Chemical Geology最新文献

{"title":"Insights into mantle metasomatism during oceanic subduction from late Paleozoic (∼260 Ma) high-Mg diorites in the northeastern Tibetan Plateau","authors":"Feng-Hui Zou ,&nbsp;Jian-Ping Zheng ,&nbsp;Cai-Lai Wu ,&nbsp;Chang-Qian Ma ,&nbsp;Li-Huan Deng","doi":"10.1016/j.chemgeo.2025.122782","DOIUrl":"10.1016/j.chemgeo.2025.122782","url":null,"abstract":"<div><div>Subduction recycled components can be incorporated into the mantle through aqueous solution/melt metasomatism; however, tracing the source and nature of metasomatic agents, as well as reconstructing the melting reactions of metasomatic mantles, has consistently posed significant challenges. In this work, we performed an extensive study involving petrology, geochronology, mineral chemistry, geochemistry including Sr-Nd-Pb-Hf isotopes, and numerical modeling on the newly discovered high-Mg diorites in the northeastern Tibetan Plateau to unravel their source reactions between subducting components and the mantle wedge. Zircon U<img>Pb data reveals that three diorites crystallized at ∼260 Ma, synchronous with the subduction of the Paleo-Zongwulong oceanic slab. These rocks show magnesian characteristics of amphibole and biotite, and most of plagioclase cores produce intermediate anorthite contents (An₃₆_–₄₉). The variable ⁸⁷Sr/⁸⁶Sr_(i) ratios ranging from 0.70656 to 0.7094 and most ε_Hf(t) values between −4.1 and + 4.7, but homogeneous ε_Nd(t) values from −5.4 to −2.3 indicate the diorites are derived from an enriched mantle source. The observed enrichment in large ion lithophile elements and depletion in high field strength elements further indicate the characteristics typical of arc igneous rocks. High Th/Nb ratios (0.54–1.37) and Th/Yb ratios (2.42–4.7), alongside low Sr/Th ratios (24.51–59.83) and narrow Pb isotopic variations (²⁰⁶Pb/²⁰⁴Pb_(i) of 18.09–18.34, ²⁰⁷Pb/²⁰⁴Pb_(i) of 15.59–15.63 and ²⁰⁸Pb/²⁰⁴Pb_(i) of 38.14–38.37), imply the presence of sediment components in the mantle source. Pyroxenites have been identified as their potential source, as indicated by whole-rock chemistry (e.g., high 10000*Zn/Fe ratios). Numerical modeling suggests that these diorites formed through the addition of ∼1 % aqueous solutions and 6 %–20 % hydrous melts into the mantle wedge. Therefore, the high-Mg diorites discovered in the northeastern Tibetan Plateau provide valuable insights into the interactions between the crust and mantle, which are associated with slab subduction during the late Paleozoic era.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122782"},"PeriodicalIF":3.6,"publicationDate":"2025-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838719","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":"Characterizing deposition and diagenesis history of post-Marinoan Snowball Earth carbonates from sedimentary pyrites","authors":"Yung-Hsin Liu ,&nbsp;Der-Chuen Lee ,&nbsp;Mao-Chang Liang ,&nbsp;Yoshiyuki Iizuka ,&nbsp;Mark H. Thiemens ,&nbsp;Yanan Shen ,&nbsp;Hsien Shang","doi":"10.1016/j.chemgeo.2025.122764","DOIUrl":"10.1016/j.chemgeo.2025.122764","url":null,"abstract":"<div><div>This study presents a comprehensive investigation of petrography, clumped isotope thermometry (T-∆₄₇), and NanoSIMS sulfur isotopic analysis of pyrites for the basal Doushantuo cap carbonates from the Jiulongwan (JLW) section. The majority of the analyzed pyrites originate from reduction of marine sulfates, primarily through thermochemical sulfate reduction (TSR), with minor contributions from microbial sulfate reduction (MSR) during dolomitization. Overall, the occurrence of pyrites and their δ³⁴S populations are controlled by H₂S generation, transportation, and storage. MSR- and TSR-derived H₂S are recorded by different pyrite generations, each exhibiting distinctive δ³⁴S_py values within a cm-sized specimen. In the case of TSR-derived pyrites, fluid pulses stored and mixed in cavities produce pyrites with variable occurrences but limited isotopic variation. In contrast, prolonged fluid alteration involves gradual pyrite precipitation during fluid transportation along the grain boundaries. This results in a broad δ³⁴S variation, even under high temperature conditions. The ∆³⁴S_CAS-py values of MSR-derived pyrites collected from two depths indicate a slight increase in seawater sulfate concentration during two transgression stages in the aftermath of the Marinoan Snowball glaciation. This study highlights the significance of employing multiple approaches at microscopic scales to elucidate sedimentation processes during post-glacial periods.