Geochimica et Cosmochimica Acta最新文献

{"title":"Self-induced differential stress and cascading reactions, fracturing, and permeability enhancement triggered by volatile-consuming reactions","authors":"Atsushi Okamoto ,&nbsp;Fukuma Sakashita ,&nbsp;Kazuki Yoshida ,&nbsp;Otgonbayar Dandar ,&nbsp;Masaoki Uno","doi":"10.1016/j.gca.2025.06.018","DOIUrl":"10.1016/j.gca.2025.06.018","url":null,"abstract":"<div><div>Reaction-induced fracturing is thought to be a key process controlling pervasive volatile-consuming reactions, including the serpentinization and carbonation of peridotites; however, the interactions between reactions, fluid flow, and fracturing remain poorly understood. We performed flow-through hydration experiments on sintered periclase aggregate [MgO + H₂O → Mg(OH)₂] samples with high and low porosities at temperatures of 180–200 °C, confining pressure of 20 MPa, and fluid pressures of 3–5 MPa. We monitored the solid volume, permeability, and axial stress simultaneously. For comparison, we also conducted batch experiments with the same samples. In the batch experiments, the high-porosity sample reacted uniformly with no macroscopic fracturing, whereas a sharp reaction front developed in the low-porosity sample. In the flow-through experiments with high-porosity samples, the reaction proceeded uniformly, with an initial decrease in permeability but no increase in volume. Axial stress then increased, and the sample subsequently yielded gradually. The reaction continued, causing circumferential expansion of the sample with no discrete failure while the permeability remained constant or increased. In the flow-through experiments with low-porosity samples, the reaction began slowly through surface layer spallation. After a prolonged initiation period, mechanical instability led to a sudden large failure. This failure triggered cascading reactions, with a build-up of reaction-induced stress followed by yielding and the formation of new fractures, resulting in the permeability increasing by two orders of magnitude and leading to reaction rates increasing by a factor of 18 compared with the batch experiments. The results suggest that (1) reaction-induced fracturing is strongly enhanced by self-induced differential stress related to the anisotropic elastic properties of the lithosphere, and (2) catastrophic failure can occur during the hydration and carbonation of impermeable mantle peridotite. These findings provide new links between microscopic failure at reaction interfaces and macroscopic fractures in a rock, and have implications for the pervasive serpentinization of the oceanic lithosphere, the formation of serpentine diapirs, and natural and anthropogenic CO₂ sequestration.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 1-15"},"PeriodicalIF":4.5,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516008","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":"Distinct patterns and drivers of total and refractory terrestrial organic carbon burial in river-dominated continental margins: From climatic control to anthropogenic perturbations","authors":"Xueshi Sun ,&nbsp;Dejiang Fan ,&nbsp;Xilin Zhang ,&nbsp;Peng Cheng ,&nbsp;Zuosheng Yang ,&nbsp;Zhigang Guo","doi":"10.1016/j.gca.2025.06.020","DOIUrl":"10.1016/j.gca.2025.06.020","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The burial of terrestrial organic carbon (OC&lt;sub&gt;terr&lt;/sub&gt;) in marine sediments is a major geological CO&lt;sub&gt;2&lt;/sub&gt; sink. The largest sink for OC&lt;sub&gt;terr&lt;/sub&gt; burial in present-day oceans lies in river-dominated continental margins, which are key components of the global carbon cycle. Climate change and anthropogenic forcing have disrupted the cycling of OC&lt;sub&gt;terr&lt;/sub&gt; at the land–ocean interface, impacting its storage at these margins. Despite this recognition, the fate of OC&lt;sub&gt;terr&lt;/sub&gt; in marine sediments and the potential feedback mechanisms of these changes remain unclear, primarily because of the lack of reliable sedimentary records from 1850 to the present that capture the substantial internal spatial and temporal heterogeneity. Here, we present a high-resolution OC&lt;sub&gt;terr&lt;/sub&gt; record covering the