Geochimica et Cosmochimica Acta最新文献

{"title":"Magmatic volatile influx promotes Cu mineralization in volcanogenic massive sulfide deposit recorded by Fe3+-rich chlorite and Hg isotopes","authors":"Bing Xiao ,&nbsp;Yuanming Pan ,&nbsp;Changzhou Deng ,&nbsp;Yuzhou Feng ,&nbsp;Mohsen Shakouri ,&nbsp;Jan J. Falkenberg ,&nbsp;Rucao Li ,&nbsp;Huayong Chen","doi":"10.1016/j.gca.2026.01.039","DOIUrl":"10.1016/j.gca.2026.01.039","url":null,"abstract":"<div><div>The leaching of underlying host rocks by circulating heated seawater can transport metals and sulfur, leading to the formation of volcanogenic massive sulfide (VMS) deposits. The introduction of magmatic volatiles in VMS systems may serve as an additional source of these elements. However, the processes through which magmatic volatiles and ore metals have been introduced into hydrothermal systems responsible for the formation of ancient VMS deposits, especially in ancient deposits, remain poorly understood. In this study, we thoroughly conducted Hg isotopic analyses of minerals (pyrite and chalcopyrite) and host rocks, combined to in-situ trace element and Fe redox states of chlorite (i.e. Fe³⁺/∑Fe determined by synchrotron X-ray absorption near-edge structure) from the Early to Middle Devonian, large-tonnage Ashele VMS deposit in the Central Asian Orogenic Belt, in order to understand the sources of ore-forming metals and metallogenic processes. Our results show that ore-associated sulfides and igneous rocks display a wide variation of 0.35‰ in Δ¹⁹⁹Hg (−0.17‰ to 0.18‰), which overlaps with those of seawater (∼0.2‰), primitive mantle (∼0‰) and continental sediments (∼-0.25‰), supporting a ternary mixing of Hg from three distinct sources. Most of the ore-associated sulfides show near-zero Δ¹⁹⁹Hg values of −0.1 to 0.1‰, suggesting that ore metals were primarily derived from magmatic fluids, rather than from leaching of underlying volcanic host rocks by heated seawater. The THg (total Hg) content in sulfides and chlorite decreases with increasing distance from the mineralization center, reflecting the variable influence of magmatic volatiles released from the underlying magmatic system, while fluid boiling likely leads to significant variations in δ²⁰²Hg (exceeding 2‰). The elevated Fe³⁺/∑Fe values, distinct Hg and Sn enrichments, and high formation temperatures (above 400 °C) recorded by Hg-rich chlorite suggest that acidic, hot, oxidized, metal-rich volatiles facilitate the transport of Cu and S from the magmatic to the hydrothermal environment, promoting the formation of large VMS deposits. We propose that the Early Devonian extensional setting enabled oxidized magmatism and volatiles, facilitating efficient Cu and S transport, during which the metal-rich magmatic-hydrothermal fluids (Δ¹⁹⁹Hg ≈ 0) mixed with seawater (Δ¹⁹⁹Hg &gt; 0) and continental sediments (Δ¹⁹⁹Hg &lt; 0), forming the Ashele VMS deposit with a wide Δ¹⁹⁹Hg range. Consequently, our results indicate Hg isotopes and the chemical composition and Fe redox states of chlorite can be applied to reveal metal source and mineralization processes in ancient VMS deposits and may also serve as a valuable exploration guide for VMS systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"420 ","pages":"Pages 340-353"},"PeriodicalIF":5.0,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135294","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":"Rubidium isotopic evidence for sedimentary input to the mantle source of Martinique lavas from the Lesser Antilles arc","authors":"Baoliang Wang,&nbsp;Frédéric Moynier,&nbsp;Catherine Chauvel","doi":"10.1016/j.gca.2026.02.023","DOIUrl":"10.1016/j.gca.2026.02.023","url":null,"abstract":"<div><div>The recycling of crustal material through subduction is considered a key driver of chemical heterogeneity in the mantle. Rubidium (Rb) is a highly incompatible element with substantial fluid mobility. Its significant enrichment in the crust relative to the mantle, along with the inherent isotope variability among crustal materials, makes Rb isotopes a promising tracer of crustal recycling. However, the limited current understanding of Rb isotope behavior during subduction-related processes hinders their effective application. Here, we present Rb isotope compositions in a set of Martinique lavas from the Lesser Antilles arc, as well as sediments from DSDP Sites 144 and 543 located in front of the Lesser Antilles trench. Sediments from both sites exhibit Rb isotope compositions similar to continental crust or mantle. In contrast, the δ⁸⁷Rb of the studied arc lavas vary from a mantle-like value at −0.08 ± 0.03‰ to variably lower values (down to −0.49 ± 0.05‰). Strong correlations