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Multidisciplinary Impact of the Deep Mantle Post-perovskite Phase Transition

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Multidisciplinary Impact of the Deep Mantle Post-perovskite Phase Transition

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  1. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Multidisciplinary Impact of the Deep Mantle Post-perovskite Phase Transition All minerals undergo phase transitions with increasing depth into the Earth. The changes in material properties across such transitions often give rise to detectable contrasts in seismic velocities and density. Strong velocities inhomogeneities are detected by seismology near the mantle's base, in a region several hundred kilometers thick called the D” region. Many processes could contribute to create these seismic anomalies at the boundary of two chemically distinct regions, the iron core and the silicate mantle. In 2004 experiments and theory demonstrated the existence of a phase transition in MgSiO3-perovskite, the major lower mantle mineral. Computations now predict that such phase transition can produce some of the enigmatic seismic anomalies observed in the D" region. These findings suggest that the new post-perovskite phase should be provide a new paradigm for interpreting the properties of this region. Multi-disciplinary scientific workshops held since this discovery and special sessions at 2004 Fall, 2005 Spring and Fall meetings of the American Geophysical Union are just the initial indicators of the broad impact across many fields that this intriguing new discovery is having. Tsuchiya et al,Phase transition in MgSiO3-perovskite in the Earth’s lower mantle, Earth Planet. Sci. Lett. 224, 241 (2004);ibid, Elasticity of MgSiO3-post-perovskite, Geophys. Res. Lett. 31, L14603, (2004);ibid,Vibrational and thermodynamic properties of MgSiO3 post-perovskite, J. Geophys. Res. 110, B02204/1-6 (2005); Wentzcovitch et al., MgSiO3 post-perovskiten at D” conditions, PNAS submitted (2005);Lay et al., Multidisciplinary impact of the deep Earth post-perovskite transition, EoS, AGU Trans. 86,1(2005). The newly discovered MgSiO3 post-perovskite phase has the uncommon CaIrO3 structure. http://vlab.msi.umn.edu

  2. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 The International Workshop on the Post-Perovskite Phase Transition in the Earth’s Deep Mantle will bring together geoscientists from various disciplines to debate the significance of this newly found mineral phase to deep mantle processes and structure. The workshop is also supported by the VLab. Organizers: Kei Hirose, David Yuen, Thorne Lay, and Masanori C. Kameyama. http://vlab.msi.umn.edu

  3. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Spin transition in Magnesiowüstite in Earth’s Lower Mantle Iron in the major lower mantle (LM) minerals undergoes a high spin (HS) to low spin (LS) transition at relevant pressures (23-135 GPa). Previous failures of standard first principles approaches to describe this phenomenon have hindered its investigation and the clarification of important geophysical consequences. Using a new rotationally invariant formulation of LDA+U we were able to successfully describe this transition in low solute concentration magnesiowüstite (Mw), (Mg1-xFex)O, (x < 0.2), the second most abundant LM phase. We show that the HS/LS transition goes through an insulating (semiconducting) intermediate mixed spins (MS) state without discontinuous changes in properties, as seen experimentally. These encouraging results open for exploration by first principles a new class of problems of profound significance to deep Earth geophysics. Tsuchiya, T., Wentzcovitch, R., de Gironcoli, S.,Spin transition in magnesiowustite in Earth’s lower mantle, Phys. Rev. Lett., submitted (2005). Pseudo-charge densities around ferrous iron in magnesiowüstite (xFe = 0.125 )at an isosurface with ρ = 0.3 e/Å3 for majority (A) and minority HS (B), and majority/minority LS (C). Polyhedral volume collapse across the spin transition (D). Six caps surrounding the ferrous ion belong to oxygens. http://vlab.msi.umn.edu

  4. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Post-Rh2O3(II) transition and the high PT phase diagram of alumina Phase diagram of alumina. The thick dashed lines are the regions where the QHA is invalid. The black, thin solid line is the melting curve of corundum. Black crosses, blue open circles, and red open triangles are conditions in which the corundum, Rh2O3II + corundum, during compression, and Rh3O3+corundum under decompression were observed experimentally, respectively. The high-pressure behavior of alumina has been investigated by first-principles computations throughout the range of calibration of the ruby pressure scale. It is found that at 0 K the transformation from corundum to Rh2O3II-type alumina at 87–113 GPa is followed by a second one to the CaIrO3 structure at 150–172 GPa. Quasiharmonic free-energy calculations show that both transformations display negative Clapeyron slope, which is a consequence of the decrease in polyhedral connectivity along the structural sequence. Like the first transformation, the second one should also have significant effects on the ruby pressure scale, especially if ruby is cycled across the phase boundaries. Tsuchiya, J. Tsuchiya, T., Wentzcovitch, R. Post-Rh2O3(II) transition and the high-pressure-temperature phase diagram of alumina,Phys. Rev. B (RC) 72, 020103 (2005). http://vlab.msi.umn.edu

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