摘要:

The origin of Apollo 11 basalts is discussed in terms of two hypotheses: (1) formation by a small degree of partial melting in the lunar interior, and (2) formation by prolonged near‐surface crystallization differentiation in a lava lake. The second hypothesis is rejected on the following grounds: Most Apollo 11 magmas are far removed from the plagioclase‐pyroxene‐ilmenite cotectic; fractional crystallization cannot explain the large variations in concentrations of incompatible trace elements in conjunction with the small variations in major‐element compositions, particularly, Mg/Fe ratios; experimentally determined partition coefficients show that the high abundances of Cr and V in Apollo 11 rocks cannot be reconciled with the previous separation of large quantities of ore minerals and pyroxenes. On the other hand, the major‐element and trace‐element contents of Apollo 11 rocks can be readily explained by partial melting of source material that buffers the major‐element compositions and causes enrichments of incompatible elements according to the degree of partial melting (first hypothesis). Two alternative sources have been suggested for Apollo 11 basalts formed by partial melting: (1) unfractionated pyroxenite source region at depths of 200–600 km, and (2) fractionated source region with incompatible elements (e.g. Ba, U, and rare earths) strongly enriched over chondritic abundances and containing plagioclase (approximate eucritic composition). Mass‐balance calculations and plagioclase‐stability conditions show that the second hypothesis requires Apollo 11 basalts to be generated by partial melting in the outer 150 km of the moon. This is very difficult to achieve one billion years after the moon's formation, since the outer 200 km will have cooled well below the solidus by conduction. Furthermore, magmas generated by partial melting of a plagioclase‐bearing source region should have plagioclase on the liquidus, which is contrary to observation. The second hypothesis accordingly appears improbable. The first hypothesis is capable of explaining the major‐element chemistry and the trace‐element abundances (Eu; see below) in terms of a simple, single‐stage model that is consistent with the moon's density, moment of inertia, and inferred thermal history. A possible explanation of the europium anomaly is suggested on the basis of the first hypothesis. It will be necessary to determine the appropriate partition coefficients in order to test this explanation. If the lunar highlands are anorthositic, extensive differentiation of the outer 150 km of the moon is required. This may have been caused by heating arising from partial conservation of gravitational potential energy during the final stage of accretion. Formation of Apollo 11 basalts by partial melting 3.7 billion years ago was probably the result of radioactive heating (U, Th) in the deep interior of the moon. A two‐stage magmatic history for the moon is thus required. Similarities between compositions of Apollo 11 and terrestrial basalts and between their respective source regions are suggestive of a genetic relationship between moon and earth. Nevertheless, important differences in trace‐element abundances, major‐element compositions, and oxidation states exist. These abundance patterns are unfavorable to the traditional fission, binary planet, and capture hypotheses of lunar origin. However, they may be explicable in terms of the precipitation hypothesis proposed by the author. This maintains that during the later stages of accretion of the earth, a massive primitive atmosphere developed that was hot enough to evaporate selectively a substantial proportion of the silicates that were accreting on the earth. Subsequently, the atmosphere was dissipated and the relatively nonvolatile silicate components were precipitated to form a swarm of planetesimals or moonle

ISSN:0148-0227    

DOI:10.1029/JB075i032p06453

年代:1970

数据来源: WILEY

摘要:

Information on the mineralogy and petrology of the Apollo 11 crystalline basaltic rocks, obtained by about 35 groups of investigators, is summarized and used as a basis for speculation. The textural assemblage indicates near‐surface, rapid crystallization from low‐viscosity basaltic magmas under low oxygen pressures. The basalts are subsilicic and subalkaline, but only locally titaniferous. Terrestrial alkali basalts could, through alkali depletion, give similar assemblages under reducing conditions, but probably no primary lunar basalt has yet been sampled. Crystal accumulation, shown by Apollo 12 specimens, would be the main control of local variations in basalt composition. Apollo 11 specimens are more residual in composition but may in part be from remelted ilmenitic cumulates. Strong fractionation within rocks leads to a residuum with both granitic and syenitic affinities, with iron enrichment and titanium depletion as a predominant fractionation trend. The mineral phases are spectacular in character and diversity, and at least 30 phases have been recognized. Crystal‐liquid fractionation gives early phases rich in Mg, Ca, Cr, and Ti, and late phases rich in Fe, Mn, Na, K, P, Si, and Zr. The Fe‐Ni‐S immiscible liquids show sulfur loss and nickel gain in the Apollo 12 suite. Rapid‐quench, metastable crystallization was soon followed by equilibrium fractionation and then by subsolidus equilibration between phases. Basaltic fragments may be derived from subhighlands layered plutons, mare lava flows, and small crystallized pools of impact‐generated melts. Primary basalt magmas probably originated from partial melting of a pyroxenite mantle. Early, large‐scale melting of the outer pyroxenite shell could have produced a primitive basalt crust that differentiated to give a highlands and subhighlands crust. Some surface basalts may be derived from the latter, rather than from later partial meltin

