Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks

Ague, Jay J.; Tassara, Santiago; Holycross, Megan; Li, Ji‐Lei; Cottrell, Elizabeth; Schwarzenbach, Esther M.; Fassoulas, Charalampos; John, Timm

doi:10.1038/s41561-022-00904-7

Cited by 43 publications

(24 citation statements)

References 78 publications

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“…Implications for the sedimentary Mo subduction cycle. Due to the anoxic conditions in the Proterozoic deep ocean, oxidised species of major and minor elements like Fe, S and Mn, were absent in deep sea sediments, thus lowering their redox budget/oxidising capacity compared to present day marine lithologies (e.g., Evans, 2012;Ague et al, 2022). This may also explain the preserved δ 98/95 Mo of a reduced Proterozoic sediment component recycled into the S-MAR mantle source, in contrast to Neoproterozoic, deep mantle recycling of low δ 98/95 Mo into mantle plume sources (see also Ma et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments

Ahmad¹,

Wille²,

Rosca³

et al. 2022

Geochem. Persp. Let.

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Under modern oxidising Earth surface conditions, dehydrated subducted slabs show Mo isotope compositions as low as δ 98/95 Mo = −1.5 ‰, compared to the depleted mantle δ 98/95 Mo = −0.2 ‰. Such light Mo isotope compositions reflect the redoxdependent aqueous mobility of isotopically heavy Mo associated with slab dehydration. Here we analysed basaltic glasses from the South-Mid Atlantic Ridge, whose parental melts are influenced by the enriched Discovery and Shona mantle plumes. We report increasingly higher δ 98/95 Mo of up to −0.1 ‰ from the most depleted samples towards those tapping more enriched mantle sources. δ 98/95 Mo values correlate with radiogenic Sr and Nd isotopes, which indicates the recycling of Proterozoic sediments with a Mo isotopic composition that was not affected by subduction-related, oxic dehydration. We propose that the Mo isotope signatures were retained during subduction and reflect anoxic conditions during deep sea sedimentation in the mid-Proterozoic. Finally, Mo isotope fractionation between different terrestrial reservoirs likely depends on the slab redox budget, and therefore on the timing of subduction with regard to Earth's surface oxygenation.

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Section: Discussionmentioning

confidence: 99%

Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments

Ahmad¹,

Wille²,

Rosca³

et al. 2022

Geochem. Persp. Let.

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“…Activity data for sulfur-bearing species in the C-H-O-S system are partially available (Evans et al 2010), but they are unknown when nitrogen-bearing species (N 2 , HCN and NH 3 ) are considered. Since a full treatment of non-ideality requires a complete knowledge of every pair-wise interaction among C-H-O-N-S-bearing species, like in the C-H-O system, existing studies choose to either ignore non-ideal mixing (Sun & Lee 2022) or only partially consider ideal mixing (Ague et al 2022). As the data for nitrogen-and sulfur-bearing species are unavailable, we assume γ i = φ i = 1 for these molecules.…”

Section: Activity Coefficientmentioning

confidence: 99%

“…As the data for nitrogen-and sulfur-bearing species are unavailable, we assume γ i = φ i = 1 for these molecules. This approach is similar to that of Ague et al (2022), who assumed non-ideal-gas components (φ i = 1) that mix ideally (γ i = 1).…”

Section: Activity Coefficientmentioning

confidence: 99%

Atmospheric Chemistry of Secondary and Hybrid Atmospheres of Super Earths and Sub-Neptunes

Tian¹,

Heng²

2023

Preprint

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The atmospheres of small exoplanets likely derive from a combination of geochemical outgassing and primordial gases left over from formation. Secondary atmospheres, such as those of Earth, Mars and Venus, are sourced by outgassing. Persistent outgassing into long-lived, primordial, hydrogen-helium envelopes produces hybrid atmospheres of which there are no examples in the Solar System. We construct a unified theoretical framework for calculating the outgassing chemistry of both secondary and hybrid atmospheres, where the input parameters are the surface pressure, oxidation and sulfidation states of the mantle, as well as the primordial atmospheric hydrogen, helium and nitrogen content. Non-ideal gases (quantified by the fugacity coefficient) and non-ideal mixing of gaseous components (quantified by the activity coefficient) are considered. Both secondary and hybrid atmospheres exhibit a rich diversity of chemistries, including hydrogen-dominated atmospheres. The abundance ratio of carbon dioxide to carbon monoxide serves as a powerful diagnostic for the oxygen fugacity of the mantle, which may conceivably be constrained by James Webb Space Telescope spectra in the near future. Methane-dominated atmospheres are difficult to produce and require specific conditions: atmospheric surface pressures exceeding ∼ 10 bar, a reduced (poorly oxidised) mantle and diminished magma temperatures (compared to modern Earth). Future work should include photochemistry in these calculations and clarify the general role of atmospheric escape. Exoplanet science should quantify the relationship between the mass and oxygen fugacity for a sample of super Earths and sub-Neptunes; such an empirical relationship already exists for Solar System bodies.

