Geochimica et Cosmochimica Acta最新文献_第8页

Apatite as a tool to quantify the volatile budget of felsic magma reservoirs 磷灰石作为量化长英质岩浆储层挥发收支的工具

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-27 DOI: 10.1016/j.gca.2025.12.054

Thomas Grocolas , Othmar Müntener

The presence of dissolved and exsolved volatiles in silicate melt plays a key role in magma differentiation by controlling their chemical and physical properties. Volatile concentrations in the melt are commonly determined from glass inclusions; however, these may have undergone post-entrapment modification or may be absent in the studied rocks. Alternatively, volatile-bearing minerals such as biotite, amphibole, and apatite offer a valuable means to reconstruct the volatile history of their parental melt. Here we investigate the volatile evolution of differentiating magmas from emplacement to interstitial melt extraction within the Western Adamello tonalite (WAT) and Re di Castello (RdC) units of the Adamello batholith (Italy), both displaying local crystal accumulation and melt segregation features. Apatite is a ubiquitous phase and exhibits a compositional trend of decreasing F, Cl and S with increasing Eu negative anomaly, the latter used here as a differentiation proxy. In both localities, apatite dominantly has low CO₂ contents (<300 μg/g), whereas S abundances are one order of magnitude higher in the RdC (600–2,000 μg/g) compared to the WAT (40–300 μg/g). In addition, some apatite cores are enriched in CO₂ (>1,000 μg/g). Variable F–Cl partitioning between apatite and its host biotite, along with the preservation of volatile zoning in apatite related to the pluton’s cooling history, suggests that volatiles in apatite did not fully re-equilibrate. Equilibrium melt volatile contents were calculated and show a consistent Cl decrease (∼500–50 μg/g) during differentiation, indicative of fluid saturation. Melt H₂O and CO₂ contents, coupled with saturation curves, were used to retrieve crystallisation pressures of ∼200–300 MPa for low-CO₂ apatite, and ∼400–700 MPa for CO₂-rich apatite, in good agreement with pressure estimates based on phase petrology and chemistry. Degassing fluid fluxes were computed by combining the calculated equilibrium fluid composition with available high-precision U–Pb zircon ages, revealing values 2 to 5 orders of magnitude lower than those of active volcanic systems, probably reflecting contrasting magma fluxes. Nevertheless, such low-density fluids, together with episodic magma recharge, likely promoted melt segregation and extraction. These results highlight apatite as a powerful proxy for evaluating the fluid saturation level of magmas, tracking the volatile budget of crystallising magma reservoirs, and reconstructing the architecture of transcrustal magmatic systems.

硅酸盐熔体中溶解和外露挥发物的存在通过控制其化学和物理性质在岩浆分异中起关键作用。熔体中的挥发性浓度通常由玻璃夹杂物测定；然而，这些可能经历了圈闭后的改造，或者可能在研究的岩石中不存在。另外，含挥发性矿物，如黑云母、角闪洞和磷灰石，为重建其母体熔体的挥发历史提供了有价值的方法。本文研究了意大利阿达梅洛基底西阿达梅洛（WAT）和Re di Castello （RdC）单元中分异岩浆从侵位到间隙熔体萃取的挥发演化过程，均表现出局部晶体聚集和熔体分离的特征。磷灰石是一种普遍存在的相，其组成呈F、Cl、S递减的趋势，而Eu负异常呈增加的趋势，本文以Eu负异常作为分异标志。在这两个地区，磷灰石主要具有低CO2含量（<300 μg/g），而在RdC中S丰度（600 - 2000 μg/g）比WAT （40-300 μg/g）高一个数量级。此外，部分磷灰石岩心富含CO2 （> 1000 μg/g）。磷灰石和寄主黑云母之间的F-Cl分配变化，以及与岩体冷却历史有关的磷灰石中挥发性分带的保存，表明磷灰石中的挥发物并未完全重新平衡。计算平衡熔体挥发物含量，发现在分化过程中Cl持续下降（~ 500-50 μg/g），表明流体饱和度较高。熔体H2O和CO2含量与饱和度曲线相结合，获得了低CO2磷灰石的结晶压力为~ 200-300 MPa，富CO2磷灰石的结晶压力为~ 400-700 MPa，与基于相岩石学和化学的压力估计非常吻合。将计算出的平衡流体组成与现有的高精度U-Pb锆石年龄相结合，计算出脱气流体通量，其值比活火山系统的值低2 ~ 5个数量级，可能反映了岩浆通量的对比。然而，这种低密度的流体，加上间歇性的岩浆补给，很可能促进了熔体的分离和提取。这些结果强调了磷灰石作为评估岩浆流体饱和度水平、跟踪结晶岩浆储层的挥发收支、重建跨地壳岩浆体系结构的有力代理。

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引用次数: 0

Late Cretaceous cerium anomalies and globally distinctive redox responses before, during and after Oceanic Anoxic Event 2 晚白垩世铈异常与海洋缺氧事件2前后全球独特的氧化还原反应

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-26 DOI: 10.1016/j.gca.2025.12.022

Cheng Cao, Xiao-Ming Liu, Jeremy D. Owens, Hugh C. Jenkyns

引用次数: 0

Microbial and abiotic approaches to carbonating stevensite: what works and what doesn’t 微生物和非生物方法碳酸化史蒂文site：什么有效，什么无效

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-24 DOI: 10.1016/j.gca.2025.12.052

Maria L. Arizaleta , Maija J. Raudsepp , Nina Zeyen , Janice P.L. Kenney , Katherine N. Snihur , Daniel S. Alessi , Sasha Wilson

Although Mg-rich clays are common in sediments, rocks and mineral wastes produced by mining, little is known about how they might contribute to carbon dioxide (CO₂) sequestration. The purpose of this study is to use previously tested mineral carbonation techniques at ambient temperature and pressure on the low-temperature Mg-rich clay mineral, stevensite [(Na₂_y·nH2O)(Mg_3–_y X_y)Si₄O₁₀(OH)₂]. This study tests the hypothesis that authigenic 2:1 Mg-clays, while less reactive to CO₂ than other Mg-rich minerals (e.g., brucite and serpentines), can transform into carbonates under high alkalinity conditions (100–1187 mEq/L, pH = 9–11). Abiotic experiments using either CO_2(g) bubbling or addition of HCl into alkaline lake water and deionized water followed by addition of NaOH to induce a pH swing did not result in carbonation of synthetic stevensite.

However, the abiotic experiments gave important insights into the role of silicate dissolution for alkalinity generation and carbon sequestration. Incubation of a natural biofilm with stevensite in highly alkaline lake water resulted in precipitation of the hydrated magnesium carbonate mineral, dypingite [Mg₅(CO₃)₄(OH)₂·∼5H2O], on the surface of synthetic stevensite as observed with X-ray diffraction and scanning electron microscopy. A Mg-rich clay phase was also precipitated in an incubation experiment containing biofilm but without the addition of synthetic stevensite. These results provide important insights and observations that can contribute towards geochemical models of environments where we observe carbonation of clay minerals, such as alkaline lakes, which can serve as natural analogues for industrial carbon sequestration projects.

虽然富含镁的粘土在沉积物、岩石和采矿产生的矿物废物中很常见，但人们对它们如何促进二氧化碳（CO2）封存知之甚少。本研究的目的是利用之前测试过的矿物碳酸化技术，在常温常压下对低温富镁粘土矿物史蒂文site [(Na2y·nH2O)(Mg3-y Xy)Si4O10(OH)2]进行碳酸化处理。本研究验证了自生2:1 mg -clay在高碱度条件下（100-1187 mEq/L, pH = 9-11）可转化为碳酸盐的假设，尽管其对CO2的反应性低于其他富镁矿物（如水镁石和蛇纹石）。采用CO2(g)鼓泡或向碱性湖水和去离子水中加入HCl，然后加入NaOH诱导pH值波动的非生物实验均未导致合成斯蒂夫尼酯的碳酸化。然而，非生物实验对硅酸盐溶解在碱度生成和碳固存中的作用提供了重要的见解。用x射线衍射和扫描电子显微镜观察到，天然生物膜在高碱性湖水中与斯蒂夫site孵养后，在合成斯蒂夫site表面析出水合碳酸镁矿物——重云母[Mg5(CO3)4(OH)2·~ 5H2O]。在含生物膜的孵育实验中，在不添加合成史蒂文site的情况下，还沉淀出了富镁粘土相。这些结果提供了重要的见解和观察结果，有助于建立环境的地球化学模型，在这些模型中，我们观察到粘土矿物的碳化作用，例如碱性湖泊，可以作为工业碳封存项目的天然类似物。

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引用次数: 0

Anhydrous lithic clasts in four CM2 carbonaceous chondrites derived from a thermally metamorphosed planetesimal with CM and CY affinities 四颗CM2碳质球粒陨石的无水岩屑碎屑来源于具有CM和CY亲缘关系的热变质星子

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-23 DOI: 10.1016/j.gca.2025.12.051

Martin R. Lee , Sammy Griffin , Ross Findlay , Xuchao Zhao , Ian A. Franchi

The CM2 meteorites Grove Mountains (GRV) 021536, Murchison, and Shidian, contain anhydrous lithic clasts that have been interpreted as fragments of a planetesimal linked to CM or CV group carbonaceous chondrites. Here we describe 57 lithic clasts in Cold Bokkeveld (CM2) that are strikingly similar to those in the other three CMs in their petrography, mineralogy, and chemical and isotopic compositions. The Cold Bokkeveld clasts are dominated by equilibrated olivine, with subordinate plagioclase feldspar (andesine), clinopyroxene (diopside), nepheline, a spinel-group oxide (ferrian chromite), pentlandite, pyrrhotite, troilite and merrillite. Their bulk chemical composition is chondritic, and olivine oxygen isotope values span a wide range, from δ¹⁸O 3.6 ‰ Δ¹⁷O −3.9 ‰ to δ¹⁸O 20.3 ‰ Δ¹⁷O 1.1 ‰. Two clusters of clasts can potentially be distinguished from the chemical composition of their olivine: Fa₃₈ and Fa₄₁. The Fa₃₈ cluster includes most of Cold Bokkeveld’s clasts and is close in chemical composition to those described from GRV 021526 and Murchison. The Fa₄₁ cluster is represented by the largest Cold Bokkeveld clast, and its olivine is compositionally comparable to that in Shidian. Anhydrous lithic clasts that occur in all four of the CM meteorites are likely to have been derived from a large planetesimal with CM and CY affinities that had undergone thermal metamorphism and metasomatism. The CV3 breccias Mokoia and Yamato 86009 contain anhydrous lithic clasts that are close in mineralogy and oxygen isotopic composition to those in the four CMs and so are likely to have been sourced from the same carbonaceous planetesimal or one with a similar geological history. The oxygen isotopic compositions of olivine in clasts from GRV 021536, Murchison, Shidian, Cold Bokkeveld, Mokoia and Yamato 86009 plot on a shared trendline in 3-oxygen isotope space that connects the CV-CK-CO, CM, and CY fields thus suggesting genetic or evolutionary links between the five carbonaceous chondrite groups. The occurrence of these distinctive clasts in four CM2 meteorites could indicate that their parent body was the same rubble pile asteroid that had been built from aqueously altered and thermally metamorphosed lithologies.

Grove Mountains (GRV) 021536、Murchison和Shidian的CM2陨石含有无水岩屑碎屑，这些碎屑被解释为与CM或CV组碳质球粒陨石相关的小行星碎片。在这里，我们描述了冷Bokkeveld （CM2）的57个岩屑碎屑，它们在岩石学，矿物学，化学和同位素组成方面与其他三个cm中的岩石碎屑惊人地相似。冷Bokkeveld碎屑以平衡橄榄石为主，次为斜长石（安长石）、斜辉石（透辉石）、霞石、尖晶石群氧化物（铁铬铁矿）、镍黄铁矿、磁黄铁矿、三黄石和美银石。其整体化学成分为球粒质，δ18O 3.6‰Δ17O−3.9‰~ δ18O 20.3‰Δ17O 1.1‰，氧同位素值变化范围广。从其橄榄石的化学成分可以潜在地区分出两组碎屑：Fa38和Fa41。Fa38星团包含了Cold Bokkeveld的大部分碎屑，其化学成分与GRV 021526和Murchison描述的相似。Fa41星团以最大的Cold Bokkeveld碎屑为代表，其橄榄石组成与石甸相当。四颗CM陨石中的无水岩屑可能来源于一颗具有CM和CY亲和力的大型星子，该星子经历了热变质和交代作用。CV3角砾岩Mokoia和Yamato 86009含无水岩屑，其矿物学和氧同位素组成与4个cm中的角砾岩接近，因此可能来自同一碳质星子或具有相似地质历史的星子。GRV 021536、Murchison、Shidian、Cold Bokkeveld、Mokoia和Yamato 86009碎屑中橄榄石的氧同位素组成在连接CV-CK-CO、CM和CY场的3-氧同位素空间中具有共同的趋势线，表明5个碳质球粒陨石群之间存在遗传或进化联系。在四颗CM2陨石中出现的这些独特的碎屑可能表明，它们的母体是同一颗碎石堆小行星，由水蚀和热变质的岩性形成。

