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Title: Thermal equation of state of lower-mantle ferropericlase across the spin crossover

Abstract

The thermal equation of state of ferropericlase [(Mg{sub 0.75}Fe{sub 0.25})O] has been investigated by synchrotron X-ray diffraction up to 140 GPa and 2000 K in a laser-heated diamond anvil cell. Based on results at high pressure-temperature conditions, the derived phase diagram shows that the spin crossover widens at elevated temperatures. Along the lower-mantle geotherm, the spin crossover occurs between 1700 km and 2700 km depth. Compared to the high-spin state, thermoelastic modeling of the data shows a {approx}1.2% increase in density, a factor of two increase in thermal expansion coefficient over a range of 1000 km, and a maximum decrease of 37% and 13% in bulk modulus and bulk sound velocity, respectively, at {approx}2180 km depth across the spin crossover. These anomalous behaviors in the thermoelastic properties of ferropericlase across the spin crossover must be taken into account in order to understand the seismic signatures and geodynamics of the lower mantle.

Authors:
; ; ;  [1];  [2]
  1. (UC)
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
NSFDOE - BASIC ENERGY SCIENCES
OSTI Identifier:
1049570
Resource Type:
Journal Article
Journal Name:
Geophys. Res. Lett.
Additional Journal Information:
Journal Volume: 38; Journal Issue: 12, 2011; Journal ID: ISSN 0094-8276
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES; DIAMONDS; HIGH SPIN STATES; PHASE DIAGRAMS; SIMULATION; SPIN; SYNCHROTRONS; THERMAL EXPANSION; VELOCITY; X-RAY DIFFRACTION

Citation Formats

Mao, Zhu, Lin, Jung-Fu, Liu, Jin, Prakapenka, Vitali B., and Texas). Thermal equation of state of lower-mantle ferropericlase across the spin crossover. United States: N. p., 2012. Web. doi:10.1029/2011GL049915.
Mao, Zhu, Lin, Jung-Fu, Liu, Jin, Prakapenka, Vitali B., & Texas). Thermal equation of state of lower-mantle ferropericlase across the spin crossover. United States. doi:10.1029/2011GL049915.
Mao, Zhu, Lin, Jung-Fu, Liu, Jin, Prakapenka, Vitali B., and Texas). Tue . "Thermal equation of state of lower-mantle ferropericlase across the spin crossover". United States. doi:10.1029/2011GL049915.
@article{osti_1049570,
title = {Thermal equation of state of lower-mantle ferropericlase across the spin crossover},
author = {Mao, Zhu and Lin, Jung-Fu and Liu, Jin and Prakapenka, Vitali B. and Texas)},
abstractNote = {The thermal equation of state of ferropericlase [(Mg{sub 0.75}Fe{sub 0.25})O] has been investigated by synchrotron X-ray diffraction up to 140 GPa and 2000 K in a laser-heated diamond anvil cell. Based on results at high pressure-temperature conditions, the derived phase diagram shows that the spin crossover widens at elevated temperatures. Along the lower-mantle geotherm, the spin crossover occurs between 1700 km and 2700 km depth. Compared to the high-spin state, thermoelastic modeling of the data shows a {approx}1.2% increase in density, a factor of two increase in thermal expansion coefficient over a range of 1000 km, and a maximum decrease of 37% and 13% in bulk modulus and bulk sound velocity, respectively, at {approx}2180 km depth across the spin crossover. These anomalous behaviors in the thermoelastic properties of ferropericlase across the spin crossover must be taken into account in order to understand the seismic signatures and geodynamics of the lower mantle.},
doi = {10.1029/2011GL049915},
journal = {Geophys. Res. Lett.},
issn = {0094-8276},
number = 12, 2011,
volume = 38,
place = {United States},
year = {2012},
month = {10}
}