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Keil, Klaus

Publications and source records attributed to Keil, Klaus.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Mineralogy and possible origin of an unusual Cr-rich inclusion in the Los Martinez (L6) chondrite

During a petrological study of the previously unclassified ordinary chondrite Los Martinez a highly unusual Cr-rich inclusion is found which is unique in both extraterrestrial and terrestrial mineralogy. Detailed SEM and TEM studies show that the inclusion consists of a highly zoned single crystal of plagioclase intergrown with chromium-rich spinel which indicates that it is the product of exsolution. The Cr-rich precursors of the inclusion probably have close affinities to the chronite-plagioclase chrondrules observed by Ramdohr (1967) in several ordinary chondrites. Based on the zoning in the inclusion it is suggested that it is the product of fractional crystallization from a melt, which may have formed as a liquid condensate, or by melting of solid condensates, in the solar nebula. Subsequent cooling of this melt condensate resulted in crystallization of the unidentified phase. After crystallization, the inclusion was probably incorporated into a parent body where it underwent metamorphism and was probably shocked to some degree. During this period of parent body metamorphism, exsolution and decomposition of the unknown precursor occurred to produce the observed intergrowth of plagioclase and chromite. Los Martinez is classified as an L6 ordinary chondrite breccia.

Brearley, Adrian J.↗
NASA NTRS1991

Spinel-bearing, Al-rich chondrules in two chondrite finds from Roosevelt County, New Mexico - Indicators of nebular and parent body processes

Two rare spinel-bearing Al-rich chondrules are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These chondrules have unusual mineralogies dominated by highly and asymmetrically zoned Al-Cr-rich spinels. Two alternatives exist to explain the origin of this zoning-fractional crystallization or metamorphism. Fractional crystallization formed the zoning of the trivalent cations and caused a localized depletion in chromites around the large Al-Cr-rich spinels. Diffusive exchange and partitioning of Fe and Mg between olivine and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the chondrules suggest affinities with the Na-Al-Cr-rich chondrules, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten chondrule was heated and the cooling rate during crystallization. These two chondrules cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating chondrule textures and localized chromite depletions.

Mccoy, Timothy J.↗
NASA NTRS1991

Additional complexity in the lunar crust - Petrology of sodic anorthosites and sulfur-rich, ferroan noritic anorthosites

Lunar breccia 67016 contains two suites of unusual highlands rocks: sulfur-rich, noritic anorthosites, and sodic anorthosites. Mineral compositions of the sulfur-rich noritic anorthosites closely match those of ferroan anorthosites. Unusually large amounts of sulfides, and sulfidation reactions involving olivine in these clasts probably reflect endogenous volatile transfer. The sodic anorthosites are mafic-poor, with mineral compositions intermediate between those of pristine ferroan and alkali anorthosites. Rare examples of pristine rocks with similar mineral compositions are known, and may represent a distinct class of lunar crustal rocks.

Norman, Marc D.↗
NASA NTRS1991

Mineral compositions in pristine lunar highland rocks and the diversity of highland magmatism

High precision electron microprobe analyses of olivine and pyroxene in pristine lunar highland rocks confirm the dichotomy between ferroan anorthosites and the Mg-suite. Ferroan-anorthosites plot as coherent trends, consistent with formation in a complex global magma system. Lack of coherent compositional trends in the Mg-suite rocks indicates derivation from numerous magmas.

Bersch, Michael G.↗
NASA NTRS1991

Composition of chondrule silicates in LL3-5 chondrites and implications for their nebular history and parent body metamorphism

The composition of 75 type-IA and type-II porphyritic olivine chondrules from nine LL type 3 to type 5 chondrites was determined and was compared with that of chondrules from the Semarkona type 3.0 meteorite. Chemical data for silicates in the LL3.3-5 chondrites indicated that porphyritic olivine chondrules in these chondrites could be derived from chondrules similar to those from the Semarkona LL3.0, the least metamorphosed one of the known LL chondrites. It is shown that the chemical trends defined by the minerals of type-IA and type-II chondrules can be satisfactorily accounted for by the process of solid-state diffusive equilibration between minerals in chondrules and the opaque matrix rather than by changes in conditions during chondrule crystallization.

