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 : 2024-11-24DOI: 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}
Pub Date : 2024-11-19DOI: 10.1016/j.gca.2024.11.012
Brendan A. Anzures , Stephen W. Parman , Ralph E. Milliken , Olivier Namur , Camille Cartier , Francis M. McCubbin , Kathleen E. Vander Kaaden , Kelsey Prissel , Kayla Iacovino , Antonio Lanzirotti , Matthew Newville
<div><div>The NASA MESSENGER mission revealed that lavas on Mercury are enriched in sulfur (1.5–4 wt%) compared with other terrestrial planets (<0.1 wt%) due to high S solubility in silicate melt under its very low oxygen fugacity (ƒO<sub>2</sub>). However, the speciation of that S remains poorly constrained. In this study, we evaluate the role of pressure, temperature, and melt composition on S solubility and speciation in reduced magmas relevant to Mercury. Sulfur speciation was determined by S K-edge XANES spectra collected in 60 experiments that span a range of pressure (0.1 to 5 GPa), temperature (1225 to 1850 °C), and ƒO<sub>2</sub> (IW-0.8 to IW-8.6). Data were analysed using new relevant XANES standards and XANES spectral unmixing techniques. Stepwise forward regression was used to develop empirical equations for S species (MgS, CaS, and TiS). We found that <em>f</em>O<sub>2</sub>, P/T, and S content in the silicate melt at sulfide saturation (SCSS) exert the main controls on MgS content (wt.%) in the silicate melt, and that <em>f</em>O<sub>2</sub> and MgS content in the silicate melt exert the main controls on SCSS.</div><div><span><math><mrow><mfenced><mrow><msub><mrow><mi>MgS</mi></mrow><mrow><mi>liq</mi></mrow></msub><mspace></mspace><mi>w</mi><mi>t</mi><mo>.</mo><mo>%</mo></mrow></mfenced><mo>=</mo><mi>a</mi><mo>+</mo><mfrac><mrow><mi>bP</mi></mrow><mi>T</mi></mfrac><mo>+</mo><mi>c</mi><mi>log</mi><msub><mrow><mi>fO</mi></mrow><mn>2</mn></msub><mo>+</mo><mi>d</mi><msub><mrow><mo>[</mo><mi>S</mi><mspace></mspace><mi>w</mi><mi>t</mi><mo>.</mo><mo>%</mo><mo>]</mo></mrow><mrow><mi>SCSS</mi></mrow></msub></mrow></math></span> (1)</div><div>We find that as ƒO<sub>2</sub> decreases from IW-2 to IW-7, S speciation in silicate melt goes through two major changes. Between IW-2 and IW-4, FeS and FeCr<sub>2</sub>S<sub>4</sub> species are destabilized, and CaS becomes the dominant S species with minor TiS. Below IW-4, MgS is the dominant S species with minor CaS. At low <em>f</em>O<sub>2</sub>, S bonding with Fe, Mg, Ca, Ti, Na, and Mn affect the activities of SiO<sub>2</sub>, MgO, CaO, TiO, Na<sub>2</sub>O, and MnO in the silicate melt. This stabilizes enstatite at the expense of forsterite, destabilizes the Ca-bearing minerals plagioclase and clinopyroxene, and shifts plagioclase chemistry from the Ca-rich endmember anorthite to the Na-rich endmember albite as understand by reprojecting silicate ternary diagrams incorporating S speciation data. At the expense of MgS, CaS is more stable in the silicate melt at higher pressures at <em>f</em>O<sub>2</sub> below IW-4 creating a pathway for CaS to be carried in the silicate melt from depth to the surface before oldhamite (CaS) crystallization. These S speciation changes have substantial impacts on physicochemical properties of silicate melt such as viscosity, melting temperature, and mineral stability, which led to the distinct evolution of Mercury and other reduced planetary interiors.</div></di
