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NASA NTRS1977

Characterization and Distribution of Lunar Mare Basalt Types Using Remote Sensing Techniques

The types of basal to be found on the moon were identified using reflectance spectra from a variety of lunar mare surfaces and craters as well as geochemical interpretations of laboratory measurements of reflectance from lunar, terrestrial, and meteoritic samples. Findings indicate that major basaltic units are not represented in lunar sample collections. The existence of late stage high titanium basalts is confirmed. All maria contain lateral variations of compositionally heterogenous basalts; some are vertically inhomogenous with distinctly different subsurface composition. Some basalt types are spectrally gradational, suggesting minor variations in composition. Mineral components of unsampled units can be defined if spectra are obtained with sufficient spectral coverage (.3 to 2.5 micron m) and spatial resolution (approximating .5 km).

Pieters, C.↗
NASA NTRS1977

Results of analyses performed on basalt adjacent to penetrators emplaced into volcanic rock at Amboy, California, April 1976

The physical and chemical modifications found in the basalt after impact of four penetrators were studied. Laboratory analyses show that mineralogical and elemental changes are produced in the powdered and crushed basalt immediately surrounding the penetrator. Optical microscopy studies of material next to the skin of the penetrator revealed a layer, 0-2 mm thick, of glass and abraded iron alloy mixed with fractured mineral grains of basalt. Elemental analysis of the 0-2 mm layer revealed increased concentrations of Fe, Cr, Ni, No, and Mn, and reduced concentrations of Mg, Al, Si, and Ca. The Fe, Cr, Ni, and Mo were in fragments abraded from the penetrator. Mineralogical changes occurring in the basalt sediment next to the penetrator include the introduction of micron-size grains of alpha-iron, magnetite, and hematite. The newly formed silicate minerals include metastable phases of silica (tridymite and cristobalite). An increased concentration of Fe, Cr, Ni, and Mo occurred in the 2-mm to 1-cm layer of penetrator no. 1, which impacted at the highest velocity. No elemental concentration increase was noted for penetrators nos. 2 and 3 in the 2-mm to 1-cm layer. Contaminants introduced by the penetrator occur up to 1 cm away from the penetrator's skin. Although volatile elements do migrate and new minerals are formed during the destruction of host minerals in the crushed rock, no changes were observed beyond the 1-cm distance.

Blanchard, M.↗
NASA NTRS1976

Lunar mare basalts - Conference summary

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.

Merrill, B.↗
NASA NTRS1976

Regional basalt types in the Luna 24 landing area as derived from remote observations

The Soviet spacecraft Luna 24 landed in Mare Crisium and returned samples that are expected to be much like the low titanium basalts from Luna 16 and Apollo 12. This conclusion is based on earth-based spectral reflectance measurements and multispectral imagery of the Mare Crisium region and uses a background of laboratory measurements of the spectral properties of Lunar soils. These data are used to describe the regional context and composition of the Crisium basaltic units. The returned sample may also contain minor components of a high-titanium basalt and a very low titanium basalt as well as highland material.

Pieters, C.↗
NASA NTRS1976

Variations in chemical composition of Apollo 15 mare basalts

Chemical analyses of 30 different Apollo 15 mare basalts were examined to evaluate the effects of closure on the pearson moment correlation coefficient. It is shown possible to describe the Apollo 15 mare basalts in terms of an opaque, an olivine/pyroxene, an anorthite, and a KREEP component, if significant correlations are identified using the expected correlations as null values. Using Q-mode cluster analysis and nonlinear mapping, it is possible to recognize three groups of the mare basalts, groups 1 and 2 belonging to the olivine normative basalt cluster and group 3 to the quartz normative cluster.

Butler, J. C.↗
NASA NTRS1976

Sr isotopic constraints on the petrogenesis of Apollo 17 mare basalts

Sr-isotopic results are obtained for three basalt samples from Station 4, and it is shown that these basalts have Rb-Sr crystallization ages and initial Sr-87/Sr-86 ratios which are nearly identical to those of other Apollo 17 basalts. However, their Rb/Sr ratios have been increased two-to-four fold more at the time of their genesis than were those of the majority of Apollo 17 basalts. It is argued that this observation is consistent with their production by small degrees of partial melting of a source containing clinopyroxene as a residual phase.

Nyquist, L. E.↗
NASA NTRS1977

Basalts from Mare Crisium

The stratified core sample returned from Mare Crisium by the Luna 24 unmanned space probe is composed primarily of a variety of subophitic to ophitic basalt with very low contents of TiO2 and MgO. This consists of clinopyroxene, calcic plagioclase, olivine, and minor amounts of silica, chromite, ulvoespinel, ilmenite, troilite, apatite, and Fe-metal. Granular metabasalts have the same bulk composition, but mineral phases exhibit less compositional variation. Fine-grained impact melts have similar compositions and are apparently derived from these basalts. It is concluded that the basalts, which are chemically distinct from the very-low-titanium basalts found elsewhere on the moon, represent the local surface flows of Mare Crisium. Sparse fragments of an olivine vitrophyre that is low in TiO2 but high in MgO and approaches the composition of the Apollo 15 green glasses may be derived from patches of dark mantling materials 20 km from the landing site.

