Geochimica et Cosmochimica Acta最新文献

英文中文

Natural foam as promoter of natural organic matter transformations in surface waters 天然泡沫作为地表水天然有机物转化的促进剂

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-17 DOI: 10.1016/j.gca.2025.12.029

Ming Zhang, Jinying Huang, Yucheng Shen, Lijian Zheng, Yujie Zhang, Fang Fang, Jiayuan Liu, Weifeng Qiu, Daoyong Zhang, Xiangliang Pan

引用次数: 0

Oxygen isotope compositions of chondrules in enstatite chondrites: insights from relict olivine, chondrule size and redox state 顽辉石球粒陨石中球粒的氧同位素组成：来自残余橄榄石、球粒大小和氧化还原状态的见解

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-17 DOI: 10.1016/j.gca.2025.12.036

Yves Marrocchi , Laurette Piani , Dorian Thomassin , Emmanuel Jacquet

The recent discovery in ordinary chondrites of a population of small, sub-TFL (i.e., negative Δ¹⁷O; TFL = Terrestrial Fractionation Line) chondrules isotopically similar to relict grains in larger chondrules offered a glimpse into the sub-TFL precursors of inner disk chondrules. This prompts a search for similar relicts and small chondrules in enstatite chondrites (EC; here the EH3 Sahara 97096, Qingzhen, Caleta el Cobre 025, NWA 14425, and the EL3-an NWA 8785). Our SIMS oxygen isotopic analyses reveal that most olivine grains in E3 chondrites are isotopically indistinguishable from enstatite and must have crystallized during the same thermal event. Yet one analyzed chondrule contains relict olivine grains, one isotopically similar to refractory inclusions (a first in EC) and others with Δ¹⁷O values ranging from −9.5 to −7.7 ‰. The latter, and similar discoveries in the literature, must have derived from preexisting chondrules. Small porphyritic chondrules or isolated pyroxene grains tend to be ¹⁶O-enriched (and more reduced), as in ordinary chondrites, but their Δ¹⁷O never goes below –2 ‰. Cryptocrystalline chondrules found in Sahara 97096 do extend to −7.3 ‰, but are olivine-free. This thus provides evidence for sub-TFL reservoirs ancestral to the E reservoir, although more than one may have existed.

最近在普通球粒陨石中发现了一群小的，亚TFL（即负Δ17O； TFL =陆地分异线）的球粒，同位素上与较大球粒中的残余颗粒相似，这为内盘球粒的亚TFL前体提供了一瞥。这促使人们在辉化辉石球粒陨石（EC， EH3 Sahara 97096、Qingzhen、Caleta el Cobre 025、NWA 14425和el3 - and NWA 8785）中寻找类似的遗迹和小球粒。我们的SIMS氧同位素分析显示，E3球粒陨石中的大多数橄榄石颗粒在同位素上与顽辉石难以区分，并且必须在同一热事件中结晶。然而，一个分析的球粒含有残余橄榄石颗粒，一个同位素与难熔包裹体相似（EC中第一次），其他球粒的Δ17O值在−9.5 ~−7.7‰之间。后者，以及文献中类似的发现，一定是源自先前存在的球粒。与普通球粒陨石一样，小的斑状球粒或孤立的辉石颗粒往往富含16o（并且更还原），但它们的Δ17O从不低于-2‰。在撒哈拉97096中发现的隐晶球粒延伸至- 7.3‰，但不含橄榄石。因此，这为次tfl水库的祖先E水库提供了证据，尽管可能存在多个。

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引用次数: 0

Corrigendum to “Oxygen and hydrogen isotope compositions in dentine collagen correlate strongly with oxygen isotope compositions of enamel carbonate”. [Geochim. Cosmochim. Acta 400 (2025) 204–213] “牙本质胶原中的氧和氢同位素组成与牙釉质碳酸盐的氧同位素组成密切相关”的勘误。[Geochim。Cosmochim。学报400 (2025)204-213]

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-16 DOI: 10.1016/j.gca.2025.12.015

L.M. Reynard, M.J. Kohn

引用次数: 0

A novel experimental V-Sc olivine-melt oxybarometer for arc magmas 一种新型的实验性V-Sc橄榄石熔体氧气压表

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-16 DOI: 10.1016/j.gca.2025.12.025

Enzo-Enrico Cacciatore, Ivano Gennaro, Kalin Kouzmanov, Alexandra Tsay, Zoltán Zajacz

