Electrical Conductivity of Ti‐Bearing Hydrous Olivine Aggregates at High Temperature and High Pressure

Dai, Lidong; Karato, Shun‐ichiro

doi:10.1029/2020jb020309

Cited by 16 publications

(17 citation statements)

References 43 publications

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“…This will reduce of the concentration of (2𝐻) 𝑀𝑔 𝑋 and (4𝐻) 𝑆𝑖 𝑋 (Muir et al, Submittedb) and thus the conductivity even further. This is in contrast to measurements by Dai and Karato (2020) where it was found that Ti increases conductivity in water poor regions where {Ti Mg would have to diffuse quickly which we find to be unlikely so this is further evidence that the mechanism by which water increases conduction in olivine is not ionic diffusion.…”

Section: The Effect Of Mg Diffusion Rate Variations On Conductivitycontrasting

confidence: 99%

Fast anisotropic Mg and H diffusion in wet forsterite

Muir¹,

Zhang²,

Walker³

2021

Preprint

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Mg diffusion, which is important for properties of forsterite such as conductivity and deformation, is a strong function of water content. The mechanism behind this effect, however, has not been fully elucidated. In this study we use Density Functional Theory to predict the diffusivity of 〖(2H)〗_Mg^X and we find that they are around 1000 times slower than H-free Mg vacancies V_Mg^''. In most wet conditions the concentration of 〖(2H)〗_Mg^X is much higher than that of V_Mg^'' and thus the primary effect of water on increasing the Mg-diffusion rate in forsterite is by producing large numbers of H-bearing Mg vacancies. A water induced increase in diffusion rate is predicted to be accompanied by a large increase in diffusional anisotropy primarily in the [001] direction. Using a previously developed model of H distribution in forsterite we predict that the effect of water on Mg diffusion is strongly dependent upon environmental conditions such as pressure or temperature. An exponent (r) describing the relationship of water concentration to Mg diffusion is found to vary between 0.5-1.6 across common experimental conditions with pressure decreasing this exponent and temperature increasing it. With 100 wt. ppm water Mg diffusion rates are predicted to increase by over 2 orders of magnitude at high temperature and low pressure (2000 K, 0 GPa) and by over 3.5 orders of magnitude at low temperature and high pressure (1000 K, 10 GPa) while the anisotropy of diffusion is predicted to increase by ~2/over 5.5 orders of magnitude respectively. A conversion from “dry” to “wet” rheological laws is predicted to occur at <~1 ppm. These results suggest that Mg diffusion in wet forsterite could vary considerably throughout mantle conditions in ways that cannot be captured with a simple one component equation. Finally we considered the effects of the diffusion of H-bearing Mg vacancies on conductivity in forsterite and olivine. We combined our diffusivity results with experimentally determined results for phonon conductivity but this predicted significaly lower conductivities than have been observed experimentally in olivine, particularly at low temperatures (~1000 K). This suggests that the effect of water on olivine conductivity is not primarily due to bulk 〖(2H)〗_Mg^X diffusion and operates via a different unknown mechanism.

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Section: The Effect Of Mg Diffusion Rate Variations On Conductivitycontrasting

confidence: 99%

Fast anisotropic Mg and H diffusion in wet forsterite

Muir¹,

Zhang²,

Walker³

2021

Preprint

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“…As usual, the relationship between the electrical conductivity of hydrous mineral and temperature satisfied with an Arrhenius relation, i.e., with the rise of temperature, and the electrical conductivity of sample will be increased, accordingly. As noted from a modified Arrhenius relation reported by Dai and Karato (2020) [9], the influences of water content and oxygen fugacity on the electrical conductivity of dry and hydrous Ti-doped polycrystalline olivine aggregates can be expressed as,…”

Section: Experimental Theory and Measurement Methodsmentioning

confidence: 99%

“…Recently, some available research found that the presence of water, either the trace molecular water (H2O) or the structural hydroxyl (OH) in hydrous mineral, plays a crucial role in many pressure-dependent physicochemical properties and their corresponding transport processes of deep Earth interior, such as electrical conductivity [9,10], elastic wave dispersion and its attenuation [11,12], grain-growth kinetics [13,14], elemental diffusion coefficient [15,16], dislocation creep [17,18], and dynamic recrystallization [19,20]. Whereas, the electrical conductivity of hydrous silicate minerals and rocks are highly sensitive to temperature, pressure, oxygen fugacity, crystallographic anisotropy, water-bearing content, dehydration effect, iron content, trace element of titanium-bearing content, oxidation-dehydrogenation effect, structural phase transition, etc.…”

Section: Introductionmentioning

confidence: 99%

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

Dai

Sun

et al. 2022

Minerals

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As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail.

