Pub Date : 2025-01-15DOI: 10.1016/j.gca.2024.10.023
Lucien Nana Yobo , Helen M. Williams , Alan D. Brandon , Chris Holmden , Kimberly V. Lau , Steven C. Bergman , James S. Eldrett , Daniel Minisini
Anomalously high metal concentrations including iron enrichments are recorded in marine carbonates deposited during Ocean Anoxic Event 2 (OAE 2). These metal enrichments have been attributed to massive submarine eruptions during the formation of one or more large igneous provinces, the proposed trigger for OAE 2 (hydrothermal hypothesis), or to the release of metals from the reoxidation of formerly anoxic marine sediment during a period of temporary cooling during OAE 2 (sediment release hypothesis). Here we use iron stable isotopes to help distinguish between the two hypotheses for a trace metal enriched interval during OAE 2 in the Iona-1 core in the Western Interior Seaway, Texas. Our results show a two-step negative excursion during OAE 2 that is coincident with osmium isotope volcanic proxies measured in the same core, with peak negative values centered on a trace metal-enriched interval. After corrections for detrital and locally supplied iron to the study setting, the δ56Fe value of the remotely supplied iron is –0.28 ± 0.05 ‰, falling in the range of iron δ56Fe values observed in modern hydrothermal plumes (–0.1 to –0.5 ‰), thus supporting the hydrothermal hypothesis as the source of iron and other associated trace metals enriched in the study core during OAE 2. By contrast, the sediment release hypothesis predicts much lower δ56Fe values, between –1.0 ‰ to –3.3 ‰ predicted for benthic supplies of iron from anoxic marine sediment overlying re-oxygenated bottom waters. This study shows that combining iron with other proxies for environmental change, particularly submarine volcanism, can distinguish hydrothermally supplied iron from dust, rivers, and shelf sediment supplies of iron despite iron’s reputation for complicated cycling.
{"title":"Iron Isotopes reveal volcanogenic input during Oceanic Anoxic Event 2 (OAE 2 ∼ 94 Ma)","authors":"Lucien Nana Yobo , Helen M. Williams , Alan D. Brandon , Chris Holmden , Kimberly V. Lau , Steven C. Bergman , James S. Eldrett , Daniel Minisini","doi":"10.1016/j.gca.2024.10.023","DOIUrl":"10.1016/j.gca.2024.10.023","url":null,"abstract":"<div><div>Anomalously high metal concentrations including iron enrichments are recorded in marine carbonates deposited during Ocean Anoxic Event 2 (OAE 2). These metal enrichments have been attributed to massive submarine eruptions during the formation of one or more large igneous provinces, the proposed trigger for OAE 2 (hydrothermal hypothesis), or to the release of metals from the reoxidation of formerly anoxic marine sediment during a period of temporary cooling during OAE 2 (sediment release hypothesis). Here we use iron stable isotopes to help distinguish between the two hypotheses for a trace metal enriched interval during OAE 2 in the Iona-1 core in the Western Interior Seaway, Texas. Our results show a two-step negative excursion during OAE 2 that is coincident with osmium isotope volcanic proxies measured in the same core, with peak negative values centered on a trace metal-enriched interval. After corrections for detrital and locally supplied iron to the study setting, the δ<sup>56</sup>Fe value of the remotely supplied iron is –0.28 ± 0.05 ‰, falling in the range of iron δ<sup>56</sup>Fe values observed in modern hydrothermal plumes (–0.1 to –0.5 ‰), thus supporting the hydrothermal hypothesis as the source of iron and other associated trace metals enriched in the study core during OAE 2. By contrast, the sediment release hypothesis predicts much lower δ<sup>56</sup>Fe values, between –1.0 ‰ to –3.3 ‰ predicted for benthic supplies of iron from anoxic marine sediment overlying re-oxygenated bottom waters. This study shows that combining iron with other proxies for environmental change, particularly submarine volcanism, can distinguish hydrothermally supplied iron from dust, rivers, and shelf sediment supplies of iron despite iron’s reputation for complicated cycling.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 157-167"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 10.1016/j.gca.2024.11.033
Yujian Wang, Jingao Liu
Secular variations in the composition of the subcontinental lithospheric mantle (SCLM) are intimately controlled by multiple geological processes, including diverse melting mechanisms and complex metasomatic processes. We present comprehensive analyses of whole rock and mineral chemistry, along with Re-Os isotopic system of the Eastern Pyrenean orogenic mantle massifs, supported by quantitative modeling through alphaMELTS thermodynamic software. The Eastern Pyrenean lherzolites display consistent negative correlations of TiO2/Al2O3, TiO2 versus MgO and relatively high and unfractionated heavy rare earth elements. These chemical features shed light on the diverse melting mechanisms responsible for these rocks, encompassing passive continuous melting in regions of lithospheric extension and decompression melting linked to the upwelling asthenospheric mantle. Some refractory harzburgites exhibit elevated TiO2/Al2O3, TiO2 contents and moderate light rare earth element enrichment. This suggests chromatographic metasomatism due to the reactive porous flow of evolved melts/fluids in the upper part of the lithosphere during their ascent to the surface. An isochron analogy between 187Os/188Os and Al2O3 yields an age of ∼ 1.5 Ga, constraining the timing of partial melting responsible for the formation of SCLM beneath the Eastern Pyrenean region. We then expand the scope of our study to encompass on– and off-cratonic SCLM on a global scale. This expanded analysis explores the variations in melting mechanisms across different tectonic settings and geological epochs and scrutinizes the role of diverse metasomatic processes in shaping the characteristics of the lithospheric mantle and its longevity on a broad scale. Silicate metasomatism typically produces fertile peridotites at the asthenosphere-lithosphere boundary, making them vulnerable to thermomechanical erosion, whereas cryptic metasomatism, commonly observed in refractory mantle rocks induced by evolved melts at decreasing melt-rock ratios (e.g., hydrocarbon-bearing silicate melt, carbonatite melt etc.), generally forms enrichment of highly incompatible elements but less significant influence on the mineral assemblages and major element geochemistry of the on-cratonic refractory SCLM, making them remain stable for extended periods.
