摘要:

This is the first of a series of five papers in which the thermodynamic properties of minerals are interpreted in terms of lattice vibrational spectra. In this paper, measured heat capacities for minerals are examined in terms of the Debye theory of lattice vibrations, and it is demonstrated that heat capacities of silicates show large deviations from the behavior expected from Debye theory. The underlying assumptions of Debye theory are critically reviewed, and it is shown that the observed thermodynamic deviations in minerals probably arise from four effects not included in the Debye model: anisotropy of elastic parameters, dispersion of acoustic waves toward Brillouin zone boundaries, optic vibrations in excess of the Debye spectrum at low frequencies, and optic vibrations at frequencies much greater than the Debye cutoff frequency predicted by acoustic measurements. Each of the four effects influences the heat capacity in a particular temperature range: anisotropy, dispersion and low‐frequency optic vibrations are important at low temperatures (0°K to ∼100°K); high‐frequency vibrations are important at higher temperatures. It is necessary to include all four effects in a generalized lattice vibrational model for minerals; such a model is developed in papers 2‐5 of this series. The minerals included in this study are halite, periclase, brucite, corundum, spinel, quartz, cristobalite, silica glass, coesite, stishovite, rutile, albite, microcline, jadeite, diopside, enstatite, tremolite, talc, muscovite, forsterite, zircon, kyanite, andalusite, sillimanite, pyrope, grossular, andradite, spessartine, almandine an

ISSN:8755-1209    

DOI:10.1029/RG017i001p00001

年代:1979

数据来源: WILEY

摘要:

General lattice vibrational properties of minerals, particularly those properties which strongly influence the thermodynamic behavior, are discussed in this paper (the second of a series relating thermodynamic and lattice vibrational properties of minerals). Infrared (IR), Raman (R), and inelastic neutron scattering (INS) data are summarized, if known, for the following minerals: halite (INS), periclase (INS), corundum (IR, R), brucite (IR, R, partial INS), quartz (R, IR, INS), cristobalite (IR, R), silica glass (IR, R, partial INS), stishovite (IR), rutile (R, IR, INS), albite (IR, R), microcline (IR), spinel (IR, R), muscovite (IR, R), jadeite (IR), diopside (IR, R), enstatite (IR, R), olivine (IR, R), zircon (IR, R), kyanite (IR), andalusite (IR), sillimanite (IR), pyrope (IR), andradite (IR), grossular (IR), and calcite (IR, R, INS). New high‐resolution infrared data are given for kyanite, andalusite, sillimanite, stishovite, coesite, jadeite, diopside, pyrope, andradite, and grossular. The data presented and summarized show that optic modes of vibration of silicates are spread over a range of frequencies, generally from wave numbers as low as 75 cm−1to wave numbers as high as 1200 cm−1. The far‐infrared (low frequency) optic modes are particularly important in this study because they strongly influence the low‐temperature heat capacity and therefore the entropy. The mid‐infrared (high frequency) optic modes generally arise from the vibrations of tightly bound clusters within the structures and can generally be recognized as isolated bands in the vibrational spectrum. A method is given for enumeration of the fraction of total vibrational modes which are internal stretching modes. Inelastic neutron scattering data are reviewed to show the magnitude of anisotropy and dispersion of acoustic modes and of dispersion of optic modes in the minerals. The combined infrared, Raman, and INS data show that, excluding the stretching modes of quasi‐molecular clusters within the minerals, the optic modes do not appear to follow a simple recognizable distribution, such as a Debye distribution, but are rather uniformly distributed across a broad range o

ISSN:8755-1209    

DOI:10.1029/RG017i001p00020

年代:1979

数据来源: WILEY

摘要:

