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At least 109 records · Page 6
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NASA NTRS1976

Petrology of lunar rocks and implication to lunar evolution

Recent advances in lunar petrology, based on studies of lunar rock samples available through the Apollo program, are reviewed. Samples of bedrock from both maria and terra have been collected where micrometeorite impact penetrated the regolith and brought bedrock to the surface, but no in situ cores have been taken. Lunar petrogenesis and lunar thermal history supported by studies of the rock sample are discussed and a tentative evolutionary scenario is constructed. Mare basalts, terra assemblages of breccias, soils, rocks, and regolith are subjected to elemental analysis, mineralogical analysis, trace content analysis, with studies of texture, ages and isotopic composition. Probable sources of mare basalts are indicated.

Ridley, W. I.↗
NASA NTRS1976

Petrology of 79215 - Brecciation of a lunar cumulate

The paper considers the modal variation and bulk composition, the petrography, and the mineral chemistry of lunar sample 79215, a holocrystalline, nearly monomict breccia that is petrologically and chemically distinct from the majority of lunar highland breccias. The bulk composition of the rock and its REE abundances suggest that the precursor was a plagioclase-olivine cumulate.

Bickel, C. E.↗
NASA NTRS1976

Apollo 17, Station 6 boulder sample 76255 - Absolute petrology of breccia matrix and igneous clasts

The matrix of 76255 is the finest-grained, most clast-laden, impact-melt polymict breccia sampled from the Station 6 boulder. The paper speculates on how the matrix of 76255 fits into and enhances existing thermal models of breccia lithification. Emphasis is on the detailed petrology of five lithic clasts, two of which display mineralogical and textural affinities to mare basalts, while three, a gabbro, a norite, and a troctolite are considered primitive plutonic rocks.

Warner, J. L.↗
NASA NTRS1977

Petrology of crystalline matrix breccias from Apollo 17 rake samples

The petrology, mineralogy, and composition of 13 crystalline matrix breccias from the Apollo 17 rake samples are described. The breccias have matrices of uniform modal mineralogy (plagioclase, 50-54%; olivine and pyroxene, 41-46%) but diverse textures. Clast characteristics, including the proportion of plagioclase, the composition in comparison with matrix, and the textures of different clast types, are reported. The majority of bulk matrix compositions plot on or very near the plagioclase-olivine cotectic in the system olivine-anorthite-silica. If the matrix compositions represent impact total melts, the inferred cotectic control requires that the source material was itself an igneous differentiate with compositions along the plagioclase-olivine cotectic. Alternatively, the proximity of the matrix compositions to the plagioclase-olivine cotectic could be accounted for if the breccia matrices represent a suite of impact-generated partial melts.

Warner, R. D.↗
NASA NTRS1977

Petrology of four clasts from consortium breccia 73215

One felsite ('granite') and three ANT-suite anorthositic gabbro clasts extracted from breccia 73215 are described. The felsite clast has two components - fragments of crystalline felsite and veins and patches of felsic glass. The crystalline felsite, which consists largely of a vermicular intergrowth of quartz and Ba-K-feldspar, crystallized from a highly differentiated melt between 3.90 and 4.05 b.y. The felsic glass component consists of crystallized brown and colorless glasses and uncrystallized colorless glass which are all K and Si rich. The relation of glass features to past heating and the breccia-forming event is considered. In the three anorthositic gabbros, which have similar mineralogies and gradational textures, plagioclase is dominant, and olivine and orthopyroxene are the major mafic minerals. The petrologic data suggest that the gabbros formed as heated, partly melted, and/or recrystallized polymict breccias. It is possible that the approximately 4.25 b.y. age obtained for the three rocks is the date of the melting/recrystallization event.

James, O. B.↗
NASA NTRS1977

Petrology and geochemistry of lithic fragments separated from the Apollo 15 deep-drill core

Petrological and geochemical analysis of lithic fragments separated from the Apollo 15 deep-drill core showed these fragments to fall into the essentially the same range of rock types as observed in surface soil samples and large rock samples. Three particles are singled out as being of special interest. One sample is a mare basalt containing extremely evolved phases. The particle may represent small-scale imperfect crystal/liquid separation in a lava flow. A green glass particle is not the ultramafic emerald green glass described from the Apollo 15 site, but rather an ANT-like light green color, and has a quite different chemical composition from the ultramafic variety. One mare basalt displays a positive Eu anomaly and is enriched in plagioclase relative to olivine plus pyroxene.