{"title":"Deciphering multiple episodes of partial melting, metasomatic and remelting processes in the Eastern Pyrenean orogenic mantle massif","authors":"Yujian Wang, Jingao Liu","doi":"10.1016/j.gca.2024.11.033","DOIUrl":"10.1016/j.gca.2024.11.033","url":null,"abstract":"<div><div>Secular variations in the composition of the subcontinental lithospheric mantle (SCLM) are intimately controlled by multiple geological processes, including diverse melting mechanisms and complex metasomatic processes. We present comprehensive analyses of whole rock and mineral chemistry, along with Re-Os isotopic system of the Eastern Pyrenean orogenic mantle massifs, supported by quantitative modeling through alphaMELTS thermodynamic software. The Eastern Pyrenean lherzolites display consistent negative correlations of TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub> versus MgO and relatively high and unfractionated heavy rare earth elements. These chemical features shed light on the diverse melting mechanisms responsible for these rocks, encompassing passive continuous melting in regions of lithospheric extension and decompression melting linked to the upwelling asthenospheric mantle. Some refractory harzburgites exhibit elevated TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub> contents and moderate light rare earth element enrichment. This suggests chromatographic metasomatism due to the reactive porous flow of evolved melts/fluids in the upper part of the lithosphere during their ascent to the surface. An isochron analogy between <sup>187</sup>Os/<sup>188</sup>Os and Al<sub>2</sub>O<sub>3</sub> yields an age of ∼ 1.5 Ga, constraining the timing of partial melting responsible for the formation of SCLM beneath the Eastern Pyrenean region. We then expand the scope of our study to encompass on– and off-cratonic SCLM on a global scale. This expanded analysis explores the variations in melting mechanisms across different tectonic settings and geological epochs and scrutinizes the role of diverse metasomatic processes in shaping the characteristics of the lithospheric mantle and its longevity on a broad scale. Silicate metasomatism typically produces fertile peridotites at the asthenosphere-lithosphere boundary, making them vulnerable to thermomechanical erosion, whereas cryptic metasomatism, commonly observed in refractory mantle rocks induced by evolved melts at decreasing melt-rock ratios (e.g., hydrocarbon-bearing silicate melt, carbonatite melt etc.), generally forms enrichment of highly incompatible elements but less significant influence on the mineral assemblages and major element geochemistry of the on-cratonic refractory SCLM, making them remain stable for extended periods.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 14-29"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841587","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 10.1016/j.gca.2025.01.005
Elizabeth M. Griffith , Matthew S. Fantle , Brittan V. Wogsland , Zijian Li , Majie Fan , David J. Wronkiewicz
Modern microbialites grow in a variety of environments including the hypersaline, turbid, low alkalinity, high magnesium (Mg) and calcium (Ca) concentrations (and Mg/Ca ∼ 4.5 mol/mol), shallow (less than 2 m deep) Storr’s Lake on San Salvador Island, The Bahamas. Rather than growing via the trapping and binding of sediments, these largely micritic microbialites form via microbial processes creating crusts and mounds with laminated to clotted structures comprised of both high-Mg calcite and aragonite. The primary objective of this study was to determine whether the mineralogy of representative microbialite mounds dictates their pre-burial metal isotopic compositions. The Mg and Ca isotopic compositions (δ26Mg, δ44/40Ca) of two mounds collected from 0.6 to 1.1 m water depth range considerably, from −3.04 to −2.33 ‰ (relative to DSM3) and 0.38 to 0.94 ‰ (relative to SRM 915a), respectively. Along with Sr/Ca and Mg/Ca molar ratios, δ26Mg and δ44/40Ca are unambiguously related to mineralogy. This stands in contrast to the carbon and oxygen isotopic compositions of the microbial carbonates, which do not correlate solely with mineralogy. A simple bimineralic mixture of aragonite and high-Mg calcite can explain the observations; such a mixture could be a consequence of both phases forming independently or as one phase recrystallizes from another prior to burial. To evaluate the latter hypothesis, we used a time-dependent advection-recrystallization model. We found that recrystallization of high-Mg calcite to aragonite would require an unreasonable Sr partition coefficient, while recrystallization of aragonite to high-Mg calcite could explain the observed geochemical variations in the two mounds. No microbial isotopic effect is apparent for Mg or Ca, however a difference is seen in the carbon isotopic composition of inorganic carbon where or when aragonite and high-Mg calcite form suggesting they form in two different (micro)environments. Consequently, investigations of ancient microbialites (and carbonates in general) need to consider whether mixtures of primary (original) carbonate minerals and/or recrystallization and transformation pre-burial could impact δ26Mg, δ44/40Ca, δ13C and their interpretation using a combination of isotopic, elemental, petrographic, and modeling methods. This is especially important for Mg, whose elemental and isotopic composition can be dominated by even small amounts of calcite or dolomite.