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122764"},"PeriodicalIF":3.6,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838716","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":"The role of sulfur on the liquidus temperature and olivine-orthopyroxene equilibria in highly reduced magmas","authors":"Fabrizio Saracino ,&nbsp;Bernard Charlier ,&nbsp;Yishen Zhang ,&nbsp;Manon Lécaille ,&nbsp;Yanhao Lin ,&nbsp;Olivier Namur","doi":"10.1016/j.chemgeo.2025.122777","DOIUrl":"10.1016/j.chemgeo.2025.122777","url":null,"abstract":"<div><div>The geochemical data provided by the NASA MESSENGER spacecraft unveiled the geochemical heterogeneity of the volcanic crust of Mercury. Surprisingly, a high amount of sulfur was detected which combined with a low iron content, imply highly reduced conditions of parental magmas. Several variables (temperature, pressure, oxygen fugacity <em>f</em>O₂, and to a lesser extent, melt composition) affect the solubility of sulfur in silicate melts. In reduced silicate melts, sulfur has an oxidation state of S²⁻ and replaces anionic oxygen to form MgS and CaS complexes. Experimental studies have shown the high S solubility in silicate melts at low <em>f</em>O₂. As observed with other volatile elements, high S contents in silicate melts can deeply affect their properties such as (1) lowering the liquidus as compared to S-free compositions and (2) changing solid-liquid phase equilibria. In this study, we performed high temperature (1500–1950 °C) and high pressure (1.5–3 GPa) piston-cylinder experiments on Fe-poor compositions relevant to the petrogenesis of Mercury's volcanic crust with the aim of quantifying the effect of sulfur on depressing their liquidus temperature and understanding its role on phase equilibria. Several compositions were prepared to track the stability fields of olivine (high melt Mg/Si ratio) and orthopyroxene (low melt Mg/Si ratio) in both S-saturated melts and S-free melts. A range of reduced conditions were obtained by using different Si/SiO₂ ratios in the mixes. S-saturated experiments show increasing S abundances in the silicate melts (∼ 1–9 wt%) as <em>f</em>O₂ decreases (from IW -2.9 to IW -6.2, IW representing the iron-wüstite thermodynamic equilibrium). Parameterizing our experimental results gives the liquidus depression as a function of the sulfur content in the melt (mol. fraction):<span><span><span><math><mo>∆</mo><msub><mi>T</mi><mi>liq</mi></msub><mfenced><mrow><mo>°</mo><mi>C</mi></mrow></mfenced><mo>=</mo><mo>−</mo><mn>65208.22</mn><mspace></mspace><msubsup><mfenced><mi>S</mi></mfenced><mi>melt</mi><mn>3</mn></msubsup><mo>+</mo><mn>16595.32</mn><mspace></mspace><msubsup><mfenced><mi>S</mi></mfenced><mi>melt</mi><mn>2</mn></msubsup><mo>+</mo><mn>532.31</mn><mspace></mspace><msub><mfenced><mi>S</mi></mfenced><mi>melt</mi></msub></math></span></span></span></div><div>(MSWD = 3.24; SEE = 35 °C)</div><div>The range of sulfur concentration in our experimental melts would cause a liquidus depression of ca. 20–190 °C. Moreover, our experiments illustrate the role of sulfur in promoting the stability field of orthopyroxene over that of olivine which has major implications for the crystallization of the Mercurian magma ocean and the primordial mineralogical stratification of the mantle. In addition, the presence of sulfur lowers the pressure and temperature conditions of the olivine-orthopyroxene cotectic.