Geochimica et Cosmochimica Acta最新文献

{"title":"Abiotic iron oxidation controlled the deposition of Neoproterozoic iron formations","authors":"Zekun Meng ,&nbsp;Kang-Jun Huang ,&nbsp;Zhenfei Wang ,&nbsp;Zhiquan Li ,&nbsp;Leslie J. Robbins ,&nbsp;Dalton S. Hardisty ,&nbsp;Kurt O. Konhauser","doi":"10.1016/j.gca.2025.10.002","DOIUrl":"10.1016/j.gca.2025.10.002","url":null,"abstract":"<div><div>Following a billion-year hiatus, iron formations (IFs) briefly re-emerged during Neoproterozoic Snowball Earth glaciations. Unlike their Archean-Paleoproterozoic counterparts, Neoproterozoic IFs (NIFs) are uniquely associated with glaciogenic diamictites and dominated by hematite, yet the drivers of this mineralogical shift remain debated. Here, we present coupled iron-carbon isotope data from Sturtian-aged NIFs in the Fulu Formation (Nanhua Basin, South China). The Fulu NIFs feature alternating bands of euhedral hematite, quartz, feldspar, Fe chlorite, as well as some siderite. The siderite exhibits exceptionally negative δ¹³C_carb values (down to −19 ‰). Isotopic equilibrium modeling supports two hypotheses for this fractionation: (i) a diminished dissolved inorganic carbon (DIC) reservoir influenced by dissimilatory iron reduction (DIR), and (ii) Fe-mediated anaerobic oxidation of methane (AOM) driven by methane diffusion. Both scenarios align with suppressed primary productivity under ice-covered oceans, where microbial activity and organic burial were limited. This low-productivity regime explains the hematite-dominated mineralogy of NIFs, contrasting sharply with the diverse diagenetic phases (e.g., siderite, magnetite) in Archean-Paleoproterozoic IFs. Heavy δ⁵⁶Fe values (up to 2.03 ‰) further indicate abiotic Fe²⁺ oxidation via meltwater-derived oxygen, rather than biological pathways like photoferrotrophy. Overall, these results support a model of an anoxic Cryogenian ocean with minimal productivity during NIFs deposition, where Fe cycling was governed by glacially mediated redox dynamics.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 634-651"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145311743","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}

{"title":"Zinc isotopic fractionation during magmatic differentiation and hydrothermal processes: implications for Li mineralization in the Jiajika granitic pegmatites, Sichuan, China","authors":"Jia-Wen Liu ,&nbsp;Shi-Hong Tian ,&nbsp;Xian-Lei Geng ,&nbsp;Ying-Li Gong ,&nbsp;Lu Chen ,&nbsp;Shi-Qi Huang","doi":"10.1016/j.gca.2025.11.031","DOIUrl":"10.1016/j.gca.2025.11.031","url":null,"abstract":"<div><div>This study provides a comprehensive analysis of zinc (Zn) isotopes to gain deep insights into their behavior during magmatic differentiation and hydrothermal processes, and their implications for the formation of the Jiajika granite–pegmatite lithium deposit. Previous geochemical evidence indicates that a crystallization sequence of the Jiajika high-Si magmas from the two-mica granites to the Li-poor pegmatites and finally to the Li-rich pegmatites. Two-mica granites exhibit higher δ⁶⁶Zn values (0.47–0.85 ‰, avg. 0.60 ‰), than other granites worldwide. Li-poor pegmatites (0.33–0.58 ‰, avg. 0.47 ‰, excluding two outliers) are lower than those of Li-rich pegmatites (0.59–1.21 ‰, avg. 0.79 ‰). Muscovites from Li-rich pegmatites have higher δ⁶⁶Zn values (0.85–1.01 ‰, avg. 0.95 ‰) than those from Li-poor pegmatites (0.40–1.00 ‰, avg. 0.69 ‰). Covariations of δ⁶⁶Zn with decreasing MgO, Y/Ho, Zr/Hf and K/Rb contradict a purely magmatic differentiation trend in Li-poor and Li-rich pegmatites, indicating that magmatic differentiation alone cannot explain their genetic relationship. The Zn isotopic fractionation between Li-poor and Li-rich pegmatites results from fluid-melt interactions, primarily driven by fluid exsolution, which is a critical mechanism for the enrichment of lithium and other rare metal elements. This study underscores the sensitivity of Zn isotopes to magmatic-hydrothermal transitions in pegmatite systems, offering new isotopic constraints on the genesis of granite-related rare metal mineralization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 372-384"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145553680","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}

