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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Thermomagnetic analysis of meteorites, 2: C2 chondrites

Samples of all eighteen of the known C2 chondrites were analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low(generally 1%) and the J sub s-T curves are irreversible. The heating curves show variable and erratic behavior, whereas the cooling curves appear to be that of Fe3O4. The saturation moment after cooling is greater (up to 10 times larger) than it is initially. This behavior is interpreted to be the result of the production of magnetite from a thermally unstable phase--apparently FeS. Four of the remaining 7 C2 chondrites contain Fe3O4 as the only significant magnetic phase: initial magnetite contents range from 4 to 13 percent. The remaining three C2 chondrites contain iron or nickel-iron in addition to Fe3O4. These seven C2 chondrites show little evidence of the breakdown of a thermally unstable phase.

Watson, D. E.↗
NASA NTRS1974

The Kelly chondrite - A parent body surface metabreccia

A study of the Kelly chondrite classes it as a monomict breccia rather than a polymict breccia as it was originally described. Microprobe analyses of differently textured clasts are very similar to each other and to well-known LL-type chondrites. Clast and matrix olivine compositions are well within the range of LL-chondrite olivine. A correlation is found between the degree of recrystallization and plagioclase composition. Petrographic observations of shocked, annealed, and unshocked clasts coupled with particle size distribution measurements indicate strongly that Kelly is similar to lunar metabreccias in mode of formation. It is theorized that Kelly is an LL-chondrite parent body metabreccia representing the final accumulation phase of the parent body.

Bunch, T. E.↗
NASA NTRS1974

Thermomagnetic analysis of meteorites. 3: C3 and C4 chondrites

Thermomagnetic analysis on all of the C3 and C4 chondrites, conducted under conditions of controlled oxygen fugacity, indicates the presence of a thermally unstable component in at least 5 of the C3 chondrites which upon heating results in magnetite production. This unstable component is most likely troilite (FeS). The presence of the unstable substance may affect the estimation of paleointensities in meteorites which contain it. Our results indicate that Grosnaja, Ornans, Kainsaz, Felix, and Warrenton are likely to be less complicated for paleointensity determinations than the other C3 chondrites. Both C4 chondrites should lead to reliable results.

Herndon, J. M.↗
NASA NTRS1975

Thermomagnetic analysis of meteorites, 2.C2 chondrites

Samples of all eighteen known C2 chondrites have been analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low (generally less than 1%) and the saturation magnetization-vs.-temperature curves are irreversible. The heating curves show variable and erratic behavior, whereas the cooling curves are similar to that of Fe3O4. The saturation moment after cooling is greater (up to 10 times) than it is initially. This behavior is attributed to the production of magnetite from a thermally unstable phase - apparently FeS. Four of the remaining seven C2 chondrites contain Fe3O4 as the only significant magnetic phase; initial magnetite contents range from 4 to 13%. The remaining three C2 chondrites contain iron or nickel-iron in addition to Fe3O4. These seven C2 chondrites show little evidence of the breakdown of a thermally unstable phase.

Watson, D. E.↗
NASA NTRS1976

Ar-40/Ar-39 dating of collisional events in chondrite parent bodies

Ar-40/Ar-39 age dating of a number of shocked ordinary chondrites is interpreted in terms of collisional degassing events of meteorite parent bodies, probably in the asteroid belt. Examples of L, H, and at least one LL chondrite show episodic degassing. Degassing ages suggest several distinct events ranging from about 0.03 aeon to 0.7 aeon and probably higher. All specimens of either the H or L chondrites are not consistent with a single age event. A direct correlation exists between the degree of shock heating and the fraction of argon lost during degassing. However, no chondrite yet analyzed shows complete degassing of its high-temperature phase. Consequently, whole rock K-Ar ages are not accurate monitors of the time of the shock event.

Bogard, D. D.↗
NASA NTRS1977

Lithic clasts in the Supuhee chondrite

Bulk chemical analyses of three foreign lithic clasts from Supuhee, a shocked and brecciated H6 chondrite, were carried out in an attempt to locate 'mysterite', a volatile-rich material postulated to be present. Clast 1 bears some similarities to C1 and C2 chondrites, but its relatively low (less than 9.4%) volatile content suggests a different set of physicochemical conditions during low-temperature condensation. Clast 2 was apparently derived from H-group chondrite material by loss of metal and sulfide. Clast 3 is an unusual meteorite type whose chemical composition is reminiscent of the unique chondrite Kakangari (Graham, et al., 1977). These chemically distinct bodies were apparently not present during the metamorphic event which affected Supuhee. Although the presence of mysterite was not confirmed or refuted, the present results indicate that conditions were favorable for the formation, incorporation and preservation of volatile-rich materials.

