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At least 271 records · Page 15
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NASA NTRS1980

Measurement of cosmic ray produced Mn-53 in deep sea metallic spherules

Cosmic ray originated Mn-53 nuclides were measured in deep sea metallic spherules by neutron activation analysis. The spherules may be fused micrometeoroids or ablation droplets from larger objects; the low activities of Mn-53 may indicate its evaporation loss resulting from the heating in the earth's atmosphere or short exposure age. The Mn-53 nuclide is now being measured in chondritic spherules, and Be-10 and Cl-36 concentrations are determined in individual spherules using ion counting methods.

Nishiizumi, K.↗
NASA NTRS1980

Elemental abundances in chondrules from unequilibrated chondrites Evidence for chondrule origin by melting of pre-existing materials

Bulk abundances of Na, Mg, Al, Ca, Sc, V, Cr, Ir, and Au were analyzed by neutron activation of chondrules separated from unequilibrated H, L, and LL chondrites and correlated with petrographic properties. The geometric mean composition of the whole-rock chondrule suites are almost indistinguishable from each other for many elements; chondrules are enriched in lithophile and depleted in siderophile elements in a pattern consistent with chondrule formation by melting of preexistent materials. The porphyritic chondrules are more enriched in refractory and siderophile elements as compared with the nonporphyrytic chondrules, indicating that these two chondrule groups may have formed from different precursors.

Gooding, J. L.↗
NASA NTRS1980

The composition of mesosiderite olivine clasts and implications for the origin of pallasites

The composition of olivine clasts from the mesosiderites Emery, Mincy and Pinnaroo is investigated, and implications of the results for the origin of the pallasites, which, although chemically distinct, may be related to the diogenites, eucrites, howardites and mesosiderites, are discussed. Centimeter-sized olivines were analyzed by electron microprobe, and instrumental neutron activation analysis was performed on one olivine each from Emery and Pinnaroo and an olivine separate from the Brenham pallasite. The olivine compositions are found to range from Fa8 to Fa28, with Emery samples having values from Fa18 to Fa28, and to require essentially total melting of a source composition rich enough in FeO to produce basaltic clasts. It is argued that the mesosiderite olivines were formed in the outer few kilometers of their parent body, as were those of the pallasites, which have the same compositions as the mesosiderite olivines. A model is then developed for the origin of the pallasites as a by-product of igneous differentiation in the external heating of a chondritic parent body.

Mittlefehldt, D. W.↗
NASA NTRS1980

Thermal metamorphism of primitive meteorites. XI - The enstatite meteorites: Origin and evolution of a parent body

The neutron activation data for Ag, As, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Se, Te, Tl, and Zn were obtained in samples of Abee heated to 1000-1400 C at low pressures. In addition, these elements were reported in nine enstatite achondrites and in the silicate part of the Mt. Egerton stony-iron. The data show trace element losses above 1000 C by diffusion-controlled processes with apparent activation energies of 8 to 55 kcal/mol; these data together with abundances of aubrites, Mt. Egerton, and E4-6 chondrites, and isotopic results link all enstatite meteorites to a common parent body. The data also indicate that aubrites and the Mt. Egerton material reflect fractional crystallization of a magma produced from enstatite chondrite-like parent material (E6) and the late introduction of chalcophiles and mobile elements transported by an FeS-Fe eutectic from an E4-6 region undergoing open-system metamorphism.

Biswas, S.↗
NASA NTRS1981

Cosmic-ray-produced Cl-36 and Mn-53 in Allan Hills-77 meteorites

Cosmic-ray-produced Mn-53 has been determined by neutron activation in nine Allan Hills-77 meteorites. Additionally, Cl-36 has been measured in seven of these objects using tandem accelerator mass spectrometry. These results, along with C-14 and Al-26 concentrations determined elsewhere, yield terrestrial ages ranging from 10,000 to 700,000 years. Weathering was not found to result in Mn-53 loss.

Nishiizumi, K.↗
NASA NTRS1981

Antimony in iron meteorites

Sb concentrations determined by radiochemical neutron activation analysis in 60 iron meteorites range from 0.2 ng/g to 36 microg/g. The meteorites with the highest Sb concentrations are those of the nonmagmatic groups IAB and IIICD, while meteorites with the lowest Sb concentrations are found in groups IVA and IVB. In all groups Sb is positively correlated with Ni; slopes on log Sb vs log Ni plots decrease with increasing Ni. This decrease may reflect an increasing tendency to avoid schreibersite during the analysis of high-Ni meteorites because Sb partitions strongly into schreibersite. It is found that schreibersite from New Westville is enriched in Cr, Ni, Ge, As, Sb, and Au and depleted in Fe, Co, Ir; the Sb content in schreibersite is 540 times higher than the bulk metal value.