引用次数: 0

Silicate weathering recorded in geochemical and lithium isotopic compositions of Mesoarchean to the early Paleoproterozoic shales 中太古代至早古元古代页岩的地球化学和锂同位素组成记录了硅酸盐风化作用

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-16 DOI: 10.1016/j.gca.2025.12.020

Su Li, Bradley M. Guy, Junsheng Nie

引用次数: 0

Time-resolved X-ray diffraction of silicate melt and glass under shear 剪切作用下硅酸盐熔体和玻璃的时间分辨x射线衍射

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-16 DOI: 10.1016/j.gca.2025.12.028

Satoshi Okumura , Kentaro Uesugi , Akio Goto , Kazuhisa Matsumoto , Masahiro Yasutake , Tatsuya Sakamaki

Silicate melts exhibit non-Newtonian behavior at high deformation rates; however, their molecular-scale origins remain unclear. In this study, we developed a shear deformation apparatus and connected it to the synchrotron radiation X-ray system of SPring-8 (Japan) to collect time-resolved X-ray diffraction of silicate melts and glasses under shear. Using this system, we conducted shear deformation experiments for andesite melts and glasses at temperatures of 700–800 °C and obtained time evolution of the intermediate-range ordering (ring structure) of silicate melts and glasses under shear. Our results exhibited no clear changes in the ring structure at low deformation rates corresponding to viscous deformation, whereas at least two types of deformation of the ring structure were found under the non-Newtonian regime. The deformation of individual rings was observed at high deformation rates, and other types of reversible deformation of the ring structure, such as the formation of a new ring by exchanging bonds between tetrahedra in adjacent rings, may occur at high deformation rates without failure. We infer that the deformed ring structure is energetically and mechanically weak, resulting in enhanced structural relaxation; hence, it reduces the apparent viscosity. The degree of elastic deformation can control shear thinning and the occurrence of brittle failure; hence, we propose a stress criterion for magma fragmentation.

硅酸盐熔体在高变形速率下表现出非牛顿力学行为；然而，它们的分子尺度起源仍不清楚。本研究开发了剪切变形仪，并将其与日本SPring-8同步辐射x射线系统连接，采集剪切作用下硅酸盐熔体和玻璃的时间分辨x射线衍射。利用该系统对安山岩熔体和玻璃进行了700 ~ 800℃的剪切变形实验，得到了剪切作用下硅酸盐熔体和玻璃的中程有序（环状结构）的时间演化。我们的研究结果表明，在低变形率下，环结构没有明显的变化，而在非牛顿状态下，环结构至少有两种类型的变形。单个环的变形是在高变形率下观察到的，而环结构的其他类型的可逆变形，如通过相邻环中四面体之间交换键形成新环，可能在高变形率下发生而不会失效。我们推断变形的环结构能量和力学弱，导致结构弛豫增强；因此，它降低了表观粘度。弹性变形程度可以控制剪切变薄和脆性破坏的发生；因此，我们提出了岩浆破碎的应力判据。

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引用次数: 0

Impact of coating structure on the rates of coupled dissolution-precipitation reactions 涂层结构对溶解-沉淀耦合反应速率的影响

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-16 DOI: 10.1016/j.gca.2025.12.031

Simon Emmanuel, Moshe Eliyahu

Coupled dissolution-precipitation reactions are central to many processes in Earth’s crust, significantly impacting natural and engineered systems. During these reactions, secondary mineral coatings often form on primary mineral surfaces, creating armoring layers that passivate the surface and dramatically reduce reaction rates. While the structure of secondary coatings is thought to influence their effect on coupled reactions, few studies have focused on characterizing their porous nature. Here, we investigated the reaction between calcite and sulfuric acid, which causes gypsum to precipitate as an armoring layer on the dissolving calcite surface. Our experiments revealed a two-stage growth pattern: initial rapid formation (<0.5 h) of a ∼20 μm thick layer of gypsum, followed by constant growth at a rate of approximately 0.71 μm h⁻¹ for 768 h, ultimately producing a layer over 500 μm thick. Consistent with previous studies, the secondary mineral layer causes the reaction rate to be several orders of magnitude lower than expected given the low pH conditions. High-resolution FIB-SEM imaging revealed a complex heterogeneous and anisotropic structure in the secondary mineral coating. The layer closest to the calcite interface exhibited extremely low porosity (1 %) with poorly connected nanoscale pores, while the outer region showed much higher porosity (31 %) with a well-connected pore network. Notably, numerous parallel cracks extended from the calcite interface into the high-porosity zone, potentially serving as the primary conduits for solute transport through the gypsum layer. A novel diffusion–reaction model containing 2 porous layers with contrasting diffusivities successfully reproduced the reaction rates we observed in our experiments. Our results demonstrate that the micrometer and nanometer scale structure of the coatings surrounding reacting minerals is a crucial factor controlling the rates of coupled dissolution-precipitation reactions in geochemical systems.