{"title":"Magnesium isotope geochemistry in continental flood basalts: implications for mantle source heterogeneity","authors":"Sakine Moradi ,&nbsp;Lie-Meng Chen ,&nbsp;Peter C. Lightfoot ,&nbsp;Kang-Jun Huang ,&nbsp;Qiao Su ,&nbsp;Song-Yue Yu ,&nbsp;Li-Juan Zhu ,&nbsp;Rui-Zhong Hu","doi":"10.1016/j.gca.2025.10.035","DOIUrl":"10.1016/j.gca.2025.10.035","url":null,"abstract":"<div><div>Recent studies have demonstrated that large variations in chemical and isotopic compositions of continental flood basalts are genetically related to variable contributions of the recycled oceanic slab components in their mantle sources. Magnesium (Mg) isotopes are regarded as sensitive tracers for identifying the contribution of recycled materials to the mantle. To investigate the origin of geochemical variations in the Permo-Triassic Siberian continental flood basalts (SCFBs), this study presents the first Mg isotopic data from basaltic rocks in the Noril’sk region, Russia. The SCFBs are classified into high-Ti and low-Ti basalts, exhibiting variable δ²⁶Mg values ranging from −0.40 ± 0.08 ‰ to −0.11 ± 0.02 ‰ and from −0.26 ± 0.09 ‰ to −0.09 ± 0.02 ‰, respectively, which stand in contrast to the narrow range observed in global oceanic island basalts (δ²⁶Mg = −0.25 ± 0.07 ‰). The Mg isotope variations in these SCFBs can hardly be explained by post-eruptive alteration, crustal contamination, fractional crystallization, and/or mantle partial melting. In contrast, the δ²⁶Mg variability, combined with arc-type trace element patterns, enriched initial Sr-Nd isotope signatures, and variable Hf isotopes, indicates mantle heterogeneity induced by the incorporation of diverse subducted components. A heterogeneous mantle source containing recycled eclogite or pyroxenite is further supported by Mg isotope data integrated with other geochemical proxies (e.g., Fe/Mn and Zn/Fe) in both groups. However, neither direct melting of altered oceanic crust nor incorporation of sediment-derived melts or fluids derived from these two components could produce the observed Mg isotope systematics. Instead, isotope modeling reveals that the high δ²⁶Mg values in the SCFBs originated from deep recycling of serpentinite-derived slab fluids, which stagnated in the mantle transition zone (MTZ). A heterogeneous deep mantle plume and its interaction with the hydrated stagnant slabs likely contributed to Mg isotope variations observed in the high-Ti basalts. Partial melting of the subcontinental lithospheric mantle metasomatized by high contents of recycled serpentinite-derived fluids, which were transported by hydrated mantle diapirs, produced the heavy Mg isotope signatures in the low-Ti basalts. This study highlights the vital role of Mg isotopes in tracing mantle source heterogeneity of continental flood basalts.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 127-144"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145412222","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}

{"title":"Average trace element composition of the upper continental crust derived from an integrated study of sedimentary and igneous rocks","authors":"Kang Chen ,&nbsp;Pengyuan Han ,&nbsp;Roberta L. Rudnick ,&nbsp;Jingliang Guo ,&nbsp;Zhaochu Hu","doi":"10.1016/j.gca.2025.11.044","DOIUrl":"10.1016/j.gca.2025.11.044","url":null,"abstract":"<div><div>We present updated estimates for the trace element composition of the upper continental crust (UCC) by integrating newly acquired geochemical data from 139 loess samples across Asia, Europe, North America, and South America with a comprehensive compilation of data from loess, shales, diamictites, and continental igneous rocks. The new concentration estimates for first-row transition metals, Li–Be–Ba, Zr–Hf, and Ga–Tl–Pb are within ±20 % of those suggested by <span><span>Rudnick and Gao (2003)</span></span>. However, our results yield markedly lower Cs (∼50 %) and higher REEs–Y–Rb–Nb–Ta–Th–U (25–65 %) and Bi (120 %) abundances. These discrepancies primarily arise from differences in La concentrations, which we constrain using La/TiO₂ correlations in sediments. We demonstrate that loess can provide robust constraints on UCC composition owing to its lower chemical weathering intensity and greater homogeneity than shales and glacial diamictites. Nevertheless, using simple averages of absolute concentrations in loess may result in unreliable estimates due to mineral dilution or enrichment effects. Furthermore, correlation-based methods may suffer from mineral sorting effects, leading to biased estimates; for example, anomalously high La/Al₂O₃ ratios in European loess reflect enrichment of accessory minerals such as titanite. Employing element pairs that exhibit consistent correlations across sedimentary rock types mitigates many of these biases. The elevated abundances of heat-producing elements (K, Th, and U) in our UCC estimates suggest that the deeper continental crust, excluding the UCC, is unlikely to be dominantly felsic; instead, it is probably mafic to intermediate, depending on the assumed mantle heat flux. The new UCC composition estimate is consistent with many key geochemical ratios proposed in previous UCC estimates, such as Nb/Ta, Zr/Hf, Zr/Sm, Ni/Co, Cr/Zn, Th/U, and La/Th. Notably, the high La/Nb ratio (∼2.6) supports the dominant role of arc magmatism, rather than intraplate magmatism, in crustal growth, while the Nb/Ta (12.6), (La/Yb)_N (8.3), and (Dy/Yb)_N (1.1) values underscore the importance of subduction-related magmatism in thick continental arcs in generating the modern continental crust.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 193-211"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731850","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}

{"title":"Whole-rock Mg isotopes distinguishing high- and low-temperature S-type granites","authors":"Yan Wang ,&nbsp;Peng Gao ,&nbsp;Zi-Fu Zhao ,&nbsp;Hai-Ou Gu ,&nbsp;Guo-Chao Sun ,&nbsp;Hui-Chan Huang ,&nbsp;Zhang-Jian Wu ,&nbsp;Changqing Yin","doi":"10.1016/j.gca.2025.05.048","DOIUrl":"10.1016/j.gca.2025.05.048","url":null,"abstract":"&lt;div&gt;&lt;div&gt;&lt;span&gt;&lt;span&gt;&lt;span&gt;Determining the temperature of crustal anatexis associated with granitic &lt;/span&gt;magmatism&lt;span&gt; is vital for understanding the petrogenesis&lt;span&gt; of granites and the processes underlying crustal anatexis. During the partial melting of metasedimentary rocks, the breakdown of &lt;/span&gt;&lt;/span&gt;&lt;/span&gt;biotite&lt;span&gt; at elevated temperatures can lead to the formation of peritectic garnet&lt;span&gt;, which is typically rare or absent at lower temperatures when melting is predominantly driven by muscovite breakdown. This distinction makes magnesium (Mg) isotopes a valuable tool for tracing relative variations in crustal melting temperatures, as garnet exhibits the lowest δ&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;26&lt;/sup&gt;&lt;span&gt;Mg values compared to other Mg-bearing phases under equilibrium fractionation. However, the extent to which temperature variations influence melt Mg isotope compositions remains inadequately understood. In this study, we present Mg and oxygen isotope&lt;span&gt; data for high- and low-temperature leucogranites&lt;span&gt; from the Himalayan orogen, alongside whole-rock major and trace element data, and zircon Ti content from previous studies. Low-temperature leucogranites, with maximum Ti-in-zircon temperatures ranging from 739 to 801 °C, display negative δ&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;26&lt;/sup&gt;Mg values between −0.70 and −0.14 ‰, aligning with most global S-type granites. Conversely, high-temperature leucogranites, exhibiting maximum Ti-in-zircon temperatures of 800 to 855 °C, possess positive δ&lt;sup&gt;26&lt;/sup&gt;Mg values ranging from 0.46 to 0.53 ‰, significantly exceeding those of Himalayan metasedimentary rocks and most global S-type granites. The high-temperature leucogranites also demonstrate relatively elevated Nb/Ta and Eu/Eu* ratios, while their whole-rock δ&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O and CIA values are comparable to those of low-temperature leucogranites. These findings suggest that fluid alteration, fractional crystallization, and crustal assimilation have a minimal impact on the Mg isotope discrepancies between the two granite groups. We propose that the positive δ&lt;/span&gt;&lt;sup&gt;26&lt;/sup&gt;&lt;span&gt;Mg values of the high-temperature leucogranites result from a greater fraction of peritectic garnet in the melting residue, attributable to higher anatectic temperatures. Phase equilibrium modeling indicates that the peritectic reaction involving muscovite breakdown is swiftly replaced by biotite breakdown as temperatures rise, leading to a steady increase in the corresponding fraction of garnet. Equilibrium fractionation calculations further corroborate that melt δ&lt;/span&gt;&lt;sup&gt;26&lt;/sup&gt;Mg values rise with an increasing fraction of peritectic garnet, with values at high temperatures significantly surpassing those at lower temperatures. Consequently, this study elucidates a causal relationship between Mg isotope composition and anatectic temperature, highlighting that whole-rock Mg isotopes can serve as a reliable indicator for distinguishing between high- and l","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 330-345"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144304950","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}

{"title":"Significant Mg isotope disequilibrium during crustal anatexis: Implications for heterogeneous Mg isotopic compositions in the continental crust","authors":"Er-Lin Zhu ,&nbsp;Qiong-Xia Xia ,&nbsp;Zhao-Ya Li ,&nbsp;Hao-Hong Shu","doi":"10.1016/j.gca.2025.09.041","DOIUrl":"10.1016/j.gca.2025.09.041","url":null,"abstract":"<div><div>Metamorphic dehydration and partial melting of continental crust are two important processes during continental collision. They are also crucial to chemical differentiation of the continental crust and crust-mantle interaction. Magnesium (Mg) isotope fractionation can be significantly influenced by water–rock interaction and crustal anatexis, which serve as important records of crustal material recycling. In this study, we present Mg isotope data for two groups of low-temperature ultrahigh-pressure (UHP) granitic gneisses affected by metamorphic dehydration (Group A) and partial melting (Group B) in the Dabie orogen, a typical continental collision zone in east-central China. Our results show that Group A rocks exhibit δ²⁶Mg values of −0.31 to −0.02 ‰, which are similar to those of the low-grade greenschists (−0.27 to −0.13 ‰) and felsic schists (−0.29 to −0.10 ‰). Group A rocks exhibit homogeneous δ²⁶Mg values but variable Ba/Th ratios, reflecting that metamorphic dehydration has not affected their Mg isotopes. In contrast, Group B rocks display significantly lower and heterogeneous δ²⁶Mg values, ranging from −0.78 to −0.26 ‰. Additionally, δ²⁶Mg values are well correlated with Nb/Sm ratios which are most sensitive to partial melting processes. Geochemical and petrographic studies reveal that Group B rocks underwent dehydration melting of phengite, forming peritectic biotite and garnet during the initial exhumation. No correlation between the δ²⁶Mg values and (Dy/Yb)_N ratios suggests that isotopically light garnet did not contribute to the observed Mg isotope variations in Group B rocks. The covariation<!--> <!-->of δ²⁶Mg values and Nb, Ta, Rb, Ti and Mg contents indicate that the Mg isotope fractionation was primarily controlled by biotite. In the incongruent melting reaction, peritectic biotite remained as a residual refractory phase in the source, and melt was extracted away from the melting source. The isotopically heavy biotite likely accounts for the significantly light Mg isotope compositions in the anatectic melts and isotopically heavy residues. Therefore, our investigation on Mg isotope fractionation during crustal anatexis demonstrates that incongruent melting processes involving distinct mineral assemblages can produce significant Mg isotope variations in both batch melts and residues. These findings highlight that in addition to carbonates, fluids and upper crustal material circulation, disequilibrium melting is also a significant factor contributing to the heterogeneous Mg isotopic compositions of the continental crust that cannot be ignored.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 512-521"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145311744","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}

{"title":"Contributions of recycled altered oceanic crust to sediment-dominated arc magma sources revealed by potassium isotopes","authors":"Zuxing Chen ,&nbsp;Fang-Zhen Teng ,&nbsp;Winnie X. Fan ,&nbsp;Robert J. Stern ,&nbsp;Ze-Zhou Wang ,&nbsp;Yuxiang Zhang ,&nbsp;Tian-Yi Huang ,&nbsp;Xiaoyuan Wang ,&nbsp;Zhigang Zeng","doi":"10.1016/j.gca.2025.11.025","DOIUrl":"10.1016/j.gca.2025.11.025","url":null,"abstract":"<div><div>Deciphering the contribution of recycled altered oceanic crust (AOC) to sediment-dominated arc magma sources is challenging, as AOC typically contains lower concentrations of incompatible elements and less radiogenic Sr but more radiogenic Nd isotopic compositions compared to sediments. Here, we present K isotopic data for a set of well-characterized arc-related lavas from the Ryukyu, Mariana, and Manus convergent margins. All samples exhibit a narrow range of δ⁴¹K values (–0.37 ‰ to –0.19 ‰), which are systematically heavier than mid-ocean ridge basalts. The heavy K isotopic compositions of samples from the southern Mariana arc and eastern Manus Basin, characterized by elevated Ba/Th ratios, less radiogenic Sr, and more radiogenic Nd isotopic signatures, are primarily controlled by AOC-derived fluids. By contrast, samples from the Okinawa Trough and northern Mariana arc display more radiogenic Sr, less radiogenic Nd isotopes and higher Th/Yb ratios, reflecting a stronger contribution from subducted sediments. Since subducting sediments near the Mariana and Ryukyu trenches typically have lighter K isotopic compositions, additional inputs from AOC-derived fluids are required to explain the observed isotopically heavy arc-related lavas. Monte Carlo mixing models indicate that adding 3–4 % AOC-derived fluid after 5–6 % sediment melt incorporation into the mantle source can reproduce the K isotopic composition of samples with higher ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd, whereas other samples require only 0.25–0.75 % AOC-derived fluid and 0–0.5 % sediment melt. Alternatively, mélanges composed of 5–15 % sediment and AOC mechanically mixed with mantle, followed by dehydration-driven self-metasomatism, provides another plausible pathway for incorporating isotopically heavy K into arc-related magmas. Regardless of the specific process of K mass transfer, contribution from AOC is essential to account for the observed heavy K isotope signatures. Our study therefore highlights K isotopes as effective tracers of recycled AOC in sources of sediment-dominated arc magmas.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 426-436"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145536296","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}

{"title":"Geochemical insights into planetary evolution: from core to surface","authors":"Fang-Zhen Teng ,&nbsp;Ricardo Arevalo ,&nbsp;Xiao-Ming Liu ,&nbsp;Ming Tang","doi":"10.1016/j.gca.2026.04.001","DOIUrl":"10.1016/j.gca.2026.04.001","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 1-8"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147598308","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}

{"title":"Extremely light potassium isotopic compositions of the continental eclogites and high-pressure metamorphic veins reveal the fluid-rock interactions in subduction zones","authors":"Haiyang Liu ,&nbsp;Ying-Yu Xue ,&nbsp;Shichao An ,&nbsp;Hai-Ou Gu ,&nbsp;He Sun ,&nbsp;Kun Wang ,&nbsp;Shun Guo ,&nbsp;Maoqiang Yan ,&nbsp;Wei-Dong Sun","doi":"10.1016/j.gca.2025.12.030","DOIUrl":"10.1016/j.gca.2025.12.030","url":null,"abstract":"<div><div>Potassium (K) stable isotopes have recently emerged as a sensitive tracer of fluid transport and crust–mantle interactions in subduction zones. However, the K isotopic compositions of the slab-derived fluids and the behavior of K isotopes during fluid evolution still remain poorly constrained. Particularly, the fractionation mechanisms of K isotopes in continental subduction settings have not yet been determined. This study presents the first K isotopic data for two well-characterized high-pressure eclogite-vein systems and associated retrogressed amphibolites from the Dabie-Sulu orogenic belt in east-central China, a typical locality of continental subduction zone. Our results show that the investigated eclogites display significantly lower δ⁴¹K