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引用次数: 0

Towards stable chemical fossils for anaerobic ammonium-oxidizing bacteria in palaeoenvironmental studies: novel cyclic aliphatic hydrocarbons as potential dia- and catagenetic products of ladderane lipids 古环境研究中厌氧氨氧化细菌的稳定化学化石：新型环脂肪烃作为阶梯烷类脂质的潜在促生和促生产物

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-23 DOI: 10.1016/j.gca.2025.12.040

Darci Rush, Jan H. van Maarseveen, Jan A.J. Geenevasen, Erik Tegelaar, Jos Pureveen, Roel Klein Nijenhuis, Nick Westerveld, Md Mahbubul Islam, Adri C.T. van Duin, Stefan Schouten, Jaap S. Sinninghe Damsté

引用次数: 0

Quantifying contributions of iron (oxyhydr)oxides and organic matter to chromium dynamics in paddy soils 水稻土中铁（氧）氧化物和有机物对铬动态的定量贡献

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-23 DOI: 10.1016/j.gca.2025.12.050

Guojun Chen , Yang Yang , Ke Zhang , Yan Ru , Zebin Hong , Xiaomin Li , Taicheng An , Pei Wang , Songxiong Zhong , Qi Wang , Shiwen Hu , Fangbai Li , Tongxu Liu

Basalt-derived paddy soils contain high concentrations of chromium (Cr) from basalt weathering. Considering the potential risks of available Cr to human health, the transformation of Cr in basalt-derived paddy soils has attracted worldwide attention. However, the mechanisms controlling the biogeochemical cycling of Cr in these soils remain unclear. Here, pot experiments were performed to investigate Cr migration and transformation throughout the flooding–drainage cycle. The dynamic changes in soil chemical (e.g., dissolved organic carbon (DOC), iron (Fe) (oxyhydr)oxides, sulfate, and nitrogen (N) species) and physical properties (e.g., UV–vis spectra, pore size distribution, and surface site concentrations) were investigated. The available Cr increased during flooding and decreased during drainage. Cr concentrations in rice grains exceeded the safety threshold, indicating high Cr availability in these soils and the associated risk to human health. A kinetic model was developed to unravel the key factors controlling Cr transformation. During flooding, the mobilization of the available Cr was primarily driven by Fe (oxyhydr)oxides (76.4%), with a smaller contribution from organic matter (OM) (23.6%). During drainage, the sequestration of the available Cr was similarly dominated by Fe (oxyhydr)oxides (76.6%), followed by OM (23.4%). Furthermore, within the Fe (oxyhydr)oxides, metastable Fe phases played a predominant role in the available Cr immobilization (accounting for 91.6% of the total Fe contribution), while stable Fe phases contributed the remaining 8.4%. These insights are vital for understanding Cr mobility and availability in paddy soils with a high geological background.

玄武岩衍生的水稻土含有高浓度的铬（Cr），来自玄武岩风化。考虑到有效态铬对人体健康的潜在风险，玄武岩水稻土中铬的转化受到了世界各国的关注。然而，控制土壤中铬的生物地球化学循环的机制尚不清楚。通过盆栽试验研究了Cr在整个洪-排水循环中的迁移和转化。研究了土壤化学（如溶解有机碳（DOC）、氧化铁（Fe）、硫酸盐和氮(N)种）和物理性质（如紫外可见光谱、孔径分布和表面位点浓度）的动态变化。有效铬在淹水过程中增加，在疏水过程中减少。稻米中的铬浓度超过安全阈值，表明这些土壤中的铬含量很高，并对人类健康构成相关风险。建立了动力学模型，揭示了控制Cr相变的关键因素。在驱油过程中，有效铬的动员主要是由铁（氧）氧化物（76.4%）驱动的，有机质（23.6%）的贡献较小。在排水过程中，有效铬的固存同样以铁（氧）氧化物为主（76.6%），其次是OM（23.4%）。此外，在Fe（氧合）氧化物中，亚稳Fe相在有效的Cr固定中起主导作用（占总Fe贡献的91.6%），而稳定Fe相贡献了剩余的8.4%。这些见解对于了解高地质背景下水稻土中铬的迁移性和有效性至关重要。

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引用次数: 0

Sedimentary thallium isotopes as a proxy for reconstructing global oceanic oxygenation during millennial-scale events 沉积铊同位素作为千年尺度事件中重建全球海洋氧合的代理

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-22 DOI: 10.1016/j.gca.2025.12.049

Fang Qian, Yi Wang, Kassandra M. Costa, Sune G. Nielsen

The thallium isotopic composition (ε 205Tl) of seawater is a promising proxy for global oceanic redox conditions due to its strong association with manganese oxide burial. Previous studies have linked ε205Tl variability to global oceanic oxygen during the last deglaciation, but these reconstructions were limited to a single core from the Arabian Sea oxygen minimum zone, leaving uncertainties about the proxy’s broader spatial applicability. Here, we present a new sedimentary ε 205Tl record from ODP Site 1017E in the Southern California Margin oxygen minimum zone spanning the past 32 ka. The ε 205Tl record suggests that global oxygen content was lower during the Last Glacial Maximum (∼23–19 ka) relative to the Holocene, with oxygenation during the Heinrich Stadial 1 (∼18–14.7 ka) and the Younger Dryas (∼12.9–11.7 ka), and deoxygenation during the Bølling-Allerød (∼14.7–12.9 ka). These trends mirror ε 205Tl records from the Arabian Sea, reinforcing the robustness of Tl isotopes as a global ocean oxygen proxy. We further investigate how the Mn cycle modulates transient ε 205Tl variability during the last deglaciation. The results show that short-lived changes in Mn oxide burial, driven by oxygen fluctuations, disrupt steady-state Tl cycling and produce millennial-scale ε 205Tl variations. By connecting the Mn and Tl cycle, we present a semi-quantitative model of mean oceanic oxygen content over the last deglaciation highlighting the potential of ε 205Tl as a paleo-oxygen proxy. However, an improved understanding of the marine Mn budget and its response to glacial-interglacial cycles is required before true quantitative reconstructions of average ocean oxygen contents with Tl isotopes are possible

海水中的铊同位素组成（ε 205Tl）与锰氧化物埋藏密切相关，因此有望作为全球海洋氧化还原条件的代表。先前的研究将ε205Tl变化与末次冰消期全球海洋氧联系起来，但这些重建仅限于来自阿拉伯海氧最小带的单个岩心，因此对代理的更广泛的空间适用性存在不确定性。在这里，我们提出了一个新的沉积ε 205Tl记录，来自南加州边缘ODP站点1017E，跨越了过去32 ka的氧最小带。ε 205Tl记录表明，末次盛冰期（~ 23-19 ka）全球氧含量相对于全新世较低，在Heinrich Stadial 1（~ 18-14.7 ka）和新仙女木期（~ 12.9-11.7 ka）发生充氧，在b ølling- allero ød（~ 14.7-12.9 ka）发生脱氧。这些趋势反映了来自阿拉伯海的ε 205Tl记录，加强了Tl同位素作为全球海洋氧代用物的可靠性。我们进一步研究了Mn周期如何调节末次消冰期间的瞬态ε 205Tl变率。结果表明，在氧波动的驱动下，Mn氧化物埋藏的短暂变化破坏了稳态Tl循环，并产生了千禧年尺度的ε 205Tl变化。通过连接Mn和Tl旋回，我们提出了最后一次消冰期平均海洋氧含量的半定量模型，突出了ε 205Tl作为古氧代用物的潜力。然而，在用Tl同位素真正定量重建海洋平均氧含量之前，需要对海洋Mn收支及其对冰期-间冰期旋回的响应有更好的了解

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引用次数: 0

Lithological influence on Li isotope fractionation during silicate weathering 硅酸盐风化过程中岩性对锂同位素分馏的影响

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-22 DOI: 10.1016/j.gca.2025.12.043

Chris T.L. Cheung , Brian Beaty , Kohen W. Bauer , Cody L. Colleps , Dan Asael , Sean A. Crowe , Noah J. Planavsky , Paul S. Savage , N. Ryan McKenzie

