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NASA NTRS1984

The Colony meteorite and the possible existence of a new chemical subgroup of CO3 chondrites

The Colony meteorite, found in Oklahoma around 1975, has an unrecrystallized texture and contains heterogeneous olivine and low Ca pyroxene, kamacite with low Ni and Co and high Cr, amoeboid inclusions with low FeO and MnO, and numerous small chondrules with clear pink glass. These characteristics are shared by members of the least metamorphosed subgroup of CO3 chondrites. Colony contains a fine grained matrix that has higher FeO and K2O and lower MgO and Na2O than normal CO3 matrices. Allan Hills A77307 is another unmetamorphosed meteorite that has many petrologic similarities to normal CO chondrites, including matrix abundance, mineral compositions and chondrule size. However, it differs from them in its abundance of magnetite and presence of iron carbides. The olivine and low Ca pyroxene compositional distributions of Colony and A77307 are very similar. The shapes of the thermoluminescence glow curves of Colony and A77307 are very similar, but differ significantly from those of normal CO chondrites. It is suggested that Colony and A77307 represent a distinct chemical subgroup of CO3 chondrites, characterized by low Ni, Co, S, Ca, Mg, Mn and, possibly, high Cd.

Rubin, A. E.↗

NASA NTRS2005

An Improved Instrument for Investigating Planetary Regolith Microstructure

The Opposition Effect (OE) is the non-linear increase in the intensity of light scattered from a surface as phase angle approaches 0 deg. It is seen in laboratory experiments and in remote sensing observations of planetary surfaces. Understanding the OE is a requirement for fitting photometric models which produce meaningful results about regolith texture. Previously we have reported measurements from the JPL long arm goniometer and we have shown that this instrument enables us to distinguish between two distinct processes which create the opposition surges, Shadow Hiding (SHOE) and Coherent Backscattering (CBOE). SHOE arises because, as phase angle approaches zero, shadows cast by regolith grains on other grains become invisible to the observer. CBOE results from constructive interference between rays traveling the same path but in opposite directions. Additional information is included in the original extended abstract.

Nelson, R. M.↗

NASA NTRS1988

Rare earth element carriers in the Shergotty meteorite and implications for its chronology

This paper reports on the results of ion-probe measurements of REE concentrations in individual grains of the Shergotty meteorite. The phases analyzed included whitlockite, apatite, baddeleyite, augite, pigeonite, maskelynite, and K-rich glass; the whitlockite and apatite phases were also analyzed for U. Results indicate that whitlockite contains the bulk of the REE in Shergotty, with no evidence for distinct light-REE patterns in texturally different whitlockites. The results on the evolution of the REE abundances in the Shergotty late-stage interstitial melt, inferred from the analysis of whitlockite, are consistent with closed system crystallization. No metasomatic alteration is required to explain the REE data. It is concluded that there is no compelling reason to attribute chronological significance to the Sm-Nd array, as was done by Jagoutz and Waenke (1986).

Lundberg, Laura L.↗

NASA NTRS1978

Investigation of the Manicouagan impact crater, Quebec - An introduction

An interdisciplinary study of the 65-km diameter Manicouagan ring structure in Quebec was undertaken to gain insight into the integrated effects of impacts on terrestrial planetary bodies. The paper serves as an introduction to several companion papers and summarizes major conclusions. Studies of the 214 m.y. old structure show that the melt rocks are texturally inhomogeneous but chemically homogeneous and can be modeled as a mixture of target lithologies. The melt rocks have a Sr-87/Sr-86 ratio compatible with the melting of crustal rocks. The melt had a two-stage cooling history with clast-melt interactions indicative of mixing superheated silicate liquid with cold clasts. Grain size, clast reactions, and thermal equilibration of clasts and melts are described.

