Geochimica et Cosmochimica Acta最新文献

{"title":"Partitioning of Nb and Ta between rutile and carbonatitic melts: Implications for genesis of arc magmas and carbon cycle at subduction zones","authors":"Wei Chen ,&nbsp;Massimo Tiepolo ,&nbsp;Guo-Liang Zhang","doi":"10.1016/j.gca.2025.09.037","DOIUrl":"10.1016/j.gca.2025.09.037","url":null,"abstract":"<div><div>Carbonatitic melts are crucial media in element transfer at subduction zones, however, their role in Nb/Ta fractionation is unclear. Here we experimentally determined the rutile-carbonatitic melt partition coefficients (D values) of Nb and Ta at 2.5–8.0 GPa and 1000–1300 ℃. The results show that D_Nb ranges from 17 to 79, D_Ta from 39 to 393, and D_Nb/D_Ta from 0.20 to 0.27. D_Nb and D_Ta strongly depend on pressure and temperature, decreasing initially and then increasing as pressure/temperature rises. Conversely, the narrow range of D_Nb/D_Ta suggests that this ratio is insensitive to either pressure or temperature. Using these new partition coefficients, we modeled behaviors of Nb and Ta in carbonatitic melts and residual rutile-bearing eclogites during slab melting. Our results demonstrate that slab melting imparts lower Nb/Ta ratios to rutile-bearing eclogites and higher Nb/Ta ratios to carbonatitic melts than their protoliths. Consequently, deeply subducted rutile-bearing eclogites cannot serve as a superchondritic Nb/Ta reservoir that could explain Earth’s Nb paradox. We quantify the contribution of slab-derived carbonatitic melts on the Nb/Ta variations of natural carbonatite assuming that their mantle sources have been impregnated by such melts. The results indicate slab-derived carbonatitic melts explain less than two orders of magnitude of Nb/Ta variation in carbonatites. After fully clarifying the Nb/Ta fractionation in various types of slab-derived liquids, we identify that the mantle source of silica-undersaturated, high Nb/Ta arc magmas is metasomatized by slab-derived carbonatitic melts, while those of silica-saturated magmas are by silicic melts originating from the basaltic part of the slab.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 71-83"},"PeriodicalIF":5.0,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218054","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":"Fate of iodate on adsorbed/coprecipitated ferrihydrite-organic matter complexes","authors":"Shilin Zhao ,&nbsp;Junxia Li ,&nbsp;Xianjun Xie ,&nbsp;Yanxin Wang","doi":"10.1016/j.gca.2025.09.034","DOIUrl":"10.1016/j.gca.2025.09.034","url":null,"abstract":"<div><div>The mobility of iodate in soils and sediments is significantly related to the states of iron minerals and natural organic matter (NOM). However, the influences of associated processes (adsorption versus coprecipitation) between iron minerals and NOM on the fate of iodate remain unclear. In this study, the iodate behavior on adsorbed or coprecipitated ferrihydrite (HFO)-humic acid (HA) complexes was investigated through batch experiments under varying conditions (pH, ionic strength, and co-existing anions). Mechanisms insights were obtained using attenuated total reflectance Fourier transform infrared spectroscopy and density functional theory. The results show that compared to pure HFO, iodate adsorption decreases in the presence of adsorbed or coprecipitated HA, due to the reduced inner-sphere adsorption sites occupied by HA. The reduction degree in iodate adsorption is greater for coprecipitated HFO-HA (HFO-cHA) complexes than for adsorbed HFO-HA (HFO-aHA) complexes. The adsorbed iodate is more prone to combine with adsorbed HA to form organic iodine compared to coprecipitated HA. With increasing pH and co-existing anions, the decreasing in iodate adsorption was observed in pure HFO and HFO-aHA/HFO-cHA complexes, but interestingly, the decreased degree in iodate adsorption follows the order of HFO-cHA complexes &gt; pure HFO &gt; HFO-aHA complexes. The dominant outer-sphere species of iodate on the complexes leads to the more sensitive surface of HFO-cHA complexes, and as the coprecipitated HA increases, the percentage of inner-sphere species of iodate was decreasing. Compared to the coprecipitated HA, the adsorbed HA can be more easily dissolved as the pH rising or as co-existing ions replace HA on the adsorption sites. Iodate can sorb and occupy sites vacated by HA desorption. The findings of this study provide new insights to understand the mobilization of soil/sediment iodate, which plays a vital role in the cycling of iodine in nature.