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122777"},"PeriodicalIF":3.6,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814984","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":"Fe(III)-mediated sediment sequestration of phosphate and humic acid: Timing of inputs regulates environmental processes","authors":"FengTing Wu ,&nbsp;ChunYan Luo ,&nbsp;YueHan Lu ,&nbsp;XueYan Li ,&nbsp;KuanYi Li ,&nbsp;YingXun Du","doi":"10.1016/j.chemgeo.2025.122778","DOIUrl":"10.1016/j.chemgeo.2025.122778","url":null,"abstract":"<div><div>The co-precipitation of dissolved organic matter (DOM) and phosphate with Fe(III) at the sediment-water interface plays a crucial role in the biogeochemical cycling of organic carbon (OC) and phosphate (P) in aquatic ecosystems. The fluxes of organic matter and phosphate may occur in a sequential manner. This study investigated how phosphate affected pre-equilibrated Fe(III)-humic acid (HA) co-precipitates and how HA influenced pre-equilibrated Fe(III)-phosphate co-precipitates under varying pH and Fe(III) concentrations. The results revealed that the addition of phosphate to the Fe-HA co-precipitation system generally promoted further precipitation of dissolved Fe(III) with phosphate, resulting in about 9.48–33.15 % of the phosphate being precipitated. This addition had minimal impact on the percentage of pre-immobilized HA but facilitated the release of high-aromaticity HA from the Fe-HA co-precipitate. Conversely, adding HA to the Fe<img>P co-precipitation system increased the concentrations of soluble Fe(III) and phosphate, likely due to the strong complexation ability of HA with Fe(III). The percentage of HA remaining dissolved was lower at lower pH levels and higher initial Fe(III) concentrations. These findings highlight how the timing of phosphate or DOM inputs influences their sequestration. This has important implications for carbon and nutrient storage in aquatic sediments, where fluxes of organic carbon and phosphate may occur in a sequential manner.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122778"},"PeriodicalIF":3.6,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143807163","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":"Source-sink process of reactive iron in shelf sediments controlled by Holocene depositional environments and redox states: Insight from the Central Yellow Sea Mud","authors":"Yu Gu ,&nbsp;Xiting Liu ,&nbsp;Qiao Liu ,&nbsp;Fanxing Kong ,&nbsp;Kai Lan ,&nbsp;Xin Chang ,&nbsp;Mingyu Zhang ,&nbsp;Guangchao Zhuang ,&nbsp;Houjie Wang","doi":"10.1016/j.chemgeo.2025.122780","DOIUrl":"10.1016/j.chemgeo.2025.122780","url":null,"abstract":"<div><div>Iron in shelf sediments is crucial in the marine iron cycle, significantly impacting the global C-S-Fe biogeochemical cycles. However, its fate in shelf sediments remains unclear. This study focuses on sediment core YSCW-1 from the Central Yellow Sea Mud, utilizing sediment grain size, redox-sensitive elements U and Mo, and iron speciation to explore the control mechanisms of redox states and sedimentary environments on highly reactive iron since the Holocene. Sediments in core YSCW-1 can be classified into U1, U2, U3, and U4 units based on lithology, grain size, and geochemical characteristics. The results indicate that iron in the Central Yellow Sea Mud is relatively enriched in the mud-depocenter, occurring in fine-grained terrestrial sediments derived from continental chemical weathering, but its fate varies among different units. In U1 (9.3–9.0 ka), iron was mainly sourced from the Yellow River, deposited under oxic–suboxic conditions with pyrite iron as the dominant reactive iron speciation. In U2 (9.0–7.3 ka), an estuarine environment with low salinity and oxidizing conditions contributed to the increase of carbonate iron. In U3 (7.3–3.1 ka), the establishment of modern circulation in the Yellow Sea led to the dominance of Yangtze River-derived sediments, and the stable, low-energy environment promoted the prevalence of pyrite iron. U4 was deposited under oxic–suboxic conditions, with the iron dissimilatory reduction being the dominant process of organic matter mineralization, resulting in a decline in pyrite iron and an increase in magnetic iron. Our findings suggest that sedimentary environments and redox states jointly control the process of iron speciation on the continental shelf.