{"title":"Mineralogic control on the calcium and magnesium stable isotopic compositions of modern microbial carbonates","authors":"Elizabeth M. Griffith , Matthew S. Fantle , Brittan V. Wogsland , Zijian Li , Majie Fan , David J. Wronkiewicz","doi":"10.1016/j.gca.2025.01.005","DOIUrl":"10.1016/j.gca.2025.01.005","url":null,"abstract":"<div><div>Modern microbialites grow in a variety of environments including the hypersaline, turbid, low alkalinity, high magnesium (Mg) and calcium (Ca) concentrations (and Mg/Ca ∼ 4.5 mol/mol), shallow (less than 2 m deep) Storr’s Lake on San Salvador Island, The Bahamas. Rather than growing via the trapping and binding of sediments, these largely micritic microbialites form via microbial processes creating crusts and mounds with laminated to clotted structures comprised of both high-Mg calcite and aragonite. The primary objective of this study was to determine whether the mineralogy of representative microbialite mounds dictates their pre-burial metal isotopic compositions. The Mg and Ca isotopic compositions (δ<sup>26</sup>Mg, <em>δ</em><sup>44/40</sup>Ca) of two mounds collected from 0.6 to 1.1 m water depth range considerably, from −3.04 to −2.33 ‰ (relative to DSM3) and 0.38 to 0.94 ‰ (relative to SRM 915a), respectively. Along with Sr/Ca and Mg/Ca molar ratios, δ<sup>26</sup>Mg and <em>δ</em><sup>44/40</sup>Ca are unambiguously related to mineralogy. This stands in contrast to the carbon and oxygen isotopic compositions of the microbial carbonates, which do not correlate solely with mineralogy. A simple bimineralic mixture of aragonite and high-Mg calcite can explain the observations; such a mixture could be a consequence of both phases forming independently or as one phase recrystallizes from another prior to burial. To evaluate the latter hypothesis, we used a time-dependent advection-recrystallization model. We found that recrystallization of high-Mg calcite to aragonite would require an unreasonable Sr partition coefficient, while recrystallization of aragonite to high-Mg calcite could explain the observed geochemical variations in the two mounds. No microbial isotopic effect is apparent for Mg or Ca, however a difference is seen in the carbon isotopic composition of inorganic carbon where or when aragonite and high-Mg calcite form suggesting they form in two different (micro)environments. Consequently, investigations of ancient microbialites (and carbonates in general) need to consider whether mixtures of primary (original) carbonate minerals and/or recrystallization and transformation pre-burial could impact δ<sup>26</sup>Mg, <em>δ</em><sup>44/40</sup>Ca, δ<sup>13</sup>C and their interpretation using a combination of isotopic, elemental, petrographic, and modeling methods. This is especially important for Mg, whose elemental and isotopic composition can be dominated by even small amounts of calcite or dolomite.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"392 ","pages":"Pages 148-164"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143020255","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}
The formation of polymers that can hold gene information and work as catalysts is a crucial step for the origin of life. The discovery of catalytic RNA (i.e., ribozyme) supports the hypothesis that RNA might have served these functions at the early stage of life on the Earth. Given this, the spontaneous formation of RNA monomers (i.e., ribonucleotides) and their polymerization on Hadean Earth are essential steps for the origin of life. Previous experiments have investigated the chemical reactions that allow the formation of ribonucleotides and their components. These works have revealed the required molecules to form biological ribonucleotides (i.e., canonical ribonucleotides). Based on geochemical perspectives, abundantly available reactive molecules spontaneously react with each other to provide abundant products. Aldehydes and ammonia are reactive molecules assumed to have been present in considerable amounts on Hadean Earth. However, little is understood about whether or not nucleotides and their components were formed from these molecules under prebiotic conditions. We investigated the incubation products of alkaline aqueous solutions of aldehydes and ammonia. The product solution contained sugars (including ribose), various imidazole derivatives, and ribosyl imidazole (i.e., imidazole ribonucleoside). Ribosyl imidazole is formed via ribosyl amine, which reveals a new reaction pathway for prebiotic ribonucleoside synthesis. The imidazole ribonucleoside was then phosphorylated to imidazole ribonucleotide via a simple dry-down reaction with phosphate. Borate ion improved the reaction yields of these nucleosides and nucleotides. Because all the reactants were available on prebiotic Earth and the reactions progressed spontaneously, imidazole ribonucleotides could have accumulated in prebiotic environments. The experimental simplicity of the present reaction suggests that imidazoles were more abundant than canonical nucleobases on the prebiotic Earth. This further implies that prebiotic oligonucleotides contained imidazole bases in addition to the canonical nucleobases. The improvement of the reaction yields by borate indicates that borate-rich environments were conducive places for the formation and accumulation of non-canonical nucleosides and nucleotides. Such environments could have facilitated the formation of primordial ribonucleic acids on Hadean Earth.