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 28-39"},"PeriodicalIF":5.0,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156530","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":"Stable carbon isotope fractionation during the transformation of amorphous CaCO3 at low water–solid ratios: impact of humidity and temperature","authors":"Maria P. Asta ,&nbsp;Sarah Bonilla-Correa ,&nbsp;Aurélie Pace ,&nbsp;Martin Dietzel ,&nbsp;Antonio García-Alix ,&nbsp;Torsten Vennemann ,&nbsp;Anders Meibom ,&nbsp;Arthur Adams","doi":"10.1016/j.gca.2025.09.029","DOIUrl":"10.1016/j.gca.2025.09.029","url":null,"abstract":"<div><div>The isotopic composition of carbonates has been widely used as a proxy for reconstructing Earth’s past environmental conditions, which requires the preservation of the isotope composition of the primary precipitate or knowledge about its transformation pathway. In this context, the formation of crystalline carbonates via amorphous precursors has been identified as a common formation process for natural carbonates, where the impact to the isotopic composition of the final CaCO₃ products is insufficiently known to date. This study focusses on the stable carbon isotope fractionation during the transformation of amorphous calcium carbonate (ACC) into crystalline carbonate in the presence/absence of atmospheric CO₂ induced by (i) humidity (from 33 to 95 % RH) at a temperature of 5 and 20 °C and (ii) solid-state transformation of ACC to calcite induced by heating up to 500 °C. During the crystallization of ACC at very low water ratios, induced by humidity, and in the presence of CO₂, δ¹³C values of the solids increased with reaction time, where the crystalline carbonate-ACC enrichment factors (¹³ε_cc−ACC) range between 2.0 and 8.4 ‰ at the final stage. This ¹³ε_cc−ACC evolution reflects the incorporation of ambient CO₂(g) alongside carbonate ions released during ACC dissolution. In contrast, without CO₂(g) the crystalline CaCO₃ almost matches the isotope composition of the ACC (¹³ε_c_c_−ACC = −0.4 ± 0.3 ‰), thus indicating non-significant CO₂ degassing and/or subsequent re-equilibration trend. The solid-state transformation of ACC to calcite during heat-induced dehydration yields a slightly negative enrichment factor (¹³ε_c_alcite_−ACC = −0.8 ± 0.3 ‰) that may reflect carbon isotope fractionation due to rapid recrystallization-rate kinetics. Our results suggest that the carbon isotope compositions of carbonates formed via an amorphous precursor at low water/solid ratios (e.g., in caves, soils or biominerals) may not accurately reflect the original conditions of the carbonate formation, hence paleoenvironmental conditions should be interpreted with care.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 56-70"},"PeriodicalIF":5.0,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156602","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":"Isolating the light dependence of carbon isotope fractionation in Gephyrocapsa (Emiliania) huxleyi","authors":"Ann Pearson ,&nbsp;Pratigya J. Polissar ,&nbsp;Susan J. Carter ,&nbsp;Elida Kocharian ,&nbsp;Samuel R. Phelps ,&nbsp;Oscar D. Hover ,&nbsp;Raquel P. Reis ,&nbsp;Emily Kuang ,&nbsp;Lorelei M. Wolf","doi":"10.1016/j.gca.2025.09.033","DOIUrl":"10.1016/j.gca.2025.09.033","url":null,"abstract":"<div><div>Estimates of past atmospheric carbon dioxide content (<em>p</em>CO₂) derived from geochemical archives are critical to the advancement of climate science. One of the most frequently used marine proxies is the biological discrimination of stable carbon isotopes (<em>ε</em>_p) recorded in long-chain ketones of the haptophyte algae, a method known as alkenone paleobarometry. In its conventional application, the fractionation of carbon isotopes is assumed to reflect the kinetic isotope effect (KIE) of the carbon-fixing enzyme Rubisco, and the cellular carbon budget is assumed to be governed by the ratio of demand by carbon fixation to diffusive CO₂ supply (demand:supply). Changes in this budget cause variation in the expression of <em>ε</em>_p, with the smallest <em>ε</em>_p values reflecting the highest ratio of demand:supply, i.e., the lowest relative CO₂ concentrations. However, prior work indicates that photosynthetic irradiance also influences expression of <em>ε</em>_p. To isolate the influence of the photosynthetic effect, we cultivated a calcifying strain of <em>Gephyrocapsa</em> (<em>Emiliania</em>) <em>huxleyi</em> in nitrate-limited chemostat culture under conditions of constant growth rate and CO₂ supply, but six different levels of irradiance. The resulting values of <em>ε</em>_p varied between 16 ‰ at photon flux density (PFD) &lt; 50 μmol m⁻² s⁻¹ to 20 ‰ at PFD &gt; 150 μmol m⁻² s⁻¹. The low-light cultures exhibited slightly decreased carbon uptake at steady-state, and as such, the smallest values of <em>ε</em>_p were recorded under the highest in-situ CO₂ concentrations, opposite to <em>ε</em>_p vs. demand:supply expectations. The data are consistent with prior batch-culture studies of <em>G. huxleyi</em> and other <em>Gephyrocapsa</em> strains, suggesting that while those experiments used different cultivation approaches, a light-dependent effect on cell carbon budgets may be universal, perhaps through direct influence on the efficiency of carbon concentrating mechanisms (CCMs). These results point toward future strategies to improve the physiological accuracy of <em>ε</em>_p models and refine <em>p</em>CO₂ reconstructions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 105-115"},"PeriodicalIF":5.0,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218056","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":"Linking source-to-sink processes, organic matter composition, and oxygen consumption on a shallow passive margin shelf sustained by small mountainous rivers","authors":"Yu-Shih Lin ,&nbsp;Chih-Lin Wei ,&nbsp;Yuan-Pin Chang ,&nbsp;Jih-Terng Wang ,&nbsp;Shu-Ying Chuang ,&nbsp;Liang-Chi Wang ,&nbsp;James T. Liu ,&nbsp;Hong-Chun Li ,&nbsp;Chieh-Wei Hsu","doi":"10.1016/j.gca.2025.09.031","DOIUrl":"10.1016/j.gca.2025.09.031","url":null,"abstract":"<div><div>Continental shelf sediments are a focal point for research on the transport, degradation, and burial of organic matter (OM), yet OM reactivity has rarely been examined within an integrated source-to-sink framework. This study investigates the relationships among source-to-sink processes, surface sediment OM composition, and oxygen consumption rates—used as a proxy for OM reactivity—of the northeastern Taiwan Strait, a passive margin shelf influenced by small mountainous rivers (SMRs). Distinct zonation of OM types was observed across the shelf. Petrogenic OM, the most abundant component, was concentrated in the depocenter, likely transported by hyperpycnal flows. Its association with low total oxygen uptake (TOU) underscores its refractory character. In contrast, fresh terrestrial OM, enriched in nearshore muds via hypopycnal flows or resuspension-advection processes, elevated TOU by nearly threefold compared to petrogenic OM-dominant sediments. As a minor component, marine OM exhibited a spatial distribution consistent with vertical delivery by the biological pump. High benthos-mediated oxygen consumption was found in silty and sandy sediments with the maximum marine OM proportion. Dissolved oxygen uptake showed a strong positive correlation with total hydrolyzable amino acids, derived from both marine and terrestrial sources. The observed connection between OM composition and oxygen consumption is attributed to the high-fidelity delivery of fresh and refractory OM from SMRs, followed by spatial partitioning driven by transport dynamics. The burial efficiency of terrestrial OM on this passive margin shelf was lower than on adjacent active margins, highlighting the critical role of shelf morphology in regulating carbon burial efficiency in SMR-sustained systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 40-55"},"PeriodicalIF":5.0,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156603","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":"NanoSIMS mapping of skeletal organic matrix relative to aragonite formation in a scleractinian cold-water coral","authors":"A.M. Gothmann ,&nbsp;J. Daniel ,&nbsp;Y. Chan ,&nbsp;P. Diaz ,&nbsp;J.B. Cliff ,&nbsp;L. Polerecky ,&nbsp;J. Granger ,&nbsp;J.L. Mottram ,&nbsp;M. Prokopenko ,&nbsp;L. Boehm Vock ,&nbsp;A. Logan ,&nbsp;N. Mersy ,&nbsp;T. Smith ,&nbsp;J. Stolarski","doi":"10.1016/j.gca.2025.09.025","DOIUrl":"10.1016/j.gca.2025.09.025","url":null,"abstract":"<div><div>Organic matrix (OM) molecules are found in coral skeletons and make up ∼ 1 % of the coral skeleton by weight. These molecules play an important role in the coral biomineralization process and can be used as environmental archives. In this study, we visualize the presence and formation of OM in coral skeletons using NanoSIMS imaging of samples from cold-water corals (CWCs) fed with a ¹⁵N-enriched diet and incubated in elementally-enriched seawater. We estimate extension rates of 0.8–2.8 μm/day for our samples, consistent with other estimates of skeletal extension in this species, suggesting that our experimental conditions did not have a noticeable deleterious impact on calcification in this study. While NanoSIMS maps reveal that N, S and organic C are mainly concentrated in thin bands parallel to the growth front of the skeleton, these elements are sometimes enriched in distinct patches and/or diffusely present throughout the skeleton. Quantitative analysis reveals that the areas enriched in N, S, and organic C overlap in space, suggesting that these regions are enriched in organic matter. Our NanoSIMS maps may be useful when considering the potential impact of OM contamination on trace element proxies. Analysis of the level and patterns of ¹⁵N enrichment in our coral skeletons indicates that part of the N source that forms the organic matrix may exist as a discrete N pool that is either small or has a short turnover rate. Our ¹⁵N data, interpreted in the context of the timing of experimental growth, also suggest that heterotrophic feeding may trigger the formation of organic-rich layers within the skeleton, implying that feeding may support biomineralization by encouraging the synthesis of organic bands.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 116-131"},"PeriodicalIF":5.0,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218057","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":"Hydrogen, single-carbon compounds, and thermal regime in the oceanic ultramafic-dominated lithosphere: insights from a deep borehole on the Atlantis Massif","authors":"Susan Q. Lang ,&nbsp;C. Geoffrey Wheat ,&nbsp;Kristin L. Dickerson ,&nbsp;Mark K. Reagan ,&nbsp;Ivan P. Savov ,&nbsp;Jordyn A. Robare ,&nbsp;William J. Brazelton ,&nbsp;Johanna Suhonen ,&nbsp;Oscar Cavazos ,&nbsp;Andrew McCaig ,&nbsp;Peter Blum ,&nbsp;Natsue Abe ,&nbsp;Rémi Coltat ,&nbsp;Jeremy R. Deans ,&nbsp;Marguerite Godard ,&nbsp;Barbara E. John ,&nbsp;Frieder Klein ,&nbsp;Rebecca Kuehn ,&nbsp;Kuan-Yu Lin ,&nbsp;C. Johan Lissenberg ,&nbsp;Fengping Wang","doi":"10.1016/j.gca.2025.09.024","DOIUrl":"10.1016/j.gca.2025.09.024","url":null,"abstract":"<div><div>Water that flows through permeable ultramafic rocks produces high abundances of molecular hydrogen (H₂), methane (CH₄), and other small organic molecules. Such products can fuel life in the rocky subseafloor, be extracted for energy, and may have played a role in pre-biological chemical synthesis on early Earth or other planetary bodies. The International Ocean Discovery Program drilled a new 1268-m-deep borehole (U1601C) into serpentinized mantle with minor gabbroic rocks on the Atlantis Massif, ∼800-m north of the Lost City hydrothermal field (30°N, Mid-Atlantic Ridge). Measured temperatures of the disturbed borehole reached 91.3 °C, and equilibrated temperatures of the deepest section are estimated to be between 110 – 140 °C. Water collected every ∼ 5-m during drilling operations had H₂ concentrations that were regularly &gt; 200 nM and spiked to &gt; 10 µM at multiple depths. In these waters, carbon monoxide was only present in deeper, hotter sections, and potentially associated with gabbroic intrusions into the peridotite host. Open borehole fluids were sampled after drilling and samples recovered from the deepest portion contained elevated short-lived 222-Radon and strontium isotope ratios similar to Lost City fluids, pointing to the presence of <em>in situ</em> subseafloor formation waters that have equilibrated with the host rock. The deepest samples were actively degassing upon recovery and contained 740 ± 360 µM H₂, 340 ± 36 µM CH₄, and 25.5 µM ∑formate (= formate and formic acid). The shallowest fluids from the open borehole also contain micromolar H₂ and ∑formate concentrations, the presence of which cannot be attributed to the upward migration of the deeper, higher concentration fluids.