past two centuries from a well-preserved sediment core in the mud depocenter of the East China Sea, using sedimentological, mineralogical, and geochemical techniques. By integrating our new results with literature data, we quantitatively evaluate the modern patterns and drivers of changes in OC&lt;sub&gt;terr&lt;/sub&gt; burial. During the climate-controlled period (pre-1950s), despite high precipitation and sediment influx driven by the East Asian summer monsoon, the observed lower and fluctuating OC&lt;sub&gt;terr&lt;/sub&gt; loadings suggest that the OC&lt;sub&gt;terr&lt;/sub&gt; accumulation rate was not directly proportional to the lithogenic sediment flux. Analyses of X-radiographs and sediment composition indicate that energetic marine processes—such as tides, waves, and typhoon events that are intensified by the East Asian winter monsoon—promoted sediment resuspension, dispersion, and redeposition. These dynamic physical processes regulate hydrodynamic particle sorting, resulting in the high variability and suppression of OC&lt;sub&gt;terr&lt;/sub&gt; burial during this interval. In contrast, the post-1950s era, marked by intensive human impact, saw a persistent decline in the overall OC&lt;sub&gt;terr&lt;/sub&gt; burial. This trend is primarily attributed to the reduced delivery of fine mineral sediments and altered sediment sources to marine environments mainly due to large-scale dam construction. Although the preservation of sedimentary OC&lt;sub&gt;terr&lt;/sub&gt; has diminished, our study provides new evidence of increased mobilization and burial of refractory OC&lt;sub&gt;terr&lt;/sub&gt; in marine sediments. Using a chemical oxidation method, we quantified the proportions of refractory organic carbon (OC) and found that, on average, 60 ± 11 % of the refractory OC exported by the Yangtze River is delivered to the adjacent continental margin. Coinciding with periods of intensive human impact (post-1950s), anthropogenic disturbances, notably inputs of fossil-derived OC, have reintroduced greater quantities of unreactive OC&lt;sub&gt;terr&lt;/sub&gt; into coastal oceans. This shift contributed to an increase of ∼ 20 % in the accumulation rate of refractory OC&lt;sub&gt;terr&lt;/sub&gt;. The contrasting responses of th","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 182-201"},"PeriodicalIF":4.5,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516024","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":"Links between forearc decarbonation and generation of high δ26Mg fluids at subarc depths: constraints from carbonate-bearing forearc serpentinites","authors":"Kai Wu ,&nbsp;Kan Li ,&nbsp;Chang Zhang ,&nbsp;Yuxiao Chen ,&nbsp;Kaiyun Chen ,&nbsp;Weidong Sun ,&nbsp;Honglin Yuan","doi":"10.1016/j.gca.2025.06.024","DOIUrl":"10.1016/j.gca.2025.06.024","url":null,"abstract":"<div><div>Subduction zones play a critical role in carbon exchange between Earth’s surface and interior. While devolatilization of forearc serpentinites has been proposed as a contributor to arc magma genesis, its role in subduction-zone carbon (C) and magnesium (Mg) cycling, as well as its influence on the Mg isotopic variability in global arc lavas, remains poorly constrained. This study investigates Mg isotope fractionation during interactions between forearc peridotites and CO₂-rich fluids in the Mianlue tectonic mélange, focusing on carbonate-bearing serpentinites from the Jianchaling and Liangyazi regions. Five Jianchaling lizardite-only serpentinites exhibit a narrow range of δ²⁶Mg values (−0.28 ± 0.02 ‰ to −0.13 ± 0.02 ‰), similar to those of four Jianchaling antigorite-lizardite serpentinites (−0.27 ± 0.03 ‰ to −0.17 ± 0.01 ‰). In contrast, seven Liangyazi antigorite-only serpentinites display a broader δ²⁶Mg range (−0.27 ± 0.03 ‰ to −0.01 ± 0.02 ‰). Magnesium isotope compositions of mineral separates reveal temperature-dependent inter-mineral Mg isotope fractionations between carbonate and co-precipitated serpentine minerals. Thermodynamic modeling and mass balance calculations indicate minimal Mg loss from peridotites to fluids during their interaction with CO₂-rich fluids. Instead, subsequent fluid infiltration and carbonate dissolution are responsible for the observed Mg isotopic