{"title":"One-pot synthesis of non-canonical ribonucleosides and their precursors from aldehydes and ammonia under prebiotic Earth conditions","authors":"Yuta Hirakawa , Hidenori Okamura , Fumi Nagatsugi , Takeshi Kakegawa , Yoshihiro Furukawa","doi":"10.1016/j.gca.2024.11.006","DOIUrl":"10.1016/j.gca.2024.11.006","url":null,"abstract":"<div><div>The formation of polymers that can hold gene information and work as catalysts is a crucial step for the origin of life. The discovery of catalytic RNA (i.e., ribozyme) supports the hypothesis that RNA might have served these functions at the early stage of life on the Earth. Given this, the spontaneous formation of RNA monomers (i.e., ribonucleotides) and their polymerization on Hadean Earth are essential steps for the origin of life. Previous experiments have investigated the chemical reactions that allow the formation of ribonucleotides and their components. These works have revealed the required molecules to form biological ribonucleotides (i.e., canonical ribonucleotides). Based on geochemical perspectives, abundantly available reactive molecules spontaneously react with each other to provide abundant products. Aldehydes and ammonia are reactive molecules assumed to have been present in considerable amounts on Hadean Earth. However, little is understood about whether or not nucleotides and their components were formed from these molecules under prebiotic conditions. We investigated the incubation products of alkaline aqueous solutions of aldehydes and ammonia. The product solution contained sugars (including ribose), various imidazole derivatives, and ribosyl imidazole (i.e., imidazole ribonucleoside). Ribosyl imidazole is formed via ribosyl amine, which reveals a new reaction pathway for prebiotic ribonucleoside synthesis. The imidazole ribonucleoside was then phosphorylated to imidazole ribonucleotide via a simple dry-down reaction with phosphate. Borate ion improved the reaction yields of these nucleosides and nucleotides. Because all the reactants were available on prebiotic Earth and the reactions progressed spontaneously, imidazole ribonucleotides could have accumulated in prebiotic environments. The experimental simplicity of the present reaction suggests that imidazoles were more abundant than canonical nucleobases on the prebiotic Earth. This further implies that prebiotic oligonucleotides contained imidazole bases in addition to the canonical nucleobases. The improvement of the reaction yields by borate indicates that borate-rich environments were conducive places for the formation and accumulation of non-canonical nucleosides and nucleotides. Such environments could have facilitated the formation of primordial ribonucleic acids on Hadean Earth.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 239-248"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 10.1016/j.gca.2024.12.012
Mao Tan , Yiping Yang , Xiao-Wen Huang , Jiaxin Xi , Nuo Li , Yu-Miao Meng , Liang Qi
Molybdenite has been established as a robust mineral for Re-Os isotope dating. However, higher-precision Re-Os molybdenite dating is necessary to accurately determine the absolute timing of metal mineralization and duration of ore-forming hydrothermal systems. To improve the precision and accuracy of molybdenite Re-Os dating, molybdenite from the Longmendian deposit—with its old age, heterogeneous distribution of Re, compression deformation, and complex polytypes—serves as a reference for enhancing the precision of in-situ Re-Os dating or grain-scale sampling during solution Re-Os isotope dating of molybdenite. High-resolution scanning transmission electron microscopy (TEM) analysis demonstrates that Re, Os, Pb, Bi, Cu, and Fe are incorporated into the molybdenite crystal through isomorphic substitution for Mo. Electron probe analysis shows that a single molybdenite grain exhibits heterogeneous textures consisting of Re-rich (∼0.29–0.82 wt%) and Re-poor (<0.29 wt%) domains. Some molybdenite grains have undergone compression deformation. Rhenium can be enriched in either the deformed or the undeformed domains of molybdenite grains. Compression deformation in some grains induces delamination cracks in Re-rich domains, facilitating ore-forming fluid infiltration and leading to an inhomogeneous distribution of Re and other elements in molybdenite grains. Re-rich domain in molybdenite is enriched in other metals, including Fe, Co, Zn, Pb, and Bi, due to the overprint of the hydrothermal fluids with a lower temperature and a relatively high oxygen fugacity, leading to the formation of heterogeneous molybdenite. Micro-X-ray diffraction (μXRD) and TEM analyses have revealed that both the Re-rich and Re-poor domains belong to the 2H1 polytype, indicating that Re concentration and distribution are not directly related to the polytype of molybdenite. The Re-poor and deformed domain of molybdenite shows the coexistence of 2H1 and 3R polytypes (in a ratio of 9:1), suggesting that compression deformation led to polytype transformation. Therefore, the diverse characteristics of molybdenite in the Longmendian deposit present challenges for obtaining primary Re-Os age information. Nondestructive pre-characterization of molybdenite is essential before dating to ensure age homogeneity. Molybdenite samples with an undeformed and uniform distribution of elements (Re) within molybdenite grains are suitable candidates for analysis. Our findings collectively offer strategies to enhance precision while advancing the understanding of elemental and isotopic geochemical behavior in the contexts of metamorphism, deformation, and fluid flow environments.