Lindstrom, M. M.↗
NASA NTRS1977

Impact cratering phenomenon for the Ries multiring structure based on constraints of geological, geophysical, and petrological studies and the nature of the impacting body

In the present paper, an attempt is made to delineate, on the basis of field and laboratory data, the phenomenon of formation of the Ries multiring basin - the best preserved very large terrestrial impact structure. The model proposed conforms to constraints imposed by geological, geophysical, and petrological studies and by the nature of the postulated impacting body. It is also based on the impact features of a stony meteorite measuring 3 km in diameter at an impact velocity of 15 km/sec. The schematic reconstruction shows that critical to the production of a shallow crater is shallow impact penetration (shallow depth of burst). This and the nonballistic ejection of excavated material appear to be genetically related, i.e., if extensive nonballistic transport is recognized, then the associated crater must be a shallow structure and vice versa. This also means the shallow configuration of a crater may not have anything to do with postcratering readjustment.

Chao, E. C. T.↗
NASA NTRS1975

Thermal regimes in impact melts and the petrology of the Apollo 17 Station 6 boulder

A progress report is presented on the petrologic study of the Station 6 boulder, taking into account the implications of its petrographic and geochemical studies to the understanding of the processes of formation and crystallization of impact melts. The interpretation of the data from the boulder suggests processes that appear reasonable for a petrogenetic model of impact events large enough to produce a layer of melt a kilometer or more wide and at most a few tens of meters thick. A summary of the model is presented. The primary difference between the new model and the previous models of Warner et al. (1973, 1974) and Simonds et al. (1973, 1974) is that melt and clasts are derived from distinctly different parts of the cratering regime. The cooling is modeled in two steps, first the rapid equilibration between clasts and matrix, and second, the much slower loss of heat to the surroundings.

Simonds, C. H.↗
NASA NTRS1978

Studies of Brazilian meteorites. XIII - Mineralogy, petrology, and chemistry of the Putinga, Rio Grande do Sul, chondrite

The Putinga, Rio Grande do Sul chondrite is described and classified as an L6. The mineral composition and some significant ratios of elements are reported, and the reasons for assignment to the L group and to petrologic type 6 are explained. The analysis suggests that maskelynite of oligoclase composition was formed by solid-state shock transformation of previously existing well-crystallized plagioclase at estimated shock pressures of about 250-350 kbar. This finding indicates that recrystallization (formation of well-crystallized oligoclase) preceded shock transformation formation of the maskelynite.

Keil, K.↗
NASA NTRS1978

Studies of Brazilian meteorites. XIV - Mineralogy, petrology, and chemistry of the Conquista, Minas Gerais, chondrite

The Conquista chondrite is described and classified as an H4. The mineral composition is reported. H-group classification is based on described microscopic, electron microprobe, and bulk chemical studies. The evidence for petrologic type 4 classification includes the pronounced well-developed chondritic texture; the slight compositional variations in constituent phases; the high Ca contents of pyroxene and the presence of pigeonite; glassy to microcrystalline interstitial material rich in alkalis and SiO2; and twinned low-Ca clinopyroxene.

Keil, K.↗
NASA NTRS1978

Mineralogy and petrology of basaltic fragments from the Luna 24 drill core

The petrology of rock fragments and monomineralic grains from Luna 24 samples is described, and a petrogenetic scheme for the derivation of Mare Crisium basalts is presented. Components of the rock fragments include subophitic basalts, metabasalts, late-stage fragments, olivine vitrophyres, and non-mare lithic fragments of possible cumulate origin. Among the monomineralic grains (which are much more abundant than the rock fragments) are pyroxene, plagioclase, olivine, ilmenite and native Fe.

Coish, R. A.↗
NASA NTRS1978

Chemistry, mineralogy and petrology of seven greater than 1 mm fragments from Mare Crisium

Results are summarized for a consortium study of the chemistry, mineralogy, and petrology of seven Luna 24 fragments greater than 1 mm in size and having a mass of about 2 mg each. The fragments include four samples of mare ferrobasalt composition, one vitrophyre with the composition of a Mg-rich VLT mare basalt, one agglutinate, and one plagioclase fragment. It is found that: (1) the ferrobasalt is a highly fractionated mare rock very low in alkalis and TiO2, is similar to the less fractionate Apollo 17 VLT basalts, and is quite low in large-ion lithophile trace-element content; (2) the rare-earth-element patterns of the ferrobasalts are typical of VLT basalt, but some ophitic basalts have positive Eu anomalies, while others have negative Eu anomalies typical of mare basalts; and (3) the agglutinate is feldspathic and similar in composition to soil fines in Fe, Cr, Ca, and Al.