variations. The concurrent precipitation of isotopically heavy silicate minerals and light carbonates in the forearc provides a plausible explanation for the elevated δ²⁶Mg values observed in some arc lavas. In subduction zones where the forearc slab-top temperatures can exceed the stability limit of antigorite (600 – 700 °C), significant forearc decarbonation produces CO₂-rich fluids that interact with forearc peridotites at the bottom of the mantle wedge, forming abundant isotopically heavy silicate minerals. The subsequent breakdown of these silicates and limited release of slab-derived carbonates at subarc depths may be responsible for the high δ²⁶Mg values and low CO₂ outfluxes characteristic of these subduction zones. In contrast, subduction zones with cooler forearc slab-top temperatures, where subarc slab-top temperatures approach the stability limit of antigorite, experience less significant forearc decarbonation. In such settings, limited formation of isotopically heavy silicate phases and enhanced release of slab carbonates at subarc depths due to infiltrations of slab-derived fluids can potentially result in arc magmas with δ²⁶Mg values close to or slightly below the normal mantle. These findings underscore the critical role of fluid-rock interactions in the forearc region in regulating deep carbon cycling and shaping the Mg isotopic signatures of arc magmas.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 202-217"},"PeriodicalIF":4.5,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516005","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":"Storage capacity and partitioning of sulfur during silicate melting of the Earth’s shallow upper mantle and the evolution of S/Dy during MORB-source melting","authors":"Anna C. Johnson ,&nbsp;Rajdeep Dasgupta ,&nbsp;Proteek Chowdhury ,&nbsp;Maitrayee Bose","doi":"10.1016/j.gca.2025.06.022","DOIUrl":"10.1016/j.gca.2025.06.022","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Sulfur (S) in the mantle has conventionally been assumed to be stored exclusively in accessory sulfide or sulfate phases, with the S content of primary mantle melts sourced entirely from these S-rich minerals. In contrast, recent works have argued that nominally S-free, major silicate mantle minerals such as clinopyroxene (cpx), orthopyroxene (opx), plagioclase (pl), and garnet (gt) may contain 10′s of ppm sulfur. However, the experimentally determined mineral-melt partition coefficients for sulfur (&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;min/melt&lt;/sup&gt;) vary significantly between studies from as low as 10&lt;sup&gt;-3&lt;/sup&gt; to as high as 10&lt;sup&gt;-1&lt;/sup&gt;. To contribute to this debate and to better understand the implications of the silicate mineral S-source for equilibrium mantle melting, here we present a series of new and existing silicate mineral-melt equilibria experiments with sulfur introduced to the system, and calculate the &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;min/melt&lt;/sup&gt; for these experiments. The reported experiments span hydrous and anhydrous basaltic starting compositions with 0.04–6.08 wt% S added as sulfide or sulfate at 1.0–3.0 GPa and 1200–1350 °C. The S content of partial melts was measured using electron microprobe, while that of silicate minerals was measured using NanoSIMS. The high spatial resolution and depth profiling enabled by NanoSIMS reveals abundant S-rich hotspots throughout samples, which increase in frequency with experimental S content; we interpret these as sulfide and sulfate nano-inclusions. When hotspots are avoided, the S-carrying capacities of both sulfide- and sulfate-saturated experiments are ≤2.44 ppm for calcic cpx, ≤1.13 ppm for gt, 0.80 ppm for pl, 0.48 ppm for pigeonite (pgt), and 0.55 ppm for opx. The sulfur capacity of the sulfide- and sulfate-saturated minerals exhibits an inverse correlation with experimental temperature, but does not appear to be affected by S speciation or pressure. At sulfide-added conditions, &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;cpx/melt&lt;/sup&gt; is ≤0.04190, &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;gt/melt&lt;/sup&gt; is ≤0.01081, &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;pl/melt&lt;/sup&gt; is 