辉钼矿已被确定为 Re-Os 同位素测年的可靠矿物。然而，要准确确定金属成矿的绝对时间和成矿热液系统的持续时间，就需要更高精度的辉钼矿Re-Os年代测定。为了提高辉钼矿Re-Os定年的精度和准确性，龙门甸矿床的辉钼矿--其年代久远、Re分布不均、压缩变形和复杂的多型性--可作为提高辉钼矿原位Re-Os定年或溶液Re-Os同位素定年过程中晶粒尺度取样精度的参考。高分辨率扫描透射电子显微镜（TEM）分析表明，Re、Os、Pb、Bi、Cu 和 Fe 是通过同构取代 Mo 的方式融入辉钼矿晶体的。电子探针分析表明，单个辉钼矿晶粒呈现出由富Re（0.29-0.82 wt%）和贫Re（0.29 wt%）域组成的异质纹理。一些辉钼矿晶粒经历了压缩变形。铼可在辉钼矿晶粒的变形或未变形域中富集。某些晶粒的压缩变形会在富铼域诱发分层裂纹，促进成矿流体的渗入，导致钼矿晶粒中的铼和其他元素分布不均。由于热液温度较低，氧富集度相对较高，导致形成异质辉钼矿，因此辉钼矿中的富集域富含其他金属，包括铁、钴、锌、铅和铋。显微 X 射线衍射（μXRD）和 TEM 分析表明，富 Re 域和贫 Re 域都属于 2H1 多晶型，表明 Re 的浓度和分布与辉钼矿的多晶型没有直接关系。辉钼矿的再贫域和变形域显示出 2H1 和 3R 多型共存（比例为 9:1），表明压缩变形导致了多型转化。因此，龙门甸矿床中辉钼矿的多样化特征为获取原始Re-Os年龄信息带来了挑战。在测年之前，必须对辉钼矿进行非破坏性预表征，以确保年龄的均一性。辉钼矿样品中的元素（Re）在辉钼矿晶粒内未变形且分布均匀，适合进行分析。我们的研究结果共同为提高精确度提供了策略，同时也推进了对变质、变形和流体流动环境下元素和同位素地球化学行为的理解。
{"title":"Rhenium residency in molybdenite, compressional textures and relationship to polytypism","authors":"Mao Tan , Yiping Yang , Xiao-Wen Huang , Jiaxin Xi , Nuo Li , Yu-Miao Meng , Liang Qi","doi":"10.1016/j.gca.2024.12.012","DOIUrl":"10.1016/j.gca.2024.12.012","url":null,"abstract":"<div><div>Molybdenite has been established as a robust mineral for Re-Os isotope dating. However, higher-precision Re-Os molybdenite dating is necessary to accurately determine the absolute timing of metal mineralization and duration of ore-forming hydrothermal systems. To improve the precision and accuracy of molybdenite Re-Os dating, molybdenite from the Longmendian deposit—with its old age, heterogeneous distribution of Re, compression deformation, and complex polytypes—serves as a reference for enhancing the precision of in-situ Re-Os dating or grain-scale sampling during solution Re-Os isotope dating of molybdenite. High-resolution scanning transmission electron microscopy (TEM) analysis demonstrates that Re, Os, Pb, Bi, Cu, and Fe are incorporated into the molybdenite crystal through isomorphic substitution for Mo. Electron probe analysis shows that a single molybdenite grain exhibits heterogeneous textures consisting of Re-rich (∼0.29–0.82 wt%) and Re-poor (<0.29 wt%) domains. Some molybdenite grains have undergone compression deformation. Rhenium can be enriched in either the deformed or the undeformed domains of molybdenite grains. Compression deformation in some grains induces delamination cracks in Re-rich domains, facilitating ore-forming fluid infiltration and leading to an inhomogeneous distribution of Re and other elements in molybdenite grains. Re-rich domain in molybdenite is enriched in other metals, including Fe, Co, Zn, Pb, and Bi, due to the overprint of the hydrothermal fluids with a lower temperature and a relatively high oxygen fugacity, leading to the formation of heterogeneous molybdenite. Micro-X-ray diffraction (μXRD) and TEM analyses have revealed that both the Re-rich and Re-poor domains belong to the 2<em>H</em><sub>1</sub> polytype, indicating that Re concentration and distribution are not directly related to the polytype of molybdenite. The Re-poor and deformed domain of molybdenite shows the coexistence of 2<em>H</em><sub>1</sub> and 3<em>R</em> polytypes (in a ratio of 9:1), suggesting that compression deformation led to polytype transformation. Therefore, the diverse characteristics of molybdenite in the Longmendian deposit present challenges for obtaining primary Re-Os age information. Nondestructive pre-characterization of molybdenite is essential before dating to ensure age homogeneity. Molybdenite samples with an undeformed and uniform distribution of elements (Re) within molybdenite grains are suitable candidates for analysis. Our findings collectively offer strategies to enhance precision while advancing the understanding of elemental and isotopic geochemical behavior in the contexts of metamorphism, deformation, and fluid flow environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 59-73"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 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 (Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of Sr as a tracer of early marine diagenesis. We used paired measurements of Sr and radiogenic Sr isotope ratios (87Sr/86Sr) 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 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 (M) and Sr lower (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 Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (2 Myr) and demonstrate that pore fluid Sr measurements are a useful addition to multi-tracer studies of diagenesis in complex marine systems.
