Chemical Geology最新文献

{"title":"Integrating detrital magnetite geochemistry and (U[sbnd]Th)/He chronometry as a sediment provenance tool in geologic and metallogenic terranes","authors":"Robert G. McDermott, Douglas C. Kreiner, James V. Jones III, Sean P. Regan, James R. Metcalf, Rebecca M. Flowers","doi":"10.1016/j.chemgeo.2026.123448","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123448","url":null,"abstract":"Magnetite is ubiquitous in porphyry Cu systems and in sediment sourcing both barren and mineralized regions, with potential as an indicator mineral in concealed and coarsely-mapped terranes. We develop and test a workflow for integrated geochemistry and (U<ce:glyph name=\"sbnd\"></ce:glyph>Th)/He (He) dating for inferring detrital magnetite (DMt) provenance in these settings. The ca. 70 Ma Taurus porphyry Cu-Mo(<ce:glyph name=\"sbnd\"></ce:glyph>Au) district in eastern interior Alaska serves as a test case. DMt from streams draining porphyry-related mineralization was characterized by geochemistry and mineral inclusion and microstructure observations, complemented by similar data for potential porphyry and host rock sources. Principal component analysis and clustering of DMt geochemical data resolve multiple populations in our samples geochemically and texturally compatible with derivation from metamorphic, porphyry-related hydrothermal, and igneous sources. Hydrothermal magnetite comprises ~16–50% of DMt nearest porphyry mineralization but diminishes to ~4% ~15 km downstream. Subsampled grains within populations yield ~160–110 Ma, ~70 Ma, ~55 Ma, and ~ 20 Ma magnetite He date modes. Combined with provenance, He dates capture Early Cretaceous regional exhumation of metamorphic host rock and Late Cretaceous porphyry Cu mineralization. DMt grains showing partial hematite replacement yield ca. 55–20 Ma dates regardless of source, overlapping regional warm/wet climatic intervals. We interpret Cenozoic dates to reflect exhumation to near-surface oxidizing conditions and(or) supergene weathering. Magnetite is thus a promising target phase for (1) tracking the spatiotemporal distribution of porphyry systems, and (2) linking the formation and exhumation of these systems to a regional geologic history, both in Alaska and globally.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"26 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147752892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical characterisation of the Ellsworth-Whitmore Mountains crustal block: a critical piece in the puzzle to unravel ice retreat in West Antarctica","authors":"Emily J. Archibald ,&nbsp;James W. Marschalek ,&nbsp;Adrian R. Muxworthy ,&nbsp;Teal R. Riley ,&nbsp;Claus-Dieter Hillenbrand ,&nbsp;Tom A. Jordan ,&nbsp;Pieter Vermeesch ,&nbsp;Michael J. Flowerdew ,&nbsp;Martin Siegert ,&nbsp;Dominic A. Hodgson ,&nbsp;Tina van de Flierdt","doi":"10.1016/j.chemgeo.2026.123290","DOIUrl":"10.1016/j.chemgeo.2026.123290","url":null,"abstract":"<div><div>The West Antarctic Ice Sheet (WAIS) is prone to major retreat. Identifying when previous WAIS retreats occurred could improve sea level rise projections, but detection of these events in marine sediments is limited by knowledge of the geochemical signature of key sediment source regions located further inland - primarily the Ellsworth-Whitmore Mountains (EWM). This is because a smaller WAIS would likely result in enhanced erosion of the EWM and permit more widespread transport of EWM detritus offshore. We here characterise the provenance signature of the EWM, showing that different stratigraphic units exhibit distinct geochemical characteristics based on unique combinations of zircon U-Pb ages and Nd and Sr isotope ratios. The oldest Heritage Group displays dominant Grenville Orogeny (1000–1250 Ma) ages, with mean ε_Nd values of ∼ − 8 and ⁸⁷Sr/⁸⁶Sr ratios of ∼0.719. The overlying Crashsite Group and Whiteout Conglomerate exhibit dominant Ross Orogeny ages (490–580 Ma), with mean ε_Nd values of ∼ − 12 and − 18 and ⁸⁷Sr/⁸⁶Sr ratios of ∼0.740 and ∼ 0.725, respectively. The youngest Polarstar Formation has common Permian zircon U-Pb ages and ε_Nd values of ∼ − 4 and ⁸⁷Sr/⁸⁶Sr ratios of ∼0.711. Outlying nunataks are assigned to the Heritage and Crashsite groups, extending our geological knowledge of the Ellsworth Subglacial Highlands. Together, our data suggest that the Ellsworth Mountains crustal block is characterised by a mean ε_Nd value of ∼ − 10, ⁸⁷Sr/ ⁸⁶Sr ratio of ∼0.728, and bimodal Ross and Grenville orogeny zircon U-Pb ages. This “provenance fingerprint” should be identifiable in offshore sediments recording times of major WAIS retreat.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"706 ","pages":"Article 123290"},"PeriodicalIF":3.6,"publicationDate":"2026-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146138458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Strontium isotopes tracing of weathering processes and tidal mixing in a mountainous river system","authors":"Ni Su ,&nbsp;Junjie Guo ,&nbsp;Xiaolei Xie ,&nbsp;Zhouyang Wu ,&nbsp;Yalong Li ,&nbsp;Shouye Yang","doi":"10.1016/j.chemgeo.2026.123289","DOIUrl":"10.1016/j.chemgeo.2026.123289","url":null,"abstract":"<div><div>Radiogenic and stable Sr isotope ratios are effective tracers of source mixing and isotopic fractionation at the land-ocean interface, yet their behavior in rivers under tidal influence remains insufficiently constrained. This study presents major element compositions together with ⁸⁷Sr/⁸⁶Sr and δ^88/86Sr data for river water, groundwater, and sediments from the Mulanxi River, a small mountainous catchment in southeast China. Major ion chemistry indicates that river water is primarily controlled by carbonate weathering, while ⁸⁷Sr/⁸⁶Sr ratios of river water and sediment leachates suggest that dissolved Sr is mainly sourced from trace carbonate phases. Sediment leaching results indicate that labile phases contribute less radiogenic but heavier Sr to river water compared to the sediment residues (means 0.70969 vs. 0.71570; 0.21‰ vs. 0.11‰). In contrast, δ^88/86Sr values of bulk and clay fractions of sediments (0.08 ± 0.08‰ and 0.07 ± 0.08‰) are indistinguishable, indicating limited isotopic fractionation during clay formation. The combined ⁸⁷Sr/⁸⁶Sr and δ^88/86Sr signatures reveal that Sr cycling in river water is primarily governed by mixing between surface water and groundwater Sr sources, while mass-dependent isotope fractionation, largely driven by calcite precipitation, alters the δ^88/86Sr composition of the dissolved Sr pool. In addition, differences in major ion chemistry between tidal and non-tidal reaches are attributed to cation exchange during freshwater-seawater mixing. Riverine ⁸⁷Sr/⁸⁶Sr ratios show no clear mixing trend due to similar compositions of freshwater and seawater end-members, whereas δ^88/86Sr values behave conservatively without measurable isotopic fractionation. Further analysis of Sr–Nd isotope variations in river sediments reflect a shift in sediment provenance. Sediments in the non-tidal reach mainly originate from local bedrock weathering, whereas those in the tidal reach mostly consist of Changjiang-derived fine sediments. These results demonstrate that integrating multi-phase analysis with dual Sr isotope tracers (⁸⁷Sr/⁸⁶Sr and δ^88/86Sr) establishes a comprehensive framework for resolving geochemical processes in tidal river systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"706 ","pages":"Article 123289"},"PeriodicalIF":3.6,"publicationDate":"2026-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146138459","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rapid hydration of rhyolitic glass at atmospheric conditions: Evidence from Diffuse Reflectance Infrared Fourier Transform spectroscopy and Temperature Conversion Elemental Analysis","authors":"Thomas Giachetti ,&nbsp;Erwan Martin ,&nbsp;Etienne Balan","doi":"10.1016/j.chemgeo.2026.123291","DOIUrl":"10.1016/j.chemgeo.2026.123291","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The molar abundance ratio of H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH of rhyolitic porous pyroclasts, obsidian pyroclasts, and flow obsidians from the 1060CE Glass Mountain eruption at Medicine Lake Volcano (USA) were obtained by Diffuse Reflectance Infrared Fourier Transform spectroscopy. Samples were also analyzed for their total water content, [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;], and isotopic composition, &lt;span&gt;&lt;math&gt;&lt;mi&gt;δ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;D, via Temperature Conversion Elemental Analysis (TC/EA). Porous clasts exhibit a H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH ratio of 0–4.63 (and a [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;] measured by Giachetti et al. (2020) of 0.34–1.2 wt%) that is positively correlated with their porosity and [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;], contrary to the low [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;] and low H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH ratios of both obsidian pyroclasts (0.32–0.72 wt.