0.00074, &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;opx/melt&lt;/sup&gt; is 0.00039, and &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;pgt/melt&lt;/sup&gt; is 0.00034. At sulfate-added conditions, the increased solubility of S&lt;sup&gt;6+&lt;/sup&gt; in the coexisting silicate melt results in reduced partition coefficients of &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;cpx/melt&lt;/sup&gt; ≤0.00105 and &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt;&lt;sup&gt;gt/melt&lt;/sup&gt; of 0.00019. These newly calculated values are orders of magnitude lower than previously published values, a consequence of the low mineral S content measured here. Finally, we apply our new partition coefficients and those of prior work to model the evolving S/Dy during adiabatic decompression melting of a sulfide-saturated MORB-source mantle. We find that minimal partitioning of S into silicate minerals, as observed in our experiments, has negligible impact on the S/Dy of MORBs. Importantly, we ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 20-36"},"PeriodicalIF":4.5,"publicationDate":"2025-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516027","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 Mesozoic high-elevation plateau in eastern North China? Evidence from detrital zircons","authors":"Ziyi Guo, Ming Tang, Hehe Jiang, Xuyang Zheng","doi":"10.1016/j.gca.2025.06.019","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.019","url":null,"abstract":"High-elevation plateaus form as the culmination of tectonic and magmatic processes, and they influence surface processes such as erosion and sedimentation. There are signs indicating high topographies in eastern North China (ENC) during the Mesozoic, coinciding with the reactivation and dramatic destruction of the North China Craton. However, the topographic evolution of ENC and how this evolution may be related to the North China Craton destruction are unclear. To constrain the topographic evolution in ENC, we measured Eu anomalies (a proxy for crustal thickness) in ∼5000 detrital zircons from modern river sands and ancient sandstones to reconstruct the crustal thickness evolution of ENC in the Mesozoic. Our results show that the ENC crust thickened to ∼60–70 km, similar to that of Tibet, from the early-middle Jurassic through the early Cretaceous, followed by a gradual thinning process during the late Cretaceous. Our crustal thickness results are consistent with whole-rock La/Yb results and geologic records that are indicative of crustal contraction and extension. We further note that a similar thickening trend is seen in multiple regions within ENC, which leads us to propose the existence of a vast Mesozoic plateau in ENC. Additionally, we find that the proportion of Mesozoic zircons in sandstones gradually increases with depositional age, reaching a peak in the Late Cretaceous, and then decreases rapidly in younger samples. This pattern likely reflects changes in erosion rates controlled by evolving topography, and thus records the growth and collapse of a plateau. Notably, the peak in Mesozoic detrital zircon proportion occurs approximately 50 Myr after the maximum uplift period of the ENC plateau, suggesting a time lag between uplift and sedimentary response. Based on our results, we model the erosion processes of the plateau and find that this time lag can be readily explained by the uplifting history reconstructed from our detrital zircon Eu anomaly data if the climate was largely arid. The intense thickening of the ENC crust was likely driven by the low-angle subduction of the Izanagi plate, with additional contributions from surrounding circum-craton orogenies. At ∼130 Ma, the rollback of the Izanagi plate likely resulted in both the collapse of the plateau and the destruction of the North China Craton.