{"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":"10.1016/j.gca.2024.10.028","url":null,"abstract":"<div><div>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 (<span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>Sr as a tracer of early marine diagenesis. We used paired measurements of <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>Sr and radiogenic Sr isotope ratios (<sup>87</sup>Sr/<sup>86</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 <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>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 (<span><math><mrow><mo>∼</mo><mn>98</mn><mspace></mspace><mi>μ</mi></mrow></math></span>M) and <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>Sr lower (<span><math><mo>∼</mo></math></span>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 <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (<span><math><mo>∼</mo></math></span>2 Myr) and demonstrate that pore fluid <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>88</mn><mo>/</mo><mn>86</mn></mrow></msup></math></span>Sr measurements are a useful addition to multi-tracer studies of diagenesis in complex marine systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 211-223"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","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":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 10.1016/j.gca.2024.09.011
Giovanna S.A. Utsumi , Ding He , William M. Berelson , Renato M. Castelao , Patricia L. Yager , Patricia M. Medeiros
The Amazon River exports ∼13.7 Tg yr−1 of particulate organic carbon (POC) to the ocean, a portion of which is transported vertically through the water column. Here, we investigated in detail the composition of POC using a multi-tracer approach, including POC concentration, stable carbon isotopes (δ13C) and a wide range of molecular biomarkers to assess the contribution of POC export from the Amazon River to the western tropical Atlantic Ocean (WTAO). For this purpose, suspended and sediment trap POC were collected at multiple depths along the Amazon River plume under high and low river discharge conditions. Concentrations of POC detected in the plume were ∼2 to 3-fold higher than those below the plume. Overall, δ13C signatures of suspended and sediment trap POC samples were enriched, averaging −19.9 ‰ and –22.8 ‰, respectively. At the surface, POC composition was mainly characterized by low molecular weight n-alkanoic acids (<C20), mono- and disaccharides (e.g., glucose, scyllo-inositol and melibiose) and triglyceride derivatives (e.g., glycerol and 2-O-glycerol-α-D-galactopyranoside), indicating fresh inputs of organic matter (OM) presumably derived from algal blooms. These biomarkers were observed in lower concentrations in sediment traps. Trap samples were marked by zooplankton- (e.g., cholesterol, occelasterol) and bacteria-derived (e.g., C15 and C17 branched n-alkanoic acids) biomarkers, indicating metabolic alteration of OM at those depths. Solvent-extractable terrestrial biomarkers (e.g., dehydroabietic acid and levoglucosan) were only found in minor concentrations in most samples, which contrasts with the dissolved fraction which has been previously shown to have a primary signature of terrigenous inputs. Our results clarify the Amazon River plume’s impact on the biological pump of the WTAO, consistent with a river plume fueling primary production, and with increased zooplankton and bacteria contributions to POC composition at depth and in the POC that is vertically exported.
{"title":"Influence of the Amazon River on the composition of particulate organic carbon in the western tropical Atlantic Ocean","authors":"Giovanna S.A. Utsumi , Ding He , William M. Berelson , Renato M. Castelao , Patricia L. Yager , Patricia M. Medeiros","doi":"10.1016/j.gca.2024.09.011","DOIUrl":"10.1016/j.gca.2024.09.011","url":null,"abstract":"<div><div>The Amazon River exports ∼13.7 Tg yr<sup>−1</sup> of particulate organic carbon (POC) to the ocean, a portion of which is transported vertically through the water column. Here, we investigated in detail the composition of POC using a multi-tracer approach, including POC concentration, stable carbon isotopes (δ<sup>13</sup>C) and a wide range of molecular biomarkers to assess the contribution of POC export from the Amazon River to the western tropical Atlantic Ocean (WTAO). For this purpose, suspended and sediment trap POC were collected at multiple depths along the Amazon River plume under high and low river discharge conditions. Concentrations of POC detected in the plume were ∼2 to 3-fold higher than those below the plume. Overall, δ<sup>13</sup>C signatures of suspended and sediment trap POC samples were enriched, averaging −19.9 ‰ and –22.8 ‰, respectively. At the surface, POC composition was mainly characterized by low molecular weight <em>n-</em>alkanoic acids (<C<sub>20</sub>), mono- and disaccharides (e.g., glucose, <em>scyllo-</em>inositol and melibiose) and triglyceride derivatives (e.g., glycerol and 2-<em>O</em>-glycerol-α-D-galactopyranoside), indicating fresh inputs of organic matter (OM) presumably derived from algal blooms. These biomarkers were observed in lower concentrations in sediment traps. Trap samples were marked by zooplankton- (e.g., cholesterol, occelasterol) and bacteria-derived (e.g., C<sub>15</sub> and C<sub>17</sub> branched <em>n-</em>alkanoic acids) biomarkers, indicating metabolic alteration of OM at those depths. Solvent-extractable terrestrial biomarkers (e.g., dehydroabietic acid and levoglucosan) were only found in minor concentrations in most samples, which contrasts with the dissolved fraction which has been previously shown to have a primary signature of terrigenous inputs. Our results clarify the Amazon River plume’s impact on the biological pump of the WTAO, consistent with a river plume fueling primary production, and with increased zooplankton and bacteria contributions to POC composition at depth and in the POC that is vertically exported.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 84-99"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143095858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 10.1016/j.gca.2024.10.021
Dorrit E. Jacob , Richard A. Stern , Janina Czas , Magnus Reutter , Sandra Piazolo , Thomas Stachel
Polycrystalline diamond aggregates (PDAs) are small rocks composed mostly of diamond grains, but often containing also peridotitic, eclogitic and/or websteritic minerals as accessory phases. PDAs are formed rapidly in Earth’s mantle, and the diamonds preserve heterogeneity not often seen in monocrystalline diamond. Here, diamond grains from forty-three PDAs from the Venetia diamond mine (RSA) with grain-sizes < 1 mm are presented. They have heterogeneous and complex cathodoluminescence signatures that are best explained by multiple, separate diamond growth episodes from compositionally distinct COH fluids/melts. The diamonds show a large range of nitrogen concentrations (0.5 to 2,891 at. ppm), δ15N (−4.3 to + 16.8 ‰) and δ13C values (−27.8 to −7.6 ‰). The positive δ15N median of + 6.4 ‰ and negative δ13C median of −21.2 ‰ indicate derivation of the diamond-forming fluid from organic materials in subducted oceanic crust and lithosphere. Two PDAs have δ13C and δ15N values typical for Earth’s mantle. Thirty-three PDAs contain websteritic garnets, or peridotitic garnets and clinopyroxenes and/or micas. Unradiogenic εNdi values in the garnets (−15.9 to −29.7) and clinopyroxene (−8.3) and δ18O values of 6.49 to 8.09 ‰ in websteritic garnets are consistent with an origin from subducted altered oceanic crust and support the findings from N and C systematics in the diamonds. Nitrogen aggregation data for the diamonds range from 25 % to 100 %B and vary by as much as 60 % within some individual PDAs. We explain the geochemical and isotopic heterogeneity of diamonds and silicates as well as the complex cathodoluminescence features with a model of episodic melt/fluid −rock interaction involving a reducing asthenospheric melt in the cratonic roots or the thermal boundary layer. We suggest that large volumes of PDA are formed in the cratonic roots and thermal boundary layer by this mechanism, making them an important reservoir for carbon storage, which is corroborated with their locally high abundance (ca. 20 %) in some kimberlites.
