Shun-ichiro Karato

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Because of their distinct chemical signatures, ocean-island and mid-ocean-ridge basalts are traditionally inferred to arise from separate, isolated reservoirs in the Earth's mantle. Such mantle reservoir models, however, typically satisfy geochemical constraints, but not geophysical observations. Here we propose an alternative hypothesis that, rather than(More)
The influence of water and stress on the lattice-preferred orientation (LPO) of olivine aggregates was investigated through large strain, shear deformation experiments at high pressures and temperatures (P=0.5–2.1 GPa, T=1470–1570 K) under both waterpoor and water-rich conditions. The specimens are hot-pressed synthetic olivine aggregates or single crystals(More)
[1] The frequency dependence of Q in Earth’s upper mantle is investigated using the continuous P wave spectra over 0.08 < f < 8.0 Hz. Regional waveform data from 23 events in the Pacific slab recorded on broadband stations in western Japan were used to create spectral ratio estimates of P waves which sample a subducting slab and mantle wedge. We assumed the(More)
It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals--for example, plastic deformation and melting temperature--and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water content of the Earth's mantle by direct sampling provides only a limited(More)
The distribution of water in the Earth's interior reflects the way in which the Earth has evolved, and has an important influence on its material properties. Minerals in the transition zone of the Earth's mantle (from approximately 410 to approximately 660 km depth) have large water solubility, and hence it is thought that the transition zone might act as a(More)
Several hypotheses have been proposed to explain trench-parallel shear wave splitting in the mantle wedge of subduction zones. These include 3-D flow effects, parallel melt filled cracks, and B-type olivine fabric. We predict the distribution of Btype and other fabrics with high-resolution thermal and stress models of subduction zones. A composite viscous(More)
[1] Shear-wave splitting observations at several subduction systems show trench-parallel fast directions in the fore-arc mantle. The presence of B-type olivine fabric in the mantle wedge may provide an explanation for this pattern of anisotropy under low-temperature and hydrated conditions. Sensitivity tests are shown that provide insights into the(More)
Materials circulation in Earth’s mantle will be modified if partial melting occurs in the transition zone. Melting in the transition zone is plausible if a significant amount of incompatible components is present in Earth’s mantle. We review the experimental data on melting and melt density and conclude that melting is likely under a broad range of(More)
The chemical evolution of the Earth and the terrestrial planets is largely controlled by the density of silicate melts. If melt density is higher than that of the surrounding solid, incompatible elements dissolved in the melt will be sequestered in the deep mantle. Previous studies on dry (water-free) melts showed that the density of silicate melts can be(More)