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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Charge composition and energy spectra of ancient solar flare heavy nuclei

Nuclear tracks in olivine grains from three carbonaceous chondrites are analyzed to determine the energy spectra and charge compositions of solar flare heavy nuclei during the early history of the solar system. Track length measurements of grains irradiated before compaction into meteorites over 4 billion years ago were performed accompanied by calibration experiments using heavy ion beams from an accelerator to identify tracks formed by very heavy (Z between 20 and 28) and very very heavy (Z greater than or equal to 30) groups of nuclei in the Murchison, Murray and Cold Bokkeveld meteorite grains. The time-averaged spectral shape of the solar flare very heavy nuclei is found to be similar to that obtained in lunar sample studies and direct observations. The meteorite grains also reproduce the currently observed enrichment of low-energy heavy ions in solar cosmic rays with respect to photospheric levels, with enhancement factors from 2 to 12 in the energy interval 6-10 MeV/n. Variations of very very heavy/very heavy nuclei abundance ratios within individual kinetic energy intervals are interpreted as representing possible changes of solar flare activity on time scales of 10,000 years.

Goswami, J. N.↗
NASA NTRS1982

Microelectrophoresis of selected mineral particles

Particle mobilities of ilmenite, labradorite plagioclase, enstatite pyroxene, and olivine were measured with a Rank microelectrophoresis system to evaluate indicated mineral separability. Sodium bicarbonate buffer suspension media with and without additives (0.0001 M DTAB and 5 percent v/v ethylene glycol) were used to determine differential adsorption by mineral particles and modification of relative mobilities. Good separability between some minerals was indicated; additives did not enhance separability.

Herren, B. J.↗
NASA NTRS1982

Occurrence and Mineral Chemistry of High Pressure Phases, Potrillo Basalt, Southcentral New Mexico

The presence of an older plagioclase-rich basalt and a younger olivine-rich basalt were confirmed by modal and chemical analysis. Chemical analysis also confirmed the presence of flows that are tholeiitic in composition and could be remnants of an original tholeittic parent magma. Eruptions from different levels of a differentiated magma chamber are proposed to account for the two members.

Sheffield, T. M.↗
NASA NTRS1981

Relict grains in chondrules

Attention is given to the fact that a significant fraction of the chondrules from ordinary chondrites contain silicate grains that survived the chondrule formation process without melting. Typically, these grains consist of coarse olivine, rarely orthopyroxene, crystals located in the core of chondrules and displaying a zoning that is inconsistent with crystallization from a silicate melt. It is noted that the relict grains still preserve the imprint of processes that occurred in the solar nebula and, in some cases, may include the isotopic record of interstellar grains. Information is presented on the chondrule precursor materials and the process of chondrule formation which was acquired by a compositional and textural study of three of the most unequilibrated type 3 ordinary chondrites.

Rambaldi, E. R.↗
NASA NTRS1981

Volcanism on Mars

In situ chemical analyses of Martian soil by the Viking lander indicate mafic to ultramafic source rocks, consistent with both remote sensing data indicating the presence of pyroxene and olivine and with petrologic modeling which suggests that Martian lavas are iron-rich and ultramafic. Photogeological analysis of the Martian surface reveals two types of volcanic morphology: (1) central volcanoes, developed by continued and prolonged eruption from a point source vent; and (2) volcanic plains, recognized by mare ridges and flow lobes. When these volcanic morphologies are combined with relative age data, a volcanic history may be derived that is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time which gradually suppresses the volcanism.

Greely, R.↗
NASA NTRS1981

Isotopic and REE studies of lunar basalt 12038 - Implications for petrogenesis of aluminous mare basalts

Sr, Nd, and Sm isotopic studies of lunar basalt 12038, one of the so-called aluminous mare basalts, are reported. The evolution of the Sr and Nd isotopic compositions and the rare earth element (REE) abundances is successfully modeled within the framework of the model developed by Nyquist et al. (1977, 1979) for Apollo 12 olivine-pigeonite and ilmenite basalts. It is pointed out that the isotopic and trace element features of 12038 can by modeled as produced by partial melting of a cumulate mantle source which crystallized from a lunar magma ocean with a chondrite-normalized REE pattern of constant negative slope. Chondrite-normalized La/Yb is equal to 2.2 for this hypothetical magma ocean pattern.

Nyquist, L. E.↗
NASA NTRS1981

Cumberland Falls chondritic inclusions - Mineralogy/petrology of a forsterite chondrite suite

The mineralogy and petrology of a suite of chondritic inclusions from the Cumberland Falls aubrite are investigated in order to clarify the relation of the inclusions to each other, forsterite chondrites, and the aubrites. Thin sections of nine chondritic inclusions and the achondritic matrix of Cumberland Falls were examined in reflected light, then analyzed for up to 12 elements by electron microprobe techniques. Minerals detected in abundant quantities include low-Ca pyroxene, olivine, plagioclase, kamacite, taenite, schreibersite, troilite, ferroan alabandite and daubreelite; diospide, oldhamite and a Ti-rich sulfide are found in one or two inclusions. The mineralogic compositions indicate similar degrees of reduction for the inclusions in the Cumberland Falls meteorites and in four meteorites identified as forsterite chondrites (Kakangari, Mt. Morris, Pontlyfni and Winona). The inclusions are found to be of a primitive composition, corresponding to petrological types 2 or 3, while the identification of jadeitic pyroxene in nearly all inclusions indicates a substantial degree of shock. The results suggest that the inclusions formed from nebular material that condensed and accreted over a broad redox range, and experienced tertiary shock in a collision with an enstatite meteorite in which the Cumberland Falls meteorite formed.

