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At least 235 records · Page 13

Geology team

Evaluating of the combined utility of narrowband and multispectral imaging in both the infrared and visible for the lithologic identification of geologic materials, and of the combined utility of multispectral imaging in the visible and infrared for lithologic mapping on a global bases are near term recommendations for future imaging capabilities. Long term recommendations include laboratory research into methods of field sampling and theoretical models of microscale mixing. The utility of improved spatial and spectral resolutions and radiometric sensitivity is also suggested for the long term. Geobotanical remote sensing research should be conducted to (1) separate geological and botanical spectral signatures in individual picture elements; (2) study geobotanical correlations that more fully simulate natural conditions; and use test sites designed to test specific geobotanical hypotheses.

Source record↗

Origin of lunar meteorite ALHA 81005 - Clues from the presence of terrae clasts and a very low-titanium mare basalt clast

Attention is given to the endogenous (or primary) lithologies of the lunar crust that can be inferred from the terrae clasts and to the significance of a fragment of very low titanium (VLT) mare basalt in thin section, ALHA 81005,9. Fragments of the norite and harzburgite have mineral compositions similar to that of ferroan anorthosite, and a clast of ferroan anorthosite has pyroxenes with lower molar Mg/(Mg+Fe) than in known pristine rocks. It is inferred that the Mg-suite protoliths for the clasts of intermediate composition are magnesian troctolites, spinel troctolites, and feldspathic lherzolites. Whereas clasts of these lithologies are not present in ALHA 81005,9, mineral fragments from them are. Based on the molar Mg/(Mg+Fe) ratio and Cr content of its pyroxenes, a single basaltic clast is determined to be of mare origin. The composition of its plagioclase and the molar Ti/(Ti+Cr) ratios of its pyroxenes suggest that the clast is a fragment of VLT mare basalt. It is noted that if this basalt is significantly younger than the last basin-forming impact event, which was approximately 3.9 x 10 to the 9th years ago, then its presence probably constrains the source crater for ALHA 81005 to be within a hundred kilometers of a VLT mare basalt flow.

Treiman, A. H.↗

Petrogenesis of the Elephant Moraine A79001 meteorite Multiple magma pulses on the shergottite parent body

The EETA 79001 achondrite consists of two distinct igneous lithologies joined along a planar, non-brecciated contact. Both are basaltic rocks composed primarily of pigeonite, augite, and maskelynite, but one contains zoned megacrysts of olivine, orthopyroxene, and chromite that represent disaggregated xenoliths of harzburzite. Both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small, shallow chamber. Many similarities between the two virtually synchronous magmas suggest that they are related. Possible mechanisms to explain their differences involve varying degrees of assimilation, fractionation from similar parental magmas, or partial melting of a similar source peridotite; of these, assimilation of the observed megacryst assemblage seems most plausible. However, some isotopic contamination may be required in any of these petrogenetic models. The meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body.

Mcsween, H. Y., Jr.↗

Application of Heat Capacity Mapping Mission data to regional geologic analysis for mineral and energy resource evaluation

Heat Capacity Mapping Mission thermal-inertia images of a diversity of terrains and geologic settings were examined in conjunction with topographic, geologic, geophysical, and LANDSAT data. The images were found to have attributes similar to bedrock maps. In the Cascades region, two new features were identified and a method was developed to characterize regional terranes using linear feature data. Two northeast-trending Lineaments were discovered in the Overthrust Belt of Montana and Idaho. The longer of the two extends from the Idaho-Oregon border, through the Idaho batholith and across the Lewis thrust. It coincides, along segments, with mapped faults and an aeromagnetic pattern change. A major lineament crossing the Colorado Plateau and the Southern Rocky Mountians was detected on several thermal-inertial images and evidence was found for the existence of a geologic discontinuity. Vegetation-covered areas in Richfield and the Silver City quadrangle (Arizona and New Mexico) displayed thermal-inertia differences within heavily vegetation areas although no apreciable correlation was found between vegetation cover and thermal inertia. Resistant ridges and knolls have high thermal inertias and thermal-inertia contrasts occurred at lithologic and fault contacts. In the heavy vegetated Pinaleno Mountains, Arizona, a Lithologic unit obscured on LANDSAT MSS data due to the vegetation cover, exhibited a thermal-inertia contrast with its surroundings.