&lt;span&gt;&lt;math&gt;&lt;mtext&gt;%&lt;/mtext&gt;&lt;/math&gt;&lt;/span&gt;, 0.14–0.63) and flow obsidians (0.04–0.07 wt.&lt;span&gt;&lt;math&gt;&lt;mtext&gt;%&lt;/mtext&gt;&lt;/math&gt;&lt;/span&gt;, 0.24–0.28). These results confirm the interpretations of Giachetti et al. (2020) that porous clasts were rehydrated for about 1000 years after the eruption via diffusion of overwhelmingly molecular, meteoric water in the matrix-glass, whereas obsidian pyroclasts and flow obsidians are essentially dense and thus rehydrate poorly. Analyses were also conducted on two size fractions of flow obsidian (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mn&gt;63&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; and 63–&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;250&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) that were ground either (1) immediately before analysis or, (2) about nine years prior to analysis and kept in closed containers ever since. Results show that the &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mn&gt;63&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; ground samples gained 0.06–0.24 wt% of meteoric water in just nine years, with a H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH ratio increasing","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"706 ","pages":"Article 123291"},"PeriodicalIF":3.6,"publicationDate":"2026-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146173000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Prolonged cooling of andesitic-dacitic lava flows produces optimal groundmass material for 40Ar/39Ar dating","authors":"Chris E. Conway ,&nbsp;Andrew T. Calvert ,&nbsp;Osamu Ishizuka ,&nbsp;Seiko Yamasaki ,&nbsp;Isoji Miyagi ,&nbsp;Yumiko Harigane ,&nbsp;Graham S. Leonard","doi":"10.1016/j.chemgeo.2026.123268","DOIUrl":"10.1016/j.chemgeo.2026.123268","url":null,"abstract":"<div><div>Organizing the eruptive histories and petrogenetic models that underpin hazard assessments at active volcanoes typically requires high-precision ages for late Pleistocene to Holocene lava flows. In this study, features of an existing ⁴⁰Ar/³⁹Ar dataset for andesitic-dacitic rocks from Ruapehu volcano, Aotearoa New Zealand, were interrogated with new microanalytical data to identify the optimal groundmass material for age determination. To understand the behavior of K and Ar within the cooling melt of lavas during their emplacement, we examined and compared the petrological features of samples from the ice-chilled margin and interior of a lava flow. The groundmass of the rapidly cooled sample comprises non-vesicular rhyolitic glass and microlites of plagioclase, orthopyroxene, and magnetite. The sample from the flow interior has minimal amounts of groundmass glass, and interstices are instead occupied by sanidine and tridymite. Thermodynamic modelling supports the interpretation that sanidine crystallized as a stable groundmass phase during slow cooling of degassed melt in the interior zones of lavas that were insulated behind their glassy margins. Our evaluation of the age data shows that sanidine contributed high yields of radiogenic argon during step-heating experiments for samples collected from lava interiors, which enabled high-precision ⁴⁰Ar/³⁹Ar ages to be determined. Using Ruapehu as an example of an arc volcano affected by lava-ice interaction, we provide a basic field guide for identifying lava flows that contain groundmass sanidine at the expense of glass. Target outcrops also offer opportunities for reconstructing geomagnetic dynamics and volcano–climate relationships during the Pleistocene and Holocene.