Geophysics

Tossing Minerals into the Mix

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Science  27 Mar 2009:
Vol. 323, Issue 5922, pp. 1647
DOI: 10.1126/science.323.5922.1647c

Numerical models of flow in Earth's mantle have helped to constrain structural hypotheses about Earth's interior derived from seismic observations, mineral physics data on phase transitions, and geochemical data on the presence of possible distinct reservoirs. Typically, however, the models have required many simplifying assumptions—most, for example, have not explicitly used the wealth of mineral physics data. Nakagawa et al. have now developed a model framework that includes the phase relations, and corresponding thermodynamic properties, across five major components that dominate the major element chemistry of the mantle: the oxides of calcium, magnesium, iron, silicon, and aluminum. Models were run for the equivalent of 4.5 billion years of Earth's history, though it is still difficult to simulate the full convective vigor of Earth. The more realistic inclusion of mantle phases doesn't drastically affect many of the results as compared with prior simulations: subducting slabs, for example, are still predicted to penetrate the major phase boundary at 660 km and accumulate near the base of the mantle. The new models do show a reduced pattern of heterogeneity that is more in line with seismic data, but some of the richness of the seismic data is not as well reproduced, particularly in the complex upper mantle. — BH

Geochem. Geophys. Geosyst. 10, 10.1029/2008GC002280 (2009).

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