Watson, K.↗

Multiseasonal variables in digital image enhancements for geological applications

Examples of enhanced multiseasonal orbital imagery illustrate the influence of multiseasonal changes in their spatial and spectral attributes, and consequently in their application to structural geology and lithological discrimination. Shadow effects associated with appropriate solar elevation and azimuth effects enhance the spatial attributes but not the spectral. In this case, variations in illumination conditions should be minimized by selecting images with high solar elevation and by the use of techniques that minimize illumination conditions. Multiseasonal imagery should be used in the identification of spectral contrast changes of rock-soil-vegetation associations which can provide evidences of related lithological units and structural features. The extraction of maximum geological information requires, at least, a fall/winter and a spring/summer scene from which spatial, spectral and multiseasonal attributes can be adequately explored.

Parada, N. D. J.↗

The impact cratering rate in recent time

The terrestrial data base for crater structures with diameters over 20 km on the North American and European cratons has been investigated for variations in the rate with time. The variation in the degree of preservation of highly eroded complex structures on the two cratons suggests that, if no contrasts exist between near-surface and uplifted lithologies, a 20 km-sized crater may be rendered virtually unrecognizable in 34 to 300 m.y. If lithological contrasts are present, it may be still recognizable as an anomalous structure for 79 to 630 m.y. It is unlikely that a significant number of craters with diameters greater than 20 km and ages in the range 0-117 m.y. are unrecognizable because of erosion. The relatively slower rate of increase in the number of craters with time for the 180-360 m.y. population may reflect a recognition problem.

Grieve, R. A.↗

Chemistry and petrology of Apollo 12 drive tube 12027

Papike et al. (1982) have provided a summary of previous petrologic and chemical studies of the lunar regolith, taking into account samples from all of the Apollo and Luna sites. On the basis of these studies, an understanding is obtained of the processes which form and characterize the lunar regolith. It is found that comminution of local lithologies by meteorite impact and soil mixing are the most important regolith-forming processes. On the basis of grain size studies of Apollo 14 surface, trench, and drive tube soils, Simin et al. (1982) and Laul et al. (1982) concluded that comminution of local lithologies and vertical soil mixing processes are most important in the formation of the soils at that site. In the present investigation, this study of chemistry and petrology of lunar soils is extended to the Apollo 12 drive tube 12027. This drive tube provides an opportunity to study lunar soil from a depositional environment involving a location at the rim of a crater. The chemical and petrologic data are found to be consistent and suggest three stratigraphic units in the 12027 core.

Smith, M. R.↗

Tertiary and Quaternary Research with Remote Sensing Methods

Problems encountered in mapping the Quaternary section of the Wind River Region using remote sensing methods are discussed. Analysis of the stratigraphic section is a fundamental aspect of the geologic study of sedimentary basins. Stratigraphic analysis of post-Cretaceous rocks in the Wind River Basin encounters problems of a distinctly different character from those involved in studying the pre-Cretaceous section. The interior of the basin is predominantly covered by Tertiary and Quaternary sediments. These rocks, except on the basin margin to the north, are mostly flat lying or gently dipping. The Tertiary section consists of sandstones, siltstones, and tuffaceous sediments, some variegated, but in general poorly bedded and of great lithologic similarity. The Quaternary sediments consist of terrace, fan, and debris tongue deposits, unconsolidated alluvium occupying the bottoms of modern watercourses, deposits of eolian origin and tufa. Terrace and fan deposits are compositionally diverse and reflect the lithologic diversity of the source terranes.

Conel, J. E.↗

Preliminary structural model for the southwestern part of the Michipicoten greenstone belt, Ontario

The southwestern part of the Michipicoten Greenstone Belt includes a 100 sq km fume kill extending northeastwards from the twon of Wawa, Ontario. Except for a strip along the Magpie River that is covered by Pleistocene gravels, outcrop in the fume kill averages about 30-50%. Within this area are all the major lithologic belts characteristic of the southwestern fourth of the Michipicoten Greenstone Belt. All of the area mapped to date lies within Chabenel Township, recently mapped at 4" = 1 mile. Following a brief reconnaissance in 1983, mapping at a scale of 1" = 400' was begun within and adjacent to the fume kill in 1984. Two objectives are sought (1) determinaion of the geometry and sequence of folding, faulting, cleavage development, and intrusion; and (2) defining and tracing lithologic packages, and evaluating the nature of the contacts between these packages. Results for objective (1) are discussed in a companion abstract; this abstract will present tentative results for objective.

