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Longhi, J.

Publications and source records attributed to Longhi, J..

32 records · Page 2
All sourcesNASA NTRSDOE OSTI
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 NTRS1976

Crystallization history of lunar picritic basalt sample 12002 - Phase-equilibria and cooling-rate studies

Experimental crystallization of a lunar picrite composition (sample 12002) at controlled linear cooling rates produces systematic changes in the temperature at which crystalline phases appear, in the texture, and in crystal morphology as a function of cooling rate. Phases crystallize in the order olivine, chromium spinel, pyroxene, plagioclase, and ilmenite during equilibrium crystallization, but ilmenite and plagioclase reverse their order of appearance and silica crystallizes in the groundmass during controlled cooling experiments. The partition of iron and magnesium between olivine and liquid is independent of cooling rate, temperature, and pressure. Comparison of the olivine nucleation densities in the lunar sample and in the experiments indicates that the sample began cooling at about 1 deg C/hr. Pyroxene size, chemistry, and growth instability spacings, as well as groundmass coarseness, all suggest that the cooling rate subsequently decreased by as much as a factor of 10 or more. The porphyritic texture of this sample, then, is produced at a decreasing, rather than a discontinuously increasing, cooling rate.

Walker, D.↗
NASA NTRS1976

Heterogeneity in titaniferous lunar basalts

Small but real chemical differences exist between subsamples of fine-grained quench-textured titaniferous lunar basalts. The existence of different textural domains with different chemistries is thought to account for most of this variation. In addition to the textural domains, lunar sample 74275 has a population of olivine 'megacrysts' as well as dunite fragments. These materials are thought to be extraneous and to compromise the primary nature of 74275. Recognition of the small chemical variations present may aid in understanding some discrepancies in the experimental-petrology literature. However, these small variations have a distressing petrogenetic significance since they severely limit resolution in recognizing the number and depth of origin of primary magmas.

Walker, D.↗
NASA NTRS1976

Fe and Mg in plagioclase

Distribution coefficients for Fe and Mg between plagioclase and basaltic liquids were measured for lunar, terrestrial and synthetic systems. The data obtained imply that lunar anorthosites crystallized from relatively iron-rich liquids, that Fe/Mg zoning in plagioclase is an indicator of crystallization processes in basaltic magmas, and that Fe/Mg heterogeneity in plagioclase is a clue to the recognition of impact melts.

Longhi, J.↗
NASA NTRS1976

Differentiation of an Apollo 12 picrite magma

The Apollo 12 olivine basalt suite shows a strong positive correlation of grain size with normative olivine content. This correlation is interpreted to mean that the suite of samples represents the basal portion of a cooling unit which differentiated by simple olivine settling. The grain size of plagioclase observed in the coarsest samples indicates the cooling unit may have been as much as 30 m thick. The amount of olivine concentration observed in the suite is quantitatively internally consistent with simple olivine settling in a magma body of this size which has the composition of the chill margin.

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 NTRS1975

Differentiation of a very thick magma body and implications for the source regions of mare basalts

Mass-balance calculations indicate that the molten layer originally covering the moon may have been several hundred kilometers deep. The solidification of this magma ocean involved some unusual effects resulting from the large-pressure differential in the thick magma layer. The sunken cumulates from this differentiation would be more iron-rich, less refractory, and would contain more incompatible elements than would be expected in simple isobaric fractional crystallization and crystal sinking models of magma differentiation. These lower cumulates can have the mineralogical and chemical properties of the source regions of the low-Ti mare basalts.

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.↗
NASA NTRS1973

Experimental petrology and origin of rocks from the Descartes Highlands

Petrographic studies of Apollo 16 samples indicate that rocks 62295 and 68415 are crystallization products of highly aluminous melts. 60025 is a shocked, crushed and partially annealed plagioclase cumulate. 60315 is a recrystallized noritic breccia of disputed origin. 60335 is a feldspathic basalt filled with xenoliths and xenocrysts of anorthosite, breccia, and anorthite. The Fe/(Fe+Mg) of plagioclase appears to be a relative crystallization index. Low pressure melting experiments with controlled Po2 indicate that the igneous samples crystallized at oxygen fugacities well below the Fe/FeO buffer. Crystallization experiments at various pressures suggest that the 62295 and 68415 compositions were produced by partial or complete melting of lunar crustal materials, and not by partial melting of the deep lunar interior.

Walker, D.↗
NASA NTRS1972

Experimental petrology and origin of Fra Mauro rocks and soil

Melting experiments over the pressure range 0 to 20 kilobars were conducted on Apollo 14 igneous rocks 14310 and 14072 and on comprehensive fines 14259. The mineralogy and textures of rocks 14310 and 14072 are presumed to be the result of near-surface crystallization. The chemical compositions of the samples show special relationships to multiply-saturated liquids in the system: anorthite-forsterite-fayalite-silica at low pressure. Partial melting of a lunar crust consisting largely of plagioclase, low calcium pyroxene, and olivine, followed by crystal fractionation at the lunar surface is proposed as a mechanism for the production of the igneous rocks and soil glasses sampled by Apollo 14.

Walker, D.↗
NASA NTRS1972

Experimental petrology and origin of Fra Mauro rocks and soil.

Results of melting experiments over the pressure range from 0 to 20 kb on Apollo 14 igneous rocks 14310 and 14072, and on comprehensive fines 14259. It is found that low-pressure crystallization of rocks 14310 and 14072 proceeds as predicted from the textural relationships displayed by thin sections of these rocks. The mineralogy and textures of these rocks are the result of near-surface crystallization. The chemical compositions of these lunar samples all show special relationships to multiply saturated liquids in the system anorthite-forsterite-fayalite-silica at low pressure. Partial melting of a lunar crust consisting largely of plagioclase, low-calcium pyroxene, and olivine, followed by crystal fractionation at the lunar surface, is a satisfactory mechanism for the production of the igneous rocks and soil glasses sampled by Apollo 14. The KREEP component of other lunar soils, may have a similar origin.

Walker, D.↗