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Description of the external form, composition, and structure of the Seminole meteorite found near Seminole Texas in 1961. Two fragments weighing 41.1 kg were recovered. Analyses show these to be the fragments of a single black olivine-bronzite, or H4-group chondrite, exhibiting brecciation and a moderate number of individual chondrules.
An 87-gram sample of the Havero ureilite has been analyzed by nondestructive gamma-ray spectrometry. The results of the measurements, in dpm/kg at time of fall, are: Na-22, 71 plus or minus 3; Al-26, 43 plus or minus 3; Sc-46, 3.4 plus or minus 2.1; Mn-54, 35 plus or minus 6; Co-60, less than or equal to 0.7, 2 sigma limit. Havero has 77 plus or minus 14% of the Al-26 activity calculated for its chemical composition. When averaged with previously reported analyses of Goalpara and Novo Urei, ureilites as a class have 74 plus or minus 7% of their expected Al-26 activity. The depletion in Al-26 could be the coincidental result of identical 'shielding' effects in three meteorites of apparently very different preatmospheric sizes. Alternatively, ureilites may have been exposed to a lower cosmic-ray flux than that experienced by most chondrites, probably the result of characteristically different orbits.
Many properties of meteorites suggest that they formed in a cooling solar nebula. Chemical differences among chondrites, encompassing nearly all known elements, can be accounted for by as few as 4 processes: loss of an early condensate (above 1300 K), loss of nickel-iron (1050 to 700 K), partial remelting of the condensate (600 to 450 K), and accretion (500 to 360 K). The same processes seem to have affected the inner planets. Reasonably concordant accretion temperatures are obtained by various cosmothermometers. These accretion temperatures are 3 times higher than present black-body temperatures in the asteroid belt, suggesting that accretion took place only during a high-temperature stage of necessarily short duration.
The test equipment installed during the Apollo 17 flight to conduct the lunar ejecta and meteorites (LEAM) investigation is described. The LEAM experiment intercepts ejecta particles created by meteoroid impact on the lunar surface and records information useful in establishing the history of the moon. The deployment of the system in the Taurus-Littrow area and the method for controlling the equipment are explained. The effects of lunar surface temperatures on the operation of the sensors are reported.
An overview is presented on the efforts being made to estimate the time that the magnetic field(s) existed and acted on meteorite parent bodies. The basic premise is that if a sample exhibits a low K-Ar age, it is the requisite amount of Ar-40. This assumption is applied to a preliminary analysis of the Farmington chondrite.
Major and trace element analyses of over 180 individual chondrules from 12 carbonaceous chondrites are reported, including individual analyses of 60 chondrules from Pueblito de Allende. Siderophile elements in most chondrules are depleted, compared to the whole chondrite. Correlations of Al-Ir and Ir-Sc among chondrules high in Ca and Al were observed. A Cu-Mn correlation was also found for chondrules from some meteorites. No correlation was observed between Au and other siderophile elements (Fe, Ni, Co and Ir). It is suggested that these elemental associations were present in the material from which the chondrules formed. Compositionally, chondrules appear to be a multicomponent mixture of remelted dust. One component displaying an Al-Ir correlation is identified as Allende-type white aggregates. The other components are a material chemically similar to the present matrix and sulfides-plus-metal material. Abundances of the REE (rare earth elements) were measured in ordinary Allende chondrules and were 50% higher than REE abundances in Mokoia chondrules; REE abundances in Ca-Al rich chondrules were similar to REE abundances in Ca-rich white aggregates.
Oxygen isotope analysis of anhydrous high-temperature phases from carbonaceous meteorite chondrites indicates a high degree of O(17) and O(18) isotope depletion. The isotope decay is believed to be a result of nuclear rather than chemical processes caused by the admixture of a component consisting of almost pure O(16). It is theorized that this component may predate the solar system and may represent interstellar dust with a separate history of nucleosynthesis.
Considerations are given concerning the interpretation of the results of two types of cosmochronological dating in order to examine the validity of the conclusions inferred from these results that the time intervals between the formation of various meteorite samples are very great. It is theorized that the isotopic differences between Angra dos Reis and other basaltic achondrites may be due to real fluctuations between the relative abundances of s-process and r-process nucleosynthesis products at a level delta about 0.001.
Criticism of the works of Vardaniants (1961) and Goretskii (1962) regarding the origin of the Puchezh-Katunki crater, and development of a new hypothesis regarding this disturbance. Although Vardaniants defines the Puchezh-Katunki disturbance as a structure of explosive nature and assumes that the explosion originated as a consequence of accumulation of gases in the crystalline basement of the Russian platform, he lacks evidence to qualify this explosion as coming from a depth. Goretskii's tectonic-injection hypothesis attributes the formation of the disturbance to penetration of an intrusion of basic and ultrabasic rocks into the Paleozoic rocks of the platform. It is shown that, even if the intrusion were spread somewhere at depth, it could not account for the extent of the deformation in the disturbance. It is suggested that this disturbance is of meteoritic origin, since the structure and morphology of the region are similar to the sloping conical surface produced by an explosive meteor crater. The energy, mass, and size of the asteroid which could cause such a disturbance are estimated, and it is shown that the probability of the occurrence of an impact of this size is finite over geological time.
The proportions of major oxides in the Allende carbonaceous chondrite after partial reduction are remarkably similar to those in possible mantle material of the earth. When heated, the Allende meteorite generates a sulfide melt, a ferrobasaltic melt, and olivine with or without pyroxene, over a wide pressure range (5 to 25 kilobar). The silicate melt contains more sodium and less titanium than lunar ferrobasalts. An aggregate of the Allende chondrite rich in calcium and aluminum produces silica-undersaturated, calcium-rich melt and spinel over a wide pressure and temperature range. It is suggested that the earth's core contains significant amounts of both nickