Fluids of the Lower Crust: Deep Is Different

Manning, Craig E.

doi:10.1146/annurev-earth-060614-105224

Cited by 121 publications

(70 citation statements)

References 168 publications

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“…Our data demonstrate that the enhanced conductivities in the mantle wedge below the volcanic arc could be caused by less than 1% of a moderately saline, interconnected aqueous fluid. For shallow crustal systems, similar conclusions were already reached by Manning ().…”

Section: Discussionsupporting

confidence: 84%

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Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa

Guo

Keppler

2019

JGR Solid Earth

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The electrical conductivity of aqueous fluids containing 0.01, 0.1, and 1 M NaCl was measured in a piston‐cylinder apparatus up to 900 °C and 5 GPa. The conductivity generally increases with NaCl concentration, while the pressure and temperature effects are more complex. At 1–2 GPa, the effect of temperature on conductivity is small, while at higher pressures, conductivity increases with temperature. Pressure also enhances conductivity, but only above 300–400 °C. This effect may be due to enhanced ion dissociation in response to an increasing dielectric constant. However, at lower temperatures, conductivity decreases with pressure, probably due to an increase in fluid viscosity. The measured conductivities of NaCl‐H2O fluids up to 900 °C and 5 GPa are reproduced (R2 = 0.953) by a numerical model with log σ = −0.919 − 872.5/T + 7.61 log ρ + 0.852 log c + log Λ0, where σ is the conductivity in S/m, T is temperature in K, c is NaCl concentration in wt%, ρ is the density of pure water (in g/cm3) at given pressure and temperature, and Λ0 is the molar conductivity of NaCl in water at infinite dilution (in S·cm2·mol−1), Λ0 = 1,573 − 1,212 ρ + 537,062/T – 208,122,721/T2. We use our data to model the elevated electrical conductivity in the mantle wedge above subducted slabs. We find that due to the strong conductivity enhancement, in most cases less than one volume percent of aqueous fluid with moderate salinity is sufficient to explain the observed conductivity anomalies.

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Section: Discussionsupporting

confidence: 84%

“…However, in the light of the very low solubility of corundum in dilute NaCl-bearing aqueous fluids, this effect is likely negligible (Newton & Manning, 2006). Moreover, the neutral H 3 AlO 3 will not contribute to solution conductivity (Manning, 2018).…”

Section: 1029/2018jb016658mentioning

confidence: 99%

Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa

Guo

Keppler

2019

JGR Solid Earth

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“…Indeed, the nearly isothermal decompression P‐T path, established in this study, slightly oversteps the wet solidus of a basaltic eclogite before the amphibolite‐facies overprint (Figure ). However, the presence of CO 2 and NaCl (see later discussion) in aqueous fluids could reduce the H 2 O activity so that the melting temperature would increase (Manning, ). Thus, using the P‐T path and solidus for a pure H 2 O‐basalt system cannot confirm whether or not partial melting in the eclogite‐vein system occurred.…”

Section: Discussionmentioning

confidence: 99%

High‐Pressure Fluid‐Rock Interaction and Mass Transfer During Exhumation of Deeply Subducted Rocks: Insights From an Eclogite‐Vein System in the Ultrahigh‐Pressure Terrane of the Dabie Shan, China