美国国家航空航天局（NASA）的MESSENGER任务发现，与其他陆地行星（0.1 wt%）相比，水星上的熔岩富含硫磺（1.5-4 wt%），这是因为在水星极低的氧富集度（ƒO2）下，硅酸盐熔体中的硫溶解度很高。然而，这些 S 的种类仍然没有得到很好的解释。在这项研究中，我们评估了压力、温度和熔体成分对与水星有关的还原岩浆中硫的溶解度和标示的作用。通过在压力（0.1 至 5 GPa）、温度（1225 至 1850 °C）和 ƒO2（IW-0.8 至 IW-8.6）范围内的 60 次实验中收集的 S K 边 XANES 图谱确定了硫的种类。利用新的相关 XANES 标准和 XANES 光谱非混合技术对数据进行了分析。采用逐步向前回归的方法为 S 种类（MgS、CaS 和 TiS）建立了经验方程。我们发现，硫化物饱和时硅酸盐熔体中的 fO2、P/T 和 S 含量（SCSS）是硅酸盐熔体中 MgS 含量（重量百分比）的主要控制因素，而硅酸盐熔体中的 fO2 和 MgS 含量则是 SCSS 的主要控制因素。MgSliqwt.%=a+bPT+clogfO2+d[Swt.%]SCSS (1)我们发现，随着ƒO2从IW-2到IW-7的减少，硅酸盐熔体中的S种类经历了两个主要变化。在IW-2到IW-4之间，FeS和FeCr2S4物种不稳定，CaS成为主要的S物种，TiS次之。在 IW-4 以下，MgS 是主要的 S 物种，CaS 为次要。在低 fO2 条件下，S 与 Fe、Mg、Ca、Ti、Na 和 Mn 的结合会影响硅酸盐熔体中 SiO2、MgO、CaO、TiO、Na2O 和 MnO 的活性。这稳定了闪长岩而牺牲了绿柱石，破坏了含钙质矿物斜长石和鳞片辉石的稳定性，并使斜长石的化学性质从富含钙质的内质阳起石转变为富含镁质的内质白云石，这一点可以通过重新绘制硅酸盐三元图来理解，其中包含 S 的标示数据。在低于IW-4的fO2条件下，硅酸盐熔体中的CaS在较高压力下更加稳定，而MgS则受到影响，这就为CaS在老汉岩（CaS）结晶之前在硅酸盐熔体中从深部被带到地表提供了一条途径。这些硅酸盐的变化对硅酸盐熔体的物理化学性质（如粘度、熔化温度和矿物稳定性）产生了重大影响，从而导致了水星和其他还原行星内部的独特演化。
{"title":"An oxygen fugacity-temperature-pressure-composition model for sulfide speciation in Mercurian magmas","authors":"Brendan A. Anzures , Stephen W. Parman , Ralph E. Milliken , Olivier Namur , Camille Cartier , Francis M. McCubbin , Kathleen E. Vander Kaaden , Kelsey Prissel , Kayla Iacovino , Antonio Lanzirotti , Matthew Newville","doi":"10.1016/j.gca.2024.11.012","DOIUrl":"10.1016/j.gca.2024.11.012","url":null,"abstract":"<div><div>The NASA MESSENGER mission revealed that lavas on Mercury are enriched in sulfur (1.5–4 wt%) compared with other terrestrial planets (<0.1 wt%) due to high S solubility in silicate melt under its very low oxygen fugacity (ƒO<sub>2</sub>). However, the speciation of that S remains poorly constrained. In this study, we evaluate the role of pressure, temperature, and melt composition on S solubility and speciation in reduced magmas relevant to Mercury. Sulfur speciation was determined by S K-edge XANES spectra collected in 60 experiments that span a range of pressure (0.1 to 5 GPa), temperature (1225 to 1850 °C), and ƒO<sub>2</sub> (IW-0.8 to IW-8.6). Data were analysed using new relevant XANES standards and XANES spectral unmixing techniques. Stepwise forward regression was used to develop empirical equations for S species (MgS, CaS, and TiS). We found that <em>f</em>O<sub>2</sub>, P/T, and S content in the silicate melt at sulfide saturation (SCSS) exert the main controls on MgS content (wt.%) in the silicate melt, and that <em>f</em>O<sub>2</sub> and MgS content in the silicate melt exert the main controls on SCSS.</div><div><span><math><mrow><mfenced><mrow><msub><mrow><mi>MgS</mi></mrow><mrow><mi>liq</mi></mrow></msub><mspace></mspace><mi>w</mi><mi>t</mi><mo>.</mo><mo>%</mo></mrow></mfenced><mo>=</mo><mi>a</mi><mo>+</mo><mfrac><mrow><mi>bP</mi></mrow><mi>T</mi></mfrac><mo>+</mo><mi>c</mi><mi>log</mi><msub><mrow><mi>fO</mi></mrow><mn>2</mn></msub><mo>+</mo><mi>d</mi><msub><mrow><mo>[</mo><mi>S</mi><mspace></mspace><mi>w</mi><mi>t</mi><mo>.</mo><mo>%</mo><mo>]</mo></mrow><mrow><mi>SCSS</mi></mrow></msub></mrow></math></span> (1)</div><div>We find that as ƒO<sub>2</sub> decreases from IW-2 to IW-7, S speciation in silicate melt goes through two major changes. Between IW-2 and IW-4, FeS and FeCr<sub>2</sub>S<sub>4</sub> species are destabilized, and CaS becomes the dominant S species with minor TiS. Below IW-4, MgS is the dominant S species with minor CaS. At low <em>f</em>O<sub>2</sub>, S bonding with Fe, Mg, Ca, Ti, Na, and Mn affect the activities of SiO<sub>2</sub>, MgO, CaO, TiO, Na<sub>2</sub>O, and MnO in the silicate melt. This stabilizes enstatite at the