耦合溶解-沉淀反应是地壳中许多过程的核心，对自然和工程系统产生重大影响。在这些反应中，次生矿物涂层通常会在原生矿物表面形成，形成盔甲层，使表面钝化并显著降低反应速率。虽然二次涂层的结构被认为会影响其对偶联反应的影响，但很少有研究集中在表征其多孔性上。在这里，我们研究了方解石和硫酸之间的反应，使石膏作为盔甲层沉淀在溶解的方解石表面。我们的实验揭示了一个两阶段的生长模式：最初快速形成约20 μm厚的石膏层（<0.5 h），然后以约0.71 μm h−1的速率持续生长768 h，最终形成超过500 μm厚的石膏层。与以往的研究一致，在低pH条件下，次生矿物层导致反应速率比预期的低几个数量级。高分辨率FIB-SEM成像显示次生矿物包覆层具有复杂的非均质和各向异性结构。最靠近方解石界面的层孔隙度极低（1%），纳米级孔隙连接不良，而外部区域孔隙度高（31%），孔隙网络连接良好。值得注意的是，许多平行裂缝从方解石界面延伸到高孔隙率区，可能成为溶质通过石膏层的主要管道。一个包含两个具有不同扩散率的多孔层的新型扩散反应模型成功地再现了我们在实验中观察到的反应速率。我们的研究结果表明，在地球化学系统中，反应矿物周围的微米和纳米尺度的涂层结构是控制溶解-沉淀耦合反应速率的关键因素。

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引用次数: 0

Contrasting Cu isotope signatures in arc magmas and lower continental crust: insights into deep crust copper reservoir 弧岩浆与下陆壳铜同位素特征对比：深部地壳铜储层研究

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-15 DOI: 10.1016/j.gca.2025.12.024

Xin Ding , Ying Yang , Zhaoqi Ren , Shubing Fang , Erik V. Sørensen , Paul M. Holm , Fang Huang

The continental crust is significantly depleted in Cu relative to primary arc magmas, yet the mechanisms governing Cu redistribution in the lower crust remain unresolved. Understanding Cu behavior during magma differentiation is crucial for constraining the formation of deep-crustal copper reservoirs. This study investigates Cu isotopic compositions of lavas from the Andagua Valley in the Central Volcanic Zone (CVZ) and reveals δ⁶⁵Cu variation ranging from 0.08‰ to 0.65‰. Garnet fractionation under high-pressure conditions reduces FeO_T contents in the magma, lowering sulfur solubility and promoting early sulfide saturation. However, sulfide segregation is dominated by monosulfide solid solution (MSS) and occurs under high-temperature conditions, which together significantly limit Cu isotope fractionation. Rayleigh fractionation modeling shows that the average mineral-melt fractionation factor (Δ⁶⁵Cu_mineral-melt value) is between –0.3‰ and –0.1‰, demonstrating that fractionation is present but not quantitatively significant. Consequently, Cu isotopes in CVZ magmas exhibit fractionation during deep-crustal differentiation, with δ⁶⁵Cu signatures remaining in a certain range.

The δ⁶⁵Cu variation in CVZ magmas contrasts with the significantly broader range in the lower crustal cumulates ranging from –3.16‰ to 2.89‰, marking a fundamental shift in Cu behavior as magmas transition from high-temperature differentiation to prolonged cooling in the lower crust. We propose that lower crustal cumulates evolve through extended differentiation, where temperature-dependent isotope fractionation leads to significantly greater δ⁶⁵Cu variations. Prolonged cooling further promotes sulfide accumulation and post-cumulus interactions, leading to Cu redistribution and ultimately contributing to the formation of deep-crustal Cu reservoirs.