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122780"},"PeriodicalIF":3.6,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143800377","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":"Attenuation of pollution risks in sulfidic lead‑zinc tailings through accelerating weathering of sulfides by indigenous Acidithiobacillus consortia","authors":"Yunjia Liu ,&nbsp;Songlin Wu ,&nbsp;Fang You ,&nbsp;Narottam Saha ,&nbsp;Ting-Shan Chan ,&nbsp;Longbin Huang","doi":"10.1016/j.chemgeo.2025.122765","DOIUrl":"10.1016/j.chemgeo.2025.122765","url":null,"abstract":"<div><div>The long-lasting pollution risks from sulfidic and metalliferous tailings are caused by the unpredictable weathering of unstable sulfidic minerals and associated release of potentially toxic soluble metals. The present study aims to investigate whether indigenous <em>Acidithiobacillus</em> consortia containing ferrous iron (Fe) and sulfide (S) oxidizing bacteria could be harnessed to accelerate the weathering of sulfidic minerals (e.g., pyrite, galena) in lead (Pb)‑zinc (Zn) tailings for rapidly attenuating the risks of toxic metal contamination. After a 72-day incubation of the tailings bioaugmented with indigenous Fe oxidizing bacteria (FeOB), sulfur oxidizing bacteria (SOB) and their combination (FeSOB), it was found that sulfidic minerals were significantly weathered to form secondary mineral cements and develop cementation structure. The combined indigenous FeSOB groups exhibited greater functional advantages over the individual groups. According to the synchrotron-based X-ray fluorescence microscopy coupled with X-ray absorption near edge fine structure spectroscopy (XFM-XANES) analysis, the mineral cements were largely composed of secondary Fe oxyhydroxides and jarosite which captured metals (such as Zn) released from the weathered minerals. Furthermore, the in situ formation of cementation structure passivated and encapsulated remnant sulfide particles, presenting a physical barrier against further weathering and toxic metal release. The study has revealed the critical role of indigenous FeSOB in sulfidic mineral weathering and toxic metal immobilization in Pb-Zn tailings, providing important basis for developing in situ field-based technologies towards pollution control of sulfidic and metalliferous tailings.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122765"},"PeriodicalIF":3.6,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143800378","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":"Effects of sulfite on oxidation and immobilization of arsenite during troilite oxygenation: A mechanistic study","authors":"Xianghao Zha ,&nbsp;Guangxia Liu ,&nbsp;Ning Chen ,&nbsp;Yu Zeng ,&nbsp;Juan Wang ,&nbsp;Ziyan Yang ,&nbsp;Huan Tang ,&nbsp;Guodong Fang","doi":"10.1016/j.chemgeo.2025.122779","DOIUrl":"10.1016/j.chemgeo.2025.122779","url":null,"abstract":"<div><div>The iron and sulfur species play key roles in the transformation and immobilization of heavy metals (e.g., As(III)) in soil environments, while the underlying mechanism of these processes was not fully explored. In this study, the effects of sulfite (an important intermediate of sulfur species) on As(III) transformation induced by troilite (FeS) were investigated. Results showed that the presence of sulfite not only greatly enhanced As(III) oxidation by FeS, with <em>k</em>_obs increased by approximated 30 times, but also significantly increased the As(III) immobilization on FeS surface. Further analysis reveal that sulfate radicals (SO₄^•−) and hydroxyl radicals (^•OH), derived from the redox reactions of surface Fe(II)/Fe²⁺ with sulfite, were the main contributors to As(III) oxidation. In addition, As(III) oxidation was significantly enhanced in the sulfite/FeS system over a wide pH range, and oxygen was a prerequisite for the generation of free radicals. Besides, the dissolved As can be efficiently immobilized on FeS surface through co-precipitation with amorphous Fe(OH)₃ phases, which was negligibly affected by the presence of anions and organic matters. This study provides new insights into the mechanism by which sulfur species drive the transformation and immobilization of As(III) during oxygenation of iron-sulfide minerals.