expense of forsterite, destabilizes the Ca-bearing minerals plagioclase and clinopyroxene, and shifts plagioclase chemistry from the Ca-rich endmember anorthite to the Na-rich endmember albite as understand by reprojecting silicate ternary diagrams incorporating S speciation data. At the expense of MgS, CaS is more stable in the silicate melt at higher pressures at <em>f</em>O<sub>2</sub> below IW-4 creating a pathway for CaS to be carried in the silicate melt from depth to the surface before oldhamite (CaS) crystallization. These S speciation changes have substantial impacts on physicochemical properties of silicate melt such as viscosity, melting temperature, and mineral stability, which led to the distinct evolution of Mercury and other reduced planetary interiors.</div></di","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 61-77"},"PeriodicalIF":4.5,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700298","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 : 2024-11-19DOI: 10.1016/j.gca.2024.11.013
R. Coltat , B. Debret , R. Tilhac , M. Andreani , C.G.C. Patten , M. Godard , J. Escartín
At slow to ultraslow-spreading ridges, tectonic mantle exhumation and magmatic processes accounts for heterogeneity in the lithosphere and drives deep hydrothermal circulation and fluids venting at the seafloor. However, the spatio-temporal evolution and the interplay between magmatic and hydrothermal processes during mantle exhumation, as well as their consequences for chemical exchange at mid-ocean ridges are poorly constrained.
We carried out a Fe, Cu and Zn isotope study of mantle rocks drilled at the Mid-Atlantic Ridge Kane (MARK) area (23′30°N) to decipher the consequences of magmatic versus hydrothermal chemical exchange on lithospheric mantle composition. At MARK, mantle rocks undergo complex melt-rock interaction during melt percolation overprinted by high temperature (HT, > 350 °C) hydrothermal circulation that leads to the formation of secondary mineral assemblages (e.g., amphibole, chlorite, ilvaite, hydro-andradite, clinopyroxene, talc, serpentine). Serpentinized peridotites cut by hydrothermally overprinted magmatic veins have increased isotopic heterogeneity to both lighter and heavier isotope compositions (δ56Fe from −0.44 to 0.07 ± 0.03 ‰; δ66Zn from −0.24 to 0.32 ± 0.04 ‰), expending the predictive unaltered composition of the primitive mantle (δ56Fe = 0.025 ± 0.025 ‰ and δ66Zn = 0.16 ± 0.06 ‰). Such variability is ascribed to diffusion-related kinetic isotope fractionation during the percolation of Fe- and Zn-rich melt in mantle rocks. Low isotopic values are due to preferential diffusion of lighter isotope in mantle rocks, while high values may involve mixing of serpentinized peridotites with isotopically heavy magmatic veins. The lower Cu content (0.5 to 23.9 ppm) and either lower or higher δ65Cu (−0.11 to 0.32 ± 0.04 ‰) of abyssal peridotites, compared to the primitive mantle (30 ppm Cu, δ65Cu = 0.07 ± 0.1 ‰), can be explained through Cu leaching during hydrothermal alteration of sulfide, and possibly oxide, at high temperature (∼ 450–600 °C). Hydrothermal veins in serpentinites formed at decreasing temperature (∼ 300 °C) from a metal- and sulfur-rich fluid interacting with serpentinized peridotites. Iron, Cu and Zn isotopes record the inventory of magmato-hydrothermal processes during mantle exhumation at (ultra-)slow spreading centers, from HT melt-rock interaction to late low-temperature (LT) fluid-rock interaction.