The influences of bedrock lithological composition on weathering fluxes, including dissolved lithium isotopes (δ⁷Li_diss), in rivers remain unclear. To assess this, we present new elemental, mineralogical, and lithium isotopic data from river localities in Hong Kong that drain either purely silicic volcanic or siliciclastic sedimentary bedrock that were sampled during both the wet (summer) and dry (winter) seasons. Our data show marked geochemical and mineralogical differences in relation to bedrock composition. The silicic volcanic-draining rivers exhibit δ⁷Li_diss values ranging from 8.6‰ to 20.9‰, elevated dissolved alkali metal concentrations, and relatively higher kaolinite abundances, whereas siliciclastic sedimentary-draining rivers yield δ⁷Li_diss values ranging from 3.2‰ to 8.6‰, higher dissolved alkaline-earth metal concentrations, and relatively greater illite abundances. Collectively, the volcanic-draining rivers have higher average δ⁷Li_diss of ∼12.5‰ and higher bedload kaolinite/illite average ratios of 2.4, compared to the siliciclastic sedimentary-draining bedrock rivers that yield average δ⁷Li_diss of 6.0‰ and kaolinite/illite of 0.5. Mechanistically, this could have been driven by the lower abundance of reactive minerals in the siliciclastic bedrock and/or a higher degree of fracturing in the volcanic rocks, which can both increase water–rock interaction times and secondary clay formation, driving higher δ⁷Li_diss values. Seasonal variations were also observed in the Li data, with higher Li concentrations and dissolved δ⁷Li values (up to 8.0‰ heavier) measured during the dry winter season. This is attributed to lower river discharges in the dry season, enabling longer residence times for clay formation, and higher riverine δ⁷Li values. Higher major, alkali, and alkaline-earth concentrations were also measured during the dry season, with Group 3, transition metals, and rare earth elements more concentrated in the wet season, reflecting the impact of elemental mobility. Overall, our study highlights the influence of both bedrock lithology and regional weather patterns on riverine geochemical signatures within the same tectono-climatic setting. These findings help enhance understanding of the Li cycle, wherein riverine δ⁷Li fluxes to the ocean reflect a combination of lithology, hydrology, and weathering regime, further refining the utility of lithium isotopes for assessing modern and ancient silicate weathering processes on Earth’s surface.

基岩岩性组成对河流风化通量（包括溶解锂同位素δ7Lidiss）的影响尚不清楚。为了评估这一点，我们提出了新的元素、矿物学和锂同位素数据，这些数据来自香港的河流地区，这些河流在湿季（夏季）和干季（冬季）采集了纯硅质火山或硅质碎屑沉积基岩。我们的数据显示，与基岩组成有关的地球化学和矿物学差异明显。硅质火山排水河流的δ7Lidiss值为8.6 ‰~ 20.9 ‰，溶解碱金属浓度升高，高岭石丰度相对较高；硅质碎屑沉积排水河流的δ7Lidiss值为3.2 ‰~ 8.6 ‰，溶解碱土金属浓度较高，伊利石丰度相对较高。总体而言，火山排水河流的平均δ7Lidiss为 ~ 12.5 ‰，层载高岭石/伊利石平均比值为2.4，而硅质排水基岩河流的平均δ7Lidiss为6.0 ‰，高岭石/伊利石平均比值为0.5。从机理上讲，这可能是由于硅质碎屑基岩中活性矿物丰度较低和/或火山岩中压裂程度较高所致，这既增加了水岩相互作用次数，又增加了次生粘土的形成，从而导致δ7Lidiss值较高。Li数据也存在季节变化，在干燥冬季测得较高的Li浓度和溶解δ7Li值（高达8.0 ‰）。这是由于旱季河流流量较低，使得粘土形成的停留时间较长，河流δ7Li值较高。旱季的主要元素、碱土和碱土浓度也较高，雨季的族(3)、过渡金属和稀土元素浓度较高，反映了元素迁移率的影响。总的来说，我们的研究强调了基岩岩性和区域天气模式对同一构造-气候背景下河流地球化学特征的影响。这些发现有助于加强对锂循环的理解，其中河流向海洋的δ7Li通量反映了岩性，水文和风化制度的组合，进一步完善了锂同位素在评估地球表面现代和古代硅酸盐风化过程中的效用。

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引用次数: 0

Constraining conditions for the preservation of oxygen atoms from hydroxyl radicals in the oxidation products 氧化产物中氧原子免受羟基自由基侵害的约束条件

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-21 DOI: 10.1016/j.gca.2025.12.048

