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- Title
Radiometric Temperature Determination in Nongray Bridgmanite: Applications to Melting Curve and Post‐Perovskite Transition Boundary in the Lower Mantle.
- Authors
Lobanov, Sergey S.; Speziale, Sergio; Lin, Jung‐Fu; Schifferle, Lukas; Schreiber, Anja
- Abstract
Experiments 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. Plain Language Summary: We modeled how the color of Earth's most abundant mineral (bridgmanite) affects temperature measurements in laser‐heated diamond anvil cell experiments with implications to the phase diagram of bridgmanite. We show that, depending on the optical properties of bridgmanite, temperature determination in such experiments may either systematically overestimate or underestimate the maximum temperature by up to 5%–10% due to the wavelength‐dependent emission and absorption in the hot sample. Overall, this study shows the phase boundaries in the bridgmanite system need revision. Key Points: Thermal radiation spectra record a nongray interaction with bridgmanite in laser‐heated diamond anvil cellsRadiometric temperature of nongray bridgmanite in laser‐heated diamond anvil cells is up to 5%–10% off the maximum sample temperatureExtant melting curves and experimental phase transition boundaries in the bridgmanite system contain this systematic error in temperature
- Subjects
RADIOMETRY; BRIDGMANITE; PEROVSKITE; EXTINCTION coefficients (Optics); LASER heating
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB021723