</div><div>We interpret these data as reflecting two distinct and interconnected regimes of fluid flow and composition. Deep waters that are channelized along faults, lithologic contacts, and other high permeability pathways host high H₂ and CH₄ concentrations plus micromolar ∑formate that closely mirror the chemistry and isotopic signatures of LCHF vent fluids. Pervasive fluid flow permeates the mesh texture and microfracture network of the serpentinized peridotite and sustains H₂ and ∑formate even in the shallowest subseafloor intervals at mild temperatures. These findings demonstrate that both focused and pervasive fluid flow contribute to the transport, and potentially the generation, of reduced volatiles and C1 compounds within the Atlantis Massif.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 84-104"},"PeriodicalIF":5.0,"publicationDate":"2025-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218055","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":"Chalcophile elements in post-subduction magmas and implications for metal recycling in oceanic and continental subduction","authors":"Xiang Wang ,&nbsp;Zaicong Wang ,&nbsp;Li-Qun Dai ,&nbsp;Wen Zhang ,&nbsp;Xiaodong Deng ,&nbsp;Xi Zhang ,&nbsp;Stephen Foley ,&nbsp;Charles H. Langmuir ,&nbsp;Wei Fang ,&nbsp;Lang Wang ,&nbsp;Tao He ,&nbsp;Aiqing Ren ,&nbsp;Zhaochu Hu ,&nbsp;Keqing Zong ,&nbsp;Yongsheng Liu ,&nbsp;Jianwei Li ,&nbsp;Huai Cheng ,&nbsp;Pingyang Zhang","doi":"10.1016/j.gca.2025.09.023","DOIUrl":"10.1016/j.gca.2025.09.023","url":null,"abstract":"<div><div>Subduction-driven recycling of chalcophile metals plays a crucial role in mantle enrichment and the formation of ore deposits. However, the role of oceanic and continental subduction in the recycling of various chalcophile elements, and their impact on the metal enrichment of metasomatized mantle and mantle-derived magmas remain poorly constrained. Here we report chalcophile element contents and S-Os isotopes for post-subduction magmas in the North China Craton. Magmas formed from mantle sources modified by oceanic subduction display elevated Ba/Nb (10–20), δ³⁴S (0 ‰ − 2 ‰) and low εNd_(t) (−4 to 5) values, along with the variable S (700–3200 μg/g) and low platinum-group elements (PGE), Au (0.1–1 ng/g), and Cu (20–50 μg/g) contents. By comparison, magmas formed following continental subduction with subsequent oceanic subduction display significantly higher Ba/Nb (100–500), δ³⁴S (2 ‰ − 6 ‰), and lower εNd_(t) (−20 to −2) values, and with higher S (up to 4700 μg/g), Au (1–4 ng/g) but similarly low PGE and Cu (20–70 μg/g) contents. The secondary processes and magmatic differentiation did not significantly affect their chalcophile element contents and patterns. The MORB-like PGE, Cu contents, together with Os/Ir, Ru/Ir, Pd/Ir, and Cu/Pd ratios in all high-Mg# (&gt; 60) hydrous and oxidizing magmas suggest relatively limited PGE and Cu addition from the subducted oceanic and continental slabs. Conversely, continental subduction likely plays a key role in the enrichment of fluid-mobile elements (e.g., Ba, K) and Sr-Nd-S isotope signatures in the affected mantle, with moderate Au enrichment as reflected by higher Au contents and Au/Pd ratios in continental subduction-related magmas. Modelling results further show that the metasomatized mantle has chalcophile metal contents similar to, or slightly higher than, those of Paleozoic depleted mantle beneath the NCC, but lower than primitive mantle. Integrating our results with compiled global data on mantle peridotites/pyroxenites and sulfides, we conclude that subduction-related mantle metasomatism contributes substantial volatiles, and may also have restored strongly chalcophile metals in depleted lithospheric mantle to a level of fertile mantle for subsequent magmatic-hydrothermal processes and mineralization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 193-210"},"PeriodicalIF":5.0,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145103481","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":"Boron isotopes trace an increase in subduction-driven recycling of fluid-mobile elements in the Neoarchean","authors":"Jeroen Goumans ,&nbsp;Matthijs A. Smit ,&nbsp;Kira A. Musiyachenko ,&nbsp;E. Troy Rasbury ,&nbsp;Wouter Bleeker ,&nbsp;Summer Caton ,&nbsp;Jaana Halla ,&nbsp;Jörg Elis Hoffmann ,&nbsp;Ellen Kooijman ,&nbsp;Klaus Mezger ,&nbsp;Om Prakash Pandey ,&nbsp;Arathy Ravindran ,&nbsp;Anders Scherstén","doi":"10.1016/j.gca.2025.09.021","DOIUrl":"10.1016/j.gca.2025.09.021","url":null,"abstract":"<div><div>The