Engineering topics
Publications and source records attributed to Hubbard, N. J..
A method of analyzing soil samples with a mass spectrometer employing a spark-discharge ion source is described, and the effectiveness of the method is demonstrated by applying it to the determination of impurities, in amounts of less than 10 mg, in lunar samples. It is shown that four parts of the Luna-20 lunar highland sample differ in their chemical composition.
A study is made of the trace elements found in ocean ridge basalts. General assumptions regarding melting behavior, trace element fractionation, and alteration effects are presented. Data on the trace elements are grouped according to refractory lithophile elements, refractory siderophile elements, and volatile metals. Variations in ocean ridge basalt chemistry are noted both for regional and temporal characteristics. Ocean ridge basalts are compared to other terrestrial basalts, such as those having La/Yb ratios greater than those of chondrites, and those having La/Yb ratios less than those of chondrites. It is found that (1) as compared to solar or chondrite ratios, ocean ridge basalts have low ratios of large, highly-charged elements to smaller less highly-charged elements, (2) ocean ridge basalts exhibit low ratios of volatile to nonvolatile elements, and (3) the transition metals Cr through Zn in ocean ridge basalts are not fractionated more than a factor of 2 or 3 from the chondritic abundance ratios.
The chemistry of the region surrounding Mare Crisium is described using improved Al/Si and Mg/Si intensity ratios derived from Apollo 15 X-ray fluorescence measurements. Mg/Si ratios are shown to increase from 0.6 in the region east of Mare Smythii to 1.0 in western Mare Serenitatis, while Al/Si ratios show sharp decreases in all mare areas. It is concluded that the terra (nonmare) material has a uniform Al/Si ratio, hence plagioclase content, and increases in the Mg/Si ratio in terra material imply similar increases of Mg in the pyroxenes and olivines of this material. The observed diversity of terra soils can be explained by an originally chemically diverse region not homogenized by heavy bombardment, or by volcanism subsequent to bombardment. Maria Crisium, Serenitatis and Smythii are found to be filled with low albedo materials which have a wide range of Mg/Si values, with small and apparently consistent differences in Al/Si ratio.
The orbital gamma-ray data yielded by the Apollo 15 and 16 missions have produced information about lunar differentiation. This information is also applicable to studying lunar petrogenesis using lunar samples. It is shown that the spatial variation in petrogenetic processes, as observed in the K/Th, Fe/Th, and Mg/Fe ratios, is of nearly the same magnitude as that of the lunar samples. The consistent relationship of both mare and nonmare basaltic surface chemical compositions, and the low surface elevation suggests a physical control on the movement of basaltic magma onto the lunar surface.
The basic goal of the conference was consideration of the origin of the planets of the solar system, based on the physical and chemical data obtained by study of the material of the moon and planets. Papers at the conference were presented in the following sessions: (1) Differentiation of the material of the moon and planets; (2) The thermal history of the moon; (3) Lunar gravitation and magnetism; (4) Chronology of the moon, planets, and meteorites; (5) The role of exogenic factors in the formation of the lunar surface; (6) Cosmochemical hypotheses about the origin and evolution of the moon and planets; and (7) New data about the planets Mercury, Venus, Mars, and Jupiter.
Nearly all rocks returned from the moon are readily divided into three broad categories on the basis of their chemical compositions: (1) mare basalts, (2) non-mare rocks of basaltic composition (KREEP, VHA), and (3) anorthositic rocks. Only mare basalts may unambiguously be considered to have original igneous textures and are widely understood to have an igneous origin. Nearly all other lunar rocks have lost their original textures during metamorphic and impact processes. For these rocks one must work primarily with chemical data in order to recognize and define rock groups and their possible modes of origin. Non-mare rocks of basaltic composition have chemical compositions consistent with an origin by partial melting of the lunar interior. The simplest origin for rocks of anorthositic chemical composition is the crystallization and removal of ferromagnesian minerals. It is proposed that the rock groups of anorthositic and non-mare basaltic chemical composition could have been generated from a single series of original, but not necessarily primitive, lunar materials.
Lunar core samples were analyzed using a spark source mass spectrometer. The analytical results for the four zones of the Lunar 20 core suggest that the core is nonuniform with depth. The higher concentrations of Ce, Sc, Sc, Ba, La, Co, Sr, and Zr in zone 2001 may be connected with the presence in this zone of a basaltic rock type seldom seen in the other zones. That is, about half of the basaltic fragments in the large size fractions in zone 2001 are of a specific porphyritic breccia-like type. Anorthositic fragments containing a notable amount of metallic iron are basically limited to zone 2004 and probably explain the lower concentrations of Ce, Rb, Ba, La, and perhaps Co in this zone. The high concentrations of Ag and Ce found previously are confirmed. Although Ag is at nearly the same concentration in all four zones of the core, Cd in the core is the result of local enrichment. In particular, in zone 2004 the concentration of Cd may be as high as 10 ppm in a sample size of 0.01 mg.
