SPring-8 is a third-generation synchrotron radiation facility that provides super-intense X-rays for basic and applied research in materials science. The bending magnet beamline, BL04B1 is one of the beamlines open for high-pressure and high-temperature research. A newly large volume high-pressure apparatus (SPEED-1500) was installed at BL04B1. This apparatus has a capability of generating pressures up to 40 GPa and a temperature of 3000 K by using a double-stage multi-anvil system with the sintered diamond anvils. High-pressure and high-temperature X-ray diffraction measurement using a combination of synchrotron radiation and SPEED-1500 makes it possible to investigate the constituent materials of the Earth's interior in the lower mantle.

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This paper reviews transformations and properties of minerals and rocks under lower mantle conditions. It is likely that most of the lower mantle consists of three minerals; orthorhombic perovskite in the system (Mg, Fe)SiO₃-Al₂O₃, cubic perovskite CaSiO₃, and magnesiowuestite (Mg, Fe)O, with the composition slightly enriched in Fe and Si compared to the upper mantle. Transformation in subducted oceanic crust at lower mantle conditions, which is crucial for under-standing the dynamics of the mantle, is still unclear.

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In situ X-ray observation using Drickamer type high pressure apparatus and its application to geophysics are discussed in detail. At first, characteristics of Drickamer apparatus are introduced by comparing with diamond anvil cell and multi anvil apparatus. Then, two topics are discussed as its applications to geophysical problems: One is the mechanism of deep-focus earthquakes and the other is the phase relation of iron which thought to be dominant component of the Earth's inner core. Nature of deep-focus earthquakes has been enigmatic. Two models describing the mechanism of deep earthquakes are proposed recently based on high pressure experiments and seismological measurements of the structure of subduction zone. These two models, frictional instability caused by pore water pressure and transformational faulting, are briefly introduced, and discussed in relation to differential stress measured by the Drickamer apparatus. Recently, the existence of two new phases of iron is proposed. One is a high temperature phase with dhcp structure, which appears at pressures of above 30GPa. The other is a very high pressure and temperature phase above 200GPa and 4000K with bcc structure which is proposed theoretically. Whether the former new phases exist or not is discussed together with X-ray and electrical resistance data obtained by the Drickamer apparatus.

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It is worthwhile to note that hydrogen atoms sructually bound to minerals can interact with network-forming oxygen atoms in minerals through hydrogen-bonding. This suggests the significance of chemical state of hydrogen on studying the role of hydrogen to the change in physicochemical and elastic properties of materials in the mantle. IR spectroscopy provides us with much information on the chemical states of OH species contained in these H-carrying minerals. This paper reviews the advantages of IR spectroscopy to the speciation of OH in minerals, quantitative analysis of hydrogen and determination of direction of OH dipole moment in a single crystal along with the several attentions to be paid on thepractical experimantal procedures. Furthermore, speciation of OH in the olivine-wadsleyite-ringwoodite system and its potential role on mantle dynamics is mentioned in detail. It is a definite fact that IR spectroscopy is one of the most promising method to study properties of hydrogen in minerals, but a complementarity use of other methods such as neutron diffraction will be necessary for thorough understanding of hydrogen in minerals.

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Experimental studies on the rheology of the Earth's mantle have been reviewed. During the past 30 years, defomation experiments of mantle minerals androcks have been conducted by constant strain-rate and constant load tests and the microstructures in recovered samples have been observed with electron microscopy and/or an oxidation decoration method in order to understand deformation mechanisms in the mantle. Rheological properties of both single crystal and polycrystal of olivine which is the major constituent in the upper mantle have been particularly investigated. The results have indicated that their plasticities are strongly influenced by water content, oxygen fugacity and grain size as well as temperature and strain rate conditions. Seismic anisotropy in the upper mantle is most certainly due to the preferred orientation of olivine which is induced by dislocation creep. Since the middle of 1980s, deformation experiments of garnet, perovskite and their analog materials have been conducted in order to clarify the dynamics in the subducting slub, mantle transition zone and lower mantle. Ordinary deformation apparatuses such as Griggs apparatus can not directly elucidatethe effect of high pressure on the plasticity in the mantle minerals due to the limitation of their generated pressure ranges. To overcome this problem, high-pressure apparatuses such as multi-anvil apparatus have been recently applied for rheological studies.

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This paper reviews the effect of H₂O in the mantle mineralsbased on the recent author's studies. The topics include the melting relations and the melt compositions of the mantle materials under hydrous conditions, the hydrous minerals in the earth interiors, especially hydrous wadsleyite and hydrous ringwoodite, the effect of H₂O in the phase transition of olivine, the elastic properties of hydrous minerals, the rheology of olivine polymorphs between anhydrous and hydrous conditions, the dehydration of the slab constituentminerals, and the generation of komatiite magma in the hydrous mantle.

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High pressure and high temperature studies on materials under the Earth's lower mantle conditions by the laserheated diamond anvil cell (DAC) experiments combined with analytical transmission electron microscopy (ATEM) are reviewed. Importance of the careful preparation of the foils and the proper procedures in the chemical analyses of the DAC samples by ATEM is described. Also, the powerfulness of the ATEM for the studies of the phase transformations and the phase relations of mantle minerals is stressed. Our recent results, based on this approach, on the phase transitions in perovskite and the post-garnet phases under the lower mantle conditions are presented together with results of other groups.

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