Yunsong Zheng , Peng Zhang , Xiuli Li , Songhu Yuan

Oxygen cycling is a fundamental biogeochemical process regulating redox transformations across Earth’s environments, with hydroxyl radicals (•OH) playing a central role as highly reactive oxidants. However, the conditions that govern oxygen atom transfer and preservation in the oxidation products remain poorly constrained. Clarifying these constraints is essential for interpreting oxygen isotope signals in redox-active systems, particularly those involving reactive oxygen species (ROS). Here, we experimentally quantify the oxygen atom exchange kinetics between •OH and H₂O (k_ex ≈ 6.5–8.2 × 10⁴ M⁻¹ s⁻¹), revealing a rapid, pH-independent process governed by water concentration rather than OH⁻ activity. Exchange completes within 0.24 μs in pure water and slows to second scale as the relative humidity decreased to 1 %. Using H₂¹⁸O and representative •OH scavengers including 5,5-dimethyl-1-pyrroline N-oxide (DMPO), phenol and sulfite, we demonstrate that preservation of •OH-derived oxygen occurs only when the radical’s lifetime is shorter than the exchange timescale. This condition can be satisfied when the total first-order rate contribution from all scavengers (∑k_ox[Scavenger]) exceeds ∼4.10 × 10⁸ s⁻¹, typically requiring millimolar concentrations. Moreover, only unsaturated organic compounds and low-valent oxide gases can capture the oxygen from •OH. In water-rich systems, DMPO–OH retains the original •OH oxygen, whereas phenol–OH undergoes progressive exchange during post-reaction storage. These findings define a preservation window governed by reaction timescale, scavenger type, and concentration, under which •OH-derived oxygen can be stably retained in products. Extrapolation to natural environments suggests that such preservation is feasible under low water activity—such as in arid soils, aerosols, mineral surfaces, or Martian regolith—where exchange can be effectively suppressed and scavenger concentrations tend to be locally elevated. Our findings constrain the kinetic and environmental boundaries of oxygen preservation in •OH-based processes, providing a mechanistic basis for refining oxygen isotope tracing in redox transformations across both Earth and planetary settings.

氧循环是调节地球环境氧化还原转化的基本生物地球化学过程，羟基自由基（•OH）作为高活性氧化剂起着核心作用。然而，控制氧化产物中氧原子转移和保存的条件仍然很差。澄清这些限制对于解释氧化还原活性系统中的氧同位素信号至关重要，特别是那些涉及活性氧（ROS）的系统。在这里，我们通过实验量化了•OH和H2O之间的氧原子交换动力学（kex≈6.5-8.2 × 104 M−1 s−1），揭示了一个由水浓度而不是OH−活性控制的快速、不依赖ph的过程。在纯水中，交换在0.24 μs内完成，当相对湿度降至1 %时，交换速度减慢至二级。使用H218O和代表性的•OH清除剂包括5,5-二甲基-1-吡啶n -氧化物（DMPO）、苯酚和亚硫酸盐，我们证明了•OH衍生氧的保存只有在自由基的寿命短于交换时间标度时才会发生。当所有清除剂（∑kox[Scavenger]）的总一级速率贡献超过~ 4.10 × 108 s−1时，通常需要千摩尔浓度，即可满足这一条件。此外，只有不饱和有机化合物和低价氧化气体才能从•OH中捕获氧气。在富水系统中，DMPO-OH保留原始的•OH氧，而苯酚- OH在反应后储存过程中进行渐进式交换。这些发现定义了一个由反应时间尺度、清除剂类型和浓度控制的保存窗口，在此窗口下，•oh衍生的氧可以稳定地保留在产物中。对自然环境的外推表明，这种保存在低水分活动条件下是可行的，例如在干旱土壤、气溶胶、矿物表面或火星风化层中，在这些条件下，交换被抑制，清除剂浓度可能局部升高。我们的研究结果限制了氧基过程中氧保存的动力学和环境边界，为在地球和行星环境下的氧化还原转化中精炼氧同位素示踪提供了机制基础。

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引用次数: 0

Aqueous alteration in the C2-ung Tarda meteorite: in situ isotopic evidence from dolomite and magnetite C2-ung塔尔达陨石的水蚀变：白云岩和磁铁矿的原位同位素证据

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-21 DOI: 10.1016/j.gca.2025.12.046

Bennett J.K. Wilson , Kazuhide Nagashima , Thomas J. Barrett , Veronica E. Di Cecco , Kimberly T. Tait , Michael G. Daly