deep recycling of surface material into Earth’s mantle is an integral process governing global water and fluid-mobile element cycles. This recycling is largely predicated on subduction operating efficiently, which may not apply for the first two billion years of Earth’s history. Tracing the initiation and evolution of the modern deep fluid-mobile element cycle requires determining when the mantle first became modified by subducted surface-derived materials on a global scale. The B isotope system provides a unique geochemical parameter to test for early signatures of such recycling, given that B is enriched and isotopically fractionated at Earth’s surface, depleted in the mantle, and mobilized by fluids and fluid-rock interaction. In this study, B isotopes of granitoids from seven Archean cratons are analyzed to trace the early signatures of recycling of surface-altered materials. When filtered for alteration and (post-)magmatic B modification, the B isotope compositions of the sample set show substantial variation. The range exhibited by sanukitoids (−8.9 ‰ to −1.6 ‰, mean: −4.7 ‰, n = 5) overlaps with other granitoids (−15.8 ‰ to +8.0 ‰, mean: −8.6 ‰, n = 30), but the average B isotope composition of sanukitoids is higher than other granitoids. The granitoids reveal a temporal diversification towards, on average, higher ¹¹B/¹⁰B values from the Neoarchean onward. The heavier B isotope values reflect the recycling of surface-derived B into the melt source along a geotherm that was cold enough to prevent total loss of B through dehydration reactions, consistent with a cold-subduction geotherm. The B data thus indicate that the subduction-driven recycling of surface-derived materials into the mantle became more prevalent since the Neoarchean, marking this era as the likely starting point for the modern deep fluid-mobile element and water cycle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 1-11"},"PeriodicalIF":5.0,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145098540","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":"Asteroid Itokawa … but when and how did it form exactly?","authors":"Fred Jourdan, Nicholas E. Timms, Tomoki Nakamura, William D.A. Rickard, Celia Mayers","doi":"10.1016/j.gca.2025.09.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.020","url":null,"abstract":"Asteroid Itokawa is made of reassembled fragments from a monolithic parent asteroid which got shattered during a collision with a large object. Data are scarce regarding the metamorphic processes that occurred on the monolithic parent body and the age and nature of the catastrophic disruption event. Here, we investigate the timing of the metamorphism inside the parent body of Asteroid Itokawa and the age and nature of the catastrophic breakup event recorded in particles returned from Itokawa. We studied three regolith dust particles recovered by the Hayabusa space craft from the rubble pile asteroid 25143 Itokawa using electron backscatter diffraction, time-of-flight secondary ion mass spectrometry, and <ce:sup loc=\"post\">40</ce:sup>Ar/<ce:sup loc=\"post\">39</ce:sup>Ar dating techniques. Our results show that none of the particles show noticeable sign of shock metamorphism. Two of the particles yielded <ce:sup loc=\"post\">40</ce:sup>Ar/<ce:sup loc=\"post\">39</ce:sup>Ar age of 4559 ± 61 and 4130 ± 33 million years (Ma), while a third particle returned a maximum error age of 703 ± 53 Ma. When combined with existing data, and diffusion models, these results show that ∼4.5 billion years (Ga) ago, Itokawa’s parent monolithic body cooled down from a peak metamorphism temperature ∼800 °C to ∼300 °C in less than 64 million years at a depth of &gt;20 km. Then at ∼4.22 Ga, Itokawa’s parent body was shattered in a collisional process involving a heterogeneous temperature distribution during the impact, with some regions escaping shock metamorphism and experiencing less than a few hundred degrees Celsius. The fragments re-agglomerated in a larger rubble pile body where they subsequently cooled down over tens of millions of years. For the next 4 billion years, Asteroid Itokawa was regularly impacted and progressively shrunk by mass wasting.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"32 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145103523","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}