Subduction factory 2. Are intermediate-depth earthquakes in subducting slabs linked to metamorphic dehydration reactions?

The thermal structure of subduction zones plays an important role in the seismicity that occurs there with e.g., the downdip limit of the seismogenic zone associated with particular isotherms (350 &#176;C - 450 &#176;C) and intermediate-depth seismicity linked to dehydration reactions that occur at specific temperatures and pressures. Therefore, accurate thermal models of subduction zones that include the complexities found in laboratory studies are necessary. One of the often-ignored effects in models is the temperature-dependence of the thermal parameters such as the thermal conductivity, heat capacity, and density.&#160;Here, we build upon the model setup presented by Van Keken et al., 2008 by including temperature-dependent thermal parameters to an otherwise clearly constrained, simple model setup of a subducting plate. We consider a fixed kinematic slab dipping at 45&#176; and a stationary overriding plate with a dynamic mantle wedge. Such a simple setup allows us to isolate the effect of temperature-dependent thermal parameters. We add a more complex plate cooling model for the oceanic plate for consistency with the thermal parameters.&#160;We test the effect of temperature-dependent thermal parameters on models with different rheologies, such as an isoviscous wedge, diffusion and dislocation creep. We find that slab temperatures can change by up to 65 &#176;C which affects the location of isotherm depths. The downdip limit of the seismogenic zone defined by e.g., the 350 &#176;C isotherm shifts by approximately 4 km, thereby increasing the maximum possible rupture area of the seismogenic zone. Similarly, the 600 &#176;C isotherm is shifted approximately 30 km deeper, affecting the depth at which dehydration reactions and hence intermediate-depth seismicity occurs. Our results therefore show that temperature-dependent thermal parameters in thermal models of subduction zones cannot be ignored when studying subduction-related seismicity.&#160;

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A 4D view on the evolution of metamorphic dehydration reactions

Scientific Reports ◽

10.1038/s41598-017-07160-5 ◽

2017 ◽

Vol 7 (1) ◽

Cited By ~ 11

Author(s):

John Bedford ◽

Florian Fusseis ◽

Henri Leclère ◽

John Wheeler ◽

Daniel Faulkner

Keyword(s):

Dehydration Reactions ◽

Metamorphic Dehydration

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PSEUDOTACHYLYTE IN THE SUBDUCTING SLAB MANTLE FROM ALPINE OPHIOLITES REVEAL FOSSIL INTERMEDIATE-DEPTH EARTHQUAKES LINKED TO DIFFERENTIAL STRESS RELEASE

10.1130/abs/2018am-319446 ◽

2018 ◽

Author(s):

Marco Scambelluri ◽

◽

Giorgio Pennacchioni ◽

Oliver Plümper ◽

Mattia Gilio ◽

...

Keyword(s):

Stress Release ◽

Differential Stress ◽

Intermediate Depth ◽

Subducting Slab

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METAMORPHIC DEHYDRATION FROM OCEANIC CRUST PROVIDES FLUID SOURCES FOR DEEP SLOW SLIP AND TREMOR IN SUBDUCTION ZONES

10.1130/abs/2020am-357702 ◽

2020 ◽

Author(s):

Cailey Condit ◽

◽

Victor Guevara ◽

Jonathan R. Delph ◽

Melodie French

Keyword(s):

Oceanic Crust ◽

Subduction Zones ◽

Slow Slip ◽

Fluid Sources ◽

Metamorphic Dehydration

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Simple theoretical models of elimination reactions on polar catalysts; Dehydration reactivity of secondary alcohols on acidic and basic catalysts

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19850920 ◽

1985 ◽

Vol 50 (4) ◽

pp. 920-929 ◽

Cited By ~ 1

Author(s):

Jiří Sedláček

Keyword(s):

Experimental Data ◽

Quantum Chemical ◽

Theoretical Models ◽

Aliphatic Alcohols ◽

Secondary Alcohols ◽

Carbonium Ion ◽

Dehydration Reactions ◽

Aromatic Alcohols ◽

Basic Catalysts ◽

Simple Models

CNDO/2 calculations for simple models of adsorption and dehydration reactions of secondary aliphatic and aromatic alcohols on polar catalysts are presented. The models involve selected stages of elimination mechanisms of various types (E1, E2 and E1cB elimination). Calculated quantum chemical quantities were correlated with reported experimental data. It is shown that reactivities for the series of substituted phenylethanols correlate very well with the ease of carbonium ion formation. In the case of aliphatic alcohols, calculated quantities correlate generally with the reactivities on SiO2 and are in anticorrelation with the reactivities on Al2O3.NaOH.