{"title":"Multi-isotopic (Fe-Cu-Zn) constraints on the magmato-hydrothermal history during mantle exhumation at slow-spreading centers","authors":"R. Coltat , B. Debret , R. Tilhac , M. Andreani , C.G.C. Patten , M. Godard , J. Escartín","doi":"10.1016/j.gca.2024.11.013","DOIUrl":"10.1016/j.gca.2024.11.013","url":null,"abstract":"<div><div>At slow to ultraslow-spreading ridges, tectonic mantle exhumation and magmatic processes accounts for heterogeneity in the lithosphere and drives deep hydrothermal circulation and fluids venting at the seafloor. However, the spatio-temporal evolution and the interplay between magmatic and hydrothermal processes during mantle exhumation, as well as their consequences for chemical exchange at mid-ocean ridges are poorly constrained.</div><div>We carried out a Fe, Cu and Zn isotope study of mantle rocks drilled at the Mid-Atlantic Ridge Kane (MARK) area (23′30°N) to decipher the consequences of magmatic versus hydrothermal chemical exchange on lithospheric mantle composition. At MARK, mantle rocks undergo complex melt-rock interaction during melt percolation overprinted by high temperature (HT, > 350 °C) hydrothermal circulation that leads to the formation of secondary mineral assemblages (e.g., amphibole, chlorite, ilvaite, hydro-andradite, clinopyroxene, talc, serpentine). Serpentinized peridotites cut by hydrothermally overprinted magmatic veins have increased isotopic heterogeneity to both lighter and heavier isotope compositions (δ<sup>56</sup>Fe from −0.44 to 0.07 ± 0.03 ‰; δ<sup>66</sup>Zn from −0.24 to 0.32 ± 0.04 ‰), expending the predictive unaltered composition of the primitive mantle (δ<sup>56</sup>Fe = 0.025 ± 0.025 ‰ and δ<sup>66</sup>Zn = 0.16 ± 0.06 ‰). Such variability is ascribed to diffusion-related kinetic isotope fractionation during the percolation of Fe- and Zn-rich melt in mantle rocks. Low isotopic values are due to preferential diffusion of lighter isotope in mantle rocks, while high values may involve mixing of serpentinized peridotites with isotopically heavy magmatic veins. The lower Cu content (0.5 to 23.9 ppm) and either lower or higher δ<sup>65</sup>Cu (−0.11 to 0.32 ± 0.04 ‰) of abyssal peridotites, compared to the primitive mantle (30 ppm Cu, δ<sup>65</sup>Cu = 0.07 ± 0.1 ‰), can be explained through Cu leaching during hydrothermal alteration of sulfide, and possibly oxide, at high temperature (∼ 450–600 °C). Hydrothermal veins in serpentinites formed at decreasing temperature (∼ 300 °C) from a metal- and sulfur-rich fluid interacting with serpentinized peridotites. Iron, Cu and Zn isotopes record the inventory of magmato-hydrothermal processes during mantle exhumation at (ultra-)slow spreading centers, from HT melt-rock interaction to late low-temperature (LT) fluid-rock interaction.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 48-60"},"PeriodicalIF":4.5,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142701273","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 : 2024-11-19DOI: 10.1016/j.gca.2024.11.015
Zibo Xu , Bin Ma , Yuanzhi Tang , Daniel C.W. Tsang
Manganese oxide (MnOx) plays crucial roles in shaping various environmental and geochemistry processes, with their reactivity largely dependent on the structure of MnOx. Tunnel MnOx effectively hosts a substantial quantity of soil elements within its tunnel structure, exerting significant control over element turnover and pertinent geochemical processes, while the precise determinants regarding the layer-to-tunnel transformation of MnOx with electron transfer remain unclear. In this study, we delved into the transformation of layer-structured MnOx during the interaction with coexisting soil redox components (pyrogenic carbon and Tl with differing redox reactivity). Our findings revealed that the transformation from layer to tunnel structure only occurred in the presence of reductive pyrogenic carbon and oxidative Tl(III) rather than sole reductants/oxidants within a short incubation period of 6 weeks. The macro reducing environment created by the pyrogenic carbon and the micro oxidizing environment related to the Tl(III) chelation was pivotal in the cyclic valence change of Mn, resulting in the generation of Mn(III) and vacancies in the Mn structure, the prerequisite for the layer-to-tunnel transformation. Anchoring of oxidative Tl(III) on the surface or inside the tunnel structure of MnOx through Tl–O–Mn bonding was the key to building a micro oxidative environment under bulk-reducing conditions. During the transformation, Tl was integrated into the tunnel of high-crystallinity MnOx, and prolonged incubation resulted in the deeper embedding of Tl and the formation of atomic clusters. The embedding of Tl inside of the tunnel MnOx led to lower solubility and bioaccessibility, with only 0.05–0.26 mg Kg−1 being extracted with soil organic acids through reductive dissolution and 8.7–8.9 % by in vitro physiologically based extraction test. This study underscores the significant role of electron-donating and electron-accepting components in triggering interconnected geochemical processes with MnOx, carbon, and trace elements.
