Redox Variables and Mechanisms in Subduction Magmatism and Volcanism

Evans, Katy; Tomkins, Andy G.

doi:10.1002/9781119473206.ch4

Cited by 6 publications

(3 citation statements)

References 250 publications

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“…There are also emerging in situ laser Raman spectroscopy analysis, laser ablation single mineral in situ major and quantitative element analysis, zircon in situ U-Pb dating and trace element analysis, zircon in situ Lu-Hf isotope analysis, etc. analytical skills [28]. The effective combination of the two can increase the spatial resolution of the correlation analysis to a range of several to hundred meters.…”

Section: Resultsmentioning

confidence: 99%

Petrology and Tectonic Geophysics of Massive and Foliated Eclogites in the North Qilian Orogenic Belt: Changes in Mineral Composition, Oxygen Fugacity, and Fabric during Exhumation

Wang

Zhou²,

Zhang

2022

Adsorption Science & Technology

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The North Qilian orogenic belt is a typical area of “cold” subduction of the early Paleozoic oceanic plate, forming a series of high pressure and low temperature metamorphic rock assemblages. Among them, eclogite is a kind of protolith, which is basaltic or gabbro high pressure metamorphic rock, mainly composed of garnet and chlorite which are two kinds of minerals. Eclogites record the entire history of subduction zone metamorphism and later exhumation. Due to the crystal habit and the developed joints, the strength of the pyroxene in the matrix is weak, so it is subjected to the main strain during deformation, whereas garnet tends to show only passive rotational deformation. This paper presents some new results in petrology and tectonic geophysics of eclogite block-like and planar eclogite. The massive and facial eclogite rocks contain eclogite facies mineral assemblages, and the peak temperature and pressure conditions are t = 450 ~ 520 °C and P = 1.9 ~ 2.3 GPa, which are consistent with the adjacent eclogite. Combined with the characteristics of in situ Lu-Hf isotopes, Ce4+/Ce3+ ratios of zircons, relative oxygen fugacity, and absolute oxygen fugacity, it is shown that the oxygen fugacity of the granodiorite porphyry (BL023, BLO31, DB048) of the folio chemical and massive eclogite deposits are all located in MH (magnetite-hematite) buffer zone. Through the calculation results of absolute oxygen fugacity of rock mass, it can be seen that the absolute oxygen fugacity of ore-bearing rock mass is significantly higher than that of non-ore-bearing rock mass. This paper systematically summarizes the research progress of the microscopic and ultrastructural deformation of eclogite minerals in high-pressure metamorphic zones, and discusses the changes of mineral composition, oxygen fugidity, and fabric of eclogite deformation characteristics during the recovery of subduction and reentry.

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Section: Resultsmentioning

confidence: 99%

Petrology and Tectonic Geophysics of Massive and Foliated Eclogites in the North Qilian Orogenic Belt: Changes in Mineral Composition, Oxygen Fugacity, and Fabric during Exhumation

Wang

Zhou²,

Zhang

2022

Adsorption Science & Technology

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“…This model is not applicable to melt, although slab melting seems likely to occur in some hot subduction zones (Syracuse et al, 2010;Hernández-Uribe et al, 2020). Here we only investigated the nature of AOC-and serpentinite-derived fluids because the oceanic crust is the volumetrically largest fluid source, and the hydrated lithospheric mantle is the major source of redox budget (Evans and Tomkins, 2021). Na 2 O and K 2 O were neglected in the abyssal serpentinites due to their low contents (Deschamps et al, 2013).…”

Section: Thermodynamic Modeling Methodsmentioning

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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“…It is generally, though not universally (cf., Lee et al, 2005Lee et al, , 2012, accepted that arc basalts have higher Fe 3+ /ΣFe contents and evolve under more oxidising conditions (approximately one log unit above fayalite-magnetite-quartz equilibrium; ∼FMQ+1) than mid-ocean ridge basalts (MORBs; close to FMQ), even if the reasons for this remain contested (Evans, 2006;Kelley and Cottrell, 2009;Gaetani, 2016;Brounce et al, 2019;Cottrell et al, 2022;Evans and Tomkins, 2022). Many ocean island basalts (OIBs) also appear to have evolved under more oxidising conditions than MORBs, though global differences between MORBs and OIBs are decidedly more ambiguous than those between MORBs and arc basalts.…”

Section: Introductionmentioning

confidence: 99%

Iron valence systematics in clinopyroxene crystals from ocean island basalts

Neave¹,

Stewart²,

Hartley³

et al. 2024

Preprint

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systems, which is commonly expressed in terms of oxygen fugacity (fO2). Magmatic fO2 varies between different tectonic settings and controls the trajectories along which magmas evolve and the properties of the volcanic gases they release into the atmosphere. Ocean island basalts (OIBs) derived at least in part from recycled mantle sources are increasingly thought to evolve under more oxidising conditions than midocean ridge basalts (MORBs) from relatively depleted sources. However, the oxybarometeric tools currently at our disposal are subject to a range of limitations, meaning that there are relatively few internally consistent estimates of fO2 across multiple settings. Our understanding of the nature and causes of fO2 variability within and between magmatic systems therefore remains limited. In Part I we demonstrated that previously discredited approaches for estimating clinopyroxene ferric iron contents can return comparably precise results to Mössbauer spectroscopy by optimising electron probe microanalysis techniques, raising the prospect of developing clinopyroxene-based oxybarometers. Here we present high-quality analyses of clinopyroxene crystals from OIBs erupted in Iceland and the Azores to determine their iron valence systematics and explore their potential use for oxybarometry. Although many studies assume that all iron in magmatic clinopyroxene crystals occurs as ferrous iron, we find that up to 50% of the total iron in magmatic clinopyroxene crystals may be ferric iron, with crystals from alkali systems typically containing more ferric iron than those from tholeiitic systems. Most ferric iron is hosted within esseneite component (CaFe3+AlSiO6), though some may also be hosted in aegirine component (NaFe3+Si2O6) in the most alkali crystals. Iron–magnesium exchange equilibria between clinopyroxene crystals and their host glasses return plausible fO2 estimates for a tholeiitic basalt from Holuhraun in Iceland and an alkali basalt from Pico in the Azores but are subject to considerable uncertainties because the influence of ferric iron on clinopyroxene-liquid equilibria are poorly understood. There is no current advantage in accounting for ferric iron when evaluating iron-magnesium exchange between clinopyroxene–glass pairs. Magmatic fO2 was also estimated by applying a recent parametrisation of ferric iron partitioning to determine the valence of iron in liquids in equilibrium with clinopyroxene crystals from Holuhraun and Pico. We infer that our samples from Holuhraun and Pico evolved at about one and half and two and a half log units above FMQ equilibrium, respectively. These values are in line with independent estimates from these eruptions and similar eruptions of OIB elsewhere, and demonstrate the considerable potential for further development of clinopyroxene-based oxybarometers.

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Redox Variables and Mechanisms in Subduction Magmatism and Volcanism

Cited by 6 publications

References 250 publications

Petrology and Tectonic Geophysics of Massive and Foliated Eclogites in the North Qilian Orogenic Belt: Changes in Mineral Composition, Oxygen Fugacity, and Fabric during Exhumation

Petrology and Tectonic Geophysics of Massive and Foliated Eclogites in the North Qilian Orogenic Belt: Changes in Mineral Composition, Oxygen Fugacity, and Fabric during Exhumation

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

Iron valence systematics in clinopyroxene crystals from ocean island basalts

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