Willis, J.↗
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 NTRS1981

Measurement of trace levels of chlorine in the stratosphere

Mathematical models of stratospheric ozone have predicted a reduction in the total ozone due to chlorofluoromethanes released into the atmosphere. Analytical procedures for the collection of air in the stratosphere and for analysis of these air samples for trace levels of chlorine, regardless of the state of chemical composition were developed. Calibration experiments are conducted in order to validate all methods and procedures. Results of neutron activation analysis calibration procedures using standard chlorine gases are included.

Warren, D. C.↗
NASA NTRS1981

Derivation of a heterogeneous lithic fragment in the Bovedy L-group chondrite from impact-melted porphyritic chondrules

Results are presented of petrographic, compositional and dating analyses of a light-colored lithic fragment in the L-group Bovedy meteorite that has a composition different from that of the host chondrite. Polished thin sections of the lithic fragment, host, and the fragment-host boundary were examined microscopically and analyzed by electron microprobe, metallic Ni-Fe, and instrumental neutron activation techniques; chips of the fragment were also used for Ar-39/Ar-40 dating and oxygen isotope analyses. The poikilitic textures, olivine, low-Ca pyroxene and kamacite composition and low Na2O, K2O and P2O5 contents of the fragment indicate that it represents a solidified, slightly fractionated impact melt formed from a source rich in porphyritic chondrules. A progressive increase on MgO content across the fragment is accounted for by the heterogeneous nucleation of MgO-rich phases. The Ar data indicate that the Bovedy lithic fragment and its host were partly degassed of radiogenic Ar less than 0.94 billion years ago, probably due to shock. The data are consistent with a cooling rate of about 5 C/million years through 500 C, which must have resulted from the burial of the assemblage beneath insulating material on the parent body at depths of at least several km.

Rubin, A. E.↗
NASA NTRS1980

Composition of the earth's upper mantle. II - Volatile trace elements in ultramafic xenoliths

Radiochemical neutron activation analysis was used to determine the nine volatile elements Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn in 19 ultramafic rocks, consisting mainly of spinel and garnet lherzolites. A sheared garnet lherzolite, PHN 1611, may approximate undepleted mantle material and tends to have a higher volatile element content than the depleted mantle material represented by spinel lherzolites. Comparisons of continental basalts with PHN 1611 and of oceanic ridge basalts with spinel lherzolites show similar basalt: source material partition factors for eight of the nine volatile elements, Sb being the exception. The strong depletion of Te and Se in the mantle, relative to lithophile elements of similar volatility, suggests that 97% of the earth's S, Se and Te may be in the outer core.

Morgan, J. W.↗
NASA NTRS1982

Total nitrogen content of deep sea basalts

An estimate of the total nitrogen content of the earth's mantle, aimed at furnishing a further constraint for earth atmosphere origin and evolution models, was attempted through thermal neutron activation analysis via N-14(n,p)C-14 for the case of deep sea basalt glasses from the East Pacific Rise, the Mid-Atlantic Rift, and the Juan de Fuca Ridge. The increased nitrogen abundance of matrix material from the same samples as the glasses may be due to the incorporation of chemically-bound nitrogen from sea water, rather than dissolved molecular nitrogen. A discussion is presented of factors affecting observed basalt nitrogen content and its interpretation in terms of mantle nitrogen abundance. A 2 ppm N lower limit is estimated for the mantle.

Norris, T. L.↗
NASA NTRS1982

Complementary rare earth element patterns in unique achondrites, such as ALHA 77005 and shergottites, and in the earth

Abundances of major, minor, and trace elements are determined in the Antarctic achondrite Allan Hills (ALHA) 77005 via sequential instrumental and radiochemical neutron activation analysis. The rare earth element (REE) abundances of ALHA 77005 reveal a unique chondritic normalized pattern; that is, the REEs are nearly unfractionated from La to Pr at approximately 1.0X chondrites, monotonically increased from Pr to Gd at approximately 3.4X with no Eu anomaly, nearly unfractionated from Gd and Ho and monotonically decreased from Ho to Lu at approximately 2.2X. It is noted that this unique REE pattern of ALHA 77005 can be modeled by a melting process involving a continuous melting and progressive partial removal of melt from a light REE enriched source material. In a model of this type, ALHA 77005 could represent either a crystallized cumulate from such a melt or the residual source material. Calculations show that the parent liquids for the shergottites could also be derived from a light REE enriched source material similar to that for ALHA 77005.