Neal, C. W.↗
NASA NTRS1981

Derivation of a heterogeneous lithic fragment in the Bovedy L-group chondrite from impact-melted porphyritic chondrules

Results are presented of petrographic, compositional and dating analyses of a light-colored lithic fragment in the L-group Bovedy meteorite that has a composition different from that of the host chondrite. Polished thin sections of the lithic fragment, host, and the fragment-host boundary were examined microscopically and analyzed by electron microprobe, metallic Ni-Fe, and instrumental neutron activation techniques; chips of the fragment were also used for Ar-39/Ar-40 dating and oxygen isotope analyses. The poikilitic textures, olivine, low-Ca pyroxene and kamacite composition and low Na2O, K2O and P2O5 contents of the fragment indicate that it represents a solidified, slightly fractionated impact melt formed from a source rich in porphyritic chondrules. A progressive increase on MgO content across the fragment is accounted for by the heterogeneous nucleation of MgO-rich phases. The Ar data indicate that the Bovedy lithic fragment and its host were partly degassed of radiogenic Ar less than 0.94 billion years ago, probably due to shock. The data are consistent with a cooling rate of about 5 C/million years through 500 C, which must have resulted from the burial of the assemblage beneath insulating material on the parent body at depths of at least several km.

Rubin, A. E.↗
NASA NTRS1982

Copernicus crater central peak - Lunar mountain of unique composition

Olivine is identified as the major mafic mineral in a central peak of Copernicus crater. Information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra (0.7 to 2.5 micrometers) obtained with earth-based telescopes. The composition of the deep-seated material comprising the Copernicus central peak is unique among measured areas. Other lunar terra areas and the wall of Copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the Apollo missions, with low-calcium orthopyroxene being the major mafic mineral.

Pieters, C. M.↗
NASA NTRS1981

New kind of type 3 chondrite with a graphite-magnetite matrix

Four clasts in three ordinary-chondrite regolith breccias are discovered which are a new kind of type 3 chondrite. As with ordinary and carbonaceous type 3 chondrites, they have distinct chondrules, some of which contain glass, highly heterogeneous olivines and pyroxenes, and predominantly monoclinic low-Ca pyroxenes. Instead of the usual, fine-grained, Fe-rich silicate matrix, however, the clasts have a matrix composed largely of aggregates of micron- and submicron-sized graphite and magnetite. The bulk compositions of the clasts, as well as the types of chondrules (largely porphyritic), are characteristic of type 3 ordinary chondrites, although chondrules in the clasts are somewhat smaller (0.1-0.5 mm). A close relationship with ordinary chondrites is also suggested by the presence of similar graphite-magnetite aggregates in seven type 3 ordinary chondrites. It is thought that this new kind of chondrite is probably the source of the abundant graphite-magnetite inclusions in ordinary-chondrite regolith breccias and that it may be more common than indicated by the absence of whole meteorites made of chondrules and graphite-magnetite.

Scott, E. R. D.↗
NASA NTRS1981

Mineralogy, petrology, and trace element geochemistry of the Johnstown meteorite - A brecciated orthopyroxenite with siderophile and REE-rich components

The compositional and petrologic characteristics of the Johnstown meteorite show it to contain uncontaminated and unbrecciated orthopyroxenite clasts of cumulative origin that (1) must have undergone subsolidus recrystalization, (2) are parental to the brecciated matrix, and (3) show no evidence of a xenolithic, meteoritic contribution to the matrix except for contamination by the projectile which crushed it on impact. The trapped liquid was not introduced in the impact process. The variability of such trace elements as the light rare earth elements, and the presence of plagioclase and olivine in only one of the thin sections studied, demonstrates the heterogeneity of coarse-grained diogenites on a millimeter scale and the difficulty of obtaining representative samples of such meteorites. The data presented indicate that this meteorite is a monominct breccia.

Floran, R. J.↗
NASA NTRS1982

Limits on the lunar temperature profile

Limits on the selenotherm are estimated using (1) a preferred set of bounds on the lunar electrical conductivity profile; (2) published laboratory conductivity vs. temperature data for an olivine and several aluminous orthopyroxenes; and (3) estimates for the Al2O3 content of the deep interior suggested by bulk composition models. The inferred limits are narrowest in the depth range 450 to 1350 km and are in accord with independent geophysical constraints. Thermal history models which yield present-day selenotherms that are in best agreement with these limits are those which permit subsolidus convection at depths greater than 800 km in the moon.