values (−0.93 ± 0.06 ‰ to −0.47 ± 0.06 ‰) than both the upper continental crust (−0.44 ± 0.05 ‰) and Bulk silicate Earth (−0.42 ± 0.07 ‰), indicating that metamorphic dehydration during continental subduction can induce substantial K isotopic fractionation. High-pressure veins yield even lower δ⁴¹K values (−2.81 ± 0.10 ‰ to −0.48 ± 0.09 ‰), with several samples recording the lightest K isotopic compositions yet reported in terrestrial materials. Such light K isotopic compositions, together with the heavy K of the investigated amphibolites (−0.45 ± 0.06 ‰ to −0.11 ± 0.09 ‰), reflecting pronounced isotopic fractionation during chemical diffusion at initial stages of exhumation and subsequent fluid evolution. These results demonstrate that deeply subducted continental crust can act as a source of isotopically light K to the deep mantle, which may be subsequently recycled to the surface via post-collisional mafic magmatism. This study highlights the potential of K isotopes as a powerful geochemical tool for tracing crustal recycling and fluid–rock interaction processes in continental subduction zones.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 522-535"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785756","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}

{"title":"Whole-rock Fe isotope compositions as mantle source and process tracers across the Hawaiian archipelago","authors":"Nicole M.B. Williamson ,&nbsp;Laura D. Bilenker ,&nbsp;Dominique Weis","doi":"10.1016/j.gca.2025.12.009","DOIUrl":"10.1016/j.gca.2025.12.009","url":null,"abstract":"<div><div>We present a geographically extensive Hawaiian Fe isotope dataset, with the primary goal of testing the use of stable Fe isotopes to identify mantle heterogeneities in the source of Hawaiian volcanoes, including whether the isotopically distinct Hawaiian geochemical groups (Loa, Kea, and Enriched Loa) exhibit distinct Fe isotope compositions. Hawai‘i is an excellent natural laboratory for assessing newer isotopic systems as it is well-studied and thoroughly geochemically characterized. We analyzed 43 carefully selected shield-stage tholeiitic basalt samples from 14 subaerial and submarine volcanoes that represent the past ∼ 5 Ma of volcanic activity along the Hawaiian chain. These samples have previously been thoroughly characterized for their major and trace element concentrations, and Pb, Sr, Nd, Hf, and Tl isotope compositions. Their compositions span the entire range of Kea, Loa and Enriched Loa Hawaiian geochemical groups. Iron isotope results reported to IRMM-14 vary from a δ⁵⁶Fe (±2SD) of 0.00 (±0.06 ‰) to 0.21 (±0.02 ‰). The data adjusted for olivine fractionation show a similar range, and the mean δ⁵⁶Fe of the new data (0.10 ± 0.10 ‰) overlaps with the average MORB value (∼0.10 ‰).</div><div>This work provides the first comprehensive, large-scale overview of Fe isotope compositions in shield-stage tholeiitic basalt across the Hawaiian archipelago. Important observations include: 1) there is no statistical difference in δ⁵⁶Fe values between Loa, Kea, and Enriched Loa geochemical groups; 2) δ⁵⁶Fe and lithophile radiogenic isotope ratios (Pb, Sr, Nd, Hf) show no correlations; and 3) δ⁵⁶Fe and ε²⁰⁵Tl (used to track the presence of recycled pelagic sediments in Hawaiian basalts) are not correlated. Hawaiian δ⁵⁶Fe values are slightly lower than those from other enriched oceanic islands (EM-I, EM-II, HIMU), including Pitcairn, Azores, and Samoa, which is a feature also observed in Iceland. On a broader scale, these observations suggest that the mantle heterogeneities contributing to the unique radiogenic isotopic signatures in Hawaiian lavas, which are interpreted as being linked to the Pacific Large Low Shear Velocity Province, do not exhibit distinct or heavy Fe isotope compositions. Alternatively, if the deep mantle reservoirs sampled by the Hawaiian plume have distinct Fe isotope compositions, these signatures are not preserved during the ascent through the mantle, melting, and eruption at the surface.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"422 ","pages":"Pages 116-126"},"PeriodicalIF":5.0,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145732624","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}