Publication

Composition dependence of spin transition in (Mg,Fe)SiO3 bridgmanite

Philippe Gillet, James Badro, Susannah McGregor Dorfman
2015
Journal Articles

Abstract

Spin transitions in (Mg,Fe)SiO3 bridgmanite have important implications for the chemistry and dynamics of Earth's lower mantle, but have been complex to characterize in experiments. We examine the spin state of Fe in highly Fe-enriched bridgmanite synthesized from enstatites with measured compositions (Mg0.61Fe0.38Ca0.01)SiO3 and (Mg0.25Fe0.74Ca0.01)SiO3. Bridgmanite was synthesized at 78-88 GPa and 1800-2400 K and X-ray emission spectra were measured on decompression to 1 bar (both compositions) and compression to 126 GPa [(Mg0.61Fe0.38Ca0.01)SiO3 only] without additional laser heating. Observed spectra confirm that Fe in these bridgmanites is dominantly high spin in the lower mantle. However, the total spin moment begins to decrease at similar to 50 GPa in the 74% FeSiO3 composition. These results support density functional theory predictions of a lower spin transition pressure in highly Fe-enriched bridgmanite and potentially explain the high solubility of FeSiO3 in bridgmanite at pressures corresponding to Earth's deep lower mantle.

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https://infoscience.epfl.ch/entities/publication/1aec144f-ad5c-45b7-9487-80701ad0faf1

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Philippe Gillet, James Badro, Susannah McGregor Dorfman
2015
Journal Articles

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/1aec144f-ad5c-45b7-9487-80701ad0faf1

About this result

Related concepts (18)

Lower mantle

The lower mantle, historically also known as the mesosphere, represents approximately 56% of Earth's total volume, and is the region from 660 to 2900 km below Earth's surface; between the transition zone and the outer core. The preliminary reference Earth model (PREM) separates the lower mantle into three sections, the uppermost (660–770 km), mid-lower mantle (770–2700 km), and the D layer (2700–2900 km). Pressure and temperature in the lower mantle range from 24–127 GPa and 1900–2600 K.

Earth's mantle

Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of and thus makes up 67% of the mass of Earth. It has a thickness of making up about 84% of Earth's volume. It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid, sometimes described as having the consistency of caramel. Partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle at subduction zones produces continental crust.

Upper mantle

The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from approximately at the upper boundary with the crust to approximately at the boundary with the lower mantle. Upper mantle material that has come up onto the surface comprises about 55% olivine, 35% pyroxene, and 5 to 10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel, or garnet, depending upon depth.

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