are observed between their δ⁸⁷Rb values and radiogenic isotopic compositions (e.g., ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, and ¹⁷⁶Hf/¹⁷⁷Hf). The Rb isotope variations cannot be explained by post-eruption alteration, mantle partial melting, magmatic differentiation or crustal assimilation during magma ascent. Instead, they reflect a binary mixing between the sub-arc mantle and isotopically light sediment melts. Because Rb isotope signatures of subducting sediments are largely unaffected by prograde metamorphism in cold subduction zones, their mantle-like pre-subduction δ⁸⁷Rb values imply that Rb isotope fractionation may occur during sediment partial melting, with the light Rb isotope preferentially migrating with melts. Overall, this study provides compelling evidence for the addition of isotopically light sediment melts to the mantle wedge, demonstrating that Rb isotopes can serve as a tracer of crustal recycling in the sub-arc mantle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"420 ","pages":"Pages 387-398"},"PeriodicalIF":5.0,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146778174","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":"The effects of sulfur on near-liquidus phase relations of highly reduced basaltic melts with implications for magmatism in Mercury","authors":"Yishen Zhang,&nbsp;Rajdeep Dasgupta","doi":"10.1016/j.gca.2026.02.034","DOIUrl":"10.1016/j.gca.2026.02.034","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Data returned from NASA’s MESSENGER mission reveal that Mercury’s surface is highly enriched in sulfur (S) and depleted in iron (Fe), consistent with a highly reduced planetary interior. Understanding such high-S and low-Fe magmatic surface requires knowledge of phase equilibria at highly reducing mafic–ultramafic systems at S-present conditions. However, experimental constraints in such systems are far from complete. In this study, we present new high-temperature (1800–1300 °C), and high-pressure (2 GPa) piston cylinder experiments on a partial melt of the EH4 chondrite Indarch to further our understanding of how sulfur influences near-liquidus phase relations and melt structure under redox conditions relevant to Mercury. Two different starting mixes with distinct redox budgets were prepared by adding 5 or 10 wt% metallic Si to the silicate starting mix, resulting in oxygen fugacity between IW−5.5 and IW–13.2. Both S-free and S-bearing near-liquidus experiments were performed. Sulfur was added as elemental S or FeS, with most S-present runs conducted under sulfide-undersaturated conditions, spanning melt S concentrations of ∼ 2–12 wt%. The experiments produced melt + orthopyroxene + quartz + Fe-metal ± clinopyroxene ± sulfide phases. The orthopyroxene liquidus lies at ∼ 1625 °C for both S-free compositions. At ∼ 4 wt% S, the liquidus is depressed by ∼ 20–70 °C. Importantly, we observe that S causes a larger liquidus depression in the more depolymerized melt composition, and the presence of S promotes quartz crystallization. These results suggest that S&lt;sup&gt;2-&lt;/sup&gt; likely substitutes for non-bridging oxygens in the silicate melt structure and bonds with network-modifying cations (e.g., Mg&lt;sup&gt;2+&lt;/sup&gt;, Ca&lt;sup&gt;2+&lt;/sup&gt;). This process destabilizes Mg-Ca-rich silicate phases and favors the crystallization of quartz. The observed liquidus depression correlates with both S content and melt polymerization. We propose an empirical model for orthopyroxene liquidus depression as a function of melt polymerization: Δ&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;mrow&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;/mrow&gt;&lt;mo&gt;°&lt;/mo&gt;&lt;/msup&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;42.1&lt;/mn&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mn&gt;7.7&lt;/mn&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msup&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mn&gt;0.5&lt;/mn&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msup&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mn&gt;1.2&lt;/mn&gt;&lt;mi&gt;N&lt;/mi&gt;&lt;mi&gt;B&lt;/mi&gt;&lt;mrow&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; where &lt;em&gt;S&lt;/em&gt; is sulfur content in wt% and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;N&lt;/mi&gt;&lt;mi&gt;B&lt;/mi&gt;&lt;mrow&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; represent the non-bridging anions per tetrahedrally coordinated cations in the melt. Our findings also provide a potential explanation for the silica-enriched surface compositions observed in several Mercury terranes. Our experimental melt differentiation trends