Ma, M.-S.↗
NASA NTRS1982

Trace element concentrations in the isotopically unique Allende inclusion, EK 1-4-1

The bulk sample and mineral separates of the isotopically unique Allende inclusion, EK 1-4-1, are analyzed by instrumental neutron activation for the concentrations of REE, Sc, Fe, Co, Cr, Na, and Ir, and REE concentrations were also determined by mass spectrometric isotope dilution for two density separates. Results show that the inclusion is enriched in light REE compared to heavy REE with a positive Yb anomaly, and has a high Cr concentration, both of which indicate group II affinity, although EK 1-4-1 is a coarse-grained group I inclusion. On the other hand, high Ir, and Sc, and low FeO and Co concentrations were found in the bulk inclusion, and low Na concentrations were found in mineral separates, which indicate an affinity to group I. In addition, for melilite and pyroxene fractions REE, Sc, Co, and Fe were determined to have distributions that were substantially different from those observed for normal Allende type B inclusions.

Nagasawa, H.↗
NASA NTRS1982

Are C1 chondrites chemically fractionated - A trace element study

Six C1 chondrite samples and a C2 xenolith from the Plainview H5 chondrite were analyzed by radiochemical neutron activation for a large variety of elements, including rare earths. The sample processing is described, including the irradiation, chemical procedure, rare earths separation, counting techniques, radiochemical purity check, and chemical yields. The results of consistency checks on a number of elements are discussed. Abundances for siderophiles, volatiles, and rare earths are presented and discussed. Tests are presented for fractionation of rare earths and other refractories, compositional uniformity of C1's, and interelement correlations. There is no conclusive evidence for nebular fractionation affecting C1's. Three fractionation-prone rare earths have essentially the same relative abundances in C1's and all other chondrite classes, and hence are apparently not fractionated in C1's.

Ebihara, M.↗
NASA NTRS1982

The Apollo 14 regolith - Chemistry of cores 14210/14211 and 14220 and soils 14141, 14148, and 14149

Neutron activation analysis was performed on bulk and size fractions from drive tube specimens from 39 cm and 16.5 cm depths, and soil samples taken at the Apollo 14 landing site. Chemical data were obtained for 31 major, minor, and trace elements in the KREEPy soils. The cores were homogeneous in chemical composition, containing 20% LKFM, 15% mare basalt, 6% ANT, and 59% high-K KREEP, according to the classifications of Laul and Papike (1980). The meteoritic fraction was 3-7% for both cores, while the chemical compositions of both cores and soils were similar. Differences were detected in the fractions finer than 10 microns, which were more feldspathic than the coarser samples. The similarities between the grains 1000-90 micron in diam and less than 10 micron in diam, in terms of chemical contents, indicates that the observed agglutinates were derived from fusion of the finest grained fraction. The dominant soil-forming processes were comminution and vertical mixing of the regolith.

Laul, J. C.↗
NASA NTRS1983

Nature of the H chondrite parent body regolith - Evidence from the Dimmitt breccia

Meteorite regolith breccias are clastic rocks which formed by lithification of fragmental regolith material that once resided at the surface of a meteorite parent body. A study is reported of the matrix and 21 clasts of various sizes (0.2-24 mm) in the Dimmitt H chondrite regolith breccia using petrographic and electron microprobe techniques. In addition, oxygen isotope studies of three clasts and instrumental neutron activation analysis (INAA) and Ar-39/Ar-40 age dating of one clast are reported. The Dimmitt meteorite was found about 1942 near Dimmitt, Texas. Attention is given to analytical procedures, the clastic matrix, equilibrated clasts, poikilitic melt-rock clast, clasts of different chondrite groups, graphite-magnetite aggregates, the origin of exotic clasts, and the complexity of parent body surfaces processes.

Rubin, A. E.↗
NASA NTRS1983

Measurement of Mn-53 in deep-sea iron and stony spherules

Cosmic-ray-produced Mn-53 (half-life, 3.7 x 10 to the 6th yr) is measured in individual and groups of deep-sea iron and stony spherules by highly sensitive neutron activation analysis. The activities found are less than 20 dpm Mn-53/kg Fe (10 to the -5th-10 to the -6th dpm Mn-53/sample) in iron spherules, with the exception of one iron spherule, whose activity is 241 + or - 73 dpm Mn-53/kg Fe. It is believed that these low activities may indicate evaporative loss of Mn-53 caused by heating in the earth's atmosphere. On the other hand, all the stony spherules are found to contain 200-260 dpm Mn-53/kg Fe, which is similar to chondritic values. It is pointed out that these spherules may be ablation debris from large objects.

Nishiizumi, K.↗
NASA NTRS1983

Refractory precursor components of Semarkona chondrules and the fractionation of refractory elements among chondrites

Instrumental neutron activation analysis has been used to measure about 20 of the lithophile elements in 30 chondrules from the Semarkona chondrite. The amounts of oxidized iron were calculated from other compositional parameters, and Si concentrations are estimated from mass-balance considerations. It is suggested that the refractory component probably forms from fine grained materials that were able to equilibrate down to lower nebular temperatures. The chondrite matrix may have had an origin similar to that of the nonrefractory material. The low abundance of refractories and Mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element/Mg ratio than that of the refractory element of the chondrules.

Grossman, J. N.↗