Geophysics

Spinning Iron in the Mantle

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Science  21 Jun 2013:
Vol. 340, Issue 6139, pp. 1379
DOI: 10.1126/science.340.6139.1379-b

Transitions in the spin state, or electronic configuration, of iron can be induced by the high temperatures and pressures in Earth's interior. Spin transitions—whether they be abrupt or gradual with depth—could influence the physical properties of abundant iron-bearing minerals or affect the interpretation of seismic data; however, laboratory experiments at such extreme conditions have often been contradictory. Wu et al. developed a simple theoretical formulation to simulate the iron spin transition and used it to calculate elasticity in ferropericlase [(Mg, Fe)O], a major mineral in the lower mantle, across a wide range of pressures and iron compositions. The calculations predict that the spin transition should not have a strong effect on some important elastic properties, such as the shear modulus (the ratio of shear stress to shear strain). Moreover, the concentration of iron in ferropericlase will strongly influence seismic wave velocities, requiring readjustment of expected mantle compositions that are based on extrapolations of experimental results.

Phys. Rev. Lett. 110, 228501 (2013).

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