Phinney, W. C.↗

NASA NTRS2019

Creating Calibration Curves to Determine Shock Pressure in Clinopyroxene

Impact cratering is an important geological process that occurs on every rocky body in the solar system. It alters the texture and mineralogy of rocks via shock metamorphism. The peak shock pressures experienced by a rock are traditionally evaluated using qualitative optical methods however, quantitative methods do exist. One such method was developed by Uchizono et al., who used X-ray Diffraction (XRD) to measure lattice strain (ε) in several artificially shocked olivine grains using XRD peak broadening as a function of tan θ, where θ is the diffraction angle. They plotted the ε values against the known peak shock pressures experienced by the olivine grains. Using this calibration curve, the precise shock pressure experienced by a grain of olivine can be determined using its measured ε value. Another method was developed by McCausland et al. and Izawa et al., who used in situ XRD to measure strain-related mosaicity (SRM) of olivine in several ordinary chondrites and enstatite in enstatite chondrites, respectively. They plotted these results against the shock stage estimates for these meteorites. Using these plots, meteorites can be assigned to shock stage bins by measuring the SRM of olivine and/or enstatite. Both methods are useful for evaluating shock metamorphism, however, they have limitations. Uchizono et al.’s calibration curve has been successfully applied to martian meteorites, however it can only be applied to olivine-bearing rocks. McCausland et al.’s and Izawa et al.’s SRM method is uncalibrated and is limited to binning meteorites by shock stage. This work aims to expand on both methods by creating calibration curves for clinopyroxene (CPX): one for ε, similar to Uchizono et al.’s calibration curve for olivine, and one for SRM. This will extend the application of shock calibration methods to a greater variety of rock types. Preliminary results are presented herein.

Jenkins, Laura E.↗

NASA NTRS1993

Primitive SNC parent magmas and crystallization: Low PH2O experiments

SNC meteorites are generally believed to present one of the best opportunities to study the composition and petrogenesis of Mars magmas. The crystallization ages, noble gas content, oxygen isotopic composition, and shocked minerals of the meteorites are consistent with a Martian origin. The samples range from dunite to clinopyroxenite to microgabbro. Efforts by researchers to determine parental magmas for the more primitive SNC meteorites have been complicated by crystal accumulation and possible melt segregation and removal. This has resulted in a range of parent magma estimates, although all appear to be Fe-rich and Al-poor. One major objective is to refine the Chassigny parent magma estimate by forcing olivine + clinopyroxene saturation upon the proposed melt composition. EETA 79001 magma compositions are also being investigated to determine the parent magma and the origin of the coarse-grained olivine and orthopyroxene megacrysts. Low pressure experiments with small but finite P(sub H2O) are being utilized to facilitate equilibrium, and to simulate the H2O indicated for these magmas. The presence of small (0.5-1.0 wt percent) amounts of H2O in SNC magmas appears to be required by the occurrence of hydrous minerals and textures in melts trapped by growing phenocrysts. This evidence for hydrous melts occurs in all SNC's except EETA 79001 and ALHA 77005, where the inclusion textures were obscured by shock effects. The lack of hydrous minerals or low temperature melts in the intercumulus regions of these rocks suggests that final emplacement was sufficiently close to the surface to allow degassing as the magma equilibrated with the low P atmosphere. Any H2O left in intercumulus phases would also tend to be lost during impact heating. Thus, although the bulk H2O of SNC's is very low, it is believed that this is explained by the near Mars surface emplacement of SNC magmas and by shock effects. Magmatic processes involving H2O need to be examined in order to characterize SNC magmas immediately prior to their final emplacement.

Ford, D. J.↗

NASA NTRS2011

Variations in Surface Texture of the North Polar Residual Cap of Mars

The northern polar residual cap (NPRC) of Mars is a water ice deposit with a rough surface made up of pits, knobs, and linear depressions on scales of tens of meters. This roughness manifests as a series of bright mounds and dark hollows in visible images; these bright and dark patches have a characteristic wavelength and orientation. Spectral data indicate that the surface of the NPRC is composed of large-grained (and therefore old) water ice. Due to the presence of this old ice, it is thought that the NPRC is in a current state of net loss of material a result potentially at odds with impact crater statistics, which suggest ongoing deposition over the past 10-20 Kyr.

Mars↗

NASA NTRS1997

Stardust to Planetesimals: A Chondrule Connection?

The unique nature of chondrules has been known for nearly two centuries. Modern techniques of analysis have shown that these millimeter sized silicate objects are among the oldest objects in our solar system. Researchers have devised textural and chemical classification systems for chondrules in an effort to determine their origins. It is agreed that most chondrules were molten at some point in their history, and experimental analogs suggest that the majority of chondrules formed from temperatures below 1600 C at cooling rates in the range of hundreds of degrees per hour. Although interstellar grains are present in chondrite matrices, their contribution as precursors to chondrule formation is unknown. Models for chondrule formation focus on the pre-planetary solar nebula conditions, although planetary impact models have had proponents.