{"title":"Layer-to-tunnel manganese oxides transformation triggered by pyrogenic carbon and trace metals: Key role of reducing and oxidizing components cooperation","authors":"Zibo Xu , Bin Ma , Yuanzhi Tang , Daniel C.W. Tsang","doi":"10.1016/j.gca.2024.11.015","DOIUrl":"10.1016/j.gca.2024.11.015","url":null,"abstract":"<div><div>Manganese oxide (MnO<sub>x</sub>) plays crucial roles in shaping various environmental and geochemistry processes, with their reactivity largely dependent on the structure of MnO<sub>x</sub>. Tunnel MnO<sub>x</sub> effectively hosts a substantial quantity of soil elements within its tunnel structure, exerting significant control over element turnover and pertinent geochemical processes, while the precise determinants regarding the layer-to-tunnel transformation of MnO<sub>x</sub> with electron transfer remain unclear. In this study, we delved into the transformation of layer-structured MnO<sub>x</sub> during the interaction with coexisting soil redox components (pyrogenic carbon and Tl with differing redox reactivity). Our findings revealed that the transformation from layer to tunnel structure only occurred in the presence of reductive pyrogenic carbon and oxidative Tl(III) rather than sole reductants/oxidants within a short incubation period of 6 weeks. The macro reducing environment created by the pyrogenic carbon and the micro oxidizing environment related to the Tl(III) chelation was pivotal in the cyclic valence change of Mn, resulting in the generation of Mn(III) and vacancies in the Mn structure, the prerequisite for the layer-to-tunnel transformation. Anchoring of oxidative Tl(III) on the surface or inside the tunnel structure of MnO<sub>x</sub> through Tl–O–Mn bonding was the key to building a micro oxidative environment under bulk-reducing conditions. During the transformation, Tl was integrated into the tunnel of high-crystallinity MnO<sub>x</sub>, and prolonged incubation resulted in the deeper embedding of Tl and the formation of atomic clusters. The embedding of Tl inside of the tunnel MnO<sub>x</sub> led to lower solubility and bioaccessibility, with only 0.05–0.26 mg Kg<sup>−1</sup> being extracted with soil organic acids through reductive dissolution and 8.7–8.9 % by in vitro physiologically based extraction test. This study underscores the significant role of electron-donating and electron-accepting components in triggering interconnected geochemical processes with MnO<sub>x</sub>, carbon, and trace elements.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 18-33"},"PeriodicalIF":4.5,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142701271","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 : 2024-11-15DOI: 10.1016/j.gca.2024.11.010
Yuki Masuda , Martin Schiller , Martin Bizzarro , Tetsuya Yokoyama
Calcium-aluminum rich inclusions (CAIs) are the oldest condensates in the Solar System. Previous studies have revealed that moderately heavy and trace element isotope anomalies (e.g., Ti, Sr, Mo, and Nd) in CAIs record large nucleosynthetic isotope variations compared to bulk meteorites. Calcium is a major element in CAIs that has six stable isotopes with multiple nucleosynthetic origins. As such, Ca isotopes in CAIs have been an important target of isotopic analysis since the 1970s. However, the Ca isotope compositions of CAIs measured by previous-generation mass spectrometers are less precise than recent isotopic data of heavy elements, which complicates their direct comparisons. Obtaining high-precision Ca isotopic data provides a stronger link between CAI-formation processes from nebular gas and the origin of their source materials.
In this study, we report high-precision Ca isotopic compositions of CAIs, amoeboid olivine aggregates, and an Al-rich chondrule from Vigarano-type carbonaceous chondrites. The obtained µ43Ca and µ48Ca values range from +5.8 ± 1.4 to +40.2 ± 5.2 and +181.2 ± 44.8 to +743.1 ± 8.3 ppm, respectively (µXCa represents the mass bias corrected relative deviation in the XCa/44Ca ratio of the sample from a standard material in parts per million). The improved precision of our measurements reveals that the Ca isotopic compositions of CAIs vary over a narrower range than previously thought. Our precise data also show that µ43Ca and µ48Ca values in CAIs are anti-correlated, which cannot be explained by analytical artifacts such as matrix effects. Additionally, the µ43Ca and µ48Ca values of CAIs increase and decrease, respectively, with increasing Ca abundances of the inclusions. These observations suggest the presence of two distinct gaseous reservoirs from which CAIs condensed, one of which was more enriched in 43Ca but depleted in 48Ca, while the other reservoir was more depleted in 43Ca but enriched in 48Ca. Given the distinct nucleosynthetic sources of 43Ca and 48Ca, this change in isotopic signature is best understood if the two reservoirs inherited material derived from distinct nucleosynthetic sites. As such, our results suggest the presence of more than two compositionally distinct gas reservoirs for Ca isotopes in the early Solar System. If correct, this suggests that the infalling material contributing to the CAI-forming reservoirs was not fully mixed.
