Nier Prize Citation for Timothy J. McCoy     

Klaus Keil 《Meteoritics & planetary science》1997,32(Z4):A4-A4

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The Fayette County,Texas, meteorites     

Timothy J. McCoy  Arthur J. Ehlmann  Klaus Keil 《Meteoritics & planetary science》1995,30(6):776-780

Abstract— We report the first petrologic examination of all stone meteorites of Fayette County, Texas. The 10 stones represent four or five different fall events. The three recovered Bluff stones represent two falls. Bluff (a), which includes the 145.5-kg Bluff #1 stone, is classified as L5(S4), whereas Bluff (b) is classified as L4(S3) and is represented by a single stone. The studied Cedar stones are classified as H4(S3), and all four Cedar stones appear to define a strewnfield. Round Top (a), classified as L5(S3) and represented by two stones, is unrelated to either Bluff or Cedar. Round Top (b) [H4(S3); 1 stone], whose exact provenance is unknown, might be a transported fragment of the Cedar shower.  相似文献   

Altered basaltic glass: A terrestrial analog to the soil of Mars     

Carlton C. Allen  James L. Gooding  Michael Jercinovic  Klaus Keil 《Icarus》1981,45(2):347-369

Analyses of Martian surface soil by Viking and Earth-based telescopes have been interpreted as indicating a regolith dominated by the weathering products of mafic or ultramafic rocks. Basaltic glass has previously been proposed as a more likely precursor than crystalline rock, given the low efficiency of surface weathering under present Martian conditions. On Earth large volumes of basaltic glass formed by quenching of magma by water. A similar interaction, between magma and ground ice, may have been a common occurrence on Mars. On the basis of this scenario palagonite, the alteration product of basaltic sideromelane glass, was studied as a possible analog to Martian soil. Samples from Iceland, Alaska, Antarctica, Hawaii, and the desert of New Mexico and Mexico were examined by optical and scanning electron microscopy, electron microprobe analysis, X-ray diffraction, spectrophotometry, and magnetic and thermogravimetric analysis. We suggest that palagonite is a good analog to the surface soil of Mars in chemical composition, particle size, spectral signature, and magnetic properties. Our model for the formation of fine-grained Martian surface soil begins with eruptions of basaltic magma through ground ice, forming deposits of glassy tuff. Individual glass shards are then altered by low-temperature hydrothermal systems to palagonitic material. Dehydration and aeolian abrasion strip the alteration rinds from the glass, and wind storms distribute the silt-sized palagonitic fragments in a planet-wide deposit.  相似文献   

The USA and the oceans: Opportunities for independence     

Alfred A.H. Keil 《Marine Policy》1977,1(1):16-25

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Enstatite meteorites and their parent bodies*     

Klaus Keil 《Meteoritics & planetary science》1989,24(4):195-208

Abstract— Enstatite meteorites are highly reduced rocks that consist of major, nearly FeO-free enstatite, variable amounts of metallic Fe, Ni and troilite, and a host of rare minerals formed under highly-reducing conditions. They are comprised of the EH and EL chondrites and the aubrites. Here I discuss some of their properties and the nature and number of their parent bodies. Conclusions: 1. EH and EL chondrites show bulk compositional differences in non-volatile major elements that were established by nebular, not planetary processes. Occurrence of abundant breccias among them but lack of clasts of EL in EH chondrites (and vice versa) suggests that EH and EL chondrites represent two separate parent bodies. 2. Aubrites were not derived from known enstatite chondrites on the same parent bodies. Aubrites represent samples from a third enstatite meteorite parent body. 3. The aubrite parent body may have experienced collisional break-up and gravitational reassembly of the debris into a rubble-pile object. 4. The aubrite source material (parent body) was probably enstatite chondrite-like in composition, but had a higher troilite/metallic Fe, Ni ratio, higher contents of titanium and diopside, and possibly less plagioclase than known enstatite chondrites. 5. Shallowater, the only non-brecciated aubrite, does not appear to have formed on the EH, EL, or aubrite parent bodies by either internal (igneous) or external (impact) melting processes. Instead, Shallowater may be a sample from yet a fourth enstatite meteorite parent body. 6. Shallowater experienced a complex three-stage cooling history, requiring an equally complex mode of origin: collisional break-up of a molten or partly molten body by impact with a solid body, followed by gravitational reassembly. 7. It is unknown why some enstatite meteorite parent bodies melted (the aubrite and Shallowater bodies), and others did not (the EH and EL bodies). 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 because they were either much smaller or much larger.  相似文献   

CLAST-LADEN MELT-ROCK FRAGMENT IN THE ADAMS COUNTY,COLORADO, H5 CHONDRITE     

R.V. Fodor  Klaus Keil  Martin Prinz  M.-S. Ma  A.V. Murali  R.A. Schmitt 《Meteoritics & planetary science》1980,15(1):41-62

