Abstract
AbstractExperiments in laser‐heated diamond anvil cells (LH DACs) are conducted to assess phase diagrams of planetary materials at high pressure‐temperature (P‐T) conditions; thus, reliable determination of temperature in LH DAC experiments is essential. Radiometric temperature determination in LH DACs relies on the assumption of sample's wavelength‐independent optical properties (graybody assumption), which is not justified for major lower mantle materials. The result is that experimental phase diagrams contain systematic unconstrained errors. Here we estimate the systematic error in radiometric temperature of nongray polycrystalline bridgmanite (Bgm; Mg0.96Fe2+0.036Fe3+0.014Si0.99O3) in a LH DAC by modeling emission and absorption of thermal radiation in a sample with experimentally‐constrained optical properties. A comparison to experimental data validates the models and reveals that thermal spectra measured in LH DAC experiments record the interaction of radiation with the hot nongray sample. The graybody assumption in the experiments on translucent Bgm (light extinction coefficient, k < ∼250 cm‐1 at 500–900 nm) yields temperatures ∼5% higher than the maximum temperature in the sample heated to ∼1900 K. In contrast, the graybody temperature of dark Bgm (k > ∼1500 cm−1), such as that produced upon melt quenching in LH DACs, underestimates the maximum temperature by ∼10%. Our experimental results pose quantitative constraints on the effect of nongray optical properties on the uncertainty of radiometric temperature determination in Bgm in the LH DACs. Evaluating nongray temperature in the future would enable a revision of the Bgm to post‐perovskite phase transition and the high‐pressure melting curve of Bgm.
Highlights
Measurements of the properties of minerals and rocks at high pressure-temperature (P-T) conditions advance our understanding of planetary interiors
Modeling thermal emission and its propagation in a nongray sample require that the wavelength-dependence of the sample's absorption and scattering coefficients are established in the spectral range of interest
We showed that the deviations of measured thermal emission from an ideal graybody behavior carry information on the interaction of light with the hot nongray Bgm in a laser-heated diamond anvil cells (LH DACs)
Summary
Measurements of the properties of minerals and rocks at high pressure-temperature (P-T) conditions advance our understanding of planetary interiors. A common experimental approach is to recreate the P-T conditions of interest in a laser-heated diamond anvil cell (LH DAC), where a small (∼10–100 μm) sample is squeezed between the tips of two diamonds and heated with IR (infra-red) lasers. This technique grants routine access to the thermodynamic conditions of planetary mantles and cores with the sample accessible to interrogation by a variety of optical, x-ray, and electrical probes (Geballe et al, 2020; Holtgrewe et al, 2019; Ohta et al, 2012; Petitgirard et al, 2014; Shen & Mao, 2017). The P-T slope of the phase boundary between bridgmanite (Bgm)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