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"705 ","pages":"Article 123268"},"PeriodicalIF":3.6,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sulfate-driven anaerobic oxidation of methane in deeply buried sediments on the Southern Campbell Plateau","authors":"Alex J. Reis ,&nbsp;Vanessa Fichtner ,&nbsp;Andrea M. Erhardt","doi":"10.1016/j.chemgeo.2026.123269","DOIUrl":"10.1016/j.chemgeo.2026.123269","url":null,"abstract":"<div><div>Sulfur is a key component in the reduction of organic carbon in marine sediments. Sulfate-driven anaerobic oxidation of methane and microbial sulfate reduction are the leading processes driving the removal of organic carbon and sulfur from the environment. Microbial sulfate reduction has been well studied in most marine depositional environments, however, studies examining sulfate-driven anaerobic oxidation of methane are primarily limited to shallow burial or methane seep environments. Sediments recovered from IODP site U1553 on the southern Campbell Plateau demonstrate evidence of a deeply buried sulfate-methane transition zone (SMTZ). In this study, we identified a deep (&gt; 500mbsf) sulfate-methane transition zone through the analysis of sulfur isotopes in sulfide minerals (d³⁴S_CRS). Three potential paleo-SMTZs were also identified as peaks in d³⁴S_CRS below the modern SMTZ, suggesting the changing seafloor and depositional conditions since the late Oligocene contributed to the upward migration of the SMTZ over time. Understanding the evolution of deep SMTZs and the processes associated with them will help further constrain how the sulfur and carbon cycles interact and drive carbon storage in marine sediments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"705 ","pages":"Article 123269"},"PeriodicalIF":3.6,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3D phase-field modeling of limestone dissolution process induced by CO2","authors":"Wenchao Dou, Mian Lin","doi":"10.1016/j.chemgeo.2026.123356","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123356","url":null,"abstract":"","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"401 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147495456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Holocene–pleistocene provenance transitions in the Cauvery Delta, South India: Evidence from Sr-Nd isotopes","authors":"Malik Zubair Ahmad ,&nbsp;Pramod Singh ,&nbsp;S. Balakrishnan ,&nbsp;Suhail Hussain Sheikh","doi":"10.1016/j.chemgeo.2026.123265","DOIUrl":"10.1016/j.chemgeo.2026.123265","url":null,"abstract":"<div><div>We investigate temporal shifts in sediment provenance through comprehensive ⁸⁷Sr/⁸⁶Sr and εNd₀ analyses of two sediment cores (Uttrangudi and Porayar) from the Cauvery Delta, South India. We assessed the role of weathering intensity and source rock variability and glacial/interglacial climate phases using isotopic signatures. Isotopic data of two cores reveal distinct shifts in provenance between the Late Pleistocene and Holocene periods. Around ∼14 ka BP, the isotopic signatures indicate enhanced contributions from the Dharwar Craton, consistent with more efficient sediment transport from the distant upper catchment when the lower sea level exposed the continental shelf. In contrast, Holocene sediments (upper core sections) reflect a dominant contribution from the Southern Granulite Terrain, driven by intensified Northeast Monsoons. Our data shows that weathering intensity may influence isotopic compositions, with Nd isotopes being particularly sensitive to these post-depositional processes. The Porayar core exhibits an unusual inverse relationship in which finer fractions correspond to less radiogenic εNd₀ values. Our findings underscore the critical influence of source rock variability, Quaternary sea-level fluctuations, and climate-driven weathering intensity on the Sr-Nd isotopic composition of deltaic sediments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"704 ","pages":"Article 123265"},"PeriodicalIF":3.6,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146015035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Crystallization of REE phases within La-Na-(Ca)-Cl-(F)-C-H-O systems","authors":"Jingui Xu ,&nbsp;Qifa Zhong ,&nbsp;Wei Zhao ,&nbsp;Dongzhou Zhang ,&nbsp;Li Zhou ,&nbsp;Yi Zhou ,&nbsp;Wei Zhang ,&nbsp;Wenge Zhou ,&nbsp;Dawei Fan","doi":"10.1016/j.chemgeo.2026.123255","DOIUrl":"10.1016/j.chemgeo.2026.123255","url":null,"abstract":"<div><div>Carbonatite-hosted rare earth element (REE) deposits provide the world's primary source of REEs. Understanding the relative stability of REE minerals within carbonatite systems is vital for deciphering the genesis of carbonatite-related REE deposits. Yet, experimental data of REE minerals at high pressure and high temperature conditions remain scarce. This study reports a series of crystallization experiments involving REE phases in the La-Na-(Ca)-Cl-(F)-C-H-O systems, conducted between 490 and 750 °C and at pressures of 0.3–0.5 GPa. In the F-free systems, Na-REE carbonate (carbocernaite) coexists with hydroxylbastnäsite and remains stable across the temperature range tested. The addition of Ca leads to their coexistence with calcite and induces a partial substitution 2Ca ↔ Na + La in carbocernaite. Increasing REE concentration promotes the formation of a completely new compound, a Cl-bearing REE carbonate (La₃(CO₃)₄Cl). In contrast, in the F-bearing systems, bastnäsite is the dominant REE phase, with elevated temperatures favoring the crystallization of REE fluoride (fluocerite, LaF₃). The addition of Ca results in bastnäsite coexisting with calcite and fluorite. Notably, Na-REE carbonates do not form in F-bearing runs, even at low F concentrations (∼0.9 wt%). These findings suggest two main implications: first, the formation of LaF₃ at higher temperatures relative to bastnäsite supports field evidence that fluocerite crystallizes at higher temperatures and serves as a precursor to bastnäsite. Second, the absence of Na-REE carbonates in F-bearing experiments may explain why some deposits have no evidence of former existence of Na-REE carbonates.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"704 ","pages":"Article 123255"},"PeriodicalIF":3.6,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Trace element signatures of a sediment-derived mobile phase in arc and back-arc basalts: Experimental constraints","authors":"Alexander G. Sokol ,&nbsp;Olga A. Kozmenko ,&nbsp;Alexey N. Kruk ,&nbsp;Sergey Yu. Skuzovatov","doi":"10.1016/j.chemgeo.2026.123254","DOIUrl":"10.1016/j.chemgeo.2026.123254","url":null,"abstract":"<div><div>The mobility of trace elements in a hydrous melt and a supercritical liquid formed from metasediment poor in volatiles (2.2 wt% H₂O and 0.9 wt% CO₂) is studied experimentally with implications for the potential contribution of slab sediment to the formation of arc and back-arc magmas. The experiments are performed by the diamond trap technique with quartz-muscovite-chlorite schist at 3.0 to 7.8 GPa and 750 to 1090 °C. The mineral assemblages (residue) and solute material entrapped in the diamond traps are analyzed by solution-based inductively coupled plasma mass spectrometry (ICP-MS) to investigate the fractionation of trace elements. The residue is composed of garnet, phengite, clinopyroxene, coesite, and kyanite, as well as accessory monazite, rutile, and zircon. The mobile phase appears upon dehydration of mica schist as hydrous melt in 3.0 GPa runs at 750 and 900 °C and as supercritical liquid (SCL) at ≥5.5 GPa and ≥ 850 °C. The mobile phase generated at 5.5 GPa and 850°С has an H₂O content typical of SCL but preserves trace element patterns of the hydrous melt. Ba, LREE, and Th in the hydrous melt (3.0 GPa, 750 and 900 °C) are comparable to Nb in mobility but become markedly less compatible in SCL (≥5.5 GPa, ≥850 °C); Th has a slightly lower SCL-metasediment partition coefficient than La (<em>D</em> = C_SCL/C_Residue). The assumption of schist-derived SCL inputs to the source of arc- and back-arc magmas in the peridotitic mantle wedge is consistent with the observed H₂O/LREE, LILE/H₂O, Ba/La, Th/La, and Nd/Sr ratios in arc basalts. The fit of trace element chemistry is the best for SCL formed from metasediment with a composition of global subducting sediment (GLOSS) at 5.5 GPa and temperatures of 850°С to 1030°С. In this case, SCL inputs can translate high Th/La ratios to the arc magma source and maintain Nb depletion relative to LREE in the partial melts. Thus, the slab flux of sediment-derived SCL to the mantle wedge region of arc- and back arc magma generation can carry sufficient amounts of LILE, LREE, Th, and U, while the resulting magma remains depleted in Nb.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"704 ","pages":"Article 123254"},"PeriodicalIF":3.6,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145962647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}