Liu

Massonne

Harlov

et al. 2019

Geochem Geophys Geosyst

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A petrological study was performed on an eclogite-vein system from the Dabie ultrahigh-pressure terrane by focusing on high-pressure (HP) fluid-rock interaction and mass transfer during exhumation. The veins comprise mainly garnet and quartz and resulted from a HP leaching process along fractures in the eclogite during exhumation. Relict peak garnet, phengite, and apatite in this rock system were altered by HP fluids forming characteristic compositional zonings. Zoned garnet in the eclogite records an isothermal exhumation from 3.3 GPa and 665-680°C. Partial dissolution of garnet and a back incorporation of Mn-heavy rare earth element (REE)-Y increased the content of these elements in the altered garnet zone in the veins. Altered phengite is characterized by a Ba-rich rim. Fluid-aided alteration reduced the light REE (LREE) contents and produced oriented monazite, calcite, and pyrrhotite inclusions within apatite, reflecting mobilization and redistribution of LREEs, CO 3 2− , Fe, and S between these minerals. The active HP fluid is proposed to have been a Si-Al-Na-Ba-rich aqueous fluid, as indicated by sodic plagioclase rims around various eclogitic minerals and by the altered phengite composition. Mass balance calculations reveal that LREEs, middle REEs, and Zr-Hf-Th-U were added to and Li, large ion lithophile elements, and Ti-Nb were removed from the quartz-garnet veins, requiring a high fluid flux. These findings shed new light on the nature and behavior of HP fluids and highlight their key role in resetting mineral chemistry and mass transfer in subduction zone metamorphic environments. . (2019). High-pressure fluid-rock interaction and mass transfer during exhumation of deeply subducted rocks: insights from an eclogite-vein system in the ultrahigh-pressure terrane of the Dabie The Dabie-Sulu orogenic belt in east-central China is considered to be one of the largest UHP terranes on Earth. This belt resulted from the Triassic continental collision between the North China and South China blocks (Ernst et al., 2007;Li et al., 1993;Zhang et al., 2009). It is separated into the eastern Sulu terrane and the western Dabie terrane by the sinistral Tanlu strike-slip fault. The western part of the Dabie terrane is further truncated by the Shangma fault and known as the Hongan terrane (Figure 1a).Several large-scale EW trending faults divide the Dabie terrane into five major lithotectonic units with different metamorphic histories (Hacker et al., 2000;Zheng et al., 2005). From north to south, these units are (1) the Beihuaiyang greenschist-facies unit made up of low-grade metasedimentary and metaigneous rocks that are overlain by Jurassic-Cretaceous sedimentary and volcanic rocks; (2) the North Dabie high-T granulite-facies unit composed of typical amphibolite-to granulite-facies rocks, migmatitic gneisses, and minor mafic to ultramafic rocks; (3) the Central Dabie medium-T/UHP eclogite-facies unit including abundant orthogneisses and paragneisses that enclose subordinate bodies of coesite-bearing eclogite, pure to imp...

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“…Similarly, the assumption of a fully volatile saturated crust is likely a simplification and in reality may be spatiotemporally heterogeneous. However, it is unclear what the appropriate saturation state is for an upper‐crustal magmatic system with lots of passive degassing and a hydrothermal system especially when considering the role of deep fluids (Manning, ). Consequently, we have chosen a spherical shape for the reservoir in a fully saturated crust since it allows simplification of the coupled equation set, derivation of an analytical solution, and coupling with the preexisting DH box model.…”

Section: Crustal Response Modelmentioning

confidence: 99%

Volatile Degassing From Magma Chambers as a Control on Volcanic Eruptions

Mittal

Richards

2019

JGR Solid Earth

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The loss of volatiles from a magma reservoir affects the magmatic overpressure responsible for driving ground deformation and eruptions. Although the high‐temperature metamorphic aureole around a magma chamber is typically considered to have low permeability, recent theoretical, experimental, and field studies have highlighted the role of transient permeability in magmatic systems. Also, direct measurements suggest that passive degassing is a significant component of total volatile loss in both basaltic and silicic volcanoes. Consequently, the effective permeability of the crust when magma is present in the system can be many orders of magnitude larger than that of exhumed rock samples. We develop a fully coupled porothermoelastic framework to account for both the flow of volatiles as well as associated effects on the stress state of the crust and calculate an analytical solution for spherical geometry. We then combine a magma chamber box model with these solutions to analyze eruption dynamics in magmatic systems. We find that in addition to viscous relaxation, magma recharge, and cooling timescales, the pore pressure diffusion timescale exerts a first‐order control on volcanic eruptions with moderately high crustal permeabilities of order 10−17 to 10−19 m2. We describe a parameter space to identify which components dominate in different regimes for volcanic eruptions according to these different timescales.

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Fluids of the Lower Crust: Deep Is Different

Cited by 121 publications

References 168 publications

Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa

Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa

High‐Pressure Fluid‐Rock Interaction and Mass Transfer During Exhumation of Deeply Subducted Rocks: Insights From an Eclogite‐Vein System in the Ultrahigh‐Pressure Terrane of the Dabie Shan, China

Volatile Degassing From Magma Chambers as a Control on Volcanic Eruptions

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