The principles of lattice dynamics are briefly reviewed in this paper, and from these principles a simple, generally applicable lattice vibrational spectrum is proposed for minerals. The spectrum can be used to calculate the thermodynamic functions in the harmonic approximation. The model proposed is consistent with lattice dynamics and is sufficiently detailed in its assumptions about the distribution of modes that the thermodynamic functions are closely specified. The primitive unit cell, containingsatoms, is chosen as the fundamental vibrating unit; it has 3sdegrees of freedom, three of which are acoustic modes. Anisotropy of these modes is included by use of anisotropic shear velocities for the two shear branches: dispersion is included by use of a sinusoidal dispersion relation between frequency and wave vector for all three acoustic branches. Optic modes, which comprise 3s–3 degrees of freedom, are represented by a uniform continuum, except for ‘intramolecular’ stretching modes (such as Si‐O stretching modes) which can be enumerated and identified as being isolated from the optic continuum. Parameters for the model are obtained from elastic and spectroscopic data; the model is independent of any calorimetric data. It is applied to give the temperature dependence ofCvover the range 0°–1000°K of halite, periclase, brucite, corundum, spinel, quartz, cristobalite, silica glass, coesite, stishovite, rutile, albite, and microcline. The specific heat of the simple Debyelike substances, halite and periclase, is reproduced well by the model. The influence of the additional formula unit of H2O on the vibrational and thermodynamic properties of brucite, as compared to periclase, is discussed. The heat capacities of the relatively simple minerals, spinel and corundum, are given accurately by the model. The heat capacities of quartz, cristobalite, and coesite are accurately predicted from spectroscopic data through the model. The heat capacity of silica glass is discussed in terms of the classic continuous random network (CRN) model and a paracrystalline model, the pentagonal dodecahedral (PD) model of Robinson (1965). The PD model appears to be more consistent with measuredCvdata than the CRN model. The heat capacity data of rutile are reasonably reproduced by the model as are the data for stishovite at temperatures above 50°K. Measured data for stishovite below 50°K appear to contain an excess heat capacity relative to the model; this excess may arise from surface energy contributions, as was suggested by Holm et al. (1967), and it is suggested that the model provides a better estimate of the low‐temperature vibrational heat capacity of stishovite than the measured data. The heat capacities of albite and microcline are reproduced well by the model. The model is only a simple approximation to real lattice vibrational spectra, but it appears to work well for a large number of minerals and is therefore useful in correlating structural, compositional, elastic, spectroscopic, and thermodynamic properties for purposes of extrapolation and prediction of t

ISSN:8755-1209    

DOI:10.1029/RG017i001p00035

年代:1979

数据来源: WILEY

摘要:

This paper reviews the simulation of earthquake occurrence by numerical and laboratory mechanical block models. Simple linear rheological elements are used with elastic forces driving the main events and viscoelastic forces being important for aftershock and creep occurrence. Friction and its dependence on velocity, stress, and displacement also play a key role in determining how, when, and where fault motion occurs. The discussion of the qualitative behavior of the simulators focuses on the manner in which energy is stored in the system and released by the unstable and stable sliding processes. The numerical results emphasize the statistics of earthquake occurrence and the correlations among source parameters.

ISSN:8755-1209    

DOI:10.1029/RG017i001p00061

年代:1979

数据来源: WILEY

摘要:

KREEP is a lunar material having very high concentrations of incompatible elements; its name is an acronym for the incompatibles K, rare‐earth elements (REE), and P. Although a few pristine (endogenously igneous) KREEPy samples were returned from the Apollo 15 and 17 sites, most KREEPy samples are polymict breccias. Most models of KREEP petrogenesis have been based on partial melting of a variety of sources. Such models fail to explain the veritable absence of variations in incompatible element patterns over the sampled portion of the moon. We have defined a KREEP component based on the average composition of Apollo 14 breccias having extremely high concentrations of incompatible elements. Normalization of accurate incompatible data for KREEPy samples from the Apollo 12, 14, 15, 16, and 17 sites to this component virtually always shows no resolvable fractionation (e.g.,<10% variation in the La/Lu ratio), whereas partial melting models typically produce larger fractionations (±20–25% in La/Lu) from a factor of 2 difference in degree of partial melting. Required is a single major source that could provide KREEP to widely separated locations on the nearside of the moon. The anorthositic crust of the moon is commonly attributed to the flotation of plagioclase on a deep, moon‐wide magma ocean. Fractional crystallization of this magma ocean would have produced large enrichments of incompatibles in a residual liquid. No other plausible major source of incompatibles has been proposed. We borrow the German prefix ur—meaning primeval and designate this residual liquid ‘urKREEP.’ We propose that all KREEPy rocks originated by dilution of urKREEP with crustal or mantle materials during assimilation, or zone‐refining (pristine samples), or impact‐induced brecciation (breccias and melt rocks). The formation of urKREEP cannot be dated precisely. Correction of breccia Rb‐Sr model ages for Rb loss or gain during the early intense bombardments yields ages that cluster in the range 4.4–4.5 Gy. This implies that crystallization of the magma ocean was essentially complete at this time and is in general agreement with U‐Pb evidence indicating crustal formation at 4.4 Gy. Assuming that the moon had the composition of an H‐group chondrite depleted in Fe‐Ni and FeS and that half the incompatibles fractionated into materials other than urKREEP, the thickness of a moon‐wide urKREEP layer was<2 km. Thorium concentrations determined by gamma ray spectroscopy indicate that about 4% of the incompatibles in an H chondritic moon are no