Hood, L. L.↗
NASA NTRS1980

Cl, P2O5, U and Br associated with mineral separates from a low and a high Ti mare basalt

Low Ti basalt 12040 and high Ti basalt 75055 have approximately the same Cl/P2O5 ratio; the Cl is that remaining after a hot water leach. Pyroxene, plagioclase and ilmenite minerals separated from the basalts also tend to have this same Cl/P2O5 ratio. This is evidence that these major minerals do not control the ratio since Cl and P would not be expected to partition to the same extent into each mineral. Olivine appears to be a special case. It is proposed that the grains measured contained inclusions with leachable and P2O5-related Cl. Dilute acid leaches of whole rock and separated minerals have the same or nearly the same Cl/P2O5 ratios as the residual samples. Apatite and whitlockite were probably the phases leached. They must be constituents of the mesostasis and are present as microminerals or coatings on major mineral grains. The acid leach results imply little or no partition of Cl and P2O5 into major minerals.

Jovanovic, S.↗
NASA NTRS1980

Lunar and Planetary Science Conference, 11th, Houston, TX, March 17-21, 1980, Proceedings. Volume 2 - Meteorite and regolith studies

Topics discussed include studies of chondrites, mesosiderites, and achondrites; isotope modeling; Antarctic weathering; irradiation effects; lunar regolith studies; the Apollo 17 drill core; soils and agglutinates; and volatiles. Particular attention is given to the proportional retention of I and Xe-129 in preheated Allende, olivine clasts from mesosiderites and howardites as clues to the nature of achondritic parent bodies, a record of solar corpuscular radiation in minerals from lunar soils, the experimental shock metamorphism of lunar soil, and the clouding of pyroxene and plagioclase in eucrites.

Merrill, R. B.↗
NASA NTRS1980

Origin of volatile-rich H chondrites with light/dark structures

The light and dark fractions of four gas-rich, brecciated H chondrites are studied in terms of petrography and volatile element chemistry in an investigation of the origin of light/dark chondrites. Petrographic constraints on the nature of the light and dark fractions of the meteorites are presented. Light clasts within the brecciated H chondrites are more highly metamorphosed than dark host material, and olivine, pyroxene and metal compositions suggest that dark fractions consist of mixtures of unequilibrated material and pulverized equilibrated H chondrite similar to the light clasts. Volatile element concentrations in the dark fractions are similar to those in the least equilibrated H3 chondrites, and no petrographic evidence for admixture of significant amounts of carbonaceous chondrite was noted. It is concluded that volatile-rich H chondrite breccias may not have incorporated carbonaceous chondrite dust as the volatile element carrier.

Mcsween, H. Y., Jr.↗
NASA NTRS1980

XPS and STEM studies of Allende acid insoluble residues

Data on Allende acid residues obtained both before and after etching with hot HNO3 are presented. X-ray photoelectron spectra show predominantly carbonaceous material plus Fe-deficient chromite in both cases. The HNO3 oxidizes the carbonaceous material to some extent. The small chromites in these residues have a wide range of compositions somewhat paralleling those observed in larger Allende chromites and in Murchison chromites, especially in the high Al contents; however, they are deficient in divalent cations, which makes them metastable and indicates that they must have formed at relatively low temperatures. It is suggested that they formed by precipitation of Cr(3+) and Fe(3+) from olivine at low temperature or during rapid cooling.

Housley, R. M.↗
NASA NTRS1980

Allan Hills A77219 - The first Antarctic mesosiderite

The abundance of orthopyroxene, inverted pigeonite, plagioclase, tridymite, kamacite, and tetrataenite, plus the whole rock analysis, indicates that ALHA 77219 is a mesosiderite. The presence of inverted pigeonite rims on orthopyroxene clasts plus the range of Fe/Mg and Fe/Mn ratios for pyroxene and olivine are characteristic of mesosiderites. All the petrographic and chemical data are consistent with classification of ALHA 77219 as a mesosiderite and, because the matrix is fine-grained and little recrystallized, as a subgroup I mesosiderite. The Fe/Mn trends in pyroxenes of mesosiderites such as ALHA 77219 can be explained by igneous fractionation of pyroxene along with metal and subsequent subsolidus reduction in the breccia.

Agosto, W. N.↗
NASA NTRS1980

Modal studies of mesosiderites and related achondrites, including the new mesosiderite ALHA 77219

The Antarctic meteorite ALHA 77219 is found to be a new mesosiderite. It contains about 25% metal + troilite (+ rust) and the brecciated silicate portion is dominated by orthopyroxene (En 68-71). These features, together with the presence of olivine surrounded by coronas, and abundant tridymite + phosphate conform to the characteristics of mesosiderites. A comparison of the modal abundances of minerals in 77219 with modes of 20 mesosiderites, 14 howardites, six basaltic eucrites, three feldspar cumulate eucrites, and one orthopyroxene cumulate eucrite shows that there are major differences between mesosiderites and howardites. These differences are described in detail.

Prinz, M.↗