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The studies carried out on the Luna 16 regolith have confirmed the data that were already published internationally. By means of activation analysis under irradiation in the reactor, activation analysis with a 14 MeV U-generator, and mass spectroscopy on samples of 10 or 20 mg, six main and 63 trace elements were quantitatively determined and compared with known data.
Impact melts and breccias from the Apollo 15 and 16 landing sites were examined optically and by electron microscope/microprobe. Major and trace element abundances were determined for selected samples. Apollo 16 breccias contained impact melts, metamorphic and primary igneous rocks. Metamorphic rocks may be the equivalents of the impact melts. Apollo 15 breccias studied were fragment-laden melts derived from gabbro and more basalt target rocks.
It is noted that the variable Rb-Sr model ages of lunar highland rocks containing a significant amount of KREEP basalt may be best explained by some fractionation of Rb from Sr during metamorphism 3.9 billion years ago, but the uniformity of the KREEP-type trace-element pattern in different highland samples indicates that elements such as the rare earth were hardly fractionated at all during the metamorphic event. Data are presented which show that the Rb/Sr fractionation 3.9 billion years ago was due to Rb mobilization alone in most cases and that this fractionation can be accounted for by coupling of Rb to other, less volatile incompatible elements. Variations of Rb in lunar highland rocks are analyzed, a correction method is applied for the Rb/Sr fractionation, and results are evaluated separately for Apollo 16 VHA and KREEP basalts, Apollo 17 noritic breccias, Apollo 14 KREEP breccias, Apollo 15 KREEP basalts, and Apollo 15-KREEP-enriched breccias. Evidence for volatilization of alkalis from glasses of impact origin is summarized, and an apparent correlation is discussed between meteoritic component (as given by the Ir/Au ratio) and rock type (as given by the U or Rb content) for many lunar highland samples.
Equilibrium thermodynamic calculations of the sequence of condensation of minerals from a cooling gas of solar composition play an important role in explaining the mineralogy and trace element content of different types of inclusions in carbonaceous chondrites. Group IV B iron meteorites and enstatite chondrites may also be direct condensates from the solar nebula. Condensation theory provides a framework within which chemical fractionations between different classes of chondrites may be understood.
KREEP basalt is an important lunar material that was formed in large quantities early in the evolutionary history of the moon. Fragments of KREEP basalt were returned from all landing sites and make up most of the material of the Apollo 14 collection. These fragments have a wide variety of textures caused by various secondary processes but they are all characterized by a large and distinctive trace-element content. They are also characterized by a general basaltic composition that is similar to the olivine-plagioclase-pyroxene peritectic in the system silica-anorthite-olivine (Fe/Fe + Mg = 0.3).
The paper analyzes the meteoritic material at five multikilometer craters: Clearwater (Lac a l'Eau Claire) East and West (22 and 32 km), Manicouagan (70 km) and Mistastin (28 km), all in Canada; and Lake Bosumtwi (10.5 km), Ghana, which is associated with Ivory Coast tektites. Radiochemical neutron activation analysis is applied to 16 crater samples for the siderophile trace elements Ir, Os, Pd, Ni, Ge, and Re, which are depleted to varying degrees in the earth's crust but are abundant in all meteorites except achondrites. It is found that only two samples, both from Clearwater, exhibit a strong meteoritic signal. The remaining ones fall within or slightly above the range for terrestrial rocks, and therefore at best contain only small meteoritic components. Clearwater East is the first terrestrial impact crater to be associated with a stony meteorite (a C1 or C2 chondrite).
The basement rocks of Manicouagan exhibit a wide compositional range (40-72% SiO2). Least squares mixing calculations indicate that the average composition of the Manicouagan melt sheet can be modeled for 9 major and 11 trace elements by a mixture of 4.5% anorthosite, 55.5% mafic gneiss, and 40.0% tan gneiss with a granitic-granodioritic composition. The underrepresentation of anorthosite relative to its present distribution is considered. The homogeneous composition of the melt (57.75 + or - 1.21% SiO2) relative to that of the postulated target is explained in a model outlining the dynamic conditions existing during the formation of the melt and its accompanying movement into the excavated cavity.