Leitch, C. A.↗
NASA NTRS1978

Thermal metamorphism of primitive meteorites. VII - Mineralogy-petrology of heated Murchison /C2/ and alteration of C30 and other chondrites

Alterations caused by week-long heating of Murchison in a low-pressure environment at 400-1400 C are of two types: thermodynamically favored kinetically controlled or thermodynamically controlled rapid processes. Kinetically controlled changes pertinent to chondritic evolution and which vary progressively with temperature in heated Murchison include: chondrule blurring; matrix coarsening; increasing mean Fa and Fs contents of ferromagnesian silicates; equilibration of olivine; increasing Mg/Si, Ca/Si, Al/Si, and Cr/Si and decreasing Fe/Si, Ni/Si, and S/Si in matrix; Cr loss from kamacite; and homogenization and Ni-zoning in taenite at high temperatures. Low-temperature thermodynamically controlled changes include: transformation of high-Ni troilite to low-Ni and formation of Ni- and Co-rich metal from pentlandite. High-temperature changes include formation of Cr-rich magnetite and formation of a Ni-rich sulfide similar to that found in highly altered chondrites. Trends resulting from processes of both kinds in Murchison are consistent with characteristics of a postulated C30 metamorphic suite, while those changes caused by reactions of the second kind are similar to those in heavily shock-heated ordinary chondrites and the heavily metamorphosed C5-6 chondrite, Mulga West. Either the simulations support the metamorphic origin of the C30 suite and other thermally induced changes or the natural alterations support the utility of laboratory simulations in studying meteoritic evolution.

Matza, S. D.↗
NASA NTRS1979

Aubrites - Their origin and relationship to enstatite chondrites

A study of aubrites and their origin and relationship to enstatite chondrites is presented. Aubrites contain enstatite, plagioclase, diopside, and olivine; based on similarities in bulk chemistry of the silicate portions and inferred oxygen fugacity it is shown that E6 chondrites are the most likely parent material for chondrites. It is concluded that the addition of 10% plagioclase of An15 composition to the bulk composition of the silicate portion of the aubrites results in good agreement with that of E6 chondrites.

Watters, T. R.↗
NASA NTRS1980

Composition of the metal phases in ordinary chondrites - Implications regarding classification and metamorphism

The paper examines the composition of metal phases and metamorphism in ordinary chondrites. It is shown that below 550 C increasing Co decreases the equilibrium kamacite Ni concentration of an alpha to gamma system, and that the equilibrated L chondrites have kamacite and taenite Co concentrations in the L-group range. Metal-phase studies of petrologic type-3 ordinary chondrites with highly unequilibrated silicates showed a wide range in the degree of matrix kamacite equilibration; in the three most unequilibrated chondrites most taenite is clear, and the high Ni content shows that metamorphic temperatures were lower than 400 C in these meteorites.

Afiattalab, F.↗
NASA NTRS1980

Measuring metamorphic history of unequilibrated ordinary chondrites

Measurements performed by a thermoluminescence sensitivity technique of the degree of metamorphism experienced by unequilibrated ordinary chondrites are reported. Samples of type 3 chondrites were ground and heated to 500 C to remove their natural thermoluminescence, then irradiated with either 50 krad from a Co-60 gamma ray source or 25 krad from a Sr-90 beta source. The resulting thermoluminescence measured as a function of temperature is found to differ as much among some type 3 chondrites as between type 3 and other types, leading to the proposal of scheme for subdividing type 3 ordinary chondrites based on their thermoluminescence sensitivity.

Sears, D. W.↗
NASA NTRS1981

Mechanical aggregation of enstatite chondrites from an inhomogeneous debris cloud

Enstatite chondrites have oxygen isotope ratios closer to those of the earth and moon than other meteorites. Their minerals are chemically reduced; metal contains Si, and some Ca, Ti, Mg and Mn are incorporated in sulphides rather than silicates. Clinoenstatite and olivine are virtually Fe-free. Two types of clinoenstatite in the Indarch enstatite chondrite have been reported, one luminescing blue and one red. Similar clinoenstatites in the Kota-Kota enstatite chondrite are associated with two distinct types of forsteritic olivine, one luminescing orange and the other blue. The textural relations and differences in chemical composition cannot be explained by progressive condensation from the solar nebula and require the mechanical mixing of material from at least two sources. It is suggested here that enstatite chondrites result from mechanical and chemical processes during aerodynamic sorting and gravitational settling of debris from a hot cloud of dust, liquid and gas produced during collision of planetesimals.

Leitch, C. A.↗
NASA NTRS1981

The Correo and Suwanee Spring meteorites - Two new ordinary chondrite finds

Two new ordinary chondrites were found about 40 km west of Albuquerque, New Mexico. Correo is an H4 chondrite with distinct chondrules and major olivine (Fo 81.4), orthopyroxene (En 82.3) and plagioclase (An 12). Suwanee Spring is an L5 chondrite with few distinct chondrules and a highly recrystallized matrix. Major minerals are olivine (Fo 75.4), orthopyroxene (En 77.7) and plagioclase (An 9). The metallic Ni-Fe phases of both meteorites are typical of slowly cooled ordinary chondrites.