ISSN:0148-0227    

DOI:10.1029/JB075i032p06480

年代:1970

数据来源: WILEY

摘要:

The Apollo 11 soil sample consists of particles derived from two rock suites, basaltic and anorthositic. Crystalline, glassy, and brecciated forms of each rock type are present. The basaltic suite (95% of identifiable soil particles) must be representative of mare rock; the anorthosites appear to derive from the lunar highlands. An anorthositic crust ∼10 km thick is required beneath the highlands to support their relief above the mare surfaces isostatically. To form such a crust via crystal fractionation requires that magma derived from initial partial melting of a substantial fraction of the moon (one‐third the volume, for a chondritic moon) be collected at the lunar surface in early times. Such a layer could not be kept hot and molten for very long; hence the young basalts collected by the Apollo 11 and 12 missions must have been produced by subsequent melting at depth, attributable to internal radioactive heating, and are not products of the early magma system that gave rise to the anorthositic crust. Basaltic lava, being less dense than solid basalt, is capable of rising into topographic basins (maria) that are already isostatically equilibrated with their higher surroundings. A lava overfilling of this type would constitute a mascon, giving rise to a positive gravity anom

ISSN:0148-0227    

DOI:10.1029/JB075i032p06497

年代:1970

数据来源: WILEY

摘要:

The α‐scattering technique of chemical analysis as used on the Surveyor lunar missions is described. Improved α sources and methods of data analyses lead to appreciably better results than those achieved previously by this technique. The accuracy of the α‐scattering method has been tested through the analysis of eleven rocks of known composition using a space Surveyor instrument. These results have provided the basis for estimation of the errors of the lunar surface analyses on Surveyors 5, 6, and 7. Some nonstandard geometrical relationships of sample to instrument, such as were encountered on the Surveyor missions, have been studied and their effects estimated. As a by‐product of this work, chemical analyses of five rocks of unknown composition were

ISSN:0148-0227    

DOI:10.1029/JB075i032p06514

年代:1970

数据来源: WILEY

摘要:

Presented here are values of dielectric permittivity, dissipation factor, and electrical conductivity of Apollo 11 lunar samples 10020, 10057, and 10046 in the frequency range 100 Hz to 10 MHz and temperature range from −196°C to + 200°C. The dielectric properties determined on earth basalts and a simulated lunar material with the composition of the Surveyor 5 results are used to characterize the dielectric properties of these lunar samples. We conclude that: (1) the lunar samples have higher values of the dielectric constant than terrestrial basalts, an effect due probably to the presence of ilmenite in the lunar samples, and the high‐frequency dielectric constant of the lunar igneous samples is about 9 to 15, whereas that of the lunar breccia is about 6 to 9; (2) the lunar samples show greater dielectric losses than terrestrial basalts, and the loss tangents measured on the lunar igneous samples are consistently higher than those of the lunar breccia, ranging from 0.09 to 0.2 for the igneous samples and 0.5 to 0.09 for the breccia; (3) the electrical conductivity values for the lunar samples are 10−9to 10−11(ohm cm)−1, and the electrical conductivity of the lunar igneous samples depends more strongly on temperature than that observed for the lunar brecica; (4) all the lunar samples show a temperature‐dependent, low‐frequency dispersion that may be due to the combined effect of impurity charges and moisture in the samples that is absorbed from

ISSN:0148-0227    

DOI:10.1029/JB075i032p06524

年代:1970

数据来源: WILEY

摘要:

Lunar powder samples returned by Apollo 11 are remarkably similar in their optical properties to those measured for an area of several square kilometers surrounding Tranquillity base, suggesting a ubiquitous covering of the same material in the region. However, there are minor exceptions to the close match: the powder sample shows large polarizations and a larger opposition effect than would be expected from previous observations. In the spectrum of the lunar rock samples, we detected a strong, broad absorption at 0.92 μ and a weaker band at ≳1.8 μ, which are likely to be caused by Fe2+in clinopyroxene. The band near one micron was absent in the powder sample (presumably because the particle sizes were too small), which suggests that the spectrophotometer may become a valuable tool in distinguishing between rocky and dusty areas on the m

ISSN:0148-0227    

DOI:10.1029/JB075i032p06532

年代:1970

数据来源: WILEY

摘要:

Infrared spectra have been acquired under simulated lunar conditions that demonstrate that, contrary to popular belief, features of high spectral contrast are available for small‐particle‐size samples. The spectral information occurs in the form of emission maxima that are associated with the principal Christiansen frequencies, and these maxima are diagnostic of gross composition. The features represent a 5 to 30% effect, depending on particle size and composition. The effect is explained in terms of the sharp thermal gradients produced close to the surface under lunar conditi

ISSN:0148-0227    

DOI:10.1029/JB075i032p06539

年代:1970

数据来源: WILEY

摘要:

It has been shown that, if the mean rate of lunar radioactive heat generation is similar to the terrestrial value, and if the moon is relatively undifferentiated, solid‐state thermal convection can be expected within the moon. Because of the larger surface‐to‐volume ratio on the moon, the cold and rigid outer shell is considerably thicker than on the earth; as a result, fragmentation of the shell has not occurred, explaining the lack of lunar seismic activity. Pressure release during convection could produce basaltic magmas consistent with the composition of the rocks returned by Apollo 11. An approximate analysis of lunar convection indicates that the convection velocities within the moon may be large. In this case complete differentiation may have occurred early in the history of the moon; however, there is presently, no way to estimate the rate of differentiation so it is not possible to conclude whether convection and differentiation are continuing on the

ISSN:0148-0227    

DOI:10.1029/JB075i032p06549

年代:1970

数据来源: WILEY

摘要:

Heat‐capacity measurements have been made on portions of lunar rocks 10017 and 10046 in the temperature region 2° to 5°K. For both specimens, the heat capacity is over 100 times greater than is predicted from acoustic wave velocities measured in the same rocks. Several possible reasons for this behavior are considered. It is concluded that the effect originates in the existence of one or more small peaks in the low‐frequency part of the vibrational frequency distribution. The ‘excess’ heat capacity of rock 10017 can be accounted for semiquantitatively by one such peak containing 3% of the normal modes at a frequency of 5 cm−1. Thermal equilibration in rock 10046 was sufficiently slow to allow a good estimate to be made of its thermal conductivity. The result,K= 2.5(±0.5) × 10−6cal/sec cm deg, is compared with values obtained by using other experimental techniques. The thermal conductivity of rock 10017 was found to be 10 to 1

ISSN:0148-0227    

DOI:10.1029/JB075i032p06553

年代:1970

数据来源: WILEY

摘要:

The mascon in a lunar ringed mare is approximately proportional to the area of the mare material in the basin. This relationship is consistent with the hypothesis that the lunar mascons are produced by dense plugs in the maria, and it means that the maximum thickness of the uncompensated rock is the same for all maria. The relationship also predicts the presence of mascons in other ringed lunar structures, such as Maria Orientale and Smythii, which are consistent with satellite Doppler data. The relative masses of the known and predicted mascons accurately predict the moon's dynamical asymmetry without any large mascons on the lunar farside. However, reconciliation of the absolute differences between the lunar moments of inertia with satellite accelerations directly above the maria requires mascons buried deeper than 250 km. Such deeply buried mascons seem unlikely. It therefore also seems unlikely that the differences in the lunar moments of inertia are completely due to the mascons. However, a converse relationship cannot be ruled out. Examination of the degree variances of harmonic analyses of lunar gravity reveals a gentle peak near degree 10. This peak is predicted by the spacing of the two largest mascons, Imbrium and Serenitatis.

ISSN:0148-0227    

DOI:10.1029/JB075i032p06558

年代:1970

数据来源: WILEY