Engineering topics

Stolper, E. M.

Publications and source records attributed to Stolper, E. M..

28 records · Page 2

NASA NTRS1989

Diffusion, phase equilibria and partitioning experiments in the Ni-Fe-Ru system

Results are presented on thin-film diffusion experiments designed to investigate phase equilibria in systems containing high concentrations of Pt-group elements, such as Ni-Fe-Ru-rich systems containing Pt, at temperatures of 1273, 1073, and 873 K. The rate of Ru diffusion in Ni was determined as a function of temperature, and, in addition, the degree of Pt and Ir partitioning between phases in a Ni-Fe-Ru-rich system and of V between phases in a Ni-Fe-O-rich system at 873 were determined. It was found that Pt preferentially partitions into the (gamma)Ni-Fe phase, whereas Ir prefers the (epsilon)Ru-Fe phase. V partitions strongly into Fe oxides relative to (gamma)Ni-Fe. These results have direct application to the origin and thermal history of the alloys rich in Pt-group elements in meteorites.

Blum, Joel D.↗

NASA NTRS1989

Origin of opaque assemblages in C3V meteorites - Implications for nebular and planetary processes

The results of analyses of meteoritic opaque assemblages (OAs) are presented and used in conjunction with literature data on phase equilibria and diffusion to further develop the hypothesis of Blum et al. (1989) for the origin of OAs in Ca,Al-rich inclusions (CAIs). Based on the results of the analyses, it is suggested that OAs formed after the crystallization of host CAIs by exsolution, sulfidation, and oxidation of precursor alloys at low temperatures (about 770 K) and higher than solar gas sulfur and oxygen fugacities. This model contrasts with previous models that call upon the formation of CAI OAs by aggregation of previously formed phases in the solar nebula prior to the crystallization of CAIs.

Blum, Joel D.↗

NASA NTRS1979

Petrogenetic relationship between Allan Hills 77005 and other achondrites

The paper presents chemical and petrologic data relating the Allan Hills (ALHA) 77005 achondrite from Antarctica and explores their petrogenetic relationship with the shergottites. Petrologic similarities with the latter in terms of mineralogy, oxidation state, inferred source region composition, and shock ages suggest a genetic relationship, also indicated by volatile to involatile element ratios and abundances of other trace elements. ALHA 77005 may be a cumulate crystallized from a liquid parental to materials from which the shergottites crystallized or a sample of peridotite from which shergottite parent liquids were derived. Chemical similarities with terrestrial ultramafic rocks suggest that it provides an additional sample of the only other solar system body with basalt source origins chemically similar to the upper earth mantle.

Mcsween, H. Y., Jr.↗

NASA NTRS1979

Allan Hills 77005 - A new meteorite type found in Antarctica

A unique 482.5 g meteorite found in Antarctica appears to be related by igneous differentiation to shergottite achondrites, which have close similarities with terrestrial basaltic rocks. Zoned maskelynite with similar compositional ranges and plagioclase of such intermediate compositions as are unknown in other achondrites occur in both shergottites and the Allan Hills meteorite. The degree of silica saturation, however, strongly distinguishes the two meteorite types. It is suggested that the Allan Hills meteorite may represent a cumulate rock formed earlier than the shergottites from the same or a similar parent magma.

Mcsween, H. Y., Jr.↗

NASA NTRS1979

Basaltic volcanism - The importance of planet size

The volumetrically abundant basalts on the earth, its moon, and the eucrite parent planet all have chemical compositions that are controlled to a large extent by dry, low-pressure, crystal-liquid equilibria. Since this generalization is valid for these three planetary bodies, we infer that it may also apply to the other unsampled terrestrial planets. Other characteristics of basaltic volcanism show variations which appear to be related to planet size: the eruption temperatures, degrees of fractionation, and chemical variety of basalts and the endurance of basaltic volcanism all increase with planet size. Although the processes responsible for chemical differences between basalt suites are known, no simple systematization of the chemical differences between basalts from planet to planet has emerged.

