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Temperature of Earth's core constrained from melting of Fe and Fe_(0.9)Ni_(0.1) at high pressures

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. (2016) Temperature of Earth's core constrained from melting of Fe and Fe_(0.9)Ni_(0.1) at high pressures. Earth and Planetary Science Letters, 447 . pp. 72-83. ISSN 0012-821X.

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The melting points of fcc- and hcp-structured Fe_(0.9)Ni_(0.1) and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mössbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time-integrated synchrotron Mössbauer 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_(0.9)Ni_(0.1) fall within the wide region bounded by previous studies. We are able to derive the γ–ϵ–l triple point of Fe and the quasi triple point of Fe_(0.9)Ni_(0.1) to be 110 ± 5GPa, 3345 ± 120K and 116 ± 5GPa, 3260 ± 120K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe_(0.9)Ni_(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_(0.9)Ni_(0.1) using our (quasi) triple points as anchors. The extrapolated Fe_(0.9)Ni_(0.1) melting curve provides an estimate for the upper bound of Earth's inner core–outer core boundary temperature of 5500 ± 200K. 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 ± 200K. 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.

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Alternate Title:Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures
Additional Information:© 2016 Elevier B.V. Received 22 December 2015. Received in revised form 24 April 2016. Accepted 26 April 2016. We thank G. Shen, M. Rivers, Y. Meng, W. Bi, A. Alatas, B. Chen and C. Ma for useful discussions and help in conducting experiments. We thank NSF (EAR-1316362) for financial support of this research as well as GeoSoilEnviroCARS and HP-CAT for allowing access to their laser drilling and the ruby fluorescence systems. Use of GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR-1128799) and Department of Energy–GeoSciences (DE-FG02-94ER14466). Use of the Advanced Photon Source is supported by the U.S. D.O.E., O.S., O.B.E.S. (DE-AC02-06CH11357). Sector 3 operations are supported in part by COMPRES under NSF Cooperative Agreement EAR 06-49658. Microprobe analyses were carried out at the Caltech GPS Division Analytical Facility (funded in part by the MRSEC Program of the NSF under DMR-0080065). We would like to thank Dr. Oliver Lord and two anonymous reviewers for constructive comments, and Dr. John Brodholt for handling the manuscript.
Group:Seismological Laboratory
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-94ER14466
Department of Energy (DOE)DE-AC02-06CH11357
NSFEAR 06-49658
Subject Keywords:Fe; Fe–Ni; melting; core; high pressure
Record Number:CaltechAUTHORS:20160523-144251907
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Official Citation:Dongzhou Zhang, Jennifer M. Jackson, Jiyong Zhao, Wolfgang Sturhahn, E. Ercan Alp, Michael Y. Hu, Thomas S. Toellner, Caitlin A. Murphy, Vitali B. Prakapenka, Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures, Earth and Planetary Science Letters, Volume 447, 1 August 2016, Pages 72-83, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67262
Deposited By: Ruth Sustaita
Deposited On:23 May 2016 22:28
Last Modified:02 Jun 2017 21:00

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