Electrical conductivity anisotropy in partially molten peridotite under shear deformation

Zhang, Baohua; Yoshino, Takashi; Yamazaki, Daisuke; Manthilake, Geeth; Katsura, Tomoo

doi:10.1016/j.epsl.2014.08.018

Cited by 46 publications

(42 citation statements)

References 51 publications

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“…Recent experimental studies have also demonstrated that hydrous olivine and partially molten rock can be highly anisotropic under the temperature and pressure conditions of the asthenosphere (e.g., Dai and Karato 2014;Zhang et al 2014;Pommier et al 2015). Therefore, the possibility of anisotropy should not be ruled out for the old oceanic mantle in our study areas.…”

Section: Possibilities Of Lateral Heterogeneity and Anisotropy Withinmentioning

confidence: 99%

Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

Baba

Tada

Matsuno

et al. 2017

Earth Planets Space

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Seafloor magnetotelluric (MT) experiments were recently conducted in two areas of the northwestern Pacific to investigate the nature of the old oceanic upper mantle. The areas are far from any tectonic activity, and "normal" mantle structure is therefore expected. The data were carefully analyzed to reduce the effects of coastlines and seafloor topographic changes, which are significant boundaries in electrical conductivity and thus distort seafloor MT data. An isotropic, one-dimensional electrical conductivity profile was estimated for each area. The profiles were compared with those obtained from two previous study areas in the northwestern Pacific. Between the four profiles, significant differences were observed in the thickness of the resistive layer beyond expectations based on cooling of homogeneous oceanic lithosphere over time. This surprising feature is now further clarified from what was suggested in a previous study. To explain the observed spatial variation, dynamic processes must be introduced, such as influence of the plume associated with the formation of the Shatsky Rise, or spatially non-uniform, small-scale convection in the asthenosphere. There is significant room of further investigation to determine a reasonable and comprehensive interpretation of the lithosphere-asthenosphere system beneath the northwestern Pacific. The present results demonstrate that electrical conductivity provides key information for such investigation.

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Section: Possibilities Of Lateral Heterogeneity and Anisotropy Withinmentioning

confidence: 99%

Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

Baba

Tada

Matsuno

et al. 2017

Earth Planets Space

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“…Only one set of measurements has been made for s of melt-bearing olivine aggregates during torsion 12 , and these experiments were performed at low crustal pressure (0.3 GPa) and only to low shear strain (c , 0.5-1), limiting the formation of noticeable melt bands. Recently, new electrical measurements on melt 1 olivine aggregates were performed during simple shear at 3 GPa, but only small strains (c , 1.8) were reached 13 .…”

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confidence: 99%

Experimental constraints on the electrical anisotropy of the lithosphere–asthenosphere system

Pommier

Leinenweber

Kohlstedt

et al. 2015

Nature

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The relative motion of lithospheric plates and underlying mantle produces localized deformation near the lithosphere-asthenosphere boundary. The transition from rheologically stronger lithosphere to weaker asthenosphere may result from a small amount of melt or water in the asthenosphere, reducing viscosity. Either possibility may explain the seismic and electrical anomalies that extend to a depth of about 200 kilometres. However, the effect of melt on the physical properties of deformed materials at upper-mantle conditions remains poorly constrained. Here we present electrical anisotropy measurements at high temperatures and quasi-hydrostatic pressures of about three gigapascals on previously deformed olivine aggregates and sheared partially molten rocks. For all samples, electrical conductivity is highest when parallel to the direction of prior deformation. The conductivity of highly sheared olivine samples is ten times greater in the shear direction than for undeformed samples. At temperatures above 900 degrees Celsius, a deformed solid matrix with nearly isotropic melt distribution has an electrical anisotropy factor less than five. To obtain higher electrical anisotropy (up to a factor of 100), we propose an experimentally based model in which layers of sheared olivine are alternated with layers of sheared olivine plus MORB or of pure melt. Conductivities are up to 100 times greater in the shear direction than when perpendicular to the shear direction and reproduce stress-driven alignment of the melt. Our experimental results and the model reproduce mantle conductivity-depth profiles for melt-bearing geological contexts. The field data are best fitted by an electrically anisotropic asthenosphere overlain by an isotropic, high-conductivity lowermost lithosphere. The high conductivity could arise from partial melting associated with localized deformation resulting from differential plate velocities relative to the mantle, with subsequent upward melt percolation from the asthenosphere.

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“…All calibrations have been normalized to the Bell calibration. Several experimental studies have shown that olivine conductivity increases when the olivine has undergone high strain (Caricchi et al, ; Pommier et al, ; Pommier et al, ; Zhang et al, ), as might be expected in the asthenosphere. However, these studies also suggest that this enhanced conductivity is a grain‐size effect caused by dislocations activated during shearing and that this therefore is only likely to be an important factor controlling conductivities at grain sizes <<1 mm when grain boundary conduction begins to dominate (Pommier et al, ).…”

Section: Methodsmentioning

confidence: 92%

“…Grain sizes in the asthenosphere are likely to be on the order of several tens to hundreds of millimeters (e.g., Behn et al, 2009), so we do not expect shearing to be a significant factor determining conductivity. Likewise, several studies have shown that the conductivity of rocks containing partial melt is anisotropic in the direction of strain (Caricchi et al, 2011;Pommier et al, 2015;Zhang et al, 2014), and anisotropic conductive zones near the lithosphere-asthenosphere boundary have been interpreted to be due to aligned Geochemistry, Geophysics, Geosystems partial melt (Baba et al, 2006;Naif et al, 2013). However, at the temperatures and pressures deeper within the asthenosphere melt distribution is more likely to be isotropic (Pommier et al, 2015), so we have not directly included conductivity anisotropy.…”

Section: Geochemistry Geophysics Geosystemsmentioning

confidence: 99%

Upper Mantle Melt Distribution From Petrologically Constrained Magnetotellurics

Selway

O’Donnell

Özaydın

2019

Geochem Geophys Geosyst

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Three parameters: temperature, hydrogen content, and the presence of partial melt, are the dominant controls on the rheology of the convecting upper mantle. As such, they determine the dynamics that control plate tectonics and continental evolution. Since hydrogen depresses the peridotite solidus temperature, these parameters are strongly linked petrologically. We have developed a genetic algorithm code to statistically assess the likelihood that a section of upper mantle contains partial melt. This code uses magnetotelluric observations and petrological constraints on composition and solidus temperatures and allows for uncertainties in the geotherm and the electrical conductivity structure. We have applied this code to the convecting upper mantle beneath (1) a stable continent (the Superior Craton); (2) a hot spot (Tristan da Cunha); (3) stable, old oceanic lithosphere (the northwest Pacific Ocean); and (4) young oceanic lithosphere (adjacent to the East Pacific Rise). Results show that the volume of melt in the convecting upper mantle is heterogeneous. The highest melt proportions are beneath the hot spot while little to no melt is required in the other regions. All regions show low water contents (generally <50 wt ppm in olivine) in the shallow convecting upper mantle, making it unlikely that water causes a large or sharp viscosity contrast between the lithosphere and the convecting mantle. Results differ significantly for different experimental olivine hydrogen conductivity models, highlighting the importance of reconciling these experimental constraints.

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Electrical conductivity anisotropy in partially molten peridotite under shear deformation

Cited by 46 publications

References 51 publications

Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

Experimental constraints on the electrical anisotropy of the lithosphere–asthenosphere system

Upper Mantle Melt Distribution From Petrologically Constrained Magnetotellurics

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