sug","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"420 ","pages":"Pages 399-417"},"PeriodicalIF":5.0,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147334711","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":"A tungsten-182 and trace element perspective on the origin of the FOcal ZOne (FOZO) component","authors":"V.A. Finlayson ,&nbsp;R.J. Walker ,&nbsp;K.R. Bermingham ,&nbsp;J.M.D. Day ,&nbsp;M.E. Schilling","doi":"10.1016/j.gca.2026.01.052","DOIUrl":"10.1016/j.gca.2026.01.052","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Small variations in &lt;sup&gt;182&lt;/sup&gt;W/&lt;sup&gt;184&lt;/sup&gt;W resulting from the decay of &lt;sup&gt;182&lt;/sup&gt;Hf to &lt;sup&gt;182&lt;/sup&gt;W while &lt;sup&gt;182&lt;/sup&gt;Hf was extant during the first ∼60 Myr of Solar System history are present in some modern ocean island basalts (OIB). The lowest ratios, or most negative μ&lt;sup&gt;182&lt;/sup&gt;W values when calculated as parts per million variations from an assumed Bulk Silicate Earth (BSE) value, correspond with elevated &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He compositions for some OIB lavas. Possible explanations for these anomalous isotopic compositions include: 1) core-mantle interaction following initial core-mantle separation or 2) early differentiation of the silicate mantle. Elevated &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He in OIB originates from a less-degassed portion of the mantle, compared to the accessible upper mantle, and has been associated with a moderately depleted mantle component with long-lived radiogenic isotope characteristics intermediate to all known extreme mantle endmembers. This component has commonly been referred to as the “FOcal ZOne” or FOZO. In addition to these characteristics, FOZO has been suggested to have anomalous enrichments in the high field strength elements (HFSE) Ti, Ta, and Nb. Tungsten is a moderately siderophile element that behaves as an HFSE in the silicate Earth, and in some OIB, μ&lt;sup&gt;182&lt;/sup&gt;W and Ti, Ta, and Nb enrichments display negative correlations. To further investigate the relation between anomalous μ&lt;sup&gt;182&lt;/sup&gt;W, &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He and Ti, Ta, and Nb enrichments in melts most closely associated with the FOZO mantle source, we analyzed basalts from three intraplate volcanic tracks, Easter-Salas y Gomez, Bowie-Kodiak, and Louisville, for μ&lt;sup&gt;182&lt;/sup&gt;W and bulk major and trace elements. The new isotopic data for each hotspot system record μ&lt;sup&gt;182&lt;/sup&gt;W values that are within the global range of OIB (Easter-Salas y Gomez μ&lt;sup&gt;182&lt;/sup&gt;W = +3 to −17; Bowie-Kodiak μ&lt;sup&gt;182&lt;/sup&gt;W = +1 to −12; and Louisville μ&lt;sup&gt;182&lt;/sup&gt;W = −1 to −9). To test whether these compositions can be explained by the crystallization of an early basal magma ocean and subsequent long-term isolation of its crystallization products, a simple fractional crystallization model was developed. We find that nearly all isotopic and trace element compositions inferred for the FOZO component can be reproduced by the chemical fractionations produced with this model. Furthermore, the model is consistent with data for additional OIB sampled globally. Finally, our model results also indicate that the Sm/Nd ratio in the inferred FOZO reservoir may not be sufficiently modified by bridgmanite fractionation to generate resolvable μ&lt;sup&gt;142&lt;/sup&gt;Nd anomalies in OIB (resulting from decay in the &lt;sup&gt;146&lt;/sup&gt;Sm-&lt;sup&gt;142&lt;/sup&gt;Nd short-lived system) relative to BSE. This is consistent with the lack of μ&lt;sup&gt;142&lt;/sup&gt;Nd anomalies in most OIB, even where negative μ&lt;sup&gt;182&lt;/sup&gt;W anomalies are largest. Collectively, the","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"420 ","pages":"Pages 354-386"},"PeriodicalIF":5.0,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135023","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":"Methane cycling and its roles in arsenic mobility in groundwater of floodplain aquifers","authors":"Song Feng, Zhipeng Gao, Yao Li, Yujie Liu, Xueda Hu, Huaming Guo","doi":"10.1016/j.gca.2026.04.021","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.021","url":null,"abstract":"The reductive dissolution of arsenic-bearing Fe(III) oxides is a key process driving groundwater arsenic mobility. In anoxic aquifers, both methane (CH<ce:inf loc=\"post\">4</ce:inf>) and organic matter are important electron donors for the Fe(III) oxide reduction. However, the relative contribution of these two pathways, i.e., Fe(III) oxide reduction