{"title":"Polycrystalline diamond aggregates and their role in Earth’s deep carbon cycle","authors":"Dorrit E. Jacob , Richard A. Stern , Janina Czas , Magnus Reutter , Sandra Piazolo , Thomas Stachel","doi":"10.1016/j.gca.2024.10.021","DOIUrl":"10.1016/j.gca.2024.10.021","url":null,"abstract":"<div><div>Polycrystalline diamond aggregates (PDAs) are small rocks composed mostly of diamond grains, but often containing also peridotitic, eclogitic and/or websteritic minerals as accessory phases. PDAs are formed rapidly in Earth’s mantle, and the diamonds preserve heterogeneity not often seen in monocrystalline diamond. Here, diamond grains from forty-three PDAs from the Venetia diamond mine (RSA) with grain-sizes < 1 mm are presented. They have heterogeneous and complex cathodoluminescence signatures that are best explained by multiple, separate diamond growth episodes from compositionally distinct COH fluids/melts. The diamonds show a large range of nitrogen concentrations (0.5 to 2,891 at. ppm), δ<sup>15</sup>N (−4.3 to + 16.8 ‰) and δ<sup>13</sup>C values (−27.8 to −7.6 ‰). The positive δ<sup>15</sup>N median of + 6.4 ‰ and negative δ<sup>13</sup>C median of −21.2 ‰ indicate derivation of the diamond-forming fluid from organic materials in subducted oceanic crust and lithosphere. Two PDAs have δ<sup>13</sup>C and δ<sup>15</sup>N values typical for Earth’s mantle. Thirty-three PDAs contain websteritic garnets, or peridotitic garnets and clinopyroxenes and/or micas. Unradiogenic εNd<sub>i</sub> values in the garnets (−15.9 to −29.7) and clinopyroxene (−8.3) and δ<sup>18</sup>O values of 6.49 to 8.09 ‰ in websteritic garnets are consistent with an origin from subducted altered oceanic crust and support the findings from N and C systematics in the diamonds. Nitrogen aggregation data for the diamonds range from 25 % to 100 %B and vary by as much as 60 % within some individual PDAs. We explain the geochemical and isotopic heterogeneity of diamonds and silicates as well as the complex cathodoluminescence features with a model of episodic melt/fluid −rock interaction involving a reducing asthenospheric melt in the cratonic roots or the thermal boundary layer. We suggest that large volumes of PDA are formed in the cratonic roots and thermal boundary layer by this mechanism, making them an important reservoir for carbon storage, which is corroborated with their locally high abundance (ca. 20 %) in some kimberlites.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 136-156"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-15DOI: 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
<div><div>Despite early hydrological studies of <sup>234</sup>U/<sup>238</sup>U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (<sup>230</sup>Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed <sup>234</sup>U enrichment is attributed to selective leaching of <sup>234</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 <sup>234</sup>U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low δ<sup>234</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<sub>2</sub> and overall rock dissolution rates. This reduction could enhance the preferential leaching of <sup>234</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<sub>2</sub>, accelerating rock dissolution rates during interstadials and interglacials, when low δ<sup>234</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<sup>234</sup>U in <em>Andromeda</em> stalagmite during MIS 3–4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain δ<sup>234</sup>U variability, highlighting the fundamental role of soil respiration and soil CO<sub>2</sub> in δ<sup>234</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<sup>234</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<sup>234</sup>U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, δ<sup>234</sup>U could serve as a valuable complement to δ<sup>13</sup>C since it is significantly influenced by soil respiration and soil CO<sub>2</sub>, thereby reflecting soil and vegetation productivity sensitive to both humidity and temperature. Secondly, since PCP does not fractionate uranium isotopes, δ<sup>234</sup>U could be used in combination with Mg/Ca or δ<sup>4
{"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":"10.1016/j.gca.2024.11.016","url":null,"abstract":"<div><div>Despite early hydrological studies of <sup>234</sup>U/<sup>238</sup>U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (<sup>230</sup>Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed <sup>234</sup>U enrichment is attributed to selective leaching of <sup>234</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 <sup>234</sup>U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low δ<sup>234</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<sub>2</sub> and overall rock dissolution rates. This reduction could enhance the preferential leaching of <sup>234</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<sub>2</sub>, accelerating rock dissolution rates during interstadials and interglacials, when low δ<sup>234</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<sup>234</sup>U in <em>Andromeda</em> stalagmite