Advantage of mineralogical approach in clarifying peculiar physical properties for materials is introduc in the review. Precise structure analyses of the diffraction and X?ray absorption fine structure (XAFS) spectroscopy methods provide the important information on the Earth and planetary materials. The information from both long-range-order structure by diffraction method and local structure by XAFS method is important for the understanding of the correlation between structures and physical properties of minerals. High pressure and high temperature in-situ diffraction and XAFS experiments were performed using a multi-anvil high-pressure device and synchrotron radiation. Both experiments are also useful as a probe of vibration dynamics and disordered structure. The pressure-dependent anharmonic effective potentials and characteristic values can be investigated using the diffraction and XAFS Debye-Waller factors. The ionic conduction mechanism has been proposed based on the effective one-particle potential and effective pair potential. Super ionic conduction of the mantle constituents resulting from anharmonic thermal vibration can produce the high electric and the low thermal conductivities in the Earth's lower mantle. Local structures of atoms in melt and glass of tetrahedrally coordinated materials change rapidly to higher coordinated states with pressure as if first-order phase transition. Unique structures are left in the local structures of the trace elements in minerals and tektite-impactite glass. The application of recently innovated techniques to the characterization of materials under extreme conditions contributes to the advancement of fundamental Earth-scientific knowledge.
Extensive lenticular-shaped ultramafic complexes that are composed of dominant amount of dunite associated with harzburgite and irregular-shaped pyroxenite cumulates, occur in the basal part of the Salahi mantle section in the northern Oman ophiolite. Petrologic characteristics such as rock types, textures and mineral compositions were examined to understand the origin of the ultramafic complex. Peridotites exhibit coarse-granular to very coarse-granular texture with grain size greater than five millimeters. The Cr#[=Cr/(Cr+Al) atomic ratio] of spinels in harzburgites ranges from 0.56 to 0.72, and is most frequent at 0.64-0.66 while spinel Cr# of dunites ranges from 0.61 to 0.84, and is most frequent at 0.76-0.82. The origin of voluminous dunite with high Cr# spinel can be explained by flux melting of residual harzburgite as a result of infiltration of large amount of fluid from the base of the ophiolite during oceanic thrusting. Dunites with very coarse-granular texture also support this hypothesis. The dunites in the central part of the complex tend to have both olivine Fo content and spinel Cr# greater than those in the host harzburgites. We speculate that not only orthopyroxene but also olivine were consumed during flux melting in this region resulted in the formation of voluminous dunites in the core of the complex. On the other hand, the dunites from the periphery of the complex have olivine with Fo content lower than those in the host harzburgites indicating precipitation of olivine from the melt. Moreover, crystallization of pyroxene formed numerous pyroxenites in this region. The southern part of the Salahi mantle section has been considered as a paleo-ridge segment end region. Our results support that the occurrence of highly refractory peridotites is spatially related to the segment end region in the northern Oman ophiolite.
Approaches to elucidate thermal history of the earth based on information of earth materials are reviewed. Limitations of these approaches are examined, and ways for the improvement and additional approaches to better constrain the thermal history of the earth are proposed. A short note of the current thermal status of the earth is followed by examination of earth's thermal history based on geophysical modeling of mantle convection, combination of which with material information is essential to deepen our understanding. There are several proxies of earth materials for secular changes of the thermal state of the earth's interior. Those often used so far are: (1) chemical composition of magmas, from which ‘potential temperatures’ of the ambient mantle are estimated, (2) pressure and temperature conditions of crustal materials (metamorphic rocks), from which ‘metamorphic geothermal gradients’ are estimated, (3) thickness of the crust and lithosphere, from which thermal gradients of the crust and lithosphere are estimated along with the temperature estimation of the bottoms, and (4) pressure and temperature of mantle materials, from which ‘mantle geothermal gradients’ of the lithosphere are estimated. Each method has problems to be resolved for quantitative estimation of the secular variation of the earth's thermal state. The following approaches are proposed: (1) coupling thickness of oceanic crust and depletion zone of residual mantle and major element composition of volcanic rocks, (2) high-resolution analysis of thermal history of crust and mantle materials to better constrain steady-state geotherms, and (3) simultaneous estimation of ambient pressure and temperature as well as mantle potential temperature from analysis of magma intrusions in the crust. Finally, the importance of extraterrestrial materials and earth-like exoplanets to reveal thermal history of the early earth, for which direct information is not available, is remarked.