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Pressure-induced transformations in deep mantle and core minerals

Published online by Cambridge University Press:  05 July 2018

R. J. Hemley ,
H. K. Mao  and
S. A. Gramsch
R. J. Hemley*
Affiliation:
Geophysical Laboratory and Center for High-Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road N.W., Washington D.C. 20015, USA
H. K. Mao
Affiliation:
Geophysical Laboratory and Center for High-Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road N.W., Washington D.C. 20015, USA
S. A. Gramsch
Affiliation:
Geophysical Laboratory and Center for High-Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road N.W., Washington D.C. 20015, USA
*
*E-mail: hemley@gl.ciw.edu
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Abstract

Recent experimental and theoretical studies provide new insight into the variety of high-pressure transformations in minerals that comprise the Earth’s deep mantle and core. Representative examples of reconstructive, displacive, electronic and magnetic transformations studied by new diamond-anvil cell techniques are examined. Despite reports for various transitions in (Mg,Fe)SiO3-perovskite, the stability field of the orthorhombic phase expands relative to magnesiowüstite + SiO2 with increasing pressure and temperature. The partitioning of Fe and Mg between Mg-rich silicate perovskite magnesiowüstite depends strongly on pressure, temperature, bulk Fe/Mg ratio, and ferric iron content. The soft-mode transition in SiO2 from the rutile- to CaCl2-type structure, originally documented by X-ray powder diffraction, Raman scattering, and first-principles theory has been explored in detail by single crystal diffraction, and transitions to higher-pressure forms have been examined. The effect of H on the transformations of various nominally anhydrous phases and transitions in dense hydrous Mg-silicates are also examined. New studies of the phase diagram of FeO include the transition to rhombohedral and higher-pressure NiAs polymorphs, and provide prototypical examples of coupled structural, electronic, and magnetic transitions. High-spin/low-spin transitions in FeO have been examined by high-resolution X-ray emission spectroscopy to 150 GPa, and the results are compared with similar studies of Fe2O3 and FeS. Finally, laser-heating studies to above 150 GPa and 2500K show that (hcp) ε-Fe has a large P-T stability field. Radial XRD measurements carried out at room temperature to 220 GPa have constrained the elasticity, rheology and sound velocities of ε-Fe at core pressures.

Keywords

high-pressurediamond cellperovskitestishoviteX-ray emission spectroscopyelastic contentsiron
Type
Research Article
Information
Mineralogical Magazine , Volume 64 , Issue 2 , April 2000 , pp. 157 - 184
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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