce:italic>) of 0.032 ± 0.002. This effect is small, but significant and was previously not observed in experimental studies. While it is insensitive to the water contents used in our study, it seems to be strongly dependent on the experimental boundary conditions, such as the ratios of B between the diffusion couple halves and the B enrichment in the melt. Solid-state NMR experiments reveal that the majority of B is in trigonal coordination in our melts, which effectively weakens the melt structure. This further suggests that coordination differences are unlikely to be the driving force for B isotope fractionation between melt and fluid during late-stage fluid exsolution in pegmatitic systems.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"23 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142804469","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 : 2024-11-24DOI: 10.1016/j.gca.2024.11.019
Shuo Xue , Yuan Li
<div><div>Carbonated melts play a significant role in mobilizing lithophile and volatile elements in the Earth’s mantle and mantle metasomatism. However, there has been limited investigation into their potential for mobilizing chalcophile and siderophile elements<!--> <!-->(CSEs). In this study, we experimentally determine the sulfide liquid–carbonated melt partition coefficients of CSEs (<span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span>) for a range of elements, including Co, Ni, Cu, Zn, Se, Mo, Ag, Cd, In, Sn, Re, and Pb, at 1300–1600 °C, 1.0–3.0 GPa, and<!--> <!-->oxygen fugacity (<em>f</em>O<sub>2</sub>) close to the graphite-CO<sub>2</sub> fluid buffer. Furthermore, the <span><math><mrow><msup><mrow><mi>D</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msup></mrow></math></span> values for lithophile elements Cr, Mn, Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, and Ta (<span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span>) are also determined. The obtained <span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> values are 34–1230 for Co, 380–75200 for Ni, 200–14900 for Cu and Ag, 0.5–28 for Zn and Mo, 42–98 for Se, 24–640 for Cd, 5–52 for In and Sn, 650–15200 for Re, and 22–2470 for Pb. The obtained <span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> values are below 1–10. The variations of <span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> and <span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> are primarily influenced by the FeO<sub>tot</sub> content in the carbonated melts. A partitioning model was developed to parameterize <span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> and <span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> as a multi-function of pressure, temperature, composition of the carbonated melt (mainly the FeO<sub>tot</sub> content), and composition of the sulfide liquid. Our parameterization ca
{"title":"The partitioning of chalcophile and siderophile elements (CSEs) between sulfide liquid and carbonated melt","authors":"Shuo Xue , Yuan Li","doi":"10.1016/j.gca.2024.11.019","DOIUrl":"10.1016/j.gca.2024.11.019","url":null,"abstract":"<div><div>Carbonated melts play a significant role in mobilizing lithophile and volatile elements in the Earth’s mantle and mantle metasomatism. However, there has been limited investigation into their potential for mobilizing chalcophile and siderophile elements<!--> <!-->(CSEs). In this study, we experimentally determine the sulfide liquid–carbonated melt partition coefficients of CSEs (<span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span>) for a range of elements, including Co, Ni, Cu, Zn, Se, Mo, Ag, Cd, In, Sn, Re, and Pb, at 1300–1600 °C, 1.0–3.0 GPa, and<!--> <!-->oxygen fugacity (<em>f</em>O<sub>2</sub>) close to the graphite-CO<sub>2</sub> fluid buffer. Furthermore, the <span><math><mrow><msup><mrow><mi>D</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msup></mrow></math></span> values for lithophile elements Cr, Mn, Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, and Ta (<span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span>) are also determined. The obtained <span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> values are 34–1230 for Co, 380–75200 for Ni, 200–14900 for Cu and Ag, 0.5–28 for Zn and Mo, 42–98 for Se, 24–640 for Cd, 5–52 for In and Sn, 650–15200 for Re, and 22–2470 for Pb. The obtained <span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> values are below 1–10. The variations of <span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> and <span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> are primarily influenced by the FeO<sub>tot</sub> content in the carbonated melts. A partitioning model was developed to parameterize <span><math><mrow><msubsup><mi>D</mi><mrow><mi>CSE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> and <span><math><mrow><msubsup><mi>D</mi><mrow><mi>LithoE</mi></mrow><mrow><mi>Sul</mi><mo>/</mo><mi>C</mi><mi>_</mi><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msubsup></mrow></math></span> as a multi-function of pressure, temperature, composition of the carbonated melt (mainly the FeO<sub>tot</sub> content), and composition of the sulfide liquid. Our parameterization ca","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 94-113"},"PeriodicalIF":4.5,"publicationDate":"2024-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142748008","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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