Reduced radiative conductivity of low spin FeO6-octahedra in FeCO3 at high pressure and temperature

Lobanov, Sergey S.; Holtgrewe, Nicholas; Goncharov, Alexander F.

doi:10.1016/j.epsl.2016.05.028

Cited by 28 publications

(35 citation statements)

References 47 publications

(100 reference statements)

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“…Iron can radically change the thermodynamic stability of carbonate phases, thereby preserving them from breaking down. This behaviour may be a direct consequence of pressure-induced spin crossover1718192021, which has been observed to occur at ∼43 GPa at room temperature to over 50 GPa at ∼1,200 K (ref. 22) for the endmember FeCO 3 .…”

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confidence: 95%

Stability of iron-bearing carbonates in the deep Earth’s interior

et al. 2017

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The presence of carbonates in inclusions in diamonds coming from depths exceeding 670 km are obvious evidence that carbonates exist in the Earth’s lower mantle. However, their range of stability, crystal structures and the thermodynamic conditions of the decarbonation processes remain poorly constrained. Here we investigate the behaviour of pure iron carbonate at pressures over 100 GPa and temperatures over 2,500 K using single-crystal X-ray diffraction and Mössbauer spectroscopy in laser-heated diamond anvil cells. On heating to temperatures of the Earth’s geotherm at pressures to ∼50 GPa FeCO3 partially dissociates to form various iron oxides. At higher pressures FeCO3 forms two new structures—tetrairon(III) orthocarbonate Fe43+C3O12, and diiron(II) diiron(III) tetracarbonate Fe22+Fe23+C4O13, both phases containing CO4 tetrahedra. Fe4C4O13 is stable at conditions along the entire geotherm to depths of at least 2,500 km, thus demonstrating that self-oxidation-reduction reactions can preserve carbonates in the Earth’s lower mantle.

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confidence: 95%

Stability of iron-bearing carbonates in the deep Earth’s interior

et al. 2017

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“…The linear temperature profile across the sample produces slabs with evenly spaced absorption coefficients, while the parabolic profile yields slabs with absorption coefficients grouping near the spectrum characteristic of T max . The produced mixed spin absorption spectra (Figure 5, left) resemble that directly measured in siderite (FeCO 3 ) upon its temperature-induced low-to-high spin transition at T <~1500 K and P = 45-55 GPa (Lobanov et al, 2016), which is a consequence of the similarity of Fp and siderite iron valence and spin configurations at 40-75 GPa.…”

Section: Spin-dependent Absorption Coefficientmentioning

confidence: 62%

“…Available spectroscopic studies of iron-bearing minerals indicate that the width and intensity of the absorption bands are moderately sensitive to temperature (Burns, 1993;Lobanov et al, 2016;Lobanov, Holtgrewe, et al, 2017;Shankland et al, 1979;Ullrich et al, 2002). Heating typically results in band broadening, due to the participation of vibrationally excited states in the electronic transition, and a red-shift due to the thermal expansion.…”

Section: Spin-dependent Absorption Coefficientmentioning

confidence: 99%

Radiometric Temperature Measurements in Nongray Ferropericlase With Pressure‐ Spin‐ and Temperature‐Dependent Optical Properties

Lobanov

Speziale

2019

JGR Solid Earth

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Accurate temperature determination is central to measurements of physical and chemical properties in laser‐heated (LH) diamond anvil cells (DACs). Because the optical properties of samples at high pressure‐temperature (P‐T) conditions are generally unknown, virtually all LH DAC studies employ the graybody assumption (i.e., wavelength‐independent emissivity and absorptivity). Here we test the adequacy of this assumption for ferropericlase (13 mol.% Fe), the second most abundant mineral in the Earth's lower mantle. We model the wavelength‐dependent emission and absorption of thermal radiation in samples of variable geometry and with absorption coefficients experimentally constrained at lower mantle P and P‐T. The graybody assumption in LH DAC experiments on nongray ferropericlase contributes moderate systematic errors within ±200 K at 40, 75, and 135 GPa and T < 2300 K for all plausible sample geometries. However, at core‐mantle boundary P‐T conditions (135 GPa, 4000 K) the graybody assumption may underestimate the peak temperature in the DAC by up to 600 K in self‐insulated samples due to selective light attenuation in highly opaque ferropericlase. Our results allow insights into the apparent discrepancy between available ferropericlase melting studies and offer practical guidance for accurate measurements of its solidus in LH DACs. More generally, the results of this work demonstrate that reliable temperature measurements in LH DACs require that the optical and geometrical properties of the samples are established.

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“…Data for transition zone minerals show that they are opaque (e.g., Thomas et al, ), suggesting low k rad . Also, although the spectra of lower mantle minerals are controversial in detail, measurements so far accumulated indicate that they are exceptionally opaque (e.g., Goncharov et al, , , ; Keppler et al, ; Lobanov et al, , ). Our models may thus be used to clarify details of opaque assemblages, but we do not contradict prior studies indicating that k rad is low in these settings.…”

Section: Geodynamic Applicationsmentioning

confidence: 99%

“…Most previous work on k rad in the Earth has been focused on values in the lower mantle and core-mantle boundary (e.g., Goncharov et al, 2008Goncharov et al, , 2009Goncharov et al, , 2015Keppler et al, 2008;Lobanov et al, 2016). This focus mainly stems from the recognition that lower mantle values control a number of important but poorly understood phenomena such as heat loss of the core (Lay et al, 2008), the generation of the Earth's magnetic field (Stevenson, 2003), and plume formation in the Earth's deep interior (Dubuffet et al, 2002;Matyska & Yuen, 2007;van den Berg et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

New Constraints on the Thermal Conductivity of the Upper Mantle From Numerical Models of Radiation Transport

Grose

Afonso

2019

Geochem Geophys Geosyst

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To address uncertainties in the values and mathematical form of the radiative thermal conductivity krad in the mantle, we developed new models for the transport, scattering, and absorption of thermal radiation in semitransparent multiphase polycrystalline assemblages. We show that the Rosseland diffusion equation correctly describes the diffusion of thermal radiation and infer the form of the effective spectral coefficients through numerical experimentation. We show that the scattering coefficient depends on the grain size and on interphase contact statistics in complicated ways, but that simplifications can be employed in practice. The effective opacity of a composite random material is a harmonically weighted mixture in the limit of infinitely large grain size and an arithmetically weighted mixture in the limit of infinitesimal grain size. Using existing absorption spectra for major upper mantle minerals, we estimate krad as a function of temperature, grain size, and petrology. In mantle assemblages, the scattering effect is important for small grain sizes (<1 mm), but the grain size effect on the effective opacity of a multiphase medium is important for grain sizes up to 10 cm. We calculate that upper mantle krad is about 2–3.5 W·m−1·K−1 for a representative mean grain size range of 0.01 to 1 cm. This translates to a total thermal conductivity of 5.5–7 W·m−1·K−1. Application of our model to the cooling of oceanic lithosphere shows that krad increases net cooling by about 25%.

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Reduced radiative conductivity of low spin FeO6-octahedra in FeCO3 at high pressure and temperature

Cited by 28 publications

References 47 publications

Stability of iron-bearing carbonates in the deep Earth’s interior

Stability of iron-bearing carbonates in the deep Earth’s interior

Radiometric Temperature Measurements in Nongray Ferropericlase With Pressure‐ Spin‐ and Temperature‐Dependent Optical Properties

New Constraints on the Thermal Conductivity of the Upper Mantle From Numerical Models of Radiation Transport

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