Pub Date : 2024-11-22DOI: 10.1016/j.gca.2024.11.016
Carlos Pérez-Mejías, Jian Wang, Youfeng Ning, Ana Moreno, Antonio Delgado-Huertas, R. Lawrence Edwards, Hai Cheng, Heather M. Stoll
Despite early hydrological studies of <ce:sup loc="post">234</ce:sup>U/<ce:sup loc="post">238</ce:sup>U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (<ce:sup loc="post">230</ce:sup>Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed <ce:sup loc="post">234</ce:sup>U enrichment is attributed to selective leaching of <ce:sup loc="post">234</ce:sup>U from damaged lattice sites, linked to the number of microfractures in the drip route and wetness frequency, which under certain conditions, may result in the accumulation of <ce:sup loc="post">234</ce:sup>U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low δ<ce:sup loc="post">234</ce:sup>U. Temperature variations significantly influence bedrock dissolution intensity. During stadial periods and glacial maxima, lower temperatures likely reduced vegetation and respiration rates, thereby decreasing soil CO<ce:inf loc="post">2</ce:inf> and overall rock dissolution rates. This reduction could enhance the preferential leaching of <ce:sup loc="post">234</ce:sup>U from bedrock surfaces due to lower bulk rock dissolution. Additionally, the temperature regime during cold periods may have facilitated more frequent freeze–thaw cycles, resulting in microfracturing and exposure of fresh surfaces. Conversely, warmer temperatures increased soil respiration rates and soil CO<ce:inf loc="post">2</ce:inf>, accelerating rock dissolution rates during interstadials and interglacials, when low δ<ce:sup loc="post">234</ce:sup>U is consistent with high bedrock dissolution rates. The contribution of a number of variables sensitive to bedrock dissolution and wetness frequency processes successfully explains 57% and 74% of the variability observed in the δ<ce:sup loc="post">234</ce:sup>U in <ce:italic>Andromeda</ce:italic> stalagmite during MIS 3–4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain δ<ce:sup loc="post">234</ce:sup>U variability, highlighting the fundamental role of soil respiration and soil CO<ce:inf loc="post">2</ce:inf> in δ<ce:sup loc="post">234</ce:sup>U through bedrock dissolution. I-STAL simulations provides the potential for a combination of Prior Calcite Precipitation (PCP) indicators like Mg/Ca with PCP-insensitive indicators of bedrock dissolution such as δ<ce:sup loc="post">234</ce:sup>U, along with growth rate data, may be useful to diagnose when PCP variations reflect predominantly changes in drip intervals and when changes in bedrock dissolution intensity contribute. The relationship between stalagmite δ<ce:sup loc="post">234</ce:sup>U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, δ<ce:sup loc="post">234</ce:sup>U could serve as a valuable complement to δ<ce:sup l
{"title":"Climate controls on speleothem initial 234U/238U ratios in midlatitude settings over two glacial cycles","authors":"Carlos Pérez-Mejías, Jian Wang, Youfeng Ning, Ana Moreno, Antonio Delgado-Huertas, R. Lawrence Edwards, Hai Cheng, Heather M. Stoll","doi":"10.1016/j.gca.2024.11.016","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.016","url":null,"abstract":"Despite early hydrological studies of <ce:sup loc=\"post\">234</ce:sup>U/<ce:sup loc=\"post\">238</ce:sup>U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (<ce:sup loc=\"post\">230</ce:sup>Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed <ce:sup loc=\"post\">234</ce:sup>U enrichment is attributed to selective leaching of <ce:sup loc=\"post\">234</ce:sup>U from damaged lattice sites, linked to the number of microfractures in the drip route and wetness frequency, which under certain conditions, may result in the accumulation of <ce:sup loc=\"post\">234</ce:sup>U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low δ<ce:sup loc=\"post\">234</ce:sup>U. Temperature variations significantly influence bedrock dissolution intensity. During stadial periods and glacial maxima, lower temperatures likely reduced vegetation and respiration rates, thereby decreasing soil CO<ce:inf loc=\"post\">2</ce:inf> and overall rock dissolution rates. This reduction could enhance the preferential leaching of <ce:sup loc=\"post\">234</ce:sup>U from bedrock surfaces due to lower bulk rock dissolution. Additionally, the temperature regime during cold periods may have facilitated more frequent freeze–thaw cycles, resulting in microfracturing and exposure of fresh surfaces. Conversely, warmer