ISSN:8755-1209    

DOI:10.1029/RG017i001p00073

年代:1979

数据来源: WILEY

摘要:

A number of field observations of coastal currents have been recently reported. Using for the most part data acquired with moored current meters, these have allowed the determination of the spectrum of coastal currents in a broad frequency band, corresponding to periods ranging from 1 cycle/month to 1 cpm, in a wide variety of geomorphological settings and climates. In addition to such statistical descriptions of the current field, certain of these observations are such as to allow the effects of different driving forces, such as seasonal and short‐term meteorological forcing, adjoining ocean current systems, and tides, to be studied separately, providing required information for the development of reliable models of coastal current

ISSN:8755-1209    

DOI:10.1029/RG017i001p00089

年代:1979

数据来源: WILEY

摘要:

The theory and observations relating to ion velocity distributions in the high‐latitudeFregion are reviewed. The review covers three basic aspects, including methods for calculating ion velocity distributions, experimental evidence for the existence of non‐Maxwellian ion velocity distributions, and the ionospheric consequences of non‐Maxwellian distributions. Specific topics covered include closed form solutions to Boltzmann's equation for a simple collision model, series solutions to the Boltzmann equation for more general collision models, retarding potential analyzer measurements, excitation of VLF electrostatic emissions, ion‐neutral reaction rates, and transport

ISSN:8755-1209    

DOI:10.1029/RG017i001p00099

年代:1979

数据来源: WILEY

摘要:

Thresholds and linear growth rates for stimulated Brillouin and Raman scattering and for the parametric decay instability are derived by using arguments of energy transfer. For this purpose an expression for the ponderomotive force is derived. Conditions under which the partial pressure force due to differential dissipation exceeds the ponderomotive force are also discussed. Stimulated Brillouin and Raman scattering are weakly excited by existing incoherent backscatter radars. The parametric decay instability is strongly excited in ionospheric heating experiments. Saturation theories of the parametric decay instability are therefore described. After a brief discussion of the purely growing instability the effect of using several pumps is discussed as well as the effects of inhomogeneity. Turning to detailed theories of ionospheric heating, artificial spreadFis discussed in terms of a purely growing instability where the nonlinearity is due to dissipation. Field‐aligned short‐scale striations are explained in terms of dissipation of the parametrically excited Langmuir waves (plasma oscillations); they might be further amplified by an explosive instability (except at the magnetic equator). Broadband absorption is probably due to scattering of the electromagnetic pump wave into Langmuir waves. This absorption is probably responsible for the ‘Overshoot’ effect: the initially observed level of parametrically excited Langmuir waves is much higher than the steady stat

ISSN:8755-1209    

DOI:10.1029/RG017i001p00135

年代:1979

数据来源: WILEY

摘要:

This survey attempts first, briefly, to identify typical lightning and then to compare the methods used for evaluating the energy dissipated in a return stroke. Energy values obtained from a large number of measurements, estimates, and theoretical models are tabulated. An attempt is made to find a typical average value.

ISSN:8755-1209    

DOI:10.1029/RG017i001p00155

年代:1979

数据来源: WILEY

摘要:

The photometric and bulk parameters of the known and suspected satellites of Saturn are presented in updated tables and are compared. The surface compositions of all the satellites are discussed in terms of modern photometry and spectroscopy; most, if not all, of the inner bodies have water frost surfaces, but the outer three satellites have surfaces of unknown composition. The few reliable mass values of some inner satellites, together with the best current values for the satellite radii, suggest mean densities representative of bulk compositions dominated by frozen volatiles, though Titan may have a substantial volume fraction of silicates. The special case of Iapetus is considered in the light of new studies of its two distinct faces and polar cap.

ISSN:8755-1209    

DOI:10.1029/RG017i001p00165

年代:1979

数据来源: WILEY