Rubin, A. E.↗
NASA NTRS1981

Graphite-magnetite aggregates in ordinary chondritic meteorites

The graphite-magnetite component has been found (1) as abundant isolated inclusions in eight ordinary-chondritic, regolith breccias; (2) as the sole matrix in a new kind of unequilibrated chondrite that forms clasts in these regolith breccias; and (3) together with a Huss matrix in six unequilibrated ordinary chondrites. It is suggested that the component was formed by low-temperature, gas-solid reactions before the accretion of the meteorite, and that the isolated inclusions of graphite-magnetite in regolith breccias were derived from bodies composed of the new kind of chondrite that has graphite-magnetite as its sole matrix.

Scott, E. R. D.↗
NASA NTRS1981

Chemical studies of L-chondrites. I - A study of possible chemical sub-groups

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.

Neal, C. W.↗
NASA NTRS1983

Summary of several recent chondrite finds from the Texas Panhandle

Eleven recent chondrite finds from the Texas Panhandle have been examined and classified according to mineralogical and petrological criteria: five H's, five L's, and one LL chondrite. Five are distinct from nearby finds, while three remain ambiguous and three are related to previously reported chondrites. In addition, data are provided to classify the Muleshoe, Silverton, and Vigo Park chondrites, all of which were previously undescribed in the literature.

Sipiera, P. S.↗
NASA NTRS1984

L Chondrite meteorites: A compilation and preliminary analyses

A compilation of those meteorites currently recognized as being L chondrites, exclusive of the numerous Antarctica finds, was made and is known as the L Chondrite Register. Data for these 576 meteorites was collected from a variety of sources, primarily the British Museum's Catalogue of Meteorites and the Appendix to the Catalogue of Meteorites. Also used was the Revised Cambridge Chondrite Compendium, which provided a convenient listing of L chondrites; other sources include Chinese Meteorites, Meteorites, by Wasson (1974), and the Meteoritical Bulletin of Meteoritics. This last source provided data for most recent falls and was referenced through March of 1982. All such data were recorded on a computer data file with a HP 2647A terminal, so that information could easily be retrieved and manipulated. For each meteorite, the petrographic class, location of find, fall date and hour, mass, mole per cent fayalite, weight per cent Fe, SiO2/MgO ratio, shock class, metal class, 4He abundance, UTh-H3 gas retention age, K-Ar gas retention age, and 21Ne cosmic ray exposure age, was recorded when known.

Silliman, A.↗
NASA NTRS1983

Evidence for relict grains in chondrules of Qingzhen, an E3 type enstatite chondrite

Petrographic and chemical studies of the Qingzhen chondrite strongly suggest that it is the most highly unequilibrated (type 3) enstatite chondrite recognized so far. Qingzhen contains abundant, well-defined chondrules, some of which were incompletely molten during the chondrule formation process. The relict olivine grains within these chondrules contain dusty inclusions of almost pure metallic Fe, which appear to be the in situ reduction product of the fayalitic component of the olivine. The reduction process presumably took place at the time of chondrule formation and the chondrule precursor material must have been more oxidized than average enstatilite chondrite material. It is believed that this oxidized material may have formed at the enstatite chondrite formation location in the solar nebula, provided fluctuations in the degree of oxidation of the nebular gas existed at such locations. Reheating of this material under more reducing conditions would lead to the observed reduction of the olivine. Igneous olivines within chondrules always contain detectable amounts of CaO, while relict olivines are essentially CaO-free. This seems to suggest thatg the relict olivines did not originate during a previous igenous process of chondrule formation and might represent condensation products from the early solar nebula.

Rambaldi, E. R.↗
NASA NTRS1984

Sm-Nd isotopic evolution of chondrites and achondrites. II

The chondrite data obtained as a result of an investigation of Sm-147-Nd-143 and Sm-146-Nd142 isotope systematics in five chondrites and the Moama and Andra dos Reis (ADOR) achondrites are consistent with previously reported reference values for the chondritic uniform reservoir (CHUR) of 0.511847 and 0.1967. The Nd-143/Nd-144 and Sm-147/Nd-144 values of the bulk chondrites analyzed suggest that the CHUR evolution is known to within 0.5 epsilon-units and 0.15 percent of the CHUR values for the entire history of the solar system. The Sm-146-Nd-142 systematics of ADOR and Moama support the hypothesis that Sm-146 was present in the early solar system, suggesting a high Sm-146/Sm-144 ratio that cannot be explained as a late injection forma supernova, and must instead be due to galactic nucleosynthesis.

Jacobsen, S. B.↗