temperatures increased soil respiration rates and soil CO<ce:inf loc=\"post\">2</ce:inf>, accelerating rock dissolution rates during interstadials and interglacials, when low δ<ce:sup loc=\"post\">234</ce:sup>U is consistent with high bedrock dissolution rates. The contribution of a number of variables sensitive to bedrock dissolution and wetness frequency processes successfully explains 57% and 74% of the variability observed in the δ<ce:sup loc=\"post\">234</ce:sup>U in <ce:italic>Andromeda</ce:italic> stalagmite during MIS 3–4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain δ<ce:sup loc=\"post\">234</ce:sup>U variability, highlighting the fundamental role of soil respiration and soil CO<ce:inf loc=\"post\">2</ce:inf> in δ<ce:sup loc=\"post\">234</ce:sup>U through bedrock dissolution. I-STAL simulations provides the potential for a combination of Prior Calcite Precipitation (PCP) indicators like Mg/Ca with PCP-insensitive indicators of bedrock dissolution such as δ<ce:sup loc=\"post\">234</ce:sup>U, along with growth rate data, may be useful to diagnose when PCP variations reflect predominantly changes in drip intervals and when changes in bedrock dissolution intensity contribute. The relationship between stalagmite δ<ce:sup loc=\"post\">234</ce:sup>U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, δ<ce:sup loc=\"post\">234</ce:sup>U could serve as a valuable complement to δ<ce:sup l","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"14 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841528","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.2024.11.014
Ninna K. Jensen, Alexander A. Nemchin, Gavin Kenny, Martin J. Whitehouse, James N. Connelly, Takashi Mikouchi, Martin Bizzarro
Impact events were frequent in the early history of our Solar System, and the dynamics of planetary crust formation were, consequently, substantially different from the processes that dominate today. Mars, a planet with stagnant lid tectonics and a unique preservation of ancient surface terrains, provides an outstanding opportunity to investigate the early processes related to the formation and reshaping of the first crust. Northwest Africa (NWA) 7034 and paired meteorites (such as NWA 7533) are fragments of polymict, regolith breccia that provide a tangible record of the ancient, brecciated crust on Mars. Zircon and baddeleyite from NWA 7034/7533 record evidence for two events of intense crustal reworking at 4442 ± 17 and 4474 ± 10 million years ago (Ma) triggered by impacts, placing important constraints on the timing and the dynamics of early crust formation on Mars. To date, only few studies have focussed on the geochronology of the igneous clasts present within NWA 7034 and its pairs. Although these studies consistently report ancient ages (∼4.4 Ga) for basaltic, basaltic andesitic and monzonitic clasts, the associated precisions are generally too low to link the different lithologies with the two age peaks inferred from NWA 7034/7533 zircon and baddeleyite. Here, we conduct an isotopic and petrographic study of igneous clasts from NWA 7533 to shed further light on the timing and nature of crustal reworking in the early history of Mars. We show that six out of seven investigated igneous clasts, representing at least four distinct types, record undisturbed Lu-Hf isotope systematics that indicate contemporaneous formation. Together with two zircons hosted in basalt and basaltic andesite clasts, these igneous clasts yield an isochron age of 4440 ± 41 Ma (2SE, MSWD = 2.1). This isochron age is consistent with clast ages inferred from zircon U-Pb geochronology, and altogether the available age constraints for the lithic components in NWA 7533 indicate that they derive from the younger of the two peaks of intense crustal reworking on early Mars (4442 ± 17 Ma). The initial εHf values (the 176Hf/177Hf ratio in the sample normalised to that of the chondritic uniform reservoir at the time of crystallisation in parts per ten thousand) of the igneous clasts range between −2.07 and −0.74, consistent with crystallisation from enriched source melts deriving from impact-induced reworking of the crust. The mean Lu-Hf isotope composition of the igneous clasts constrains the timing of primordial crust formation and reveals planet formation and differentiation within the first 10 Myr of the history of the Solar System, in consistence with the conclusions in earlier reports. The results presented here suggest a 176Lu/177Hf ratio of ∼ 0.0135 or higher in the primordial martian crust.