Mccoy, Timothy J.↗
NASA NTRS1991

Mineralogy of an unusual Cr-rich inclusion in the Los Martinez (L6) chrondritic breccia

During the petrological study of the L6 chondritic breccia, Los Martinez, we discovered a large, highly unusual Cr-rich inclusion whose mineralogy appears to be unique in both terrestrial and extraterrestrial occurrences. We carried out electron microprobe, scanning electron microscopy, and transmission electron microscopy investigations of this inclusion in order to determine its composition and mineralogy in detail and to establish its origin and possible relationship to other Cr-rich objects in chondritic meteorites. Details of the chemical composition, origin, and thermal history are given.

Brearley, Adrian J.↗
NASA NTRS1990

The Olton, Texas, H chondrite regolith breccia - Paired with Dimmitt

The Olton ordinary chondrites (two stones found in 1948) are H group, solar wind-bearing regolith breccias. The proximity of the recovery site to the Dimmitt strewnfield, and the similarity in texture, composition, noble gas contents and isotopic ratios to Dimmitt indicate that Olton is paired with Dimmitt.

Keil, Klaus↗
NASA NTRS1990

Classification of five new chondrite finds from Roosevelt County, New Mexico

Five small, weathered meteorites recovered from Roosevelt County, New Mexico, USA, are called Roosevelt County 066-070. Based on optical microscopy and electron microprobe analysis of mafic minerals, RC 066-070 are classified as L5a chondrites. RC 068 and 069 are tentatively paired. RC 066 and RC 067 are not paired with RC 068 and RC 069. RC 066, 067 and 070 do not appear to be paired with each other or with RC 001-031.

Pun, Aurora↗
NASA NTRS1990

Classification of four ordinary chondrites from Spain

Based on optical microsocpy and electron microprobe analysis of mafic minerals, four previously poorly described ordinary chondrites from Spain are classified. The classifications of Guarena (H6), Olmedilla de Alarcon (H5) and Reliegos (L5) are confirmed. Molina is reclassified as H5, based on new data.

Mccoy, T. J.↗
NASA NTRS1989

The Shallowater aubrite - Evidence for origin by planetesimal impacts

This paper presents the results of petrographic, mineralogic, and bulk trace element analyses of Shallowater aubrite samples, and interprets them in terms of the meteorite's origin. On the basis of these analyses, it is argued that Shallowater did not form on the aubrite parent body but represents a fourth enstatite meteorite body (in addition to the H and L enstatite chondrite and aubrite parent bodies). It is shown that its peculiar composition, texture, and cooling history can best be explained by an origin involving a low-velocity collision and breakup of a molten or a partly molten asteroid, consisting largely of a melt of MgSiO3 composition, with a solid, enstatite meteoritelike object.

Keil, Klaus↗
NASA NTRS1989

Enstatite meteorites and their parent bodies

The properties of enstatite meteorites (which are known to be comprised of the EH and EL chondrites and the aubrites) are discussed together with the nature and number of their parent bodies. It is pointed out that the bulk compositional differences in nonvolatile major elements exhibited by EH and EL chondrites in nonvolatile major elements were established by nebular rather than planetary processes. The occurrence of abundant breccias among these chondirites and a lack of clasts suggest that EH and EL chondrites represent two separate parent bodies. Aubrites are considered to represent samples from a third enstatite meteorite parent body, which may have experienced collisional break-up and gravitational reassembly of the debris. Shallowater may be a sample from yet a fourth enstatite meteorite parent body. It is suggested that, if unipolar dynamo induction by a primordial T Tauri sun was the dominant heat source that heated asteroidal-sized bodies in the early solar system, then the aubrite and Shallowater parent bodies may have melted because they were of intermediate sizes, whereas the EH and EL bodies did not melt.