The Adams County, Colorado, H5 chondrite contains a lithic fragment, 1 cm in size, that is texturally and mineralogically quite different from the chondritic host. It is composed of: a groundmass of fine-grained euhedral to subhedral olivine (3–15 μm) and interstitial glass enclosing larger olivine and pyroxene grains (0.15-0.5 mm; about 15 vol %); an assemblage of enstatite grains (subfragment within) and an assemblage of olivine plus orthopyroxene (a second subfragment); and about 11 vol % grains of mixed troilite and nickel-iron metal. Analyses yielded these results: (i) olivine grains of the fragment groundmass have a compositional range (Fa_12–45) and most grains contain substantial CaO and Cr₂O₃ (～ 0.20 and 0.30 avg. wt%, respectively); interstitial glass has ～ 55 wt% SiO₂; (ii) larger olivine grains of the fragment are similarly high in CaO and Cr₂O₃ and also have a wide FeO/MgO range; one unusual pyroxene is an Mg-rich pigeonite; (iii) the metal is martensite in composition (11–14 wt% Ni); and (iv) major and trace element analyses by INAA indicate an H-group bulk composition for the entire 1 cm lithic fragment. On the basis of its texture and bulk and mineral compositions, the fragment is interpreted to represent unequilibrated H-group material that was partly melted by impact. The Ca- and Cr-enriched groundmass olivine and interstitial glass resulted from rapid crystallization of the chondritic melt. The Ca- and Cr-enriched larger silicate grains, including the enstatite sub-fragment and the pigeonite grain, are residual, unmelted clasts from the target material (this is supported by the presence of similar material in actual H3 chondrites). Further impact brecciation of the clast-laden melt material, and resultant impact-splashing accounts for the presence of the fragment in the H-group Adams County host and documents the coexistence of unequilibrated and equilibrated H-group material as surface regolith on one parent body.  相似文献   

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

Aurora Pun  T. J. McCoy  Klaus Keil  Ivan E. Wilson 《Meteoritics & planetary science》1990,25(3):233-234

Abstract— 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.  相似文献   

Classification of four ordinary chondrites from the Monnig Meteorite Collection     

Arthur J. Ehlmann  Klaus Keil 《Meteoritics & planetary science》1992,27(4):470-472

Abstract— We classified four ordinary chondrites from the Monnig Meteorite Collection into compositional groups, petrologic types and shock stages, based on optical microscopy in transmitted and reflected light, and electron microprobe and modal analyses. These meteorites are Allen, Texas, H4(S2); May Day, Kansas, H4(S2); Pony Creek, Texas, H4(S3); and Springer, Oklahoma, H5(S3).  相似文献   

FRAGMENTAL BRECCIAS AND THE COLLISIONAL EVOLUTION OF ORDINARY CHONDRITE PARENT BODIES     

Alan E. Rubin  Angeline Rehfeldt  Eric Peterson  Klaus Keil  Eugene Jarosewich 《Meteoritics & planetary science》1983,18(3):179-196

Our survey of type 4–6 ordinary chondrites indicates that gas-poor, melt-rock and/or exotic clast-bearing fragmental breccias constitute 5%, 22% and 23%, respectively, of H, L and LL chondrites. These abundances contrast with the percentages of solar-gas-rich regolith breccias among ordinary chondrites: H (14%), L (3%) and LL (8%) (Crabb and Schultz, 1981). Petrologic study of several melt-rock-clast-bearing fragmental breccias indicates that some acquired their clasts prior to breccia metamorphism and others acquired them after metamorphism of host material. In general, the melt-rock clasts in gas-poor H chondrite fragmental breccias were acquired after breccia metamorphism and were probably formed by impacts into boulders or exposed outcrops of H4-6 material in the H chondrite parent body regolith. In contrast, most of the melt-rock clasts in gas-poor L and LL fragmental breccias were acquired prior to breccia metamorphism. The low abundance of regolith breccias among L chondrites and evidence that at least two-thirds of the L chondrites suffered a major shock event 0.5 Gyr ago, suggest that the L parent body may have been disrupted by a major collision at that time and that the remaining parent body fragments were too small to develop substantial regoliths (e.g., Heymann, 1967; Crabb and Schultz, 1981). Such a disruption would have exposed a large amount of L chondrite bedrock, some of which would consist of fragmental breccias that acquired melt-rock clasts very early in solar system history, prior to metamorphism. The exposed bedrock would serve as a potential target for sporadic meteoroid impacts to produce a few fragmental breccias with unmetamorphosed melt-rock clasts. The high proportion of genomict brecciated LL chondrites reflects a complex collisional history, probably including several episodes of parent body disruption and gravitational reassembly. Differences in the abundances of different kinds of breccias among the ordinary chondrite groups are probably due to the stochastic nature of major asteroidal collisions.  相似文献   

THE KRAMER CREEK,COLORADO METEORITE: A NEW L4 CHONDRITE     

Everett K. Gibson  David E. Lange  Klaus Keil  Terry E. Schmidt  J. Michael Rhodes 《Meteoritics & planetary science》1977,12(2):95-107

The Kramer Creek, Colorado, chondrite was found in 1966 and identified as a meteorite in 1972. Bulk chemical analysis, particularly the total iron content (20.36%) and the ratio of Fe_total/SiO₂ (0.52), as well as the compositions of olivine (Fa_21.7) and orthopyroxene (Fs_18.3) place the meteorite into the L-group of chondrites. The well-defined chondritic texture of the meteorite, the presence of igneous glass in the chondrules and of low-Ca clinopyroxene, as well as the slight variations in FeO contents of olivine (2.4% MD) and orthopyroxene (5.6% MD) indicate that the chondrite belongs to the type 4 petrologic class.  相似文献