相对于原弧岩浆，大陆地壳中的Cu含量明显减少，但控制下地壳中Cu再分配的机制仍未明确。了解岩浆分异过程中铜的行为对控制深部铜储层的形成具有重要意义。本文研究了中部火山区安达瓜谷熔岩的Cu同位素组成，发现δ 6 - 5Cu的变化范围为0.08‰~ 0.65‰。高压条件下石榴石分选降低了岩浆中FeOT含量，降低了硫的溶解度，促进了早期硫化物饱和度。然而，硫化物偏析以单硫化物固溶体（MSS）为主，并发生在高温条件下，这两者共同限制了Cu同位素分馏。Rayleigh分馏模型显示，平均矿物-熔体分馏因子（Δ⁶5矿物-熔体值）在-0.3‰~ -0.1‰之间，表明分馏存在，但数量不显著。因此，在深部地壳分异过程中，CVZ岩浆中的Cu同位素表现出分异特征，δ 26 - Cu特征保持在一定范围内。CVZ岩浆δ 26 - Cu的变化与下地壳沉积δ 26 - Cu的变化范围（-3.16‰~ 2.89‰）形成鲜明对比，标志着岩浆从高温分异向下地壳长时间冷却转变过程中Cu行为发生了根本性转变。我们认为，下地壳堆积是通过扩展分化演化而来的，其中依赖于温度的同位素分馏导致了更大的δ 26 - cu变化。长时间的冷却进一步促进了硫化物的聚集和积云后的相互作用，导致Cu的重新分布，最终形成深部Cu储层。

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引用次数: 0

High magnesium isotope ratios in subglacial icelandic waters: impacts of carbonate precipitation and implications for CO2 sequestration 冰岛冰下水域的高镁同位素比率：碳酸盐降水的影响及其对CO2封存的影响

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-13 DOI: 10.1016/j.gca.2025.12.017

Philip A.E. Pogge von Strandmann , Xianyi Liu , Chun-Yao Liu , Sigurður R. Gíslason , Kevin W. Burton

Magnesium isotopes are increasingly used to trace silicate weathering, one of the key removal processes of atmospheric CO₂. Generally, silicate weathering processes are thought to drive Mg isotopes in river waters to isotopically lighter compositions than silicate rocks. An anomaly in this behaviour has been glacially-sourced rivers from Iceland, which are isotopically heavier. This study examines this phenomenon further, by analysing more high-pH glacial and groundwaters from Iceland, which tend to have high δ²⁶Mg values. Mineral Mg/Si stoichiometry shows that the cause of this isotopic change is unlikely to be associated with Mg-silicate secondary minerals, but rather with the sub-glacial and groundwater precipitation of calcite. The riverine δ²⁶Mg of specifically sub-glacial and groundwaters also co-vary with pH and the calcite saturation index. This likely dominance of the Mg isotope fractionation by a single phase allows the calculation of how much of that phase is forming, given “known” fractionation factors. This suggests that calcite formation fluxes are on average ∼0.7 t/km²/yr for the Langjökull glacier, and 25 t/km²/yr for the considerably larger Vatnajökull icecap. Overall, this study apparently answers the enigma of isotopically heavy surface waters in Iceland, and also demonstrates the potential use of Mg isotopes in determining carbonate precipitation rates, and their effects on atmospheric pCO₂.

镁同位素越来越多地用于痕量硅酸盐风化，这是大气CO2去除的关键过程之一。一般认为，硅酸盐风化过程使河水中的Mg同位素组成比硅酸盐岩石的同位素轻。这种行为的一个异常是来自冰岛的冰川河流，它们的同位素更重。本研究进一步研究了这一现象，通过分析更多来自冰岛的高ph冰川和地下水，这些水往往具有高δ26Mg值。矿物Mg/Si化学计量表明，这种同位素变化的原因不太可能与镁硅酸盐次生矿物有关，而是与冰下方解石和地下水降水有关。冰下和地下水的δ26Mg也随pH和方解石饱和度指数的变化而变化。在已知分馏因子的情况下，单一相的Mg同位素分馏可能占主导地位，从而可以计算出该相的形成量。这表明，Langjökull冰川的方解石形成通量平均为~ 0.7 t/km2/yr，而相当大的Vatnajökull冰盖的方解石形成通量平均为25 t/km2/yr。总的来说，这项研究显然回答了冰岛地表水同位素重的谜团，也证明了Mg同位素在确定碳酸盐沉淀率及其对大气二氧化碳分压的影响方面的潜在用途。

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引用次数: 0

Underplating of H2O-rich magmas in post-collisional tectonic settings 碰撞后构造环境下富氢岩浆的下覆

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-12-13 DOI: 10.1016/j.gca.2025.12.018

