Laboratory‐based electrical conductivity in the Earth's mantle

Xu, Yongfu; Shankland, T. J.; Poe, Brent T.

doi:10.1029/2000jb900299

Cited by 204 publications

(205 citation statements)

References 54 publications

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“…6A) show that the spin transition in the earth's lower mantle is a continuous cross-over. Considering the P-T conditions along a geotherm (47), the smooth transformation of the spin state takes place at pressures between 55 GPa and 90 GPa, corresponding to the mid-lower mantle conditions over a depth of ∼1,500-1,900 km. Because lower-mantle ferropericlase is expected to be subjected to pressures up to 136 GPa and temperatures as high as ∼2,800 K, the extreme pressure is expected to increase the spin gap and thus to increase the T S value.…”

Section: Discussionmentioning

confidence: 99%

Quantum critical point and spin fluctuations in lower-mantle ferropericlase

Lyubutin

Struzhkin

Mironovich

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Ferropericlase [(Mg,Fe)O] is one of the most abundant minerals of the earth's lower mantle. The high-spin (HS) to low-spin (LS) transition in the Fe 2+ ions may dramatically alter the physical and chemical properties of (Mg,Fe)O in the deep mantle. To understand the effects of compression on the ground electronic state of iron, electronic and magnetic states of Fe 2+ in (Mg 0.75 Fe 0.25 )O have been investigated using transmission and synchrotron Mössbauer spectroscopy at high pressures and low temperatures (down to 5 K). Our results show that the ground electronic state of Fe 2+ at the critical pressure P c of the spin transition close to T = 0 is governed by a quantum critical point (T = 0, P = P c ) at which the energy required for the fluctuation between HS and LS states is zero. Analysis of the data gives P c = 55 GPa. Thermal excitation within the HS or LS states (T > 0 K) is expected to strongly influence the magnetic as well as physical properties of ferropericlase. Multielectron theoretical calculations show that the existence of the quantum critical point at temperatures approaching zero affects not only physical properties of ferropericlase at low temperatures but also its properties at P-T of the earth's lower mantle. , which has a 79% abundance (1-6). Great interest recently has been focused on the pressure-induced electronic transition in (Mg,Fe)O, in which the Fe 2+ ions transform from the high-spin (HS) state [total spin momentum (S) = 2] to the low-spin (LS) state (S = 0) (7-14). A series of observed physical and chemical properties of (Mg,Fe)O have been altered dramatically by the spin transition in the relevant range of pressure-temperature (P-T) conditions of the deep earth's mantle, including thermal (15, 16) and electrical (17) conductivity, density (18,19), incompressibility (18), and sound velocity (20). Most previous investigations on the spin transition of iron in ferropericlase were performed at either room temperature or high temperatures. At pressures near the spin cross-over, the Fe ions may exist in a mixed condition, with HS and LS states coexisting as the result of thermal fluctuations. This mixed state results in a wide cross-over with a smooth, continuous transition from the HS to the LS state with a pressure interval (ΔP) of ∼20 GPa (9, 14). Studies on the electronic and magnetic states at low temperatures may provide crucial information on the ground state of the Fe ions in ferropericlase at high pressures (21).We have investigated electronic and magnetic properties of Fe 2+ in two representative compositions of ferropericlase (Mg 1-x Fe x )O (x = 0.25 and 0.2) at high pressures and low temperatures using transmission Mössbauer spectroscopy (TMS) and synchrotron Mössbauer spectroscopy (also called nuclear forward scattering, NFS) in diamond anvil cells (DACs) up to 90 GPa. Hyperfine parameters of iron ions derived from the Mössbauer spectra are used to construct the magnetic phase diagram. We find quantum critical point in the phase diagram at 55 GPa and low temperatures wher...

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Section: Discussionmentioning

confidence: 99%

Quantum critical point and spin fluctuations in lower-mantle ferropericlase

Lyubutin

Struzhkin

Mironovich

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…Typical values quoted for the resistivity of the electrical asthenosphere are in the range of 5-25 -m, whereas at depths of 200-250 km a dry mantle mineralogy on an adiabat will yield a resistivity of hundreds of ⋅m (Xu et al, 2000).…”

Section: Elas Layermentioning

confidence: 99%

“…The bulk conductivity of the mantle is primarily controlled by temperature and composition (e.g., Xu et al, 2000;Ledo and Jones, 2005), but can be dramatically enhanced by the presence of an interconnected conducting phase such as melt or graphite, which is typically a minor constituent of the rock matrix. For these reasons, conductivity in the mantle lends itself to the identification of key upper mantle boundaries, both vertically and laterally.…”

Section: Elas Layermentioning

confidence: 99%

The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

Eaton

Darbyshire

Evans

et al. 2009

Lithos

393

288

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The lithosphere-asthenosphere boundary (LAB) is a first-order structural discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Although it is the most extensive type of plate boundary on the planet, its definitive detection, especially beneath cratons, is proving elusive. Different proxies are used to demarcate the LAB, depending on the nature of the measurement. Here we compare interpretations of the LAB beneath three The seismic LAB beneath cratons is typically regarded as the base of a high-velocity mantle lid, although some workers infer its location based on a distinct change in seismic anisotropy.Surface-wave inversion studies provide depth-constrained velocity models, but are relatively insensitive to the sharpness of the LAB. The S-receiver function method is a promising new seismic technique with complementary characteristics to surface-wave studies, since it is 2 sensitive to sharpness of the LAB but requires independent velocity information for accurate depth estimation. Magnetotelluric (MT) observations have, for many decades, imaged an "electrical asthenosphere" layer at depths beneath the continents consistent with seismic lowvelocity zones. This feature is most easily explained by the presence of a small amount of water in the asthenosphere, possibly inducing partial melt. Depth estimates based on various proxies considered here are similar, lending confidence that existing geophysical tools are effective for mapping the LAB beneath cratons.

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“…In the isotropic model ( Figure 3a) the conductivity at depths greater than ~100 km is significantly greater than that predicted from laboratory data for dry peridotite at a potential temperature of 1350 o C. The laboratory-based conductivity profiles are calculated using a temperature profile for 3 Ma old lithosphere assuming a mantle comprised of 75% olivine and 25% orthopyroxene 12 . There is almost no error associated with extrapolation of the experimental data because the measurements were made at the conditions of interest.…”

mentioning

confidence: 99%

Geophysical evidence from the MELT area for compositional controls on oceanic plates

Evans¹,

Hirth²,

Baba

et al. 2005

Nature

222

210

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Magnetotelluric (MT) and seismic data, collected during the MELT experiment at the Southern East Pacific Rise (SEPR) 1,2 , constrain the distribution of melt beneath this mid-ocean-ridge spreading center and also the evolution of the oceanic lithosphere during its early cooling history. In this paper, we focus on structure imaged at distances ~100 to 350 km east of the ridge crest, corresponding to seafloor ages of ~1.3 to 4.5 Ma, where the seismic and electrical conductivity structure is nearly constant, independent of age. Beginning at a depth of about 60 km, there is a large increase in electrical conductivity and a change from isotropic to transversely anisotropic electrical structure with higher conductivity in the direction of fast propagation for seismic waves. Because conductive cooling models predict structure that increases in depth with age, extending to about 30 km at 4.5 Ma, we infer that the structure of young oceanic plates is instead

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Laboratory‐based electrical conductivity in the Earth's mantle

Cited by 204 publications

References 54 publications

Quantum critical point and spin fluctuations in lower-mantle ferropericlase

Quantum critical point and spin fluctuations in lower-mantle ferropericlase

The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

Geophysical evidence from the MELT area for compositional controls on oceanic plates

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