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“…However, there is a continuing debate on whether the redox state of fluid speciation is oxidized or reduced. Most previous studies on fluid inclusions in highpressure (HP) metamorphic rocks, experiments, isotope evidence, and thermodynamic calculations suggested that the slab-derived fluids are highly oxidized (Scambelluri and Philippot, 2001;Frezzotti et al, 2011;Frezzotti and Ferrando, 2015;Pons et al, 2016;Rielli et al, 2017;Gerrits et al, 2019;Walters et al, 2020a;Iacovino et al, 2020;Maurice et al, 2020;Zhang et al, 2021;Ague et al, 2022), whereas some argued for rather reduced fluids (Song et al, 2009;Frezzotti and Ferrando, 2015;Brovarone et al, 2017;Tao et al, 2018;Chen et al, 2019;Piccoli et al, 2019;. As a result, the redox state of slab-derived fluids is proposed to have a broad fO 2 range varying from △FMQ+5 to △FMQ-4 (e.g., Evans and Powell, 2015;Debret and Sverjensky, 2017;Piccoli et al, 2019;Walters et al, 2020b;Wang et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Based on the newly developed geochemical thermodynamic model-Deep Earth Water (DEW) model (Sverjensky et al, 2014;Huang and Sverjensky, 2019), some efforts have been made to investigate the effects of thermal structure, rock lithologies, and the redox state of the pre-subduction slab on the redox state of slab-derived fluids to reconcile these two opposite views (e.g., Sverjensky et al, 2014;Walters et al, 2020a;Evans and Frost, 2021;Ague et al, 2022). For example, Sverjensky et al (2014) found that the major carbon species in fluids equilibrated with oceanic crust are organic (CH 3 CH 2 COO − and HCOO − ) and inorganic ionic carbon species, whereas those equilibrated with peridotite generally contain CH 4 and CO 2 /HCO − 3 /CO 2− 3 .…”

Section: Introductionmentioning

confidence: 99%

Redox species and oxygen fugacity of slab-derived fluids: Implications for mantle oxidation and deep carbon-sulfur cycling

Chen

et al. 2022

Front. Earth Sci.

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The generation and migration of slab-derived fluids modulate subduction zone seismicity, arc magmatism, and deep volatile cycling. However, the redox species and oxygen fugacity (fO2) (hereafter expressed as log units relative to the fayalite–magnetite–quartz buffer, △FMQ) of slab-derived fluids are highly debated. Here we conducted phase equilibria modeling on altered oceanic crust (AOC) and serpentinites along typical subduction geotherms in the C-S-bearing system over a pressure range of 0.5–6 GPa. With the averaged compositions of AOC and serpentinite, our calculated results show that oxidized carbon-sulfur species dominate slab-derived fluids during slab subduction. As a result, slab-derived fluids are highly oxidized and at or above the typical △FMQ values of arc magmas at forearc to subarc depths. The predicted oxidized carbon and sulfur species are compatible with natural observations in fluid inclusions from many oceanic HP metamorphic rocks. More importantly, it is revealed that, the redox state of slab-derived fluids is primarily controlled by the redox budget (RB) of the slab prior to subduction. Subduction-zone thermal structure, however, only exerts a minor influence on the slab-derived fluid fO2, which is supported by the similar fO2 ranges in arc lavas from cold and hot subduction zones. Our models further show that, if an open system is assumed, most of carbon (>70%) and sulfur (>50%) in cold subducted AOC and serpentinite would be lost at subarc depths. Small amounts of carbon and sulfur could be transported into the deeper mantle via closed-system subduction and open-system cold subduction, supplying the source materials for volatile-rich intraplate magmas and superdeep diamonds.

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Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks

Cited by 43 publications

References 78 publications

Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments

Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments

Atmospheric Chemistry of Secondary and Hybrid Atmospheres of Super Earths and Sub-Neptunes

Redox species and oxygen fugacity of slab-derived fluids: Implications for mantle oxidation and deep carbon-sulfur cycling

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