The origin and evolution of the solar system is discussed based on ground and satellite observations.
A combination of Al/Mg ratios and Al/Si ratios has provided high-quality geochemical and geological information from the Apollo orbital X-ray fluorescence data. The high sensitivity of the characteristic Si X-rays to alterations in the energy spectra of the solar X-ray flux limits the analytical usefulness of the ratios involving Si. A photometric study indicates that the Si concentration in lunar materials varies by less than about + or - 15% of the Si present. In addition, particle size and surface roughness are shown to have small effects on the characteristic fluorescent X-ray radiation of Si.
Compositionally, lunar mare basalts are similar to some very young subalkaline basalts from terrestrial mid-ocean ridges and to very old pods of basaltic material incorporated into ancient metamorphic rocks. Basalt flows in Mare Imbrium are considered, taking into account the results of orbital gamma ray spectroscopic studies. The results of the analyses of lunar samples obtained from the Apollo missions are evaluated and various models are discussed in connection with an interpretation of the observed conditions.
Major- and trace-element data is presented for a large number of petrographically diverse Apollo 17 basalts, and an attempt is made to evaluate what proportion of the total compositional variance can be attributed to near-surface crystal fractionation and what proportion to magma-generating processes such as partial melting and source heterogeneity. Three well-defined and self-consistent basalt types were identified on the basis of data for fine-grained, rapidly-chilled samples.
Four lines of recent evidence show that the moon is more modestly endowed in refractory elements and heat sources than previously thought. However, even this reduced endowment is adequate for the genesis of known lunar rock types. The thickness and nature of the initially molten zone and the structure of the crust and the lithosphere produced from it are the major uncertainties in models of lunar petrogenesis.
A 'cool' thermal model of the moon's early history is discussed in terms of lunar petrology. Heat from the totally molten outer half of the moon's volume was, according to the model, lost to space and to the lunar interior, so that, barring additions of heat from external sources, all petrogenesis operating exclusively on material of the initially totally molten zone must have occured in an environment of decreasing temperatures. Mare basalts would result from hybridization by migration, mixing, and reequilibration of a variety of intercumulus liquids. Evidence is considered for the layered structure and a significant structural boundary that should result from differentiation of the approximately 350-km-thick initially totally molten zone. Magnetization of lunar rocks is considered.
Nearly all rocks returned from the moon are readily divided into three broad categories on the basis of their chemical compositions: (1) mare basalts, (2) non-mare rocks of basaltic composition (KREEP, VHA), and (3) anorthositic rocks. Only mare basalts may unambiguously be considered to have original igneous textures and are widely understood to have an igneous origin. Nearly all other lunar rocks have lost their original textures during metamorphic and impact processes. It is shown that for these rocks one must work primarily with chemical data in order to recognize and define rock groups and their possible modes of origin. Non-mare rocks of basaltic composition have chemical compositions consistent with an origin by partial melting of the lunar interior. The simplest origin for rocks of anorthositic chemical composition is the crystallization and removal of ferromagnesian minerals. It is proposed that the rock groups of anorthositic and non-mare basaltic chemical composition could have been generated from a single series of original but not necessarily primitive lunar materials.
Within the wide compositional range of the Apollo 17 soils, three distinct chemical groups have been recognized, each one corresponding broadly with a major geological and physiographic unit. These groups are: (1) Valley Floor type soils, (2) South Massif type soils, and (3) North Massif type soils. The observed chemical variations within and between these three groups is interpreted by means of mixing models in terms of lateral transport and mixing of prevailing local rock types, such as high-titanium basalts, KREEP-like noritic breccias, anorthositic gabbro breccias and orange glass. According to these models, North Nassif types evolved on the lower slopes of the North Massif and Sculptured Hills where anorthositic gabbro predominates over noritic breccia and where lateral mixing with basalt is effective, whereas the South Massif type soils originally developed on the upper slopes of the South Massif, where anorthositic breccia and noritic breccias are equally abundant, and where lateral mixing with basalt was minimal.
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A chemically distinct group of lunar rocks with the trace element characteristics of basaltic lunar rocks is apparently ubiquitous on the lunar surface. Such rocks have been found at the Apollo 15, Apollo 16, and Luna 20 landing sites. They may be derived from the plains-forming material that has been designated Cayley Formation.
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