Experimental petrology of lunar material: the nature of mascons, seas, and the lunar interior

One-atmosphere melting data show that Apollo 11 samples are near cotectic. Melting relations at pressures up to 35 kilobars show that clinopyroxenite or amphibole peridotite are possible lunar interiors. Mascons cannot be eclogite; they may be ilmenite accumulate. Hot lunar surface material will boil off alkalis.     

Pyroxferroite: Stability and X-ray Crystallography of Synthetic Ca0.15Fe0.85SiO3 Pyroxenoid

Synthetic Ca(0.15)Fe(0.85)SiO(3) pyroxenoid has the same (pyroxmangite) structure and very nearly the same composition as pyroxferroite, a new mineral found in Apollo 11 lunar samples. The synthetic material is not stable below pressures of approximately 10 kilobars. It appears likely that the lunar pyroxferroite has persisted in a metastable state for some billions of years.     

Specific heats of lunar surface materials from 90 to 350 degrees Kelvin

The specific heats of lunar samples 10057 and 10084 returned by the Apollo 11 mission have been measured between 90 and 350 degrees Kelvin by use of an adiabatic calorimeter. The samples are representative of type A vesicular basalt-like rocks and of finely divided lunar soil. The specific heat of these materials changes smoothly from about 0.06 calorie per gram per degree at 90 degrees Kelvin to about 0.2 calorie per gram per degree at 350 degrees Kelvin. The thermal parameter gamma=(kpC-(1/2) for the lunar surface will accordingly vary by a factor of about 2 between lunar noon and midnight.     

Compressibilities of lunar crystalline rock, microbreccia, and fines to 40 kilobars

The compressibilities of three lunar samples were studied at room temperature from 0 to 40 kilobars. The samples were a fine-grained vesicular crystalline rock (type A), a microbreccia (type C), and fines (type D). All samples were porous. The microbreccia and fines were quite compressible at all pressures; the compressibility of the crystalline rock was somewhat less, being 8.4 megabar(-1) at 1 atmosphere and 1.5 megabar(-1) at 35 kilobars. Some porosity appeared to remain in the samples at all pressures. Thus the pressure-volume data derived from these samples may be representative of porous surface and near-surface material in the vicinity of the Apollo 11 landing site but may not be representative of lunar material at depth.     

Shock-wave damage in minerals of lunar rocks

The mineral fragments that constitute the Apollo 11 microbreccia and fines show a number of shock-induced microstructural effects including multiple twinning on (001) in clinopyroxene and incipient development of lattice-controlled discontinuities in olivine. These structures coupled with the effects of shock-induced melting as manifested by spherules and angular fragments of glass and their partly to completely crystallized equivalents indicate that Apollo 11 materials were subjected to weak to moderate shocks with associated peak pressures of the order of 100 to 200 kilobars.     

Cordierite-spinel troctolite, a new magnesium-rich lithology from the lunar highlands

A clast of spinel troctolite containing 8 percent cordierite (Mg(2)Al(4)Si(5)O(18)) has been identified among the constituents of Apollo 15 regolith breccia 15295. The cordierite and associated anorthite, forsteritic olivine, and pleonaste spinel represent a new, Mg-rich lunar highlands lithology that formed by metamorphism of an igneous spinel cumulate. The cordierite-forsterite pair in the assemblage is stable at a maximum pressure of 2.5 kilobars, equivalent to a depth of 50 kilometers, or 10 kilometers above the lunar crust-mantle boundary. The occurrence of the clast indicates that spinel cumulates are a more important constituent of the lower lunar crust than has been recognized. The rarity of cordierite-spinel troctolite among lunar rock samples suggests that it is excavated only by large impact events, such as the one that formed the adjacent Imbrium Basin.     