coupled with CH<ce:inf loc=\"post\">4</ce:inf> oxidation (AOM-Fe(III) reduction) and dissimilatory Fe(III) oxide reduction driven by organic matter degradation (DIR-Fe(III) reduction) to arsenic enrichment in groundwater remains poorly understood. Groundwater samples were taken along a groundwater flow path in the Hetao Basin (China) to determine δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">CH4</ce:inf> and δ<ce:sup loc=\"post\">56</ce:sup>Fe and geochemical characteristics. Groundwater CH<ce:inf loc=\"post\">4</ce:inf>, with concentrations from 0.002 to 29.9 mg/L, were mainly sourced from biogenic methanogenesis, as evidenced by δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">CH4</ce:inf> values &lt;−860‰ in around 88% of groundwater samples. The observed decrease in CH<ce:inf loc=\"post\">4</ce:inf> concentrations, accompanied by a rapid increase in δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">CH4</ce:inf> values in reducing groundwater, indicated the occurrence of anaerobic oxidation of CH<ce:inf loc=\"post\">4</ce:inf>. Groundwater DOC, CH<ce:inf loc=\"post\">4</ce:inf>, Fe(II), and arsenic concentrations simultaneously increased along the groundwater flow path, indicating that both dissolved organic matter (DOM) and CH<ce:inf loc=\"post\">4</ce:inf> were electron donors for Fe(III) oxide reduction. The more negative δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">CH4</ce:inf> and higher δ<ce:sup loc=\"post\">56</ce:sup>Fe values in the flat plain compared to the transition area suggested a decrease in the relative contribution of AOM-Fe(III) reduction from the transition area to the flat plain. The preferential use of CH<ce:inf loc=\"post\">4</ce:inf> as electron donors in the transition area may be due to the limited biodegradable DOM. However, the DIR-Fe(III) reduction was stronger in the flat plain than that in the transition area, being supported by higher DOC concentrations and higher δ<ce:sup loc=\"post\">56</ce:sup>Fe values in the plain. Overall, the contribution of AOM-Fe(III) reduction to arsenic mobilization was more evident in the transition area, while arsenic enrichment in groundwater was primarily caused by the DIR-Fe(III) reduction in the flat plain. Our study highlights the importance of AOM-Fe(III) reduction in arsenic enrichment in groundwater, which provides a new perspective on the underlying mechanism of arsenic mobilization in floodplain aquifers.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"13 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736826","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":"Reversible anaerobic oxidation of methane, carbon assimilation, and mineral authigenesis in pockmark sediments over the past 40 kyr: Insights from C–S–O isotopes and diagenetic modelling","authors":"Jurjen Rooze, Pierre Sansjofre, Christof Meile, Michael Ernst Böttcher, Gwenael Jouet, Lucie Pastor","doi":"10.1016/j.gca.2026.04.020","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.020","url":null,"abstract":"The long-term effects of deeply sourced methane (CH<ce:inf loc=\"post\">4</ce:inf>) seepage on sediment geochemistry, authigenic mineral formation, and stable isotope signatures were investigated by comparing sediment cores retrieved from a seep and a reference non-seep site on the northwestern continental margin of Madagascar. To constrain the underlying diagenetic processes, measurements of C, S, and Fe in solid and dissolved phases, stable isotope (δ<ce:sup loc=\"post\">13</ce:sup>C, δ<ce:sup loc=\"post\">34</ce:sup>S, δ<ce:sup loc=\"post\">18</ce:sup>O) signatures, and <ce:sup loc=\"post\">14</ce:sup>C sediment dating were combined with reaction-transport modeling. This approach enabled distinction between effects related to seepage and anaerobic oxidation of methane (AOM) and those associated with organic matter mineralization.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"327 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736827","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":"Carbon and phosphorus regeneration during organic matter decomposition in aquatic ecosystems: characteristics, mechanisms, and environmental effects","authors":"Chao Yin, Yan Zeng, Jingan Chen, Peng Liao, Jia Yu, Guangrong Ran, Baohua Xiao, Xudong Guo, Ziyan Zhang, Jingfu Wang, Haiquan Yang, Quan Yuan","doi":"10.1016/j.gca.2026.04.018","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.018","url":null,"abstract":"Carbon (C) and phosphorus (P) are essential biogenic elements on Earth, significantly influencing ecosystems and climate change through their cycles within the Earth’s spheres. During organic matter (OM) formation, C