Paque, Julie↗

NASA NTRS2017

A New Method of Absorption-Phase Nanotomography for 3D Observation of Mineral-Organic-Water Textiles and its Application to Pristine Carbonaceous Chondrites

Pristine carbonaceous chondrites contain fine-grained matrix, which is composed largely of amorphous silicates, sub-micron silicate and sulfide crystals, and organic materials. They are regarded as primitive dust in the early Solar System that have suffered minimal alteration in their parent bodies. The matrix generally has different lithologies; some of them are unaltered but some are more or less aqueously altered. Their textures have been examined in 2D usually by FE-SEM/EDS, TEM/EDS, nano-SIMS and micro-XRD. Observation of their complex fine textures, such as spatial relation between different lithologies in 3D, is important for understanding aggregation and alteration processes. Synchrotron radiation (SR)-based X-ray tomography reveals 3D structures nondestructively with high spatial resolution of approximately greater than 100 nm. We have developed a new technique using absorption contrasts called "dual-energy tomography" (DET) to obtain 3D distribution of minerals at SPring-8, SR facility in Japan, and applied successfully to Itokawa particles. Phase and absorption contrast images can be simultaneously obtained in 3D by using "scanning-imaging x-ray microscopy" (SIXM) at SPring-8, which can discriminate between void, water and organic materials. We applied this technique combined with FIB micro-sampling to carbonaceous chondrites to search for primitive liquid water. In this study, we combined the DET and SIXM to obtain three dimensional submicron-scale association between minerals, organic materials and water and applied this to pristine carbonaceous chondrites.

Tsuchiyama, A.↗

NASA NTRS1977

Coarse-grained basalt 71597 - A product of partial olivine accumulation

Rock 71597, a coarse-grained plagioclase-poikilitic basalt that contains 15.8% MgO and 19.3% modal olivine, is described. Olivine and ilmenite crystals occur in two size generations, and large subequant olivine crystals, small 'matrix' olivines, and large ilmenite crystals are characterized. Since large olivine and ilmenite crystals with skeletal habits suggestive of crystallization under relatively rapid cooling are found in a rock whose texture is consonant with slower cooling, it is suggested that the large skeletal crystals formed toward the more rapidly cooled margin of a flow and accumulated by gravitational crystal settling toward the flow's interior. In support of this hypothesis, calculations indicate that the observed olivine compositions are approximately 10 mol% too Fe-rich to have crystallized from a melt of composition corresponding to that of 71597.

Warner, R. D.↗

NASA NTRS1980

The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace structural applications

The microstructure and tensile properties of two powder metallurgy processed aluminum-lithium alloys were determined. Strength properties of 480 MPa yield and 550 MPa ultimate tensile strength with 5% strain to fracture were attained. Very little reduction in area was observed and fracture characteristics were brittle. The magnesium bearing alloy exhibited the highest strength and ductility, but fracture was intergranular. Recrystallization and grain growth, as well as coarse grain boundary precipitation, occurred in Alloy 2. The fracture morphology of the two alloys differed. Alloy 1 fractured along a plane of maximum shear stress, while Alloy 2 fractured along a plane of maximum tensile stress. It is found that a fixed orientation relationship exists between the shear fracture plane and the rolling direction which suggests that the PM alloys are strongly textured.

Pizzo, P. P.↗

NASA NTRS1972

Petrology of basaltic and monomineralic soil fragments from the Sea of Fertility.

Basaltic and monomineralic fragments from the 150-425 micron size fractions of the Luna 16 core obtained from the Sea of Fertility were studied by optical petrographic, electron microprobe, and single-crystal X-ray diffraction techniques. Three textural varieties were identified in the basalts (intersertal, subophitic, and recrystallized). These textures, the assemblages, and individual mineral compositions (especially pyroxenes) indicate that these basalts crystallized under conditions very similar to those from Apollo 11. The pyroxenes have slightly lower Ti/Al (atomic) ratios than the Apollo 11 pyroxenes. We interpret the presence of octahedral Al as being due to the low TiO2/Al2O3 (weight %) ratio in the bulk rock. All observations made on the fine-grained basalt fragments are consistent with a rapid, near-surface, one-stage crystallization history.

Bence, A. E.↗

NASA NTRS2001

Petrology and Geochemistry of D'Orbigny, Geochemistry of Sahara 99555, and the Origin of Angrites