The reported investigation was mainly concerned with the precise determinations of major-, minor-, and trace-element abundances, especially the REE abundances in the bulk howardites in order to establish the bulk rock composition for the future chemical-mineralogical, petrographic studies of different rock types on the chemically unique howardites and diogenites if they exist. From the chemical data for the major-element abundances and the REE patterns of the howardites analyzed, it is evident that these howardites are predominantly composed of eucritic and diogenitic components. The analytical results for howardites and diogenites are shown in two tables together with the results for CRB-1. The chondritic normalized K, Sr, Ba, REE, Hf, and Sc abundances of these howardites are plotted in two graphs.
The dispersions in composition observed among samples of terrestrial basalts with known field relationships are compared with those of various subgroups of lunar mare basalts. The comparison indicates that there are no substantial reasons based on trace-element data to require that large numbers of different basalts were sampled at each Apollo site. The Apollo 15 olivine and quartz normative basalts and the Apollo 12 ilmenite and olivine basalts show compositional variations which are no more pronounced than those found within single terrestrial flows, whose inhomogeneity in horizontal section has been demonstrated. The inhomogeneities of the parent rocks in the case of the Apollo 12 and 15 basalts on a scale of centimeters overshadow any differences which might exist among different general regions of the lava flows from which these samples might have derived.
The experiments discussed were conducted for the purpose of placing additional constraints on the origin of lunar highlands noritic compositions. The sample 63545 represents a fine-grained, crystalline melt rock consisting of pink spinel, plagioclase, divine, interstitial glass, minor oxides, and metal. According to Chao (1973), 76055 is an olivine-bearing micronorite hornfels with abundant xenocrysts and xenoliths. The sample 76015 is a vesicular, poikilitic impact melt with a homogeneous matrix. The obtained experimental melting relations of 63545, 76055, and 76015, are examined, taking into account experimental petrology and trace element chemistry of mare basalts. It is concluded that the studied compositions do not represent magmas derived by partial melting of either cosmic or differentiated source regions at any pressure in the moon. Presently available information would seem to favor an origin by impact-fusion of several highlands components.
It is shown that the interdisciplinary study of the nonmare lunar rocks based on trace element, major element, and isotopic data plus petrographic evidence can succeed in amassing a large suite of demonstrably pristine rocks, and that the relative numbers of these rocks are not in accord with statistics amassed on soil fragments and glasses. The term 'pristine' is taken to mean rocks with primary compositions (albeit not necessarily textures) produced by lunar endogenous igneous processes. Melt rocks and crystalline matrix breccias produced by impact processes are excluded. A petrographic synonym for pristine would be 'unremelted, monomict'. It is found that anorthositic norites and noritic anorthosites were rare as primary nonmare rocks. Mechanical mixing appears to have been the dominant petrogenetic process on the highlands.
The fact that 53 Apollo 15 igneous KREEP basalts show a range of 100 Mg/(Mg + Fe) from 73 to 35, and that there are systematic variations in K2O and trace element abundances with the Mg/(Mg + Fe) ratio, suggests that the KREEP basalts are a magma series generated by fractional crystallization processes. Experimental and chemical evidence indicate that this magma series results from low-pressure, possibly subvolcanic, fractional crystallization of a magnesian parental liquid (100 Mg/(Mg + Fe) equal to approximately 72) by removal of low-Ca pyroxene and plagioclase, with eventual production of liquids similar in composition to 15405 quartz-monozodiorites. One soil sample, SAO 465-11, corresponds to the postulated parental liquid, which might have been a direct partial melt of troctolitic materials in the deep lunar crust.
Noble gas and trace element analyses of matrix and a clast from breccia 14307 are reported. This sample was exposed to a large neutron fluence, as seen by an elevated Sm-150/Sm-149 ratio and by noble gases, particularly Xe-136 from neutron fission of U-235. Strong constraints on the exposure history result from combined consideration of Sm-150, Xe-136, and spallation noble gases. Both clast and matrix were irradiated for about 1 AE under substantial shielding beginning at least 2 AE ago, probably more than 3 AE ago. The manifestations of soil exposure seen in the matrix - solar wind gases, glass formation, etc. - thus must have been acquired in an ancient epoch. The matrix has had a longer exposure to cosmic rays than the clast, presumably during its prebrecciation history as a soil. Brecciation probably occurred more than 1 AE ago, perhaps more than 3 AE ago, but at least 0.4 AE after the formation of the matrix constituents.