Mcgill, G. E.↗

The rock components and structures of Archean greenstone belts: An overview

Knowledge of the character and evolution of the Earth's early crust is derived from the studies of the rocks and structures in Archean greenstone belts. Ability to resolve the petrologic, sedimentological and structural histories of greenstone belts, however, hinges first on an ability to apply the concepts and procedures of classical stratigraphy. Unfortunately, early Precambrian greenstone terrains present particular problems to stratigraphic analysis. Many current controversies of greenstone belt petrogenesis, sedimentology, tectonics and evolution arise more from an inability to develop a clear stratigraphic picture of the belts than from ambiguities in interpretation. Four particular stratigraphic problems that afflict studies of Archean greenstone belts are considered: determination of facing directions, correlation of lithologic units, identification of primary lithologies and discrimination of stratigraphic versus structural contacts.

Lowe, D. R.↗

Department of Geology/NASA-GSFC geobotanical investigation

Geobotanical mapping in the southern Appalachians and soil metal associated changes in vegatation spectral responses in the reflective and emissive portions of the electromagnetic spectrum (EMS) is studied. It is determined whether deciduous forest vegetation reflection and emission characteristics show detectable changes that can be related to residual soil characteristics. Analyses of such related characteristics enhances the ability to discriminate underlying lithologies as well as variances within lithologies associated with natural heavy metal occurences. An understanding is developed of the factors which contribute to the differing spectral signatures of various lithology/soil types. A combination of field data and remote spectral analysis is studied.

Source record↗

Alkali norite, troctolites, and VHK mare basalts from breccia 14304

Six pristine rocks, two mare basalts, and four nonpristine highlands rocks were separated from breccia 14304 for consortium study. The pristine highlands rocks include representatives of the Mg troctolite-anorthosite and alkali suites of the Apollo 14 site. Two troctolite clasts have olivine and plagioclase compositions similar to one group of Apollo 14 troctolites and one also contains spinel. Incompatible element abundances in one are similar to those of 14305 troctolites, although the heavy rare earth elements pattern is distinct among Apollo 14 troctolites. Alkali lithologies include an alkali anorthosite and an alkali norite, the latter having a pristine igneous texture and resembling alkali gabbronites from Apollo 14 and 67975 in mineralogy and mineral compositions. It is suggested that Apollo 14 alkali lithologies and PO4-bearing Mg anorthosites formed from Mg-rich magmas that assimilated various amounts of material rich in P and REE. Another pristine clast from 14304 is an Mg-gabbronorite. The two mare basalt clasts are very high potassium basalts, whose parent magmas could have formed from a typical low-Ti, high-Al basaltic magmas by assimilation of K-rich material. Nonpristine 14304 clasts include melt-textured anorthosites and an augite-rich poikilitic melt rock.

Goodrich, C. A.↗

Martian volatiles in shergottite EETA 79001 - New evidence from oxidized sulfur and sulfur-rich aluminosilicates

Two equivalent chips of lithology A (lith-A) and lithology C (lith-C) taken from the same interior portion of EETA 79001 shergottite have been analyzed for volatile species produced by high-vacuum pyrolysis. The lith-C was found to contain an oxidized sulfur component that does not occur in lith-A. The preterrestrial origin of this component in lith-C is supported by the occurrence in lith-C of sulfur- and chlorine-rich aluminosilicates that are not the same as Antarctic weathering products found in the control samples. The oxidation state and distribution of sulfur found in lith-C are consistent with the interpretation of EETA 79001 as a rock from Mars.

Gooding, J. L.↗

Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs, Wash volcanic centers, Southern Nevada

LANDSAT Thematic Mapper imagery was evaluated over 3 Tertiary calderas in southern Nevada. Each volcanic center derived from a highly evolved silici magmatic system represented today by well exposed diverse lithologies. Distinctive imagery contrast between some of the late ash flows and earlier units follows from the high relative reflectance in longer wavelength bands (bands 5 and 7) of the former. Enhancement techniques provide color composite images which highlight some of the units in remarkable color contrast. Inasmuch as coatings on the tuffs are incompletely developed and apparently largely dependent spectrally on rock properties independent of petrochemistry, it is felt that the distinctive imagery characteristics are more a function of primary lithologic or petrochemical properties. Any given outcrop is backdrop for a variety of cover types, of which coatings, at various stages of maturity, are one. Petrographic and X-ray diffraction analysis of the outer air-interface zone of coatings reveal they are composed chiefly of amorphous compounds, probably with varying proportions of iron and manganese. Observations support an origin for some outer (air-interface) coating constituents exogenous to the underlying host.