Preliminary examination of lunar samples from apollo 14

The major findings of the preliminary examination of the lunar samples are as follows: 1) The samples from Fra Mauro base may be contrasted with those from Tranquillity base and the Ocean of Storms in that about half the Apollo 11 samples consist of basaltic rocks, and all but three Apollo 12 rocks are basaltic, whereas in the Apollo 14 samples only two rocks of the 33 rocks over 50 grams have basaltic textures. The samples from Fra Mauro base consist largely of fragmental rocks containing clasts of diverse lithologies and histories. Generally the rocks differ modally from earlier lunar samples in that they contain more plagioclase and contain orthopyroxene. 2) The Apollo 14 samples differ chemically from earlier lunar rocks and from their closest meteorite and terrestrial analogs. The lunar material closest in composition is the KREEP component (potassium, rare earth elements, phosphorus), "norite," "mottled gray fragments" (9) from the soil samples (in particular, sample 12033) from the Apollo 12 site, and the dark portion of rock 12013 (10). The Apollo 14 material is richer in titanium, iron, magnesium, and silicon than the Surveyor 7 material, the only lunar highlands material directly analyzed (11). The rocks also differ from the mare basalts, having much lower contents of iron, titanium, manganese, chromium, and scandium and higher contents of silicon, aluminum, zirconium, potassium, uranium, thorium, barium, rubidium, sodium, niobium, lithium, and lanthanum. The ratios of potassium to uranium are lower than those of terrestrial rocks and similar to those of earlier lunar samples. 3) The chemical composition of the soil closely resembles that of the fragmental rocks and the large basaltic rock (sample 14310) except that some elements (potassium, lanthanum, ytterbium, and barium) may be somewhat depleted in the soil with respect to the average rock composition. 4) Rocks display characteristic surface features of lunar material (impact microcraters, rounding) and shock effects similar to those observed in rocks and soil from the Apollo 11 and Apollo 12 missions. The rocks show no evidence of exposure to water, and their content of metallic iron suggests that they, like the Apollo 11 and Apollo 12 material, were formed and have remained in an environment with low oxygen activity. 5) The concentration of solar windimplanted material in the soil is large, as was the case for Apollo 11 and Apollo 12 soil. However, unlike previous fragmental rocks, Apollo 14 fragmental rocks possess solar wind contents ranging from approximately that of the soil to essentially zero, with most rocks investigated falling toward one extreme of this range. A positive correlation appears to exist between the solar wind components, carbon, and (20)Ne, of fragmental rocks and their friability (Fig. 12). 6) Carbon contents lie within the range of carbon contents for Apollo 11 and Apollo 12 samples. 7) Four fragmental rocks show surface exposure times (10 x 10(6) to 20 x 10(6) years) about an order of magnitude less than typical exposure times of Apollo 11 and Apollo 12 rocks. 8) A much broader range of soil mechanics properties was encountered at the Apollo 14 site than has been observed at the Apollo 11, Apollo 12, and Surveyor landing sites. At different points along the traverses of the Apollo 14 mission, lesser cohesion, coarser grain size, and greater resistance to penetration was found than at the Apollo 11 and Apollo 12 sites. These variations are indicative of a very complex, heterogeneous deposit. The soils are more poorly sorted, but the range of grain size is similar to those of the Apollo 11 and Apollo 12 soils. 9) No evidence of biological material has been found in the samples to date.     

Supercooling of Water to -92{degrees}C Under Pressure

The temperature at which "clean" supercooled water freezes has been determined as a function of pressure up to 3 kilobars, using a differential thermal analysis technique on subdivided water samples. The supercooling limit of such samples, -38 degrees C at normal pressure, is lowered by initial increase of pressure, reaching a minimum value of -92 degrees C at 2.00 kilobars.     

Pressure dependence of the radioactive decay constant of beryllium-7

Diamond anvil presses of a new design were used to compress samples of beryllium-7 oxide to 120, 210, and 270 kilobars. The decay constant for the conversion of beryllium-7 to lithium-7 by electron capture was measured for compressed and uncompressed samples. A least-squares fit of the equation (lambda(c)-lambda)/lambda = KpP to the experimental data, where lambda(C) and lambda are the decay constants of the compressed sample and an uncompressed sample, respectively, and P is pressure, yields a value of (2.2 +/- 0.1) x 10(-5) kbar(-1) for the constant K(p).     

Orthopyroxene-plagioclase fragments in the lunar soil from apollo 12

Rock fragments consisting of orthopyroxene-calcic plagioclase assemblages appear to be more common in Apollo 12 soil samples than in the breccias or soil from Apollo 11 and are mineralogically and chemically different from any of the crystalline rocks returned by either Apollo 11 or Apollo 12. Compositionally, these fragments are orthopyroxenites and feldspathic orthopyroxenites. They are probably not fragments of meteorites; other considerations point to a near-surface lunar origin.     

Magnetic transitions observed in sulfide minerals at elevated pressures and their geophysical significance

The magnetic behavior of iron in chalcopyrite (CuFeS(2)) and pyrrhotite (Fe(7)S(8)) in the pressure range from 1 atmosphere to 20 kilobars has been studied by M?ssbauer spectroscopy. Both chalcopyrite and pyrrhotite exhibit transitions from magnetically ordered to disordered states over the range from 5 to 16 kilobars. Both transitions, particularly the loss of ferrimagnetism in pyrrhotite, have geophysical consequences.     

