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_2.01 Overview – Mineral Physics: Past, Present, and Future_, G. D. Price, University College London, London, UK ВЄ 2007 Elsevier B.V. All rights reserved. Mineral physics involves the application of physics and chemistry techniques to understand and predict the fundamental behavior of Earth materials (e.g., Kieffer and Navrotsky, 1985), hence providing solutions to large-scale problems in Earth and planetary sciences. Mineral physics is relevant to all aspects of solid Earth sciences, from surface processes and environmental geochemistry to the deep Earth and the nature of the core. In this volume, however, we focus only on the geophysical applications of mineral physics (see also Ahrens (1995), Hemley (1998), and Poirier (2000)). These applications are not just constrained to understanding structure of the Earth (see Volume 1) and its evolution (see Volume 9), but will play a vital role in our understanding of the dynamics and evolution of other planets in our solar system (see Volume 10 and Oganov et al. (2005)). As a discipline, mineral physics has only been recognized for some 30 years or so, but it can trace its origins back to the very foundations of solid Earth geophysics itself. For example, the work of Oldham (1906) and Gutenberg (1913), which defined the seismological characteristics of the core, led to the inference on the basis of materials physics that the outer core is liquid because it cannot support the propagation of shear waves. A landmark paper in the history of applying mineral physics to understanding the solid Earth is "Density of the Earth" by Williamson and Adams (1923). Here, elastic constants of various rock types were used to interpret the density profile as a function of depth within the Earth that had been inferred from seismic and gravitational data. Their work was marked by taking into account the gravitationally induced compression of material at depth within the Earth, which is described by the Williamson–Adams relation explicitly linking geophysical observables (g(r), the acceleration due to gravity as a function of radius, r, and the longitudinal and shear seismic wave velocities Vp and Vs) with mineral properties (Ks, the adiabatic bulk modulus and density, x1a), via d x1aГ°r Гћ = – gГ°r Гћdr _jГ°r Гћ, ВЅ1ВЉ where j(r) is the seismic parameter as a function of radius, and is given by j(r) = V2 p (r)–4_3V2 s (r) = Ks (r) x1a (r) ВЅ2ВЉ. Further progress in inferring the nature of Earth's deep interior rested upon experimental determination of the elastic properties of rocks and minerals as a function of pressure and temperature. Notably, this work was pioneered over several decades by Bridgman (1958). In parallel with experimental studies, however, a greater understanding of the theory behind the effect of pressure on compressibility was being made by Murnaghan (1937) and Birch (1938). These insights into the equations of state of materials enabled Birch (1952) to write his classic paper "Elasticity and the Constitution of the Earth's Interior," which laid the foundations for our current understanding of the composition and structure of our planet. One notable outcome from investigating the effect of pressure and temperature on material properties was the discovery of new high-density polymorphs of crustal minerals. Thus, Coes (1953) synthesized a new high-density polymorph of SiO2 (subsequently named coesite), and Ringwood (1959) reported the synthesis of the spinel-structured Fe2SiO4 (that had previously been predicted by Bernal (1936)). Ringwood and colleagues went on to make a variety of other high-density silicate polymorphs, including phases now thought to make up the transition zone of the mantle, namely the spinelloids wadsleyite (-Mg2SiO4) and ringwoodite (-Mg2SiO4), and the garnet-structured polymorph of MgSiO3 (majorite). Further insights into the probable nature of deep Earth minerals came from Stishov and Popova (1961) who synthesized the rutile-structured polymorph of SiO2 (stishovite) that is characterized by having Si in octahedral coordination, and Takahashi and Bassett (1964) who first made the hexagonal close-packed polymorph of Fe, which today is thought to be the form of Fe found in the Earth's core (but see Chapter 2.05). As high-pressure and -temperature experimental techniques evolved, still further phases were discovered, the most important of which was the postspinel perovskite-structured polymorph of MgSiO3 (Liu, 1975). It was thought for some time that this discovery and subsequent work on the details of the high-pressure phase diagrams of silicate minerals had enabled a robust mineralogical model for the mantle to be established. This view, however, has had to be revised in recent years after the recent discovery of a postperovskite phase (Murakami et al., 2004; Oganov and Ono, 2000), which may be stable in the deepest part of the lower mantle. Notwithstanding this possibility of further new discoveries, the mineralogy and composition of the mantle and core are now relatively well defined. The current view of the mineralogy of the mantle is summarized in Figure 2, while as suggested by Birch (1952), the core is considered to be composed of iron (with minor amounts of nickel) alloyed with light elements (probably O, S, or Si). The solid inner core is crystallizing from the outer core and so contains less light elements. The current status of our understanding of the nature of the deep Earth is reviewed in detail in Chapters 2.02, 2.03, 2.04, and 2.05. Chapter Stixrude provides a general overview of the structure of the mantle. The nature of the lower mantle is still relatively controversial since generating lower mantle pressures (25–130 GPa) and temperatures (2000–3000 K) is still experimentally challenging, and mineral physics data and phase upper mantle TZ lower mantle Dі layer core 14 24 Cpx + Opx Pressure (GPa) 70 Ca-perovskite (Cubic or Tetragonal) CMB 125 136 CalrO3-type phase Mineral proportions Garnet Olivine Fe- and Al-bearing Mg-perovskite Ringwoodite Wadsleyite Liquid Fe Ferropericlase (High spin) (Low spin) 410 660 Depth (km) 2000 2700 2900 Figure 2 Phase relations of pyrolitic mantle composition as a function of depth. From Ono S and Oganov AR (2005) In situ observations of phase transition between perovskite and CaIrO3-type phase in MgSiO3 and pyrolitic mantle composition. Earth and Planetary Science Letters 236: 914–932. relations for the minerals thought to be found here are less robust. Furthermore, the recent discovery of the postperovskite phase has added even greater uncertainty to the nature of the D0 zone and the core-mantle boundary. The problems of the lower mantle and the core-mantle boundary are therefore reviewed in Chapter 2.03. Although the major element chemistry of the mantle is quite well studied, it is probably fair to say that understanding of trace elements chemistry and role of volatiles in the deep mantle is still in its infancy. This aspect of mantle chemistry, however, is vital if we are to fully understand processes involved in planetary formation, core segregation, and subsequent evolution of the Earth (see Volumes 9 and 10). The Chapter 2.04 provides a review of our understanding of this aspect of the mantle, while considerable progress in our understanding of nature and evolution of the core is provided in Chapter 2.05. As indicated above, our understanding of lower mantle and core are limited to some extent by inability easily to reproduce high-pressure and temperature conditions found in planetary interiors. To obtain greater insight, theory and experiment must be used together, and Chapters 2.06 and 2.13 present reviews of the theory underlying high-pressure, high-temperature physics, and major experimental methods being developed to probe this parameter space. The Chapter 2.06 outlines thermodynamic basis behind high-pressure-high-temperature behavior, expanding in greater detail on equations of state and way in which density and elastic properties of materials respond to changes in pressure and temperature. Macroscopic behavior of minerals depends upon microscopic or atomistic interactions within mineral structure. Thus, for example, free energy (and eventually phase stability) depends in part upon entropy, which in turn is dominated (for silicates at least) by lattice vibrations. Hence, in Chapter 2.07, a detailed analysis of lattice vibrations and spectroscopy of mantle minerals is presented. For the past 20 years, advances in computing power have enabled computational mineral physics to make contributions to our understanding of thermodynamic, thermo-elastic, and dynamical properties of high-pressure minerals. Initially, results of simulations based on inter-atomic potentials provided semiquantitative insights into lattice vibrations and thermodynamics of mantle phases (e.g., Price et al., 1987; Wall and Price, 1988). But more recently, quantum mechanical simulations of mantle and core phases have achieved precision and accuracy comparable with that achievable experimentally. As such, ab initio modeling must now be seen as a legitimate complement to experimental study. Therefore in this volume, theory and results from ab initio studies of some deep Earth phases are reviewed in Chapter 2.13. Despite the power and insight provided by theory, mineral physics is dependent upon quantitative high-pressure and -temperature experiments._ Ключевые слова: mantle, earth, core, high, mineral, physics, pressure, understanding, phase, minerals, temperature, chapter, nature, density, deep, volume, function, properties, experimental, theory, polymorph, phases, chemistry, materials, planetary, solid, structure, evolution, work, elastic