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"27 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516026","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":"Radon and radium isotope signatures on a massive ice- and permafrost-rich coastline","authors":"Lauren Kipp ,&nbsp;Gwénaëlle Chaillou ,&nbsp;Markus Kienast ,&nbsp;Joseph Tamborski ,&nbsp;Dustin Whalen","doi":"10.1016/j.gca.2025.06.014","DOIUrl":"10.1016/j.gca.2025.06.014","url":null,"abstract":"<div><div>Rapid warming in the Arctic is degrading permafrost and massive ice deposits, which releases solutes previously trapped in ice and frozen soils into groundwater, rivers, and the coastal ocean. Radium and radon isotopes are enriched in groundwaters and may therefore have utility as tracers for the delivery of permafrost-derived solutes to the ocean, particularly if massive ice- or permafrost-derived meltwaters have a distinct isotopic ratio. The ratio of radium isotopes within massive ice deposits can also be used to constrain timescales of ice segregation, as the four isotopes will decay with known rates once removed from contact with sediments. Here we present the first measurements of radium and radon in massive ice deposits along the Beaufort Sea coast in the Northwest Territories, Canada. Measurable levels of short-lived radium and radon isotopes indicate relatively recent ice segregation and/or inputs from sediment grains frozen within the ice lenses; the radium-224/radium-228 ratio is used to identify ice samples that must have experienced segregation within the last five years, and desorption experiments provide evidence that sediment within the ice can support the radium activities observed in older ice. Short- to long-lived isotope ratios were low in ice and increased in meltwater and groundwater, while coastal ocean ratios were similar to those of the nearby Mackenzie River. Thus, we find that the radium isotope ratio of massive ice is not preserved during transport, and the river is the main control on the coastal radionuclide distribution in this region. A distinctly low (&lt;1) radium-224/radium-228 ratio was measured in massive ice deposits, similar to previous observations in permafrost, suggesting that this low ratio may be characteristic of cryogenic environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 166-181"},"PeriodicalIF":4.5,"publicationDate":"2025-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337613","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":"Evaporation kinetics of silicon carbide in a low-pressure H2-H2O gas mixture: Implications for the survivability of presolar silicon carbide grains in the protosolar disk","authors":"Daiki Yamamoto ,&nbsp;Aki Takigawa ,&nbsp;Lily Ishizaki ,&nbsp;Ryosuke Sakurai ,&nbsp;Yuki Inoue ,&nbsp;Junji Yamamoto ,&nbsp;Sota Arakawa ,&nbsp;Shogo Tachibana","doi":"10.1016/j.gca.2025.06.010","DOIUrl":"10.1016/j.gca.2025.06.010","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Presolar silicon carbide (SiC) grains found in primitive extraterrestrial materials would preserve the pre-accretion thermal history of dust in the protosolar disk. Three series of evaporation experiments of SiC were conducted at total pressures of 0.5 and 2.5 Pa of H&lt;sub&gt;2&lt;/sub&gt;-H&lt;sub&gt;2&lt;/sub&gt;O gas mixture with controlled H&lt;sub&gt;2&lt;/sub&gt;/H&lt;sub&gt;2&lt;/sub&gt;O ratios of ∼ 52–140 and temperatures of 1523–1779 K. The STEM-EDS and Raman spectroscopic analyses of the heated samples indicated the absence of an oxide layer on the sample surface; however porous carbon-rich layers were occasionally observed. This suggests that the evaporation of SiC under the experimental conditions proceeded without the formation of a protective steady-state SiO&lt;sub&gt;2&lt;/sub&gt; layer. Under all the experimental conditions, the evaporation flux (&lt;em&gt;J&lt;/em&gt;) has little/no dependence on temperatures typically higher than ∼1610–1670 K, while larger temperature dependences were observed at lower temperatures. The little/no temperature-dependence of &lt;em&gt;J&lt;/em&gt; suggests that the evaporation reaction rate is controlled by the gaseous supply of H&lt;sub&gt;2&lt;/sub&gt;O to the SiC surface under low-pressure conditions prevailing in the protosolar disk. The overall reaction rates would be limited by the surface chemical reactions in the large-temperature dependent regime. The large activation energies in this regime obtained in this study compared with those reported from the previous studies are likely associated with the transition regime from the SiC evaporation without continuous SiO&lt;sub&gt;2&lt;/sub&gt; formation to that accompanied by the SiO&lt;sub&gt;2&lt;/sub&gt; formation.