Walker, D.↗

NASA NTRS1978

A numerical treatment of melt/solid segregation - Size of the eucrite parent body and stability of the terrestrial low-velocity zone

Crystal sinking to form cumulates and melt percolation toward segregation in magma pools can be treated with modifications of Stokes' and Darcy's laws, respectively. The velocity of crystals and melt depends, among other things, on the force of gravity (g) driving the separations and the cooling time of the environment. The increase of g promotes more efficient differentiation, whereas the increase of cooling rate limits the extent to which crystals and liquid can separate. The rate at which separation occurs is strongly dependent on the proportion of liquid that is present. The observation of cumulates and segregated melts among the eucrite meteorites is used as a basis for calculating the g (and planet size) required to perform these differentiations. The eucrite parent body was probably at least 10-100 km in radius. The earth's low velocity zone (LVZ) is shown to be unstable with respect to draining itself of excess melt if the melt forms an interconnecting network. A geologically persistent LVZ with a homogeneous distribution of melt can be maintained with melt fractions only on the order of 0.1% or less.

Walker, D.↗

NASA NTRS1977

Slowly cooled microgabbros 15555 and 15065

An experimental study involving equilibration of Apollo 15 samples 15555 and 15065 in high-purity iron capsules is described. Comparison of mineral zoning trends with the experimental sequence suggests that the early crystallizing phases in the rock maintained surface equilibrium with the liquid. Olivine and pyroxene chemistry indicates that 15555 cooled slightly more rapidly than 15065, which cooled at approximately 0.2-0.3 C/day. It is suggested that 15065 and 15555 represent liquid compositions, and that these liquids appear to have been fractionated during ascent through the crust (15065), or to have been derived from an olivine-pyroxene source (15555) with Fe/(Fe + Mg) approximately equal to 0.73 at a depth between 150-200 km.

Walker, D.↗

NASA NTRS1975

Origin of titaniferous lunar basalts

Delineation of low pressure phase equilibria in the composition space relevant to titaniferous lunar basalts demonstrates a significant degree of control by those equilibria on the compositions of the basalts. The existence of two distinct chemical groups of basalts (high and low K) which cannot be related one to the other by fractional crystallization at any pressure, suggests that melting is responsible for the two groups. Consideration of the pressure shift required to produce the differences between groups constrains magma segregation to have occurred in the outer 150 km of the moon. It is difficult to relate low-Ti and high-Ti basalts to the same source region. The preferred source region of high-Ti basalts, based on phase equilibrium considerations, is a late ilmenite-rich cumulate produced from the residual liquid of the primordial differentiation of the outer portions of the moon. This ilmenite-rich layer is sandwiched between the lunar feldspathic crust and a complementary mafic cumulate.

Walker, D.↗

NASA NTRS1974

The petrology of the Apollo 17 mare basalts

Petrographic studies of Apollo 17 mare basalts indicate that 70215 and 71569 arrived at the lunar surface as liquids. Low-pressure melting experiments show that compositional variations within the Apollo 17 and Apollo 11 ophitic basalt suites may be generated by near-surface fractional crystallization of liquids with compositions similar to 70215 and 70017. High-pressure melting experiments show that liquids similar in composition to 70017 and 70215 can be generated by partial melting of an olivine+clinopyroxene+Fe-Ti-oxide source at depths of 100-150 km within the moon.

Longhi, J.↗

NASA NTRS1973

Origin of lunar feldspathic rocks

Melting experiments and petrographic studies of lunar feldspathic rocks reveal possible genetic relationships among several compositionally and mineralogically distinct groups of lunar rocks and soil fragments. Dry, low PO2 partial melting of crustal anorthositic norites of the anorthositic-noritic-troctolitic (ANT) suite produces liquids of the KREEP-Fra Mauro basalt type; dry, low PO2 partial melting of pink spinel troctolite (PST) produces liquids of the 'very high alumina basalt' or microtroctolite type. Both ANT and PST are probable components of the primitive terra crust. If crystal fractionation in a cooling basaltic liquid could have produced such a crust, it would also produce a mafic interior capable of yielding mare basalts by later remelting at depth.

Walker, D.↗