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122779"},"PeriodicalIF":3.6,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143808034","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":"Astronomically forcing hydrological controls on salinity variations during the late Ordovician-early Silurian in the Upper Yangtze area: Responses to the monsoon climate and HICE","authors":"Min Xiong ,&nbsp;Lei Chen ,&nbsp;Chongjie Liao ,&nbsp;Xin Chen ,&nbsp;Xiucheng Tan ,&nbsp;Jian Cao ,&nbsp;Shuaicai Wu ,&nbsp;Hexing Qin ,&nbsp;Zuyou Zhang ,&nbsp;Gaoxiang Wang ,&nbsp;Dazhong Li ,&nbsp;Jiaxun Lu","doi":"10.1016/j.chemgeo.2025.122772","DOIUrl":"10.1016/j.chemgeo.2025.122772","url":null,"abstract":"<div><div>Salinity, a key indicator of watermass conditions, is crucial for understanding the interactions between watermass conditions and climate change. This study presents novel insights into the paleosalinity variations with astronomically forced hydrological changes in Late Ordovician - Early Silurian marine shales of the Upper Yangtze area, based on high-resolution cyclostratigraphic analysis of the gamma-ray (GR) series. Watermass conditions proxies and organic carbon isotope (δ¹³C_org) are significantly in-phase variations with ∼405 kyr long eccentricity cycles. The astronomically forced climate controls the hydrological conditions by modulating the expansion and shrinkage of ice sheet, resulting in lower paleosalinity in interglacial interval than glacial interval. Specifically, during the eccentricity maxima, increased monsoon precipitation established a positive feedback mechanism between continental runoff and marine water, significantly decreasing salinity. The Kwangsian Orogeny induced tectonic-sedimentary patterns created substantial spatial heterogeneity in salinity distribution across different sedimentary centers. Furthermore, we focused on the Hirnantian Isotopic Curve Excursion (HICE) event during the Ordovician – Silurian (O-S) transition, identified by minimum GR, TOC values, positive excursions in δ¹³C_org with organic–lean shale. Hence, under the regional tectonic-sedimentary setting, the astronomically forcing monsoon system, sea level fluctuations and the dynamic changes in glacier have been the decisive factors for the salinity variations. This study advances our understanding of orbital-scale climate forcing influences salinity dynamics in a restricted marine basin, providing new insights for paleoenvironmental reconstruction in deep-time sedimentary systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122772"},"PeriodicalIF":3.6,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143807165","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":"Sedimentation rates control trace element composition of sedimentary phosphorites: Anomalously low uranium and cadmium levels in Paleozoic shelly phosphorites from the Baltica Paleobasin","authors":"Kaarel Lumiste ,&nbsp;Johannes Vind ,&nbsp;Kairi Põldsaar ,&nbsp;Lauri Joosu ,&nbsp;Elina Kuusma ,&nbsp;Päärn Paiste ,&nbsp;Kalle Kirsimäe","doi":"10.1016/j.chemgeo.2025.122776","DOIUrl":"10.1016/j.chemgeo.2025.122776","url":null,"abstract":"<div><div>Phosphorites – made up of chemically precipitated authigenic apatite or composed of bioapatitic fossil remains – become enriched in a variety of trace elements such as Rare Earth Elements (REE), Cd, and U during diagenesis. The Cambrian-Ordovician phosphorites of the Baltica Paleobasin that are almost exclusively made up of fossilized remains of phosphatic brachiopod shells are, however, exceptional in this regard, showing abnormally low levels of trace elements. In this study, we examined the depositional environment and the trace elemental composition of the Baltic Paleobasin shelly phosphorites. We show that hydrodynamic conditions during deposition exert control on the trace elemental composition of shelly phosphorites. A combination of high sedimentation rates, redox conditions, and the biogenic origin of the shells led to the depletion of bio-toxic Cd and U relative to other similar phosphorite deposits. Similarly, the concentrations of REE are below the global phosphorites average; however, the shelly phosphorites show a higher degree of Middle Rare Earth Element (MREE) enrichment. These findings have further implications for exploration — phosphorites that contain abundant bioapatite and/or were deposited in areas with high sedimentation rates and oxic conditions are likely less enriched in trace elements.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122776"},"PeriodicalIF":3.6,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143815600","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":"Origins of rodingite-forming fluids from the seafloor to exhumed terranes: Insights from calcium, strontium, and oxygen isotopes","authors":"E. Hostettler ,&nbsp;J.D. Barnes ,&nbsp;J.C. Lassiter ,&nbsp;B. Dragovic ,&nbsp;A. Satkoski","doi":"10.1016/j.chemgeo.2025.122775","DOIUrl":"10.1016/j.chemgeo.2025.122775","url":null,"abstract":"<div><div>Rodingites are metasomatic Ca-rich, Si-poor rocks typically formed on the seafloor during interaction of a gabbroic dike with seawater. However, rodingites are also common in exhumed metamorphic terranes, in which their formation and tectonic history are more complex. Here we measure the O, Ca, and Sr isotope compositions of seafloor and Alpine rodingites from various tectonic settings (obducted oceanic lithosphere, subducted oceanic lithosphere, fossil rifted margins). We focus on andradite-grossular garnet, one of the first phases to crystallize during rodingitization, and clinopyroxene to discern the origins of rodingite-forming fluids and thus the tectonic setting of rodingitization. δ^44/40Ca values of plagioclase (pl), clinopyroxene (cpx), and calculated whole rock (WR) from altered gabbro (i.e., rodingite protoliths) from the Mid-Atlantic Ridge span a range of ∼0.2 ‰ (1.24 to 1.40 ‰ for pl, <em>n</em> = 2; 1.30 ‰ for cpx, <em>n</em> = 1; 1.29 ‰ for WR, n = 1), whereas, garnet (grt), cpx, and WR from the Western and Central Alpine rodingites span ∼2.8 ‰ (0.01 to 2.52 ‰ for grt, <em>n</em> = 9; −0.32 to 1.58 ‰ for cpx, n = 9; −0.22 to 1.92 ‰ for WR, n = 9). ⁸⁷Sr/⁸⁶Sr ratios of mineral separates from the seafloor span from 0.702606 to 0.703700 (0.703516 to 0.703700 for pl, <em>n</em> = 2; 0.702606 for cpx, <em>n</em> = 1) and 0.70330 to 0.710559 for Alpines rodingites (0.704756 to 0.710559 for grt, <em>n</em> = 9; 0.70330 to 0.707080 cpx, n = 9). Lastly, δ¹⁸O values span ∼1.6 ‰ for the seafloor (5.7 to 6.4 ‰ for pl, <em>n</em> = 2; 4.8 ‰ for cpx. n = 2) and ∼ 6.4 ‰ for Alpine rodingites (−0.4 to 4.5 ‰ for grt, <em>n</em> = 9; 1.7 to 6.0 ‰ for cpx, <em>n</em> = 8). Isotope mass balance modeling shows that these data are overall consistent with rodingitization of a gabbroic dike via seawater on the seafloor and subsequent recrystallization with limited isotopic modification during subduction. A few Alpine rodingites with distinctly high or low δ^44/40Ca values compared to mantle values (e.g., δ^44/40Ca_WR = 1.92 ‰ at Erro-Tobbio and δ^44/40Ca_WR = −0.22 ‰ at Lago di Cigana) cannot be explained via metasomatism by seawater using the model presented here, requiring either evolution of the fluid source during rodingitization and associated serpentinization and/or Ca isotope disequilibrium.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122775"},"PeriodicalIF":3.6,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143807162","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}