&lt;/div&gt;&lt;div&gt;The survivability of presolar SiC grains was then compared with that of presolar amorphous silicate grains. We found that the lifetime of 0.1–1 μm-diameter SiC grain in the protosolar disk would have little/no temperature dependence at temperatures higher than ∼1500–1700 K, whereas it has a large temperature dependence at lower temperatures. The survival of these presolar SiC grains during the formation of igneous calcium-aluminum-rich inclusions would largely depend on the heating conditions of high-temperature events. Effective SiC evaporation reaction would occur at ∼1200–1400 K, whereas oxygen isotopic signatures of 0.1 μm-diameter presolar amorphous silicate grains would be erased at ∼ 600–800 K in the accreting ptotosolar disk. At temperatures lower than ∼ 600–700 K, the presolar silicate/SiC number ratio normalized to its initial ratio increases with increasing the heliocentric distance from the Sun (&lt;em&gt;r&lt;/em&gt;), reaching values of ∼ 0.7–0.9 at &lt;em&gt;r&lt;/em&gt; &gt; 4–5 au if the particles were released at ∼ 6–12 au. Assuming that the primitive interplanetary dust particles (IDPs) have an initial presolar silicate/SiC ratio of ∼ 6, the IDP-normalized ratios in primitive carbonaceous chondritic meteorites are in the range of ∼ 0.15–1. The high normalized presolar silicate/SiC ratios (&gt;∼0.7) in meteorites imply that precurso","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 388-409"},"PeriodicalIF":4.5,"publicationDate":"2025-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337641","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":"Initial 244Pu/238U ratios and search for presolar SiC in Ca-Al-rich inclusions from CV3 chondrites using noble gas and trace element abundances","authors":"Daisuke Nakashima, Jon M. Friedrich, Ulrich Ott","doi":"10.1016/j.gca.2025.06.016","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.016","url":null,"abstract":"Noble gas isotopes and trace element abundances in five Ca-Al-rich inclusions (CAIs) from two CV3 chondrites (Allende and Axtell) were analyzed. The noble gases consist of spallogenic, radiogenic, fission, and trapped components. The old U/Th-<ce:sup loc=\"post\">4</ce:sup>He ages of the CAIs (4.0 – 5.4 Ga) suggest no significant loss of radiogenic <ce:sup loc=\"post\">4</ce:sup>He and, by inference, no significant disturbance of the initial (<ce:sup loc=\"post\">244</ce:sup>Pu/<ce:sup loc=\"post\">238</ce:sup>U) ratios, (<ce:sup loc=\"post\">244</ce:sup>Pu/<ce:sup loc=\"post\">238</ce:sup>U)<ce:inf loc=\"post\">0</ce:inf>, which are derived using concentrations of <ce:sup loc=\"post\">244</ce:sup>Pu-fission <ce:sup loc=\"post\">136</ce:sup>Xe. The abundances of rare earth elements and U in the CAIs suggest variable formation temperatures, which is reflected in variable (Pr/<ce:sup loc=\"post\">238</ce:sup>U)<ce:inf loc=\"post\">0</ce:inf> ratios. The (<ce:sup loc=\"post\">244</ce:sup>Pu/<ce:sup loc=\"post\">238</ce:sup>U)<ce:inf loc=\"post\">0</ce:inf> ratios of the CAIs are variable from 0.0103 ± 0.0010 to 0.0419 ± 0.0031, which correlate with the (Pr/<ce:sup loc=\"post\">238</ce:sup>U)<ce:inf loc=\"post\">0</ce:inf> ratios. The correlation suggests Pu-Pr-U fractionation during CAI formation. From the intersection between the correlation line and the calculated early Solar System Pr/<ce:sup loc=\"post\">238</ce:sup>U ratio of 9.27, the <ce:sup loc=\"post\">244</ce:sup>Pu/<ce:sup loc=\"post\">238</ce:sup>U ratio before Pu-Pr-U fractionation in the CAI formation region is calculated as 0.0108 ± 0.0051, which is similar to those derived using other Solar System materials such as chondrites, achondrites, chondrules, and terrestrial zircons. We thus suggest that the initial <ce:sup loc=\"post\">244</ce:sup>Pu/<ce:sup loc=\"post\">238</ce:sup>U ratio has been spatially homogeneous in the inner part of the early solar nebula including the innermost solar nebula, where CAIs formed.