Twenty-eight major, minor, and trace-element abundances have been determined in nine fines fractions of core 60010 by instrumental thermal and 14 MeV neutron activation analysis. With the exception of the elements Fe, Co, and Ni, core section 60010 exhibits a much more uniform composition than the lower section (60009) of the double drive tube collected at the Apollo 16 LM site. The siderophilic meteorite indicator elements Fe, Co, and Ni are significantly enriched in subsample 40, which is located 3.0-4.5 cm below the lunar surface, and are highly variable throughout the 60010 core section. Microscopic examination of subsample 40 revealed the presence of numerous metallic fragments including an approximately 1-mm metal fragment exhibiting only Fe, Co, Ni, and Ir gamma-ray peaks and having a composition typical of a coarse octahedrite. Composition profiles of 60010 exhibit small variations in lithophilic element abundances which can be related to most of the seven stratigraphic units of Duke and Nagle (1976). Although the basal portion of 60010 has been described as texturally similar to the upper unit of 60009, the present chemical studies show a marked compositional difference at this interface.
The Ganapathy-Anders seven-component model is used as the basis for an analysis of conditions in the early solar nebula as they pertain to the formation of the moon. Calculations incorporating improved geological data and petrological constraints are presented in terms of a model moon which meets trace element restrictions and conforms to known parameters of heat flow, density, and moment of inertia ratio, ie., 40 ppb U, and a core of 2% by weight. It is noted that a melt of the model composition approximates that of Apollo 15 green glass, together with a residuum of olivine, plus 3-4% spinel.
Aluminous mare basalts have been found at several lunar sites, although they are not abundant. A group of crystalline clasts in breccia 14063 are also aluminous mare basalts with higher TiO2, Na2O, Mg/Fe ratio and lower FeO than other aluminous mare basalts. Composition of ilmenite clinopyroxene, and plagioclase confirm that crystallization took place from a melt with high TiO2 and Mg/Fe. A review of ages and siderophile trace-element abundances for aluminous mare basalts, suggests they are not hybrid rocks produced by melting of a mare + terra rock mix, but are pristine igneous melts from the lunar interior. Consideration of rare-earth element abundances indicate the source for aluminous mare basalts is pyroxenitic, with variable clinopyroxene/orthopyroxene ratio, and is not significantly different from the sources(s) of normal mare basalts.
A chemical and petrographic study is reported of the phases from the rock 78235 which was returned on the Apollo 17 mission. Petrographic analysis of the thin sections from the bounder confirm its cumulate origin. In order to develop further the crystallization history for 78235, its subsequent shock history, and its relationship to other lunar crustal rocks, orthopyroxene, plagioclase, glass, and whole-rock samples were prepared and analyzed for major, minor, and trace elements. It is speculated that an early fractional crystallization event producing a layer of orthopyroxene-plagioclase cumulate with varying amounts of trapped liquid took place within 20 km of the surface of the moon.
Agglutinates are aggregates of crystalline grains and lithic fragments bonded together by glass. It is thought that glassy agglutinates are formed at the upper surface of the lunar regolith by impact-related melting and welding of soil particles, in response to meteoroid and micrometeoroid bombardment. A description is presented of an investigation in which bulk soils were separated into 'agglutinate' and 'nonagglutinate' fractions. The obtained fractions were analyzed for major, minor, and trace elements. The obtained chemical data for agglutinate and nonagglutinate fractions of lunar soils indicate that agglutinitic glass is enriched in mafic and most lithophile elements relative to the bulk soils. A model involving preferential melting and assimilation of mesostasis material and mafic soil components is proposed to account for the observed chemical data. It is suggested that glassy agglutinates may form more readily in mafic soils than in more feldspathic ones. Such selectivity should be most effective between mare and highland soils, but may possibly operate on a more local scale.