during MIS 3–4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain δ<sup>234</sup>U variability, highlighting the fundamental role of soil respiration and soil CO<sub>2</sub> in δ<sup>234</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<sup>234</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<sup>234</sup>U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, δ<sup>234</sup>U could serve as a valuable complement to δ<sup>13</sup>C since it is significantly influenced by soil respiration and soil CO<sub>2</sub>, thereby reflecting soil and vegetation productivity sensitive to both humidity and temperature. Secondly, since PCP does not fractionate uranium isotopes, δ<sup>234</sup>U could be used in combination with Mg/Ca or δ<sup>4","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 265-279"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","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}
Fifteen elements, including most of the major elements, were quantified using neutron-induced prompt gamma-ray analysis for five Antarctic carbonaceous chondrites with CI affinities and seven with CM affinities. Common among the twelve meteorites is the depletion of volatile elements H and chlorine, showing a positive correlation and being depleted compared to non-Antarctic CI levels. This depletion is not thought to have occurred after the fall on Antarctica, but to have been caused by thermal metamorphism on the parent body. Among the meteorites analyzed in this study, six meteorites (Y-86029, Y 980115 and Y-82162 (with CI affinities), and Y-86720, Y-86789 and B-7904 (with CM affinities)) have previously been proposed to constitute a new meteorite group, the Yamato-type (CY), based on their oxygen isotopic compositions and petrological features. The elemental compositional characteristics of the remaining six meteorites analyzed in this study, Y-86737 and Y 980134 (with CI affinities), and Y-86770, Y-86771, Y-86772 and Y-86773 (with CM affinities), suggest that these meteorites are all classified into the same chemical group CY. Based on the abundance of moderately volatile elements Mn and S, the twelve meteorites can be divided into two groups: one with levels similar to non-Antarctic CI and the other with intermediate levels between CI and CM. These results suggest that CY chondrites originate from two distinct parent bodies. To facilitate further discussions on CY chondrites, we propose naming the groups with compositions close to CI and CM as CYi and CYm, respectively.
利用中子诱导瞬时伽马射线分析，对五块具有 CI 亲缘关系的南极碳质陨石和七块具有 CM 亲缘关系的南极碳质陨石的十五种元素（包括大多数主要元素）进行了定量分析。这十二块陨石的共同点是挥发性元素 H 和氯的消耗，与非南极 CI 水平相比，这两种元素的消耗呈正相关。这种损耗被认为不是在陨落到南极洲之后发生的，而是由母体的热变质作用引起的。在这项研究分析的陨石中，有六块陨石（Y-86029、Y 980115 和 Y-82162（具有 CI 亲缘关系），以及 Y-86720、Y-86789 和 B-7904（具有 CM 亲缘关系））曾被根据它们的氧同位素组成和岩石学特征而提议构成一个新的陨石群--大和类型（CY）。本研究分析的其余六块陨石，即 Y-86737 和 Y 980134（具有 CI 亲缘关系），以及 Y-86770、Y-86771、Y-86772 和 Y-86773（具有 CM 亲缘关系）的元素组成特征表明，这些陨石都被归入同一化学组 CY。根据中等挥发性元素 Mn 和 S 的丰度，这 12 块陨石可分为两组：一组的含量与非南极 CI 相似，另一组的含量介于 CI 和 CM 之间。这些结果表明，CY 陨石起源于两个不同的母体。为了便于进一步讨论CY软玉，我们建议将成分接近CI和CM的组别分别命名为CYi和CYm。
{"title":"Chemical characteristics of the Yamato-type (CY) carbonaceous chondrites","authors":"Mitsuru Ebihara , Naoki Shirai , Takahito Osawa , Akira Yamaguchi","doi":"10.1016/j.gca.2024.10.026","DOIUrl":"10.1016/j.gca.2024.10.026","url":null,"abstract":"<div><div>Fifteen elements, including most of the major elements, were quantified using neutron-induced prompt gamma-ray analysis for five Antarctic carbonaceous chondrites with CI affinities and seven with CM affinities. Common among the twelve meteorites is the depletion of volatile elements H and chlorine, showing a positive correlation and being depleted compared to non-Antarctic CI levels. This depletion is not thought to have occurred after the fall on Antarctica, but to have been caused by thermal metamorphism on the parent body. Among the meteorites analyzed in this study, six meteorites (Y-86029, Y 980115 and Y-82162 (with CI affinities), and Y-86720, Y-86789 and B-7904 (with CM affinities)) have previously been proposed to constitute a new meteorite group, the Yamato-type (CY), based on their oxygen isotopic compositions and petrological features. The elemental compositional characteristics of the remaining six meteorites analyzed in this study, Y-86737 and Y 980134 (with CI affinities), and Y-86770, Y-86771, Y-86772 and Y-86773 (with CM affinities), suggest that these meteorites are all classified into the same chemical group CY. Based on the abundance of moderately volatile elements Mn and S, the twelve meteorites can be divided into two groups: one with levels similar to non-Antarctic CI and the other with intermediate levels between CI and CM. These results suggest that CY chondrites originate from two distinct parent bodies. To facilitate further discussions on CY chondrites, we propose naming the groups with compositions close to CI and CM as CYi and CYm, respectively.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 200-210"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673645","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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