Search NASA⌕ Search

SEARCH · Search NASA

Results for “eucrite”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Neutron Absorption Measurements Constrain Eucrite-Diogenite Mixing in Vesta's Regolith

The NASA Dawn Mission s Gamma Ray and Neutron Detector (GRaND) [1] acquired mapping data during 5 months in a polar, low altitude mapping orbit (LAMO) with approx.460-km mean radius around main-belt asteroid Vesta (264-km mean radius) [2]. Neutrons and gamma rays are produced by galactic cosmic ray interactions and by the decay of natural radioelements (K, Th, U), providing information about the elemental composition of Vesta s regolith to depths of a few decimeters beneath the surface. From the data acquired in LAMO, maps of vestan neutron and gamma ray signatures were determined with a spatial resolution of approx.300 km full-width-at-half-maximum (FWHM), comparable in scale to the Rheasilvia impact basin (approx.500 km diameter). The data from Vesta encounter are available from the NASA Planetary Data System. Based on an analysis of gamma-ray spectra, Vesta s global-average regolith composition was found to be consistent with the Howardite, Eucrite, and Diogenite (HED) meteorites, reinforcing the HED-Vesta connection [2-7]. Further, an analysis of epithermal neutrons revealed variations in the abundance of hydrogen on Vesta s surface, reaching values up to 400 micro-g/g [2]. The association of high concentrations of hydrogen with equatorial, low-albedo surface regions indicated exogenic delivery of hydrogen by the infall of carbonaceous chondrite (CC) materials. This finding was buttressed by the presence of minimally-altered CC clasts in howardites, with inferred bulk hydrogen abundances similar to that found by GRaND, and by studies using data from Dawn s Framing Camera (FC) and VIR instruments [8-10]. In addition, from an analysis of neutron absorption, spatial-variations in the abundance of elements other than hydrogen were detected [2].

Prettyman, T. H.↗
NASA NTRS2017

Excess Silica Substitution in Plagioclase Grains in the Pasamonte Eucrite

Pasamonte is a clast-rich polymict basaltic breccia with O- and Cr-isotopic compositions that are resolved from those of most eucrites. It is dominated by two mafic clast types: (i) very-fine- to fine-grained, variolitic, subophitic and ophitic basalts, usually containing zoned pyroxenes; and (ii) fine- to medium grained hypidiomorphic-granular and allotriomorphic-granular microgabbros containing pyroxenes composed of augite lamellae in homogeneous pigeonite hosts. Minor clast types are fine-grained impact-melt, mafic-breccia and mafic-granular clasts; coarse matrix mineral fragments include pyroxene, plagioclase, silica, ferroan olivine and ilmenite. Our petrologic studies include determination of plagioclase compositions for the two major clast types and matrix grains, which we report here.

Mittlefehldt, D. W.↗
NASA NTRS1985

Origin of howardites, diogenites and eucrites - A mass balance constraint

Two petrogenetic models for the noncumulate-basaltic parts of howardite meteorites are discussed. A mass balance constraint is developed which indicates that more than half of the basaltic components in howardites formed as residual liquids from fractional crystallization of melts that had earlier produced diogentelike pyroxene cumulate components. Other model constriants involving scandium trends, clustering near olivine-pyroxene-plagioclase peritectic, and MgO/(MgO + FeO) ratios are discussed.

Warren, P. H.↗
NASA NTRS1983

Sm-Nd isotopic systematics and REE abundance studies of the ALH-765 eucrite

Analyses of Sm-Nd systematics and REE concentrations were carried out for the whole rock and mineral separates from the ALH-765 meteorite. A Sm-Nd age of 4.52 + or - 0.09 (2 sigma) b.y. and an initial Nd-143/Nd-144 ratio of 0.50675 + or 0.00011 (2 sigma) have been obtained. The previously reported Ce irregularities have been re-examined in this work. The large Ce anomalies and some minor Sm-Nd system disturbances observed for the meteorite may be interpreted as results of terrestrial weathering effects.

Nakamura, N.↗
NASA NTRS1987

Diverse eucritic pebbles in the Vaca Muerta mesosiderite

Seven 5-cm basaltic pebbles from the Vaca Muerta mesosiderite were studied by neutron activation and electron microprobe analysis, and three additional pebbles were studied petrographically. The cumulate pebbles had low REE concentrations and high Eu/Sm ratios, indicating the absence of intercumulus liquid. Siderophile interelement ratios were similar to those found in Vaca Muerta metal except for anomalously low Ir concentrations. The presence of 20 percent impact-melt breccias among the pebbles and 35-40 percent melt breccias among the mesosiderite whole-rocks suggests that the mesosiderites were more extensively impact melted than the howardites. Three alternative models to explain this greater proportion of impact-melted material among the mesosiderites are proposed.

Rubin, Alan E.↗
NASA NTRS1999

Pairing Among the EET87503 Group of Howardites and Polymict Eucrites

The ten HED polymict breccias EET82600, EET87503, EET87509, EET87510, EET87512, EET87513, EET87518, EET87528, EET87531, and EET92022 were found over a broad area in the Elephant Moraine collecting region of Antarctica. Locations are scattered among the Main (Elephant Moraine), Meteorite City, and Texas Bowl icefields and the Northern Ice Patch. It was previously suggested that these polymict breccias are paired. However, degree of terrestrial alteration among these meteorites varies from relatively pristine (type A) to extensively altered (type B/C) and there are textural, mineralogical, and compositional differences. This study is a reevaluation of the pairing of these meteorites.

Buchanan, Paul C.↗
NASA NTRS2000

Pairing Among the EET87503 Group of Howardites and Polymict Eucrites

The ten HED polymict breccias EET82600, EET87503, EET87509, EET87510, EET87512, EET87513, EET87518, EET87528, EET87531, and EET92022 were found over a broad area in the Elephant Moraine collecting region of Antarctica. Locations are scattered among the Main (Elephant Moraine), Meteorite City, and Texas Bowl icefields and the Northern Ice Patch. It was previously suggested that these polymict breccias are paired. However, degree of terrestrial alteration among these meteorites varies from relatively pristine (type A) to extensively altered (type B/C) and there are textural, mineralogical, and compositional differences. This study is a reevaluation of the pairing of these meteorites.

Buchanan, P. C.↗
NASA NTRS2003

A Liquidus Geothermometer for SNC, Lunar, and Eucritic Magmas

Two very useful pieces of information about a basalt are its liquidus temperature and liquid line of descent. To determine these, experiments are performed at various temperatures on the composition of interest between the solidus and liquidus. There are numerous examples of such experiments in the literature.

Jones, J. H.↗