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Consideration on modeling of Nb sorption onto clay minerals

Radiochimica Acta ◽

10.1515/ract-2020-0006 ◽

2020 ◽

Vol 108 (11) ◽

pp. 873-877

Author(s):

Tetsuji Yamaguchi ◽

Saki Ohira ◽

Ko Hemmi ◽

Logan Barr ◽

Asako Shimada ◽

...

Keyword(s):

Distribution Coefficient ◽

Clay Minerals ◽

Safety Assessment ◽

Distribution Coefficients ◽

Surface Species ◽

Complex Species ◽

Intermediate Depth ◽

Speciation Model ◽

Surface Phases ◽

High Distribution Coefficient

AbstractSorption distribution coefficient (Kd) of niobium-94 on minerals are an important parameter in safety assessment of intermediate-depth disposal of waste from core internals etc. The Kd of Nb on clay minerals in Ca(ClO4)2 solutions were, however, not successfully modeled in a previous study. The high distribution coefficients of Nb on illite in Ca(ClO4)2 solutions were successfully reproduced by taking Ca–Nb–OH surface species into account. Solubility of Nb was studied in Ca(ClO4)2 solutions and the results were reproduced by taking an aqueous Ca–Nb–OH complex species, CaNb(OH)6+, into account in addition to previously reported Nb(OH)6− and Nb(OH)72−. Based on this aqueous speciation model, the Ca–Nb–OH surface species responsible for the sorption of Nb on illite in Ca(ClO4)2 solutions was presumed to be X_OCaNb(OH)6. Although uncertainties exist in the speciation of aqueous Ca–Nb–OH species, the result of this study proposed a possible mechanism for high distribution coefficient of Nb on illite in Ca(ClO4)2 solutions. The mechanism includes Ca–Nb–OH complex formation in aqueous, solid and surface phases.

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Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet

Contributions to Mineralogy and Petrology ◽

10.1007/s00410-021-01806-4 ◽

2021 ◽

Vol 176 (7) ◽

Author(s):

Thomas Bovay ◽

Daniela Rubatto ◽

Pierre Lanari

Keyword(s):

Oxygen Isotope ◽

Western Alps ◽

Large Contribution ◽

Chemical Mapping ◽

Rock Interaction ◽

Rock Density ◽

Chemical Zoning ◽

Dehydration Reactions ◽

Subducted Oceanic Crust ◽

Eclogite Facies

AbstractDehydration reactions in the subducting slab liberate fluids causing major changes in rock density, volume and permeability. Although it is well known that the fluids can migrate and interact with the surrounding rocks, fluid pathways remain challenging to track and the consequences of fluid-rock interaction processes are often overlooked. In this study, we investigate pervasive fluid-rock interaction in a sequence of schists and mafic felses exposed in the Theodul Glacier Unit (TGU), Western Alps. This unit is embedded within metaophiolites of the Zermatt-Saas Zone and reached eclogite-facies conditions during Alpine convergence. Chemical mapping and in situ oxygen isotope analyses of garnet from the schists reveal a sharp chemical zoning between a xenomorphic core and a euhedral rim, associated to a drop of ~ 8‰ in δ18O. Thermodynamic and δ18O models show that the large amount of low δ18O H2O required to change the reactive bulk δ18O composition cannot be produced by dehydration of the mafic fels from the TGU only, and requires a large contribution of the surrounding serpentinites. The calculated time-integrated fluid flux across the TGU rocks is 1.1 × 105 cm3/cm2, which is above the open-system behaviour threshold and argues for pervasive fluid flow at kilometre-scale under high-pressure conditions. The transient rock volume variations caused by lawsonite breakdown is identified as a possible trigger for the pervasive fluid influx. The calculated schist permeability at eclogite-facies conditions (~ 2 × 10–20 m2) is comparable to the permeability determined experimentally for blueschist and serpentinites.

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