and P are assimilated in specific stoichiometric ratios. However, it has long been debated whether C and P regeneration follows the same proportional relationship during OM decomposition. In this study, typical terrestrial plants and aquatic algae were selected for decomposition simulation experiments. The content of organic carbon (C<ce:inf loc=\"post\">org</ce:inf>) and organic phosphorus (P<ce:inf loc=\"post\">org</ce:inf>), along with their speciation, was systematically investigated to uncover differences in their regeneration behaviors. The results showed that the (C:P)<ce:inf loc=\"post\">org</ce:inf> ratios (in mol) of OM residues generally increased during the early decomposition stage, then decreased as decomposition continued. These ratios were higher under anoxic conditions compared to oxic conditions and remained consistently above their initial values throughout the process. This indicated that the preferential regeneration of P over C mainly occurred in the early decomposition stage and was more pronounced under anoxic conditions. Moreover, the preferential regeneration of P was more pronounced in more labile OM. Fourier transform infrared spectroscopy (FTIR) results indicated that the low bond energies of P<ce:inf loc=\"post\">org</ce:inf>-functional groups were the primary factor underlying preferential regeneration of P relative to C. Consistently, <ce:sup loc=\"post\">31</ce:sup>P-Nuclear magnetic resonance spectroscopy (<ce:sup loc=\"post\">31</ce:sup>P NMR) and <ce:sup loc=\"post\">13</ce:sup>C-Nuclear magnetic resonance spectroscopy (<ce:sup loc=\"post\">13</ce:sup>C NMR) data also indicated that P<ce:inf loc=\"post\">org</ce:inf> was regenerated more rapidly than C<ce:inf loc=\"post\">org</ce:inf> during the early stage of OM decomposition. Global warming and enhanced aquatic hypoxia are expected to intensify the preferential regeneration of P, thereby promoting eutrophication and increasing carbon sequestration. This study provides new insights into mechanisms sustaining eutrophication under global warming and for accurately assessing carbon sink-source dynamics in aquatic ecosystems.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"20 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736828","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":"Distribution and evolution of manganese minerals in polymetallic nodules from the Clarion-Clipperton Fracture Zone: implications for nickel and copper enrichment","authors":"Zedong Fan, Xiaohu Li, Yanhui Dong, Bruno Lanson, Zhongkuan Wu, Weilin Ma, Zhenggang Li, Junming Zhou, Yi Ding, Hao Wang, Zhimin Zhu, Jie Li, Xingwei Meng, Huaiming Li, Fengyou Chu","doi":"10.1016/j.gca.2026.04.016","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.016","url":null,"abstract":"Mn oxides in polymetallic nodules act as pivotal reservoirs for Ni and Cu, governing the biogeochemical cycling of these metals in marine environments. However, accurate identification of Mn-oxide phases—such as buserite, asbolane, and todorokite—remains challenging due to their similar X-ray diffraction characteristics. By applying an integrated mineralogical approach, this study elucidates the distribution and mineralogical controls of Ni and Cu in two diagenetic nodules from the Clarion-Clipperton Fracture Zone. Our results demonstrate a distinct mineralogical zonation: todorokite is predominantly concentrated in the inner layers (constituting up to ∼ 68% of the Mn-oxide assemblage), while the outer layers are dominated by 10 Å vernadite (buserite) and asbolane. XANES analysis reveals a significantly higher proportion of Mn(III) in the inner layers (15–25%) compared to the outer layers (8–10%). This Mn(III) enrichment, which we interpret as resulting from early nodule growth under high-productivity-driven suboxic conditions, likely promotes the transformation of 10 Å vernadite into todorokite. This mineralogical transition induces to a 40–50% decrease in Ni content in the inner layer, consistent with the lower compatibility of Ni in the todorokite structure. In contrast, Cu<ce:sup loc=\"post\">2+</ce:sup>, as a Jahn–Teller active element, appears to be compatible with the todorokite structure and exhibits similar contents in both todorokite and asbolane. As nodule growth proceeds into more oxic environments, the Increased Stability of Mn(IV), most likely inhibited tectomanganate formation and may have favored the phyllomanganate stability. Furthermore, the precipitation metal (hydr)oxides in phyllomanganate interlayers could have led to the asbolane formation. Collectively, our findings underscore that fine-scale mineralogical characterization is indispensable for deciphering the distinct biogeochemical behaviors of Ni and Cu governed by specific Mn oxides.