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Title: Temperature of Earth's core constrained from melting of Fe and Fe 0.9Ni 0.1 at high pressures

Abstract

The melting points of fcc- and hcp-structured Fe 0.9Ni 0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mossbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time integrated synchrotron Mfissbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe 0.9Ni 0.1 fall within the wide region bounded by previous studies. We are able to derive the gamma-is an element of-1 triple point of Fe and the quasi triple point of Fe0.9Ni0.1 to be 110 ± 5 GPa, 3345 ± 120 K and 116 ± 5 GPa, 3260 ± 120 K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe 0.9Ni 0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe 0.9Ni 0.1 using our (quasi) triple points as anchors. The extrapolated Fe 0.9Ni 0.1 melting curve provides an estimate formore » the upper bound of Earth's inner core-outer core boundary temperature of 5500 ± 200 K. The temperature within the liquid outer core is then approximated with an adiabatic model, which constrains the upper bound of the temperature at the core side of the core -mantle boundary to be 4000 ± 200 K. We discuss a potential melting point depression caused by light elements and the implications of the presented core -mantle boundary temperature bounds on phase relations in the lowermost part of the mantle.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF). Directorate for Geosciences Division of Earth Sciences (GEO/EAR)
OSTI Identifier:
1340498
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Earth and Planetary Science Letters; Journal Volume: 447; Journal Issue: C
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Zhang, Dongzhou, Jackson, Jennifer M., Zhao, Jiyong, Sturhahn, Wolfgang, Alp, E. Ercan, Hu, Michael Y., Toellner, Thomas S., Murphy, Caitlin A., and Prakapenka, Vitali B.. Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures. United States: N. p., 2016. Web. doi:10.1016/j.epsl.2016.04.026.
Zhang, Dongzhou, Jackson, Jennifer M., Zhao, Jiyong, Sturhahn, Wolfgang, Alp, E. Ercan, Hu, Michael Y., Toellner, Thomas S., Murphy, Caitlin A., & Prakapenka, Vitali B.. Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures. United States. doi:10.1016/j.epsl.2016.04.026.
Zhang, Dongzhou, Jackson, Jennifer M., Zhao, Jiyong, Sturhahn, Wolfgang, Alp, E. Ercan, Hu, Michael Y., Toellner, Thomas S., Murphy, Caitlin A., and Prakapenka, Vitali B.. 2016. "Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures". United States. doi:10.1016/j.epsl.2016.04.026.
@article{osti_1340498,
title = {Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures},
author = {Zhang, Dongzhou and Jackson, Jennifer M. and Zhao, Jiyong and Sturhahn, Wolfgang and Alp, E. Ercan and Hu, Michael Y. and Toellner, Thomas S. and Murphy, Caitlin A. and Prakapenka, Vitali B.},
abstractNote = {The melting points of fcc- and hcp-structured Fe0.9Ni0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mossbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time integrated synchrotron Mfissbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe0.9Ni0.1 fall within the wide region bounded by previous studies. We are able to derive the gamma-is an element of-1 triple point of Fe and the quasi triple point of Fe0.9Ni0.1 to be 110 ± 5 GPa, 3345 ± 120 K and 116 ± 5 GPa, 3260 ± 120 K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe0.9Ni0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe0.9Ni0.1 using our (quasi) triple points as anchors. The extrapolated Fe0.9Ni0.1 melting curve provides an estimate for the upper bound of Earth's inner core-outer core boundary temperature of 5500 ± 200 K. The temperature within the liquid outer core is then approximated with an adiabatic model, which constrains the upper bound of the temperature at the core side of the core -mantle boundary to be 4000 ± 200 K. We discuss a potential melting point depression caused by light elements and the implications of the presented core -mantle boundary temperature bounds on phase relations in the lowermost part of the mantle.},
doi = {10.1016/j.epsl.2016.04.026},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 447,
place = {United States},
year = 2016,
month = 8
}