Ryder, G.↗
NASA NTRS1978

Oxygen fugacity of basaltic magmas and the role of gas-forming elements

It is suggested that major variations in the relative oxygen fugacity of a basaltic magma are caused primarily by gas-forming elements, especially carbon and hydrogen. According to this theory, carbon, present in the source region of a basaltic magma, reduces the host magma during ascent, as isothermally carbon becomes more reducing with decreasing pressure. For an anhydrous magma such as lunar basalts, this reduction continues through the extrusive phase and the relative oxygen fugacity decreases rapidly until buffered by the precipitation of a metallic phase. For hydrous magmas such as terrestrial basalts, reduction by carbon is eventually superceded by oxidation due to loss of H2 generated by the reaction of C with H2O and by thermal dissociation of H2O. The relative oxygen fugacity of a hydrous magma initially decreases as a magma ascends from the source region and then increases until magnetite crystallization curbs the rising trend of the relative oxygen fugacity.

Sato, M.↗
NASA NTRS1977

Laser Ar-39-Ar-40 study of Apollo 17 basalts

Three Apollo 17 basalts were studied by the laser Ar-39-Ar-40 method. The 70215 basalt has a normal well-behaved Ar-39-Ar-40 release pattern; the 70017 basalt has a disturbed release pattern which indicates a limited intermediate maximum age followed by a broad low-age region; and the 75035 basalt has a pattern initially similar to 70017 that is followed by a high-temperature maximum age. The laser study shows that all mineral systems in 70215 have small and uniform temperature losses, while the laser-determined ages for 70017 and 75035 are, apparently, primarily controlled by the minerals containing mesostasis inclusions. It is possible that the drop in ages observed by the conventional Ar-39-Ar-40 method was due not only to recoil of Ar-39 during neutron irradiation but also to gas loss from some minerals. It is suggested that the plagioclases are the best minerals to use for a reliable age.

Schaeffer, O. A.↗
NASA NTRS1978

Partitioning of Ni/2+/ between basaltic and synthetic melts and olivines An experimental study

Olivine/liquid distribution coefficients for Ni in basaltic and simple synthetic melts are found in the 1400-1070 C temperature range. The results suggest that: (1) the Ni distribution coefficients and NiO activity coefficients are strongly temperature dependent, (2) the Ni distribution coefficients are functions of melt composition and structure at a constant temperature although the dependence is small for most basaltic magmas, (3) differences in melt composition do not significantly influence generally 'basaltic' melts, (4) the Ni distribution coefficients may be used as geothermometers to predict the olivine crystallization temperatures of basaltic magmas to within plus or minus 50 C, (5) the Ni distribution coefficients are greater than one at all natural magmatic temperatures, and (6) the Ni distribution coefficients do not significantly vary as functions of the Ni content of the melt to at least one mole percent.

Leeman, W. P.↗
NASA NTRS1975

Mare basalts - Melting experiments and petrogenetic interpretations

Equilibrium crystallization sequences are determined in melting experiments in vacuum at Fe saturation on synthetic mare basalt compositions 70215 and 15318 Red Glass (both high-Ti) as well as 15555-15016 (low-Ti). The experiments confirm that much of the chemical variation within both the high- and low-Ti suites is controlled by near-surface fractionation processes, although the two suites cannot be related by such mechanisms. The components and crystallization products of the liquidus at various temperatures and pressures are reported. Mare basalt petrogenesis is interpreted in terms of high-pressure equilibria at Fe saturation; it is suggested that low-Ti basalts represent partial melts of a differentiated olivine-pyroxenite lunar mantle at 240 km or deeper, while cumulus clinopyroxene in the source is responsible for their REE characteristics. The formation of high-Ti basalts is considered.

Kesson, S. E.↗
NASA NTRS1978

A chemical study of the impact glasses and basalts from Lonar Crater, India

Twenty-nine elements were determined by instrumental neutron activation analysis in two impact glasses and four basalts from Lonar Crater, India, and the glasses and the underlying core basalt samples are found to be very similar in major, minor, and trace element abundances. This finding seems to indicate that impact-induced chemical fractionation during formation of the glasses from basalt is minimal for many of the principal rock and mineral-forming elements. Since most volatile trace elements were not determined in this study, differences in the volatile trace element contents of the glasses and basalts can not be excluded.