Keil, Klaus↗
NASA NTRS1989

Chemical, isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites

Results are presented of a combined chemical, isotopic, and mineralogical study of fine-grained opaque matrix material from a type-3 ordinary chondrite Allan Hills A77299. It was found that the matrix of this chondrite (in contrast to chondrules) shows no siderophile element depletions and is remarkably unfractionated relative to CI chondrites. It was also found that the matrix lump has a unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine-grained matrix lumps and chondrule rims from Semarkona chondrules (Grossman and Wasson, 1987; Grossman et al., 1987); the mineralogy and textures of the matrix lump (which consists of rare angular grains of pyroxene and olivine embedded within a ground-mass of rounded fine-grained olivines), as well as its major element composition, are typical of matrix material of other type-3 chondrites studied. It is concluded that the matrix lump in these chondrites consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates.

Brearley, Adrian J.↗
NASA NTRS1988

Classification of six ordinary chondrites from Texas

Based on optical microscopy, modal and electron microprobe analyses, six ordinary chondrites from Texas were classified in compositional groups, petrologic types, and shock facies. These meteorites are Comanche (stone), L5c; Haskell, L5c; Deport (a), H4b; Naruna (a), H4b; Naruna (b), H4b; and Clarendon (b), H5d.

Ehlmann, Arthur J.↗
NASA NTRS1988

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↗
NASA NTRS1988

Spectral alteration effects in chondritic gas-rich breccias - Implications for S-Class and Q-Class asteroids

Reflection spectra were obtained from sawed or freshly broken surfaces of gas-rich matrix regions in a number of ordinary chondrites (Dubrovnik, Cangas de Onis, Olivenza, and Dimmitt) which are believed to represent lithified portions of asteroid regoliths that were once directly exposed to space, with the purpose of relating these chondrites to Class S asteroids. However, the observations did not detect curved red continuum characteristic for Class S asteroid spectra, suggesting that it is unlikely for any well-observed Class S asteroid to be a source of ordinary chondrites. It is suggested that the newly discovered spectral class 'Q', of which asteroid 1982 Apollo is the prototype, provides a viable alternative of a parent body.

Bell, Jeffrey F.↗
NASA NTRS1987

Roosevelt County 027 - A low-shock ureilite with interstitial silicates and high noble gas concentrations

The RC027 lightly-shocked ureilite contains less than 1 percent of a fine-grained interstitial silicate that has an igneous texture indicating crystallization from an interstitial liquid. RC027 is also noted to exhibit the strongest olivine preferred-orientation thus far observed in a ureilite; its fabric is characteristic of fabrics formed by tabular minerals in a fluid laminar flow regime, and is unlike those formed by synectonic recrystallization and plastic flow. The elemental and isotopic compositions of noble gases in RC027 are typical of previously analyzed ureilites.

Goodrich, Cyrena Anne↗
NASA NTRS1987

A search for spectral alteration effects in chondritic gas-rich breccias

Several samples of gas-rich breccias were selected, including slabs of the Kapoeta howardite, the ordinary chondrites Dubrovnik, Cangas de Onis, and Dimmit. Numerous 0.8 to 2.5 micron reflection spectra of selected areas on sawed or broken surfaces were measured with the Planetary Geosciences Division spectrogoniometer. While these spectra are not directly comparable to those of powered samples, comparisons within the data set should reveal any spectral differences due to weathering. These results indicate that unknown regolith processes do not confer the ordinary-chondrite parent bodies with an altered layer exhibiting S-class spectral properties. This is consistent with recent interpretations of the new Q-class of asteroids as the ordinary-chondrite parent bodies. However, significant spectral effects do occur in asteroid regoliths: darkening and suppression of absorption bands in highly shocked material, as seen previously in the so-called black chondrites; and segregation of metal in large impact melt pools on chondritic asteroids, which may have achondritic spectra. Neither of these effects is likely to be significant in interpreting current integral-disk spectra, but should be searched for in spectral maps returned by future spacecraft.

Bell, J. F.↗