Microtektites and tektites: a chemical comparison

Elemental abundance (20 trace elements, 3 major elements) comparisons for Ivory Coast microtektites and Australasian microtektites indicate that there are distinct chemical similarities between microtektites and nearby tektites. Several trace element abundances in microtektites are quite different from those observed in Apollo 11 and Apollo 12 samples.     

Apollo 15 Geochemical X-ray Fluorescence Experiment: Preliminary Report

Although only part of the information from the x-ray fluorescence geochemical experiment has been analyzed, it is clear that the experiment was highly successful. Significant compositional differences among and possibly within the maria and highlands have been detected. When viewed in the light of analyzed lunar rocks and soil samples, and the data from other lunar orbital experiments (in particular, the Apollo 15 gamma-ray spectroscopy experiment), the results indicate the existence of a differential lunar highland crust, probably feldspathic. This crust appears to be related to the plagioclase-rich materials previously found in the samples from Apollo 11, Apollo 12, Apollo 14, Apollo 15, and Luna 16.     

Cosmic ray production of rare gas radioactivities and tritium in lunar material

The argon radioactivities (37)Ar and (39)Ar were obtained by vacuum melting from interior and exterior portions of rock 10057 and from a portion of the fines from the bulk sample container. The release of argon and tritium as a function of the temperature was followed for the fine material. A comparison is made of the activities observed in the lunar samples with those expected from the spallation of iron, titanium, and calcium. From these data and the (38)Ar content, the cosmic ray exposure age of rock 10057 is deduced as 110 x 10(6) years.     

Multielement analysis of lunar soil and rocks

Results for multielement analysis of lunar soil and of seven rocks returned by Apollo 11 are presented. Sixty-six elements were determined with spark source mass spectrography and neutron activation. U. S. Geological Survey standard W-1 was used as a comparative stanadard. Results indicate an apparent uniformity of composition among the samples. Comparison with solar, meteoritic, and terrestrial abundances reveals depletiozt of volatile elements and enrichment of the rare earths titaniunm, zirconium, yttriuntm, and hafnium. Althouglh there is an overall similarity of the lunar material to basaltic achondrites amid basalts, the differences suggest detailed geochemical processes to the history of this material.     

Neutron activation analysis of milligram quantifies of lunar rocks and soils

A neuttron activation scheme for determining 25 elements in lunar samples weighing 20 milligrams is described and applied to a suite of Apollo 11 lunar materials. Concentrations of titanium, chromium, scandium, tantalum, hafnium, and rare earths are higher than in avercage basalt, whereas cobalt, nickel, and copper are lower. Chemical variations show groupings of elements possibly associated with the major phases, pyroxene, plagioclase, and ilmenite. The high concentration of "refractory oxides" and low volatile content implies that the raw material for the Apollo 11 samples was condensed from the primitive solar nebula at high temperatures.     

Apollo 12 lunar samples: trace element analysis of a core and the uniformity of the regolith

Four core and soil samples from Apollo 12 are enriched in a number of trace elements of meteoritic origin to virtually the same degree as Apollo 11 soil. An average meteoritic influx rate of about 4 x 10(-9) gram per square centimeter per year thus seems to be valid for the entire moon. A sample from a light gray, coarse-grained layer in the core resembles lunar basalts in composition, but is enriched by factors of 10(4) to 10(5) in bismuth and cadmium.     

Melting of normal hydrogen under high pressures between 20 and 300 kelvins

The melting curve of normal hydrogen has been determined up to 52 kilobars between 20 and 300 Kelvins. The results are in excellent agreement with the modified Simon equation proposed for hydrogen below 19 kilobars, but not with the existing theoretical predictions. The results also provide an independent check on the validity of the ruby high-pressure scale at low temperature.     

California earthquakes: why only shallow focus?

Frictional sliding on sawcuts and faults in laboratory samples of granite and gabbro is markedly temperature-dependent. At pressures from 1 to 5 kilobars, stick-slip gave way to stable sliding as temperature was increased from 200 to 500 degrees Celsius. Increased temperature with depth could thus cause the abrupt disappearance of earthquakes noted at shallow depths in California.     

Cation disorder in shocked orthopyroxene

The distribution of magnesium and iron over the M1 and M2 positions in Bamle enstatite shocked at 1 megabar is highly disordered. It corresponds to an equilibrium distribution of at least 1000 degrees C. The distribution in samples shocked at 450 kilobars or less is undisturbed.