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736501","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":"The importance of basaluminite formation on controlling the fate of Al(III) in aqueous solutions at pH 4–5","authors":"Hoda Moradi, Gerhard Furrer, Sergio Carrero, Rosemarie Pöthig, Daniel Rentsch, Ilche Gjuroski, Julien Furrer, Christoph Wanner","doi":"10.1016/j.gca.2026.04.017","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.017","url":null,"abstract":"The formation of secondary Al-hydroxysulfates is environmentally important as they regulate aluminum concentrations in acidic environments and may serve as efficient sinks for geogenic toxic elements such as arsenic and selenium. Based on recent studies, nanocrystalline basaluminite [Al&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;(OH)&lt;ce:inf loc=\"post\"&gt;10&lt;/ce:inf&gt;(SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;) x 5(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)] appears to be the most frequent Al-phase in such settings. A few studies, however, have postulated that secondary Al-hydroxysulfates include the ɛ-Keggin polyoxocation, [Al&lt;ce:inf loc=\"post\"&gt;12&lt;/ce:inf&gt;(AlO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;)(OH)&lt;ce:inf loc=\"post\"&gt;24&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;12&lt;/ce:inf&gt;]&lt;ce:sup loc=\"post\"&gt;7+&lt;/ce:sup&gt;, commonly referred to as Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt;, and that the entire low temperature geochemistry of Al passes through the Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt; metastability field. To better understand what controls the type of Al-hydroxysulfates forming in natural and anthropogenically affected settings, here we present results from titration experiments leading to the formation of Al-hydroxysulfates from solutions with either presence or absence of aqueous Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt;. Both the synthesized precipitates as well as the corresponding supernatant solutions were analyzed by standard and advanced analytical techniques including chemical analyses, &lt;ce:sup loc=\"post\"&gt;27&lt;/ce:sup&gt;Al Nuclear Magnetic Resonance (NMR) spectroscopy, synchrotron-based high energy X-ray diffraction and subsequent pair distribution analyses, and a kinetic photometric method for the quantification of aqueous Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt;. While the chemical composition of the synthesized precipitates are similar, their structures strongly differ depending on the presence or absence of Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt; in solutions. The synthesis from sulfate-bearing solutions with a large compositional range resulted in instantaneous precipitation of nanocrystalline basaluminite. In contrast, crystalline Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt;-sulfate formed in experiments where aqueous Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt; was synthesized from AlCl&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt; solutions before sulfate was added at a later stage. Based on these results and complimentary geochemical modelling, we conclude that the presence of sulfate leads to a strong complexation of monomeric aluminum. This inhibits the formation of aqueous Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt; and thus the precipitation of Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt;-sulfate, while promoting the precipitation of nanocrystalline basaluminite instead. Since sulfuric acid is a primary source of acidity in most natural acidic environments, the formation of aqueous Al&lt;ce:inf loc=\"post\"&gt;13&lt;/ce:inf&gt; in nature is likely less important than previously thought. Instead, due to its chemical and structural variability, the formation of basaluminite an","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"3 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736500","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":"Corrigendum to “Tracing material transport during subduction inception: Insights from potassium isotopes in the crustal sequence of the Troodos ophiolite” [Geochim. Cosmochim. Acta 373 (2024) 259–270]","authors":"Qi-Qi Pan, Yan Xiao, Ben-Xun Su, Paul T. Robinson, Wen-Jun Li, Jing Wang, Xia Liu","doi":"10.1016/j.gca.2026.04.004","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.004","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"23 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736502","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}