Stroube, W. B., Jr.↗
NASA NTRS1978

On the origin of Luna 24 basalts and soils

Analyses of fine-grained very low titanium (VLT) basalt from the Luna 24 drill core suggest that a single homogeneous magma is represented by the sample. In particular, the small variation in MgO contents of the fine-grained basalt, together with the tight clustering of the compositions of brown glasses (which may be pyroclastic equivalents of the VLT basalt), provides evidence for the single-magma hypothesis. The high-Mg component in the soil samples, though not obviously explainable in petrographic terms, may be derived from material similar to olivine vitrophyre and its degraded products, or from some other high-Mg VLT basalt.

Ryder, G.↗
NASA NTRS1978

VLT mare basalts - Impact mixing, parent magma types, and petrogenesis

Available major-element compositions of very low-Ti (VLT) mare basalt lithic fragments and glasses are examined. Many of the lithic fragments contain relic mineral and sometimes lithic clasts, which suggests that many samples of VLT mare basalt glasses and lithic fragments were formed by impact melting. Therefore, some may have compositions that represent mixtures of VLT mare basalts and other types of rocks, not authentic igneous rock compositions. In spite of this problem, a number of possible parent magma compositions are identified. These hypothetical magmas vary in CaO/Al2O3(0.9-1.1), FeO (17 to 24 wt. %), Fe/(Fe + Mg) (0.34-0.46), and K2O (0-0.2 wt. %). Each may have differentiated to produce a wide variety of derivative magmas. Calculations involving olivine fractionation from the proposed parent magmas indicate the Luna 24 ferrobasalts might have formed from a magma whose composition is similar to that of a group of high-MgO (about 13-14 wt. %) Apollo 17 VLT mare basalt glasses.

Taylor, G. J.↗
NASA NTRS1978

Green glass vitrophyre 78526 - An impact of very low-Ti mare basalt composition

Rake sample 78526 is an 8.77 g rock consisting primarily of vitrophyric pale green glass with subordinate mineral and lithic relics. Petrographic and compositional evidence leads to the following conclusions: (1) the bulk composition represents that of a mixture formed by impact melting of at least two different textural and compositional varieties of VLT mare basalt that are now present in the rock as lithic relics and a poorly defined low-Ti mare basalt component observed in thin section only in the form of isolated mineral relics; (2) the admixed VLT mare basalts had REE abundances lower than those found in other mare basalts (but probably higher than emerald green glass) and REE patterns showing significant enrichment of the heavy relative to light REE's, suggesting that they were derived by comparatively high degrees of partial melting of a clinopyroxene-rich source region; and (3) the impact melt supercooled to produce the vitrophyre, with rather sharply contrasting textural domains present in the vitrophyre resulting from differences in nucleation kinetics and degrees of supercooling in various portions of the sample.

Warner, R. D.↗
NASA NTRS1979

Pyroxenes from planetary basalts - Characterization of 'other' than quadrilateral components

The paper reports on a synthesis of the silicate mineralogy of a planetary basalt suite, which concerns itself only with specific aspects of pyroxene cation substitutional couples. Consideration is given to the mineral chemistry and the basalt suites in an overview fashion. Attention is given to those characteristics of pyroxene chemistry that reflect planetary constraints on the host basalts from which the pyroxenes crystallized. It is concluded that the inspection of a large number of high quality silicate analyses of pyroxenes demonstrates conclusively that these phases carry a signature of the planetary body in which they evolved. In addition, it is noted that there are planetary probes capable of constraining thermodynamic parameters that were obtained during the petrogenesis of their host basaltic liquids

Papike, J. J.↗
NASA NTRS1979

The petrology of the Apollo 12 pigeonite basalt suite

A study of the petrology of the Apollo 12 pigeonite basalt samples 12011, 12043, and 12007 is presented. In this suite, the abundances of olivine and Cr-spinel decrease with increasing grain size, while the abundances of plagioclase and ilmenite increase. The petrochemical and textural variations indicate that the pigeonite basalts were derived from the olivine basalts, but the compositional gap between the olivine and pigeonite basalts indicates that they could not have crystallized together from a single, initially homogeneous magma body.

Baldridge, W. S.↗
NASA NTRS1979

Petrology, chemistry, and chronology of Apollo 14 KREEP basalts

The results of petrographic, major and trace element geochemical, and Rb-Sr isotopic studies of four crystalline matrix breccias and two intergranular to subophitic basalts are reported. Emphasis is placed on the relationship of the basalt fragments to other Apollo 14 KREEP basalts, and the origin of this group as a whole. Considering the high siderophile element content, the balance of evidence favors origin of the Apollo 14 KREEP basalts by impact melting, probably a single melt with slight chemical and isotopic heterogeneities.

Mckay, G. A.↗