{"title":"Calcium isotope evidence for the formation of early condensates in the Solar System from unmixed reservoirs with distinct nucleosynthetic origins","authors":"Yuki Masuda , Martin Schiller , Martin Bizzarro , Tetsuya Yokoyama","doi":"10.1016/j.gca.2024.11.010","DOIUrl":"10.1016/j.gca.2024.11.010","url":null,"abstract":"<div><div>Calcium-aluminum rich inclusions (CAIs) are the oldest condensates in the Solar System. Previous studies have revealed that moderately heavy and trace element isotope anomalies (e.g., Ti, Sr, Mo, and Nd) in CAIs record large nucleosynthetic isotope variations compared to bulk meteorites. Calcium is a major element in CAIs that has six stable isotopes with multiple nucleosynthetic origins. As such, Ca isotopes in CAIs have been an important target of isotopic analysis since the 1970s. However, the Ca isotope compositions of CAIs measured by previous-generation mass spectrometers are less precise than recent isotopic data of heavy elements, which complicates their direct comparisons. Obtaining high-precision Ca isotopic data provides a stronger link between CAI-formation processes from nebular gas and the origin of their source materials.</div><div>In this study, we report high-precision Ca isotopic compositions of CAIs, amoeboid olivine aggregates, and an Al-rich chondrule from Vigarano-type carbonaceous chondrites. The obtained µ<sup>43</sup>Ca and µ<sup>48</sup>Ca values range from +5.8 ± 1.4 to +40.2 ± 5.2 and +181.2 ± 44.8 to +743.1 ± 8.3 ppm, respectively (µ<sup>X</sup>Ca represents the mass bias corrected relative deviation in the <sup>X</sup>Ca/<sup>44</sup>Ca ratio of the sample from a standard material in parts per million). The improved precision of our measurements reveals that the Ca isotopic compositions of CAIs vary over a narrower range than previously thought. Our precise data also show that µ<sup>43</sup>Ca and µ<sup>48</sup>Ca values in CAIs are anti-correlated, which cannot be explained by analytical artifacts such as matrix effects. Additionally, the µ<sup>43</sup>Ca and µ<sup>48</sup>Ca values of CAIs increase and decrease, respectively, with increasing Ca abundances of the inclusions. These observations suggest the presence of two distinct gaseous reservoirs from which CAIs condensed, one of which was more enriched in <sup>43</sup>Ca but depleted in <sup>48</sup>Ca, while the other reservoir was more depleted in <sup>43</sup>Ca but enriched in <sup>48</sup>Ca. Given the distinct nucleosynthetic sources of <sup>43</sup>Ca and <sup>48</sup>Ca, this change in isotopic signature is best understood if the two reservoirs inherited material derived from distinct nucleosynthetic sites. As such, our results suggest the presence of more than two compositionally distinct gas reservoirs for Ca isotopes in the early Solar System. If correct, this suggests that the infalling material contributing to the CAI-forming reservoirs was not fully mixed.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673695","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 : 2024-11-15DOI: 10.1016/j.gca.2024.11.011
Damanveer S. Grewal , Surjyendu Bhattacharjee , Gabriel-Darius Mardaru , Paul D. Asimow
Understanding the relationships between the nitrogen (N) isotope ratios of early solar system planetesimals and terrestrial reservoirs is crucial for tracing the origin of volatiles on Earth. The Earth primarily grew from planetesimals and planetary embryos that accreted rapidly (within ∼1–2 Ma after CAIs) in the inner solar system, also known as the non-carbonaceous (NC) reservoir. Magmatic iron meteorites, which sample the metallic cores of the earliest solar system planetesimals, have emerged as a promising proxy in this exercise. NC irons are distinctly 15N-poor compared to their CC (carbonaceous or outer solar system) counterparts. However, the utility of this proxy is limited by the lack of knowledge of N isotope fractionation during core crystallization. Using high pressure-high temperature experiments, we show that equilibrium N isotopic fractionation between solid and liquid metal (Δ15Nsolid–liquid = δ15Nsolid − δ15Nliquid) is limited (≤1.2 ‰) under conditions relevant for core crystallization. This, combined with the siderophile character of N and limited equilibrium N isotope fractionation during core-mantle differentiation, suggests that the δ15N values of iron meteorites accurately represent the N isotopic composition of their parent bodies. Unlike the variation in the N isotope ratios of NC and CC chondrites, which can be attributed to the effects of parent-body processes acting on organic precursors, the 15N-poor nature of NC irons relative to CC irons likely offers the most definitive evidence for the distinct N isotopic compositions of the earliest inner and outer solar system planetesimals. The N isotopic composition of Earth’s primordial mantle (δ15N = <−40 ‰) suggests that it retains the memory of the early accretion of 15N-poor NC iron meteorite parent body-like planetesimals. The early accreted 15N-poor nitrogen may be stored in the deep mantle, segregated into the core, or lost to space during atmospheric loss caused by impacts. This signature was overprinted by the subsequent accretion and admixing of CC materials, which is reflected in the relatively 15N-rich nature of Earth’s atmosphere (δ15N = 0) and convecting mantle (δ15N = −5 ‰).