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"42 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337636","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":"Examining the Effect of Heat from the Yellowstone Plume on the Release of Helium from the Crust","authors":"D.T. Halford, R. Karolytė, P.H. Barry, R.L. Tyne, D.J. Hillegonds, E.O. Adeniyi, D.V. Bekaert, M.W. Broadley, M.R. Hudak, K.G. Lloyd, B. Marty, C.J. Ramirez, A.M. Seltzer, C.J. Ballentine","doi":"10.1016/j.gca.2025.06.015","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.015","url":null,"abstract":"Helium (He), which is an irreplaceable resource in low-carbon technologies, medical applications, and various science and engineering sectors, is currently being explored as a primary resource. The correlation between crustal helium (He) release and heat flow in certain geologic environments (e.g., mid-ocean ridge and continental hydrothermal systems) is well established, but few studies have evaluated how past igneous processes influence current gas release/storage from crustal rocks. Here, we report bulk gas and noble gas geochemistry data (n = 43) gathered from thermal springs in and around the Yellowstone National Park (YNP), USA. Samples outside the YNP (near the plume track) are dominantly N<ce:inf loc=\"post\">2</ce:inf>-rich, while most samples collected within the active caldera area are CO<ce:inf loc=\"post\">2</ce:inf>-rich. Samples outside the YNP typically have much lower <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He than those within the caldera (i.e., near the current plume head). We explore the relationship between thermal aureoles and He isotopic signatures using heat flow data coupled with bulk gas and noble gas geochemistry data. Data are used to determine gas origins, to understand fluid flow in a regional context, and to assess how different environments impact He release from crustal minerals. Models indicate that advection is the dominant process controlling heat and volatile loss from mantle to crustal systems from the Yellowstone Caldera. In contrast, the influence of conduction/boiling of crustal hydrothermal fluids is more substantial for samples outside of the Yellowstone Caldera. Helium-4 is enriched in the samples which are frontal and near the eruptive center, likely due to recent crustal degassing of <ce:sup loc=\"post\">4</ce:sup>He accumulated over long periods in the underlying craton. Ultimately, He and other volatiles are released due to tectonic activity and/or they are enriched as other gases partition out of groundwater (i.e., gas stripping from groundwater). However, elevated heat flow zones likely constitute poor He retention zones. We propose a twofold approach to help identify preferential zones of He release: 1) focusing on areas that are distal from active igneous zones (i.e., areas that have not been fully degassed) with localized moderate heat flow to release trapped crustal He, and 2) utilizing isotope models to constrain groundwater interactions (i.e., migration and accumulation potential).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"16 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337638","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":"Phosphate behavior during submarine hydrothermal alteration of ca. 3.455 Ga basaltic seafloor rocks from Pilbara, Western Australia","authors":"Yuya Tsukamoto, Takeshi Kakegawa","doi":"10.1016/j.gca.2025.06.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.013","url":null,"abstract":"Phosphorus is an essential element for various biomolecules and biochemical processes. A phosphate-poor ocean model is popular for the Archean oceans, because of the potential absence of continental land masses and phosphorus scavenging by BIF. On the other hand, recent studies have suggested the possibility of a high phosphorus flux from Archean submarine hydrothermal activity, yielding phosphate-rich oceans. Here, we performed mineralogical and geochemical analyses for the 3.455 Ga Apex Basalt in ABDP#1 core from East Pilbara Terrane of the Pilbara Craton, Australia, to examine whether Archean submarine hydrothermal activity could play the role of a phosphate source to contemporary oceans.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"47 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337640","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}