Taranik, James V.↗

The composition and history of breccia 67015 from North Ray Crater

Feldspathic fragmental breccia (FFB) 67015 from the rim of North Ray Crater was examined and was found to be the most diverse and complex of the Apollo 16 FFBs. It contains a wider range of clast types than any of the others and is not dominated by any single lithology. Several crystalline lithologies, occurring in minor amounts, were identified that represent highland plutonic rocks. Plagioclase fragments are the most abundant breccia constituent, followed by clasts of impact melt rocks and granulites. The impact melts are of two main types: feldspathic fragment-laden melts and mafic, KREEPy melt rocks of VHA basalt composition. Textural evidence indicates that some of the VHA melts were hot and plastic when they accumulated into the breccia. Ar-40 - Ar-39 dates show that both types of melts solidified about 3.9 x 10 to the 9th years ago. Magnetic measurements on clasts show a scatter of NMR directions, making it impossible to read a consistent imprint of an ancient dipolar magnetic field. Previous studies of Apollo 16 stratigraphy suggested that KREEPy melt rocks were introduced to the site as Imbrium impact ejecta, about 3.8 million years ago. Present results indicate that the highlands crust contained KREEP components as early as 3.9 x 10 to the 9th years ago.

Marvin, Ursula B.↗

An integrtated approach to the use of Landsat TM data for gold exploration in west central Nevada

This paper represents an integration of several Landsat TM image processing techniques with other data to discriminate the lithologies and associated areas of hydrothermal alteration in the vicinity of the Paradise Peak gold mine in west central Nevada. A microprocessor-based image processing system and an IDIMS system were used to analyze data from a 512 X 512 window of a Landsat-5 TM scene collected on June 30, 1984. Image processing techniques included simple band composites, band ratio composites, principal components composites, and baseline-based composites. These techniques were chosen based on their ability to discriminate the spectral characteristics of the products of hydrothermal alteration as well as of the associated regional lithologies. The simple band composite, ratio composite, two principal components composites, and the baseline-based composites separately can define the principal areas of alteration. Combined, they provide a very powerful exploration tool.

Mouat, D. A.↗

Igneous history of the aubrite parent asteroid - Evidence from the Norton County enstatite achondrite

Numerous specimens of the Norton County enstatite achondrite (aubrite) were studied by optical microscopy, electron microprobe, and neutron-activation analysis. Norton County is found to be a fragmental impact breccia, consisting of a clastic matrix made mostly of crushed enstatite, into which are embedded a variety of mineral and lithic clasts of both igneous and impact melt origin. The Norton County precursor materials were igneous rocks, mostly plutonic orthopyroxenites, not grains formed by condensation from the solar nebula. The Mg-silicate-rich aubrite parent body experienced extensive melting and igneous differentiation, causing formation of diverse lithologies including dunites, plutonic orthopyroxenites, plutonic pyroxenites, and plagioclase-silica rocks. The presence of impact melt breccias (the microporphyritic clasts and the diopside-plagioclase-silica clast) of still different compositions further attests to the lithologic diversity of the aubrite parent body.

Okada, Akihiko↗

Martian sample sites: Examples based on a global geologic perspective

Ten areas were selected that each include several rock units of varying lithology and age. These areas were chosen to optimize the geologic and chronologic data return from Mars. Geologic mapping and stratigraphic studies identify stratigraphic ages, rock types, and information on Martian geologic history that samples of a given site may yield. Volcanic rocks occur over much of the planet and in virtually all stratigraphic positions, and they are amenable to radioisotopic dating. Therefore, a reasonable and essential goal for a sample return mission is to return datable rocks from widely varying strata. Generally, about three or four major geologic units can be sampled at any of the given sites, most of which can probably be dated. The Mars Observer mission will aid greatly in interpreting lithology and defining contacts at the high resolution required to actually pinpoint good sample acquisition sites within these areas.

Scott, D. H.↗