了解太阳系早期行星胚胎和陆地储层的氮（N）同位素比率之间的关系对于追溯地球上挥发性物质的起源至关重要。地球主要是由内太阳系迅速（CAIs 后 1-2 Ma 内）吸积的类行星和行星胚胎（也称为非碳质（NC）储层）生长而来的。岩浆铁陨石对太阳系最早的类行星的金属内核进行了取样，在这项研究中已成为一种很有前途的替代物。与 CC（碳质或外太阳系）对应物相比，NC 铁明显缺乏 15N。然而，由于缺乏对内核结晶过程中 N 同位素分馏的了解，这种替代方法的实用性受到了限制。我们利用高压高温实验表明，在与内核结晶相关的条件下，固态和液态金属之间的平衡N同位素分馏（Δ15Nsolid-liquid = δ15Nsolid - δ15Nliquid）是有限的（≤1.2 ‰）。这一点，再加上N的亲硒特性以及在核心-幔块分异过程中有限的平衡N同位素分馏，表明铁陨石的δ15N值准确地代表了其母体的N同位素组成。NC铁陨石和CC铁陨石的N同位素比值的变化可归因于母体过程对有机前体的影响，而NC铁陨石相对于CC铁陨石的贫15N性质则不同，它可能为最早的太阳系内行星和外行星的不同N同位素组成提供了最确切的证据。地球原始地幔的 N 同位素组成（δ15N = <-40‰）表明，它保留了早期贫 15N NC 铁陨石母体类星体吸积的记忆。早期吸积的贫15N氮可能储存在深地幔中，或被分离到地核中，或在撞击造成的大气流失过程中流失到太空中。这一特征被随后的CC物质的吸积和混合所覆盖，这反映在地球大气（δ15N = 0）和对流地幔（δ15N = -5‰）相对富含15N的性质上。
{"title":"Tracing the origin of volatiles on Earth using nitrogen isotope ratios in iron meteorites","authors":"Damanveer S. Grewal , Surjyendu Bhattacharjee , Gabriel-Darius Mardaru , Paul D. Asimow","doi":"10.1016/j.gca.2024.11.011","DOIUrl":"10.1016/j.gca.2024.11.011","url":null,"abstract":"<div><div>Understanding the relationships between the nitrogen (N) isotope ratios of early solar system planetesimals and terrestrial reservoirs is crucial for tracing the origin of volatiles on Earth. The Earth primarily grew from planetesimals and planetary embryos that accreted rapidly (within ∼1–2 Ma after CAIs) in the inner solar system, also known as the non-carbonaceous (NC) reservoir. Magmatic iron meteorites, which sample the metallic cores of the earliest solar system planetesimals, have emerged as a promising proxy in this exercise. NC irons are distinctly <sup>15</sup>N-poor compared to their CC (carbonaceous or outer solar system) counterparts. However, the utility of this proxy is limited by the lack of knowledge of N isotope fractionation during core crystallization. Using high pressure-high temperature experiments, we show that equilibrium N isotopic fractionation between solid and liquid metal (Δ<sup>15</sup>N<sup>solid–liquid</sup> = δ<sup>15</sup>N<sup>solid</sup> − δ<sup>15</sup>N<sup>liquid</sup>) is limited (≤1.2 ‰) under conditions relevant for core crystallization. This, combined with the siderophile character of N and limited equilibrium N isotope fractionation during core-mantle differentiation, suggests that the δ<sup>15</sup>N values of iron meteorites accurately represent the N isotopic composition of their parent bodies. Unlike the variation in the N isotope ratios of NC and CC chondrites, which can be attributed to the effects of parent-body processes acting on organic precursors, the <sup>15</sup>N-poor nature of NC irons relative to CC irons likely offers the most definitive evidence for the distinct N isotopic compositions of the earliest inner and outer solar system planetesimals. The N isotopic composition of Earth’s primordial mantle (δ<sup>15</sup>N = <−40 ‰) suggests that it retains the memory of the early accretion of <sup>15</sup>N-poor NC iron meteorite parent body-like planetesimals. The early accreted <sup>15</sup>N-poor nitrogen may be stored in the deep mantle, segregated into the core, or lost to space during atmospheric loss caused by impacts. This signature was overprinted by the subsequent accretion and admixing of CC materials, which is reflected in the relatively <sup>15</sup>N-rich nature of Earth’s atmosphere (δ<sup>15</sup>N = 0) and convecting mantle (δ<sup>15</sup>N = −5 ‰).</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 34-47"},"PeriodicalIF":4.5,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142701272","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 : 2024-11-10DOI: 10.1016/j.gca.2024.11.008
Yuri Amelin, Qing-Zhu Yin, Piers Koefoed, Renaud Merle, Yuki Hibiya, Magdalena H. Huyskens, Tsuyoshi Iizuka, Julia A. Cartwright
In this study we test the possibility that radiogenic 207Pb/206Pb ratios (207Pb*/206Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in 207Pb*/206Pb* ratios, corresponding to the age bias of ca. 1–2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M – 5 M HF caused irregular 207Pb*/206Pb* fractionation between leaching steps, and generally higher 207Pb*/206Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between α-recoil tracks in the decay chains of 238U and 235U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic 207Pb* and 206Pb* fractionation.