We have done detailed petrologic study of the angrite, D'Orbigny, and geochemical study of it and Sahara 99555. D'Orbigny is an igneous-textured rock composed of Ca-rich olivine, Al-Ti-diopside-hedenbergite, subcalcic kirschsteinite, two generations of hercynitic spinel and anorthite, with the mesostasis phases ulv6spinel, Ca-phosphate, a silicophosphate phase and Fe-sulfide. We report an unknown Fe-Ca-Al-Ti-silicate phase in the mesostasis not previously found in angrites. One hercynitic spinel is a large, rounded homogeneous grain of a different composition than the euhedral and zoned grains. We believe the former is a xenocryst, the first such described from angrites. The mafic phases are highly zoned; mg# of cores for olivine are approx.64, and for clinopyroxene approx.58, and both are zoned to Mg-free rims. The Ca content of olivine increases with decreasing mg#, until olivine with approx.20 mole% Ca is overgrown by subcalcic kirschsteinite with Ca approx.30-35 mole%. Detailed zoning sequences in olivine-subcalcic kirschsteinite and clinopyroxene show slight compositional reversals. There is no mineralogic control that can explain these reversals, and we believe they were likely caused by local additions of more primitive melt during crystallization of D'Orbigny. D'Orbigny is the most ferroan angrite with a bulk rock mg# of 32. Compositionally, it is virtually identical to Sahara 99555; the first set of compositionally identical angrites. Comparison with the other angrites shows that there is no simple petrogenetic sequence, partial melting with or without fractional crystallization, that can explain the angrite suite. Angra dos Reis remains a very anomalous angrite. Angrites show no evidence for the brecciation, shock, or impact or thermal metamorphism that affected the HED suite and ordinary chondrites. This suggests the angrite parent body may have followed a fundamentally different evolutionary path than did these other parent bodies.

Mittlefehldt, David W.↗

NASA NTRS1993

Soil texture and granulometry at the surface of Mars

Attention is given to a characterization of the physical behavior of the Martian upper surface in its first few decimeters on the basis of mutual relationships between three parameters: the linear polarization of the reflected light, the visual albedo, and the thermal inertia. Polarimetric scans raked a strip covering two contrasting regions, the dark-hued Mare Erythraeum, and the light-hued Thaumasia. Erythraeum is characterized everywhere by a uniform polarization response, despite the large geomorphological diversity of the surface. A ubiquitous coating or mantling with small dark grains of albedo 12.7 percent, with a radius of 10 to 20 microns, is indicated. Thaumasia exhibits a large variety of soil properties. A typical location with albedo of 16.3 percent has a surface covered with orange grains, probably very dispersed in size, for which the largest grains are 20 to 40 microns.

Dollfus, Audouin↗

NASA NTRS1979

Pyroxenes in Serra de Mage - Cooling history in comparison with Moama and Moore County

Thin sections and single grains of pyroxenes from the Serra de Mage feldspar cumulate eucrites were studied by X-ray crystallography, electron microprobe and optical techniques. It was concluded that the pyroxene crystallized as pigeonite. On cooling augite was exsolved along (001) and inverted to hypersthene, with exsolution of (100) augite from hypersthene during continued slow cooling. The estimated original bulk composition of the pigeonite pyroxene is Wo10En51Fs39. The compositional data, textural relations, and existence of P2 sub 1 ca hypersthene suggest very low cooling (about 0.0004 deg C/year) below 800 deg. The Serra de Mage augite lamellae were found to be as thick or thicker than those of Moore County and Moama meteorites.

Harlow, G. E.↗

NASA NTRS1983

Snow reflectance from thematic mapper

Calculations of snow reflectance in all 6 TM reflective bands (i.e., 1,2,3,4,5, and 7) using a delta Eddington model show that snow reflectance in bands 4,5, and 7 is sensitive to grain size. Efforts to interpret the surface optical grain size for the spectral extension of albedo are described. Results show the TM data include spectral channels suitable for snow/cloud discrimination and for snow albedo measurements that can be extended throughout the solar spectrum. Except for band 1, the dynamic range is large enough that saturation occurs only occasionally. The finer resolution gives much better detail on the snowcovered area and might make it possible to use textural information instead of the snowline as an index to the amount of snow melt runoff.

Dozier, J.↗

NASA NTRS1985

Snow Reflectance from Thematic Mapper

Dozier, J.↗

NASA NTRS2015

Characterization of Apollo Regolith by X-Ray and Electron Microbeam Techniques: An Analog for Future Sample Return Missions

The Apollo missions collected 382 kg of rock and regolith from the Moon; approximately 1/3 of the sample mass collected was regolith. Lunar regolith consists of well mixed rocks, minerals, and glasses less than 1-centimeter n size. The majority of most surface regolith samples were sieved into less than 1, 1-2, 2-4, and 4-10- millimiter size fractions; a portion of most samples was re-served unsieved. The initial characterization and classification of most Apollo regolith particles was done primarily by binocular microscopy. Optical classification of regolith is difficult because (1) the finest fraction of the regolith coats and obscures the textures of the larger particles, and (b) not all lithologies or minerals are uniquely identifiable optically. In recent years, we have begun to use more modern x-ray beam techniques [1-3], coupled with high resolution 3D optical imaging techniques [4] to characterize Apollo and meteorite samples as part of the curation process. These techniques, particularly in concert with SEM imaging of less than 1-millimeter regolith grain mounts, allow for the rapid characterization of the components within a regolith.

Zeigler, Ryan A.↗