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“…The electrical conductivities of geological samples at high temperatures and high pressures are required to invert the MT profiles. Numerous studies have therefore investigated the conductivity of the dominant geological materials in the Earth's interior (Reynard et al, 2011;Saltas et al, 2013Saltas et al, , 2020Manthilake et al, 2015Manthilake et al, , 2016Dai and Karato, 2020). Dehydration, metasomatism, and magmatism processes are considerably more active in subduction zones than in the stable continental lithosphere.…”

Section: Introductionmentioning

confidence: 99%

“…The Ol-NaCl-H 2 O system is therefore a relevant representation of the composition of wet regions in the uppermost mantle, e.g., mantle wedges of subduction zones. Although numerous studies have reported the high-pressure electrical conductivity of olivine single crystals and polycrystalline aggregates (Dai et al, 2010;Dai and Karato, 2014a;Dai and Karato, 2014b;Dai and Karato, 2014c;Dai and Karato, 2014d;Dai and Karato, 2020), the detailed Ol-NaCl-H 2 O system has not been previously reported under high-temperature and high-pressure conditions. In addition to the effects of pressure and oxygen fugacity, the molar percentages of magnesium and iron in synthetic olivine also exert a significant effect on the electrical conductivity of anhydrous samples at high temperatures and pressures (Dai and Karato, 2014b).…”

Section: Introductionmentioning

confidence: 99%

Influence of Saline Fluids on the Electrical Conductivity of Olivine Aggregates at High Temperature and High Pressure and Its Geological Implications

Sun

Dai

et al. 2021

Front. Earth Sci.

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The electrical conductivities of hydrous olivine (Ol) aggregates and Ol–H2O, Ol–NaCl–H2O (salinity: 1–21 wt%; fluid fraction: 5.1–20.7 vol%), Ol–KCl–H2O (salinity: 5 wt%; fluid fraction: 10.9–14.0 vol%) and Ol–CaCl2–H2O systems (salinity: 5 wt%; fluid fraction: 10.7–13.7 vol%) were measured at 2.0–3.0 GPa and 773–1073 K using a multi-anvil apparatus. The electrical conductivity of saline fluid-bearing olivine aggregates slightly increases with increasing pressure and temperature, and the electrical conductivities of both hydrous and saline fluid-bearing samples are well described by an Arrhenius relation. The dihedral angle of the saline fluids is approximately 50° in the Ol–NaCl–H2O system with 5 wt% NaCl and 5.1 vol% fluids, which implies that the fluids were interconnected along grain boundaries under the test conditions. The electrical conductivities of the Ol–NaCl–H2O system with 5 wt% NaCl and 5.1 vol% fluids are ∼two to four orders of magnitude higher than those of hydrous olivine aggregates. The salinity and fluid fraction moderately enhance the sample electrical conductivities owing to the interconnectivity of the saline fluids. The activation enthalpies of the electrical conductivities for the Ol–NaCl–H2O systems range from 0.07 to 0.36 eV, and Na+, Cl−, H+, OH−, and soluble ions from olivine are proposed to be the main charge carriers. For a fixed salinity and fluid fraction, the electrical conductivities of the Ol–NaCl–H2O system resemble the Ol–KCl–H2O system but are slightly higher than that of the Ol–CaCl2–H2O system. The Ol–NaCl–H2O system with a salinity of ∼5 wt% NaCl and fluid fraction larger than 1.8 vol% can be employed to reasonably explain the origin of the high-conductivity anomalies observed in mantle wedges.

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Electrical Conductivity of Ti‐Bearing Hydrous Olivine Aggregates at High Temperature and High Pressure

Cited by 16 publications

References 43 publications

Fast anisotropic Mg and H diffusion in wet forsterite

Fast anisotropic Mg and H diffusion in wet forsterite

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

Influence of Saline Fluids on the Electrical Conductivity of Olivine Aggregates at High Temperature and High Pressure and Its Geological Implications

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