{"title":"Fractionation of radiogenic Pb isotopes in meteorites and their components induced by acid leaching","authors":"Yuri Amelin, Qing-Zhu Yin, Piers Koefoed, Renaud Merle, Yuki Hibiya, Magdalena H. Huyskens, Tsuyoshi Iizuka, Julia A. Cartwright","doi":"10.1016/j.gca.2024.11.008","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.008","url":null,"abstract":"In this study we test the possibility that radiogenic <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb ratios (<ce:sup loc=\"post\">207</ce:sup>Pb*/<ce:sup loc=\"post\">206</ce:sup>Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in <ce:sup loc=\"post\">207</ce:sup>Pb*/<ce:sup loc=\"post\">206</ce:sup>Pb* ratios, corresponding to the age bias of ca. 1–2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M – 5 M HF caused irregular <ce:sup loc=\"post\">207</ce:sup>Pb*/<ce:sup loc=\"post\">206</ce:sup>Pb* fractionation between leaching steps, and generally higher <ce:sup loc=\"post\">207</ce:sup>Pb*/<ce:sup loc=\"post\">206</ce:sup>Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between α-recoil tracks in the decay chains of <ce:sup loc=\"post\">238</ce:sup>U and <ce:sup loc=\"post\">235</ce:sup>U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic <ce:sup loc=\"post\">207</ce:sup>Pb* and <ce:sup loc=\"post\">206</ce:sup>Pb* fractionation.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"8 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142718918","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 : 2024-11-10DOI: 10.1016/j.gca.2024.10.035
Chen Li , Yang Li , Kuixian Wei , Xiumin Chen , Kairui Tai , Zhuang Guo , Rui Li , Han Yu , Xiongyao Li , Wenhui Ma , Jianzhong Liu
The formation of a unique microstructure of minerals on the surface of airless bodies is attributed to space weathering. However, it is difficult to distinguish the contributions of meteorite impacts and solar wind to the modification of lunar soil, resulting in limited research on the space weathering mechanism of airless bodies. The thermochemical reactivity of troilite can be used to distinguish the contributions of impact events and solar wind to the modification of lunar soil and provide evidence for space weathering of lunar soil. We examined the structure of troilite particles in the Chang’e-5 lunar soil and determined whether an impact caused the thermal reaction. Microanalysis showed that troilite underwent substantial mass loss during thermal desulfurization, forming a crystallographically aligned porous structure with iron whiskers, an oxygen-rich layer, and other crystallographic and thermochemical evidence. We used an ab initio deep neural network model and thermodynamic calculations to conduct experiments and determine the anisotropy and crystal growth of troilite. The surface microstructure of troilite was transformed by the thermal reaction in the vacuum on the lunar surface. Similar structures have been found in near-Earth objects (NEOs), indicating that small bodies underwent the same impact-induced thermal events. Thus, thermal reactions in a vacuum are likely ubiquitous in the solar system and critical for space weathering alterations of the soil of airless bodies.
{"title":"Vacuum-thermal alteration of lunar soil: Evidence from iron whiskers on troilite in Chang’e-5 samples","authors":"Chen Li , Yang Li , Kuixian Wei , Xiumin Chen , Kairui Tai , Zhuang Guo , Rui Li , Han Yu , Xiongyao Li , Wenhui Ma , Jianzhong Liu","doi":"10.1016/j.gca.2024.10.035","DOIUrl":"10.1016/j.gca.2024.10.035","url":null,"abstract":"<div><div>The formation of a unique microstructure of minerals on the surface of airless bodies is attributed to space weathering. However, it is difficult to distinguish the contributions of meteorite impacts and solar wind to the modification of lunar soil, resulting in limited research on the space weathering mechanism of airless bodies. The thermochemical reactivity of troilite can be used to distinguish the contributions of impact events and solar wind to the modification of lunar soil and provide evidence for space weathering of lunar soil. We examined the structure of troilite particles in the Chang’e-5 lunar soil and determined whether an impact caused the thermal reaction. Microanalysis showed that troilite underwent substantial mass loss during thermal desulfurization, forming a crystallographically aligned porous structure with iron whiskers, an oxygen-rich layer, and other crystallographic and thermochemical evidence. We used an <em>ab initio</em> deep neural network model and thermodynamic calculations to conduct experiments and determine the anisotropy and crystal growth of troilite. The surface microstructure of troilite was transformed by the thermal reaction in the vacuum on the lunar surface. Similar structures have been found in near-Earth objects (NEOs), indicating that small bodies underwent the same impact-induced thermal events. Thus, thermal reactions in a vacuum are likely ubiquitous in the solar system and critical for space weathering alterations of the soil of airless bodies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"387 ","pages":"Pages 28-37"},"PeriodicalIF":4.5,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662824","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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