Elasticity of glaucophane, seismic velocities and anisotropy of the subducted oceanic crust

Bezacier, L.; Reynard, Bruno; Bass, Jay D.; Wang, J.; Mainprice, David

doi:10.1016/j.tecto.2010.09.011

Cited by 69 publications

(92 citation statements)

References 37 publications

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“…Petrophysical models and acoustic measurements along different directions give access to anisotropy. Seismic velocities obtained from petrophysical modeling (Bascou, et al 2001;Bezacier, et al 2010a;Bezacier, et al 2010b;Cao, et al 2013) are in good agreement with measurements on rock aggregates (Ji, et al 2013;Shao, et al 2014). They provide a basis for estimating the proportion of water stored in minerals.…”

Section: Seismologysupporting

confidence: 78%

“…1b) when the large anisotropy typical of hydrated minerals and rocks is taken into account (Bezacier, et al 2010a;Bezacier, et al 2010b;Mainprice and Ildefonse 2009). Large seismic anisotropy of hydrated minerals is a primary cause of anisotropy in deformed rocks of subduction zones.…”

Section: Seismologymentioning

confidence: 99%

“…In foliated serpentinites, the combination of intrinsic mineral anisotropy due to the layered structure of phyllosilicates and their strong alignment in deformed rocks due to the plateshaped crystals results in a range of V P /V S ratio spanning most of that of typical subduction zone rocks (Bezacier, et al 2010a). Anisotropy of blueschists is also marked because of alignment of anisotropic amphiboles and epidotes (Bezacier, et al 2010b). Absolute velocities and V P /V S ratio are also drastically decreased by the presence of overpressurized fluids (Peacock, et al 2011).…”

Section: Seismologymentioning

confidence: 99%

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Mantle hydration and Cl-rich fluids in the subduction forearc

Reynard

2016

Prog. in Earth and Planet. Sci.

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In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not only with the thermal state of the subduction zone, but also with time for a given thermal state through variations of fluid salinity. High-Cl fluids produced by serpentinization can mix with the source rocks of the volcanic arc and explain geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc hot springs. These observations suggest the existence of fluid circulations between the forearc mantle and the hot spring hydrothermal system or the volcanic arc. Such circulations are also evidenced by recent magnetotelluric profiles.

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Section: Seismologysupporting

confidence: 78%

Section: Seismologymentioning

confidence: 99%

Section: Seismologymentioning

confidence: 99%

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Mantle hydration and Cl-rich fluids in the subduction forearc

Reynard

2016

Prog. in Earth and Planet. Sci.

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“…Its chemical formula shows differences compared to the glaucophane individual of Bezacier et al (2010), but the elastic data of Bezacier et al (2010) sample. The composition of garnet is close to the almandine end member in the pyrope-almandinespessartine system, which justifies the use of the almandine elastic constants of Babuska et al (1978).…”

Section: Accepted M Manuscriptmentioning

confidence: 85%

Crystallographic preferred orientations of exhumed subduction channel rocks from the Eclogite Zone of the Tauern Window (Eastern Alps, Austria), and implications on rock elastic anisotropies at great depths

et al. 2015

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“…At near surface P-T conditions, the main hydrous minerals in these rocks are chlorites and zeolites, which give the rock a~5% H 2 O content by weight. At intermediate P-T conditions, where chlorite remains stable, a significant portion of the mineral-bound water is also carried by amphiboles, which have been shown to exhibit strong seismic anisotropy (see, e.g., Bezacier et al 2010b), and by lawsonite. The evolution of the water content and seismic velocities of hydrated metabasalts with increasing P-T conditions, as calculated by Hacker et al (2003a) is shown in the bottom panels of Fig.…”

Section: Effects On Seismic Propertiesmentioning

confidence: 99%

Mapping the Distribution of Fluids in the Crust and Lithospheric Mantle Utilizing Geophysical Methods

Unsworth

Rondenay

2012

Lecture Notes in Earth System Sciences

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Geophysical imaging provides a unique perspective on metasomatism, because it allows the present day fluid distribution in the Earth's crust and upper mantle to be mapped. This is in contrast to geological studies that investigate midcrustal rocks have been exhumed and fluids associated with metasomatism are absent. The primary geophysical methods that can be used are (a) electromagnetic methods that image electrical resistivity and (b) seismic methods that can measure the seismic velocity and related quantities such as Poisson's ratio and seismic anisotropy. For studies of depths in excess of a few kilometres, the most effective electromagnetic method is magnetotellurics (MT) which uses natural electromagnetic signals as an energy source. The electrical resistivity of crustal rocks is sensitive to the quantity, salinity and degree of interconnection of aqueous fluids. Partial melt and hydrogen diffusion can also cause low electrical resistivity. The effects of fluid and/or water on seismic observables are assessed by rock and mineral physics studies. These studies show that the presence of water generally reduces the seismic velocities of rocks and minerals. The water can be present as a fluid, in hydrous minerals, or as hydrogen point defects in nominally anhydrous minerals. Water can further modify seismic properties such as the Poisson's ratio, the quality factor, and anisotropy. A variety of seismic analysis methods are employed to measure these effects in situ in the crust and lithospheric mantle and include seismic tomography, seismic reflection, passive-source converted and scattered wave imaging, and shear-wave splitting analysis. A combination of magnetotelluric and seismic data has proven an effective tool to study the fluid

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Elasticity of glaucophane, seismic velocities and anisotropy of the subducted oceanic crust

Cited by 69 publications

References 37 publications

Mantle hydration and Cl-rich fluids in the subduction forearc

Mantle hydration and Cl-rich fluids in the subduction forearc

Crystallographic preferred orientations of exhumed subduction channel rocks from the Eclogite Zone of the Tauern Window (Eastern Alps, Austria), and implications on rock elastic anisotropies at great depths

Mapping the Distribution of Fluids in the Crust and Lithospheric Mantle Utilizing Geophysical Methods

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