Laul, J. C.↗
NASA NTRS1978

Chemistry and petrology of Luna 24 lithic fragments and less than 250-micron soils - Constraints on the origin of VLT mare basalts

Results are reported on a combined INAA-petrologic study of 17 small (0.2-1.5 mg) Luna 24 lithic and mineral fragments and INAA study of 5 bulk soils and mineral separates from gabbro 24170. Lithic and mineral fragments are classified into VLT mare basalts (ferrobasalt and metabasalts), low-Ti, variolitic mare basalt, gabbros, melt rock and soil breccia. Data indicate 5 possible magma types, represented by: (1) VLT ferrobasalt and gabbro fragments, with low-TiO2 (about 1%), slightly bow-shaped REE pattern, and low REE concentrations (5-10X chondritic); (2) a ferrobasalt (Laul et al., 1978) and metabasalt fragments with major and trace element contents similar to (1), but positive Eu anomalies; (3) one gabbro fragment with distinctive pyroxene compositional trend (increasing Ti with nearly constant Fe/Fe + Mg) and highest REE contents of any Luna 24 mare basaltic sample, (4) a gabbro fragment with considerably less V and Cr2O3 than ferrobasalt and metabasalt fragments; and (5) variolitic basalt fragment with higher Ti2(2.3%) than other Luna 24 basalts and pyroxene that has increasing then decreasing Ti with increasing Fe/Fe + Mg. Trace element data place constraints on the nature of the source region and possible parent magmas for the Luna 24 VLT ferrobasalt.

Ma, M.-S.↗
NASA NTRS1978

Petrology, chemistry, age and irradiation history of Luna 24 samples

The results of petrological, chemical, isotopic age determination and irradiation studies of sample 24170 from the 170 cm depth of the regolith core returned from Mare Crisium by Luna 24 are presented. The sample is found to be comprised of fragments from a single igneous rock, with mineralogical evidence indicating it to be a mare basalt. The crystallization age is determined by Sm-Nd and Ar(40)-Ar(39) ages to be 3.30 AE, establishing the presence of relatively young flows. All soil samples show low trace element compositions with minimum contamination by KREEPUTh-rich materials. Rb-Sr and Sm-Nd relations reflect the absence of significant fractionation at ages younger than 4.5 AE. One soil sample shows extremely large neutron capture effects, imposing a new lower limit to the neutron production rate in the regolith and requiring the addition of irradiated materials from depth.

Wasserburg, G. J.↗
NASA NTRS1978

Comparative petrology and possible genetic relations among the Apollo 11 basalts

A comparative petrological study has been performed on 19 large Apollo-11 basalt fragments as well as two smaller vitrophyres in order to determine how many igneous bodies are presented by this suite of rocks. Detailed petrographic and mineral chemical studies have been performed on each sample along with an electron microprobe point count, which gives the mode, the range and distribution of all mineral zonation and the bulk composition. These data confirm the twofold division of the Apollo-11 basalts into high-K (type A) and low-K (type B) basalts.

Beaty, D. W.↗
NASA NTRS1979

The petrology of the Apollo 12 pigeonite basalt suite

A study of the petrology of the Apollo 12 pigeonite basalt samples 12011, 12043, and 12007 is presented. In this suite, the abundances of olivine and Cr-spinel decrease with increasing grain size, while the abundances of plagioclase and ilmenite increase. The petrochemical and textural variations indicate that the pigeonite basalts were derived from the olivine basalts, but the compositional gap between the olivine and pigeonite basalts indicates that they could not have crystallized together from a single, initially homogeneous magma body.

Baldridge, W. S.↗
NASA NTRS1979

A summary of the petrology and geochemistry of pristine highlands rocks

The petrology and geochemistry of pristine lunar highlands rock samples consisting of ferroan anorthosites, norites, troctolites, spinel troctolites/dunite/lherzolite, and KREEP, are described. In addition, petrographic and chemical evidence is presented which shows that low-siderophile rocks are the result of endogenous igneous activity and not impact melt differentiation. For example, these rocks contain Fe-metal as a late-crystallizing phase, and have W/La ratios higher than polymict breccias.

Norman, M. D.↗
NASA NTRS1979

The Apollo 17 drill core - Petrologic systematics and the identification of a possible Tycho component

Modal data support a five-unit stratigraphy for the Apollo 17 drill core. The upper unit E (0-22 cm depth) is marked by high content of fused soil, brown glass, and mare basalt fragments. This unit corresponds with a portion of the core excavated and refilled within the last 2 m.y. The underlying unit D (22071 cm depth) has a low abundance of fused soil (i.e., low maturity) and is rich in coarse (less than 200 microns) mare fragments. A large section of the core, unit C (71-224 cm depth), is finer-grained, more mature (richer in agglutinates), more feldspathic and has more highland lithic, mineral and glass fragments than unit D. The next underlying unit, B (224-256 cm depth), has yellow/colorless KREEP glasses with a high Si, low-alkali composition unlike the common Apollo 15 or Apollo 17 KREEP series. The petrologic (fused soil) and Is/FeO maturity of this layer is also lower than the units above and below. The deepest unit, A (256-284 cm depth), is marked by its relatively higher maturity and lower yellow/colorless KREEP glass content. The most prominent petrographic/stratigraphic indicators are the pyroxene-rich immature mare unit D and the abundance of KREEP glass in unit B. This KREEP glass is distinctive petrographically and compositionally, and is probably exotic to the Apollo 17 site. It is suggested here that the KREEP glass in unit B is derived from Tycho, which implies widespread distribution of KREEP on the lunar nearside.

Vaniman, D. T.↗