Davide Mariani, Riccardo Tribuzio, Tong Liu, Fu-Yuan Wu, Alberto Zanetti

The Southern Alps expose the Permian Mafic Complex, an 8 km thick gabbro-diorite intrusion formed during the post-collisional phase of the Variscan orogeny. The lower sector of the Mafic Complex mainly consists of amphibole-rich gabbros, thereby suggesting the emplacement of H2O-rich magmas in deep levels of the extending continental crust. To ascertain the nature of these magmas and the processes driving to their chemical differentiation, we have carried out a petrological-geochemical study of a 2.5 km thick section from the Lower Mafic Complex. The amphibole gabbros display a widespread foliation developed under hyper-solidus conditions and locally include concordant layers consisting of: (i) amphibole-free norites enclosing granulite-facies metasedimentary lenses, and (ii) amphibole-rich ultramafic rocks. The amphibole gabbros display Mg# [molar Mg/(Mg + Fe2+tot) × 100] ranging from 48 to 68, associated with nearly homogeneous incompatible trace element signature and Nd-Sr-O isotopic compositions. The Mg# variations therefore record a magmatic differentiation process with no substantial assimilation of crustal material. In detail, the amphibole gabbros have an enriched Nd-Sr isotopic signature (i.e., initial εNd ca. −3.3, initial 87Sr/86Sr ca. 0.7071) that is coupled with a moderate O isotopic enrichment (δ18OWR = +6.3 ‰ to +6.5 ‰, δ18OPx = +6.4 ‰ to +6.9 ‰). The norites typically have an evolved chemical signature and slightly enriched Nd-Sr-O isotopic compositions compared to the amphibole gabbros, indicating that the two rock-types were cogenetically related through a process of crustal contamination. Assimilation of crustal material was driven by anhydrous melts released from basement granulite-facies metasediments and was promoted by extensional deformation. We estimated that 15 % crustal component inhibited the crystallization of Ca-rich mafic silicates (i.e., amphibole and clinopyroxene) and triggered the orthopyroxene saturation in the melt. The ultramafic rocks interlayered with the amphibole gabbros provide evidence for involvement of chemically distinct magma pulses and record reaction processes with melts derived from the adjacent crystallizing gabbros. The primary magmas forming the studied section of the Lower Mafic Complex were most likely generated from a H2O-rich mantle source of subcontinental lithospheric origin undergoing different extents of partial melting. The building of the whole Mafic Complex involved primary magmas derived from mantle sources having markedly heterogeneous compositions.

南阿尔卑斯山暴露了二叠纪基性杂岩，这是一个8 公里厚的辉长闪长岩侵入物，形成于瓦里斯坎造山运动的后碰撞阶段。基底杂岩下部主要为富含角闪岩的辉长岩，表明在伸展的大陆地壳深部有富氢岩浆侵位。为了确定这些岩浆的性质和推动其化学分化的过程，我们对下基底杂岩2.5 km厚的剖面进行了岩石地球化学研究。角闪洞辉长岩在超固相条件下发育广泛的片理，局部包括和谐层，由(i)包裹麻粒岩相变质沉积透镜体的无角闪岩和（ii）富含角闪岩的超基性岩组成。闪孔辉长岩的Mg#[摩尔Mg/（Mg + Fe2+tot） × 100]值在48 ~ 68之间，具有几乎均匀的不相容微量元素特征和Nd-Sr-O同位素组成。因此，镁#的变化记录了一个岩浆分异过程，没有大量的地壳物质同化。角闪洞辉长岩具有富集的Nd-Sr同位素特征（初始εNd ca.−3.3，初始87Sr/86Sr ca. 0.7071），并具有中等富集的O同位素特征（δ18OWR = +6.3 ‰~ +6.5 ‰，δ18OPx = +6.4 ‰~ +6.9 ‰）。与角闪洞辉长岩相比，黑长岩具有演化的化学特征和略富的Nd-Sr-O同位素组成，表明这两种岩石类型通过地壳污染过程具有共成关系。基底麻粒岩相变质沉积物释放的无水熔体推动了地壳物质的同化作用，伸展变形促进了地壳物质的同化作用。15 %的地壳成分抑制了富钙基性硅酸盐（即角闪孔和斜辉石）的结晶，并引发了熔体中正辉石的饱和。超镁铁质岩与角闪洞辉长岩互层提供了化学上不同的岩浆脉冲参与的证据，并记录了与邻近辉长岩结晶产生的熔体的反应过程。形成下基性杂岩研究剖面的原生岩浆极有可能是由源自次大陆岩石圈的富氢地幔源经过不同程度的部分熔融形成的。整个镁铁质杂岩的形成涉及来自地幔源的原始岩浆，它们的成分明显不均匀。

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