{"title":"Timing of crustal reworking on Mars inferred from the Lu-Hf isotope systematics of igneous clasts in NWA 7533","authors":"Ninna K. Jensen, Alexander A. Nemchin, Gavin Kenny, Martin J. Whitehouse, James N. Connelly, Takashi Mikouchi, Martin Bizzarro","doi":"10.1016/j.gca.2024.11.014","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.014","url":null,"abstract":"Impact events were frequent in the early history of our Solar System, and the dynamics of planetary crust formation were, consequently, substantially different from the processes that dominate today. Mars, a planet with stagnant lid tectonics and a unique preservation of ancient surface terrains, provides an outstanding opportunity to investigate the early processes related to the formation and reshaping of the first crust. Northwest Africa (NWA) 7034 and paired meteorites (such as NWA 7533) are fragments of polymict, regolith breccia that provide a tangible record of the ancient, brecciated crust on Mars. Zircon and baddeleyite from NWA 7034/7533 record evidence for two events of intense crustal reworking at 4442 ± 17 and 4474 ± 10 million years ago (Ma) triggered by impacts, placing important constraints on the timing and the dynamics of early crust formation on Mars. To date, only few studies have focussed on the geochronology of the igneous clasts present within NWA 7034 and its pairs. Although these studies consistently report ancient ages (∼4.4 Ga) for basaltic, basaltic andesitic and monzonitic clasts, the associated precisions are generally too low to link the different lithologies with the two age peaks inferred from NWA 7034/7533 zircon and baddeleyite. Here, we conduct an isotopic and petrographic study of igneous clasts from NWA 7533 to shed further light on the timing and nature of crustal reworking in the early history of Mars. We show that six out of seven investigated igneous clasts, representing at least four distinct types, record undisturbed Lu-Hf isotope systematics that indicate contemporaneous formation. Together with two zircons hosted in basalt and basaltic andesite clasts, these igneous clasts yield an isochron age of 4440 ± 41 Ma (2SE, MSWD = 2.1). This isochron age is consistent with clast ages inferred from zircon U-Pb geochronology, and altogether the available age constraints for the lithic components in NWA 7533 indicate that they derive from the younger of the two peaks of intense crustal reworking on early Mars (4442 ± 17 Ma). The initial εHf values (the <ce:sup loc=\"post\">176</ce:sup>Hf/<ce:sup loc=\"post\">177</ce:sup>Hf ratio in the sample normalised to that of the chondritic uniform reservoir at the time of crystallisation in parts per ten thousand) of the igneous clasts range between −2.07 and −0.74, consistent with crystallisation from enriched source melts deriving from impact-induced reworking of the crust. The mean Lu-Hf isotope composition of the igneous clasts constrains the timing of primordial crust formation and reveals planet formation and differentiation within the first 10 Myr of the history of the Solar System, in consistence with the conclusions in earlier reports. The results presented here suggest a <ce:sup loc=\"post\">176</ce:sup>Lu/<ce:sup loc=\"post\">177</ce:sup>Hf ratio of ∼ 0.0135 or higher in the primordial martian crust.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"39 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841592","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}
Pub Date : 2024-11-09DOI: 10.1016/j.gca.2024.10.028
Madison M. Wood, Clara L. Blättler, Ana Kolevica, Anton Eisenhauer, Adina Paytan
A remnant of glacial seawater preserved in the pore fluids of sediment cores from the Maldives Inner Sea provided an opportunity to investigate the stable strontium isotopic composition (<mml:math altimg="si13.svg" display="inline"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of <mml:math altimg="si13.svg" display="inline"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr as a tracer of early marine diagenesis. We used paired measurements of <mml:math altimg="si13.svg" display="inline"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr and radiogenic Sr isotope ratios (<ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr) in pore fluids and surrounding carbonate sediments to constrain the diagenetic history of the preserved glacial water mass at IODP Sites U1466 and U1468. These pore fluid profiles document variability in <mml:math altimg="si13.svg" display="inline"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr in a shallow marine setting, revealing distinct diagenetic processes dominating within different depth intervals. We find evidence for isotope fractionation during secondary calcite precipitation at intermediate depths and observe that in aragonite-dominated settings, fractionation during recrystallization may be obscured by the dissolution of aragonite in the uppermost sediments. Correcting for the effect of carbonate recrystallization on pore fluid Sr concentration ([Sr]) and isotopic composition, we estimate that glacial seawater [Sr] was higher (<mml:math altimg="si5.svg" display="inline"><mml:mrow><mml:mo>∼</mml:mo><mml:mn>98</mml:mn><mml:mspace width="1em"></mml:mspace><mml:mi mathvariant="normal">μ</mml:mi></mml:mrow></mml:math>M) and <mml:math altimg="si13.svg" display="inline"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr lower (<mml:math altimg="si7.svg" display="inline"><mml:mo>∼</mml:mo></mml:math>0.32‰) compared to the modern ocean, consistent with hypotheses attributing the present-day disequilibrium of the ocean Sr budget to glacial/interglacial changes in shelf carbonate weathering and burial. Our results provide evidence that the ocean [Sr] and <mml:math altimg="si13.svg" display="inline"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (<mml:m
{"title":"Stable and radiogenic strontium isotopes trace the composition and diagenetic alteration of remnant glacial seawater","authors":"Madison M. Wood, Clara L. Blättler, Ana Kolevica, Anton Eisenhauer, Adina Paytan","doi":"10.1016/j.gca.2024.10.028","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.028","url":null,"abstract":"A remnant of glacial seawater preserved in the pore fluids of sediment cores from the Maldives Inner Sea provided an opportunity to investigate the stable strontium isotopic composition (<mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr as a tracer of early marine diagenesis. We used paired measurements of <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr and radiogenic Sr isotope ratios (<ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr) in pore fluids and surrounding carbonate sediments to constrain the diagenetic history of the preserved glacial water mass at IODP Sites U1466 and U1468. These pore fluid profiles document variability in <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr in a shallow marine setting, revealing distinct diagenetic processes dominating within different depth intervals. We find evidence for isotope fractionation during secondary calcite precipitation at intermediate depths and observe that in aragonite-dominated settings, fractionation during recrystallization may be obscured by the dissolution of aragonite in the uppermost sediments. Correcting for the effect of carbonate recrystallization on pore fluid Sr concentration ([Sr]) and isotopic composition, we estimate that glacial seawater [Sr] was higher (<mml:math altimg=\"si5.svg\" display=\"inline\"><mml:mrow><mml:mo>∼</mml:mo><mml:mn>98</mml:mn><mml:mspace width=\"1em\"></mml:mspace><mml:mi mathvariant=\"normal\">μ</mml:mi></mml:mrow></mml:math>M) and <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr lower (<mml:math altimg=\"si7.svg\" display=\"inline\"><mml:mo>∼</mml:mo></mml:math>0.32‰) compared to the modern ocean, consistent with hypotheses attributing the present-day disequilibrium of the ocean Sr budget to glacial/interglacial changes in shelf carbonate weathering and burial. Our results provide evidence that the ocean [Sr] and <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (<mml:m","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"57 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673701","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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