Rheological properties of the lower mantle have strong influence on the dynamics and evolution of Earth. By using the improved methods of quantitative deformation experiments at high pressures and temperatures, we deformed a mixture of bridgmanite and magnesiowüstite under the shallow lower mantle conditions. We conducted experiments up to about 100% strain at a strain rate of about 3 × 10⁻⁵ second⁻¹. We found that bridgmanite is substantially stronger than magnesiowüstite and that magnesiowüstite largely accommodates the strain. Our results suggest that strain weakening and resultant shear localization likely occur in the lower mantle. This would explain the preservation of long-lived geochemical reservoirs and... read more

Deep inside the earth, seismic observations reveal that three distinct structures make up the boundary between the earth's metallic core and overlying silicate mantle at a depth of about 2,900 kilometers—an area whose composition is key to understanding the evolution and dynamics of our planet. These structures include remnants of subducted plates that originated near the earth's surface, ultralow-velocity zones believed to be enriched in iron, and large dense provinces of unknown composition and mineralogy. A team led by Caltech's Jennifer Jackson, professor of mineral physics has new evidence for the origin of these features that occur at the core-mantle boundary.

In addition to the pressure-volume-temperature diffraction... read more

Using a numerical model we include the intrinsic density change that occurs from high to low-spin ferropericlase around 50 GPa [ Sturhahn et. al., 2005 ]. This generates buoyancy similar to a discrete phase change. However, in pressure-temperature space the spin transition occurs over an extended pressure range for warmer material (Figure 1). The temperature broadening effect distributes spin- buoyancy over a large pressure range for warm plumes a nd a tight pressure range for cold slabs. In the deep mantle, spin-buoyancy works with therma l buoyancy and convection is enhanced for both upwellings and downwellings. In the shallow lowe r mantle spin-buoyancy m ildly hinders convection.

Although the additional buoyancy does not... read more