The Tarda meteorite is a recently recovered C2-ungrouped carbonaceous chondrite that preserves evidence of early Solar System aqueous alteration. Tarda was found to share reflectance spectra with P-type asteroids, possibly enabling these elusive asteroids to be studied in the laboratory for the first time. Furthermore, Tarda has been shown to share many petrological and isotopic affinities with Tagish Lake – a pristine C2-ungrouped chondrite that is widely considered to source a D-type asteroid. Thus Tarda, Tagish Lake, and their respective spectral classes are probably genetically related, and potentially source a shared parent body. Despite their similarities, however, Tagish Lake hosts different lithologies and carbonate species than Tarda, suggesting distinct aqueous alteration histories between the two meteorites. Here, we present in-situ oxygen, carbon, and ⁵³Mn–⁵³Cr isotopic analyses of dolomite and magnetite in Tarda using Secondary Ion Mass Spectrometry to (i) investigate the conditions associated with aqueous alteration on the early Tarda parent body, and to (ii) compare our findings with Tagish Lake to assess heterogeneous aqueous alteration of their unique and likely shared parent body. For dolomite, we found that δ¹³C ranged from 55.8 ‰ to 72.9 ‰, while δ¹⁸O ranged from 23.3 ‰ to 28.8 ‰ with an average Δ¹⁷O of 0.1 ± 1.6. Dolomite additionally contained widespread ⁵³Cr excesses that, if interpreted to have chronological significance, corresponds to a live [(⁵³Mn/⁵⁵Mn)₀] value of (

3.08 \pm 0.52) \times 10^{- 6}

. For magnetite, the δ¹⁸O values ranged from −5.5 ‰ to 5.8 ‰ with an average Δ¹⁷O of 2.4 ‰ ± 1.7. Oxygen isotope thermometry of a co-precipitating dolomite–magnetite pair indicates alteration temperatures of

87_{- 24}^{+ 28}

°C. Compared to carbonates in Tagish Lake, dolomite in Tarda exhibits systematically lower δ¹⁷O, δ¹⁸O, and Δ¹⁷O signatures, but similar δ¹³C signatures. Temporally, the carbonates in both meteorites have identical ages within uncertainty. We conclude that Tarda has experienced greater aqueous alteration than Tagish Lake, likely due to increased water–rock interaction and/or higher temperatures.

塔尔达陨石是最近发现的一颗c2 -未分类的碳质球粒陨石，它保存了早期太阳系水蚀变的证据。Tarda被发现与p型小行星具有相同的反射光谱，这可能使这些难以捉摸的小行星首次在实验室中进行研究。此外，Tarda已被证明与塔吉什湖（Tagish Lake）具有许多岩石学和同位素相似性——塔吉什湖是一个原始的c2 -未分类球粒陨石，被广泛认为是d型小行星的来源。因此，塔尔达、塔吉什湖和它们各自的光谱类可能在遗传上是相关的，并且可能来自一个共同的母体。然而，尽管它们有相似之处，塔吉什湖的岩性和碳酸盐种类却与塔尔达湖不同，这表明两颗陨石之间存在不同的水蚀变历史。本文采用二次离子质谱法对塔尔达白云岩和磁铁矿进行了原位氧、碳和53Mn-53Cr同位素分析，以(i)研究塔尔达早期母体水蚀变的相关条件，（ii）将我们的发现与塔吉什湖进行比较，以评估它们独特的和可能共有的母体的非均质水蚀变。白云岩δ13C值为55.8‰~ 72.9‰，δ18O值为23.3‰~ 28.8‰，平均值Δ17O为0.1±1.6。白云岩还含有广泛的53Cr过量，如果解释为具有时间意义，则对应于活[(53Mn/55Mn)0]值（3.08±0.52）×10-6。磁铁矿δ18O值为−5.5‰~ 5.8‰，平均Δ17O为2.4‰±1.7。共沉淀白云岩-磁铁矿对氧同位素测温表明蚀变温度为87 ~ 24+28℃。与塔吉什湖碳酸盐岩相比，塔吉什湖白云岩δ17O、δ18O和Δ17O特征较低，δ13C特征相似。在时间上，两颗陨石中的碳酸盐在不确定的范围内具有相同的年龄。我们得出结论，塔尔达湖经历了比塔吉什湖更大的水蚀变，可能是由于水岩相互作用的增加和/或更高的温度。

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引用次数: 0