摘要:

Lunar crustal rocks can be divided into two groups: the terra, or highland, types and the mare basalts. Interpretation of the highland samples is complicated by their derivative nature, which resulted from a series of crystallization, shock, and brecciation events. In contrast, mare basalts appear to be much less complicated and to have been rather uncompromised since their arrival at the lunar surface; thus a synthesis appears possible at this time. Although the mare basalts comprise less than 1% of the lunar crust, they contain much information about the thermal history of the moon and the nature of the lunar interior. It is now known that a complete suite of basalts, sampling all of the chemically and temporally distinct units, was not sampled by the Apollo and Luna missions. The mare basalts that have been studied have ages between 3.15 and 3.96 Gy. However, photogeologic evidence (crater counts and crater degradation studies) indicates that basalts as young as 2.5 Gy exist on the moon and were not sampled. The returned samples can be divided into two broad groups: the older, high‐titanium group (ages, ∼3.55–3.85 Gy; TiO2, 9–14 wt %) and the younger, low‐titanium group (ages, 3.15–3.45 Gy; TiO2, 1–5 wt %). Basalts from Apollo 11 and 17 fall into the older, high‐titanium group; basalts from Apollo 12 and 15 and Luna 16 fall into the younger, low‐titanium group. The two major groups of basalts can be further subdivided on the basis of major‐ and minor‐element chemistry. Within each of these subgroups a variety of grain sizes and textures, which result from different cooling histories, are present. Near‐surface fractionation of these basalts involved mainly olivine in the low‐titanium basalts and olivine plus iron‐titanium oxides in the high‐titanium basalts. The alkali‐depleted mare basalts evolved by rapid cooling at the lunar surface under extremely reducing conditions (∼10−13atm at 1150°C). This low oxygen fugacity resulted in reduced valence states for Ti (Ti4+→ Ti3+) and Cr (Cr3+→ Cr2+), which in turn affected both the chemistry and the stability of the mare basalt minerals. The most important mineralogical species in these rocks are the silicates (pyroxene, feldspar, and olivine) and the Fe‐Ti oxides (ilmenite, spinel, and armalcolite). Models for the source regions of the mare basalts remain controversial. Three basic models for mare basalt source regions have been advanced. These include the cumulate source model (remelting of cumulates resulting from early lunar differentiation), the primitive source model (melting of deep undifferentiated mantle), and the assimilation model (primary melts are contaminated by assimilation). All of these models have problems. If one assumes that at least some of the lunar basalt samples arrived at the surface with unaltered chemistry, the high‐pressure experimental phase equilibria approach can provide constraints on the nature of the source regions for these rocks. Results of these studies indicate that the low‐ and high‐Ti mare basalt groups were derived from mineralogically distinct source regions. The low‐Ti basalts could have been derived from an olivine‐pyroxene source rock at depths ranging from 200 to 500 km, while the high‐Ti basalts could have been derived from olivine‐pyr

ISSN:8755-1209    

DOI:10.1029/RG014i004p00475

年代:1976

数据来源: WILEY

摘要:

The determination of the elastic properties of composite materials (multiphase aggregates, polycrystals, and porous or cracked solids) from the elastic properties of the components may be approached in several ways. The problem may be treated statistically, via scattering theory, through variational principles, or by the assumption of specific geometries for the material under consideration. Each of these methods is reviewed in turn. The widely used Voigt‐Reuss‐Hill average can be a poor approximation for both two‐phase composites and polycrystals, and its replacement by the two Hashin‐Shtrikman bounds is recommended. For pore‐containing or crack‐containing media, specific geometry models must be considered if useful results are to be obtained. If aggregate theory is used to estimate the moduli of individual components of a composite whose bulk properties are known, the shear moduli of the component phases must be matched (within a factor of 2 or 3) for the method to be useful. Results for nonlinear composites (which allow calculation of the pressure variation of aggregate moduli) have been obtained for only a few sp

ISSN:8755-1209    

DOI:10.1029/RG014i004p00541

年代:1976

数据来源: WILEY

摘要:

This paper seeks to collect together and to assess the many measurements of stratospheric humidity which have been reported over the last 25 years, with a view to determining the average distribution of water vapor in the stratosphere and its variations in time and space. Variations with height, latitude, time, and season are considered. In addition, some consideration is given to the proper use of experimental values of humidity in discussions of the water budget and circulation of the stratosphere; it is emphasized that the considerable uncertainties which often exist in measured data often can preclude the drawing of quantitative conclusions.

ISSN:8755-1209    

DOI:10.1029/RG014i004p00565

年代:1976

数据来源: WILEY

摘要:

Two extensive series of measurements of magnetospheric ULF waves in the Pc 3 frequency range (22–100 mHz) have been carried out in pairs of conjugate areas (Kerguelen‐Sogra and Siple‐Lac Rebours) which have approximately the same geomagnetic latitudes (L∼ 3.5–4.0) but are separated by more than 8 hours in local time. The results of these measurements are compared in this review, and some differences in the results are discussed in terms of possibly differing ionospheric and ground conditions in the conjugate areas. Additional, possibly cooperative, studies to investigate further the magnetospheric wave phenomena in this frequency range are

ISSN:8755-1209    

DOI:10.1029/RG014i004p00577

年代:1976

数据来源: WILEY

摘要:

A variety of magnetometer systems have been constructed utilizing superconducting quantum interference device (Squid) sensors. The magnetometers have high sensitivity and fast response times and eliminate the need for spinning or vibrating the sample to make measurements. The magnetometers have superconducting sense coils in which a dc persistent current is induced by the insertion of the sample. The current gives, via a flux transformer, a field at the Squid sensor, which is detected as the measure of the magnetization of the sample. The sense coils, the transformer, and the detector are housed within a superconducting shield. It was the advent of the Josephson junction devices which permitted the use of critical currents so small that flux‐switching sensors such as those used in the magnetometers could be developed. The particular Squid used in these magnetometers is an RF‐driven weak link sensor. The magnetometers have been used to observe magnetic transitions to identify magnetic phases. A high‐field susceptometer with a superconducting magnet permits determination of saturation magnetization and magnetic characteristics. Standard paleomagnetic samples can be measured at a magnetic moment sensitivity of 10−8G cm³. Small samples have been measured with a 3‐mm access system whose noise level is 2 × 10−10G cm³. Long cores can be measured by using a horizontal open access system. Continuous thermal demagnetization and intensity determinations are b

ISSN:8755-1209    

DOI:10.1029/RG014i004p00591

年代:1976

数据来源: WILEY

摘要:

This paper reviews the methods which may be used to estimate the state of the atmosphere, i.e., the distribution of temperature and composition, from measurements of emitted thermal radiation such as are made by remote sounding instruments on satellites. The principles of estimation theory are applied to a linear version of the problem, and it is shown that many of the apparently different methods to be found in the literature are particular cases of the same general method. As an aid to understanding, the optimum linear solution is described in terms of the geometry ofndimensions, withn= 3 for illustration. In generalizing the approach to the nonlinear problem there are two stages: (1) finding any member of the infinite family of possible solutions, which may be done by any convenient iterative method, and (2) finding the optimum solution by satisfying appropriate constraints.

ISSN:8755-1209    

DOI:10.1029/RG014i004p00609

年代:1976

数据来源: WILEY

摘要:

The status of analysis and significant results of the ultraviolet spectrometer observations of Mercury, the moon, the interplanetary medium, the comet Kohoutek, and Venus are summarized.

ISSN:8755-1209    

DOI:10.1029/RG014i004p00625

年代:1976

数据来源: WILEY

摘要:

Naturally occurring whistlers provide a powerful ground‐based technique for probing the magnetosphere. The major features of the theory of whistler propagation in ducts in the plasmasphere are well understood. The details of how the whistler propagates upward from its source and excites the duct and how it escapes from the duct and reaches the ground are not so clear. Recent direction‐finding experiments are designed to find the point at which the signal emerges from the lower ionosphere; from this the motion in longitude of the duct in which the whistler has propagated is inferred. It is thus important to understand the propagation of the signal between the duct and the lower ionosphere in order to interpret direction‐finding experiments. Another problem of current interest is the amplification of whistlers. In this paper, existing theoretical understanding of the propagation of whistlers is reviewed. The region between the lower ionosphere and the ducts and the mechanisms of excitation of and leakage from the ducts are discussed. An attempt is made to identify those problems which require solution if the whistler technique is to be used to its full e

ISSN:8755-1209    

DOI:10.1029/RG014i004p00629

年代:1976

数据来源: WILEY