Electronic Spin Transition of Iron in the Earth's Lower Mantle

University Of Texas At Austin, Austin TX

Investigators

Abstract

Seismic waves traveling through the Earth have provided fundamental knowledge of the Earth?s interior. Mineralogical models of the planet indicate that the lower mantle, the most voluminous layer extending from 670 km to 2900 km in depth (~23 GPa to 140 GPa in pressures and approximately 1800 K to 4000 K in temperatures), consists of approximately 30% ferropericlase [(Mg,Fe)O] and 70% silicate perovskite containing minor amounts of aluminum [Al-(Mg,Fe,)SiO3], in addition to a small amount of calcium silicate perovskite (CaSiO3). Silicate perovskite transforms to a post-perovskite structure just above the core-mantle boundary. The properties of the Earth?s lower mantle are thus thought to be governed by this mineral assemblage, in which iron is the most abundant transition metal that can undergo electronic spin and valence transitions under high pressures and temperatures, and may alter the properties of these minerals. This proposal aims to study the nature of electronic spin transitions of iron in the lower mantle mineral assemblage, including ferropericlase, perovskite, and post-perovskite, with emphasis on associated properties influencing the chemical and physical dynamics of the lower mantle. Using a combination of laboratory and synchrotron-based facilities with high pressure-temperature diamond anvil cells, these experiments will probe physical properties most relevant to modeling the structure and geodynamics of the lower mantle including thermal equations of state, deformation and strength, sound velocities, and transport properties. With an emphasis on the spin transitions, these studies aim broadly to understand properties of the lower-mantle minerals at various pressure-temperature-composition conditions, providing direct mineral physics results for input into understanding the state of the lower-mantle at a time when tomographic images and geophysical models of the lower mantle are rapidly advancing. The expected results are fundamental to geophysics and geodynamics of the Earth and will provide new aspects of information to modeling satisfactorily the seismic, mineralogical, and geodynamic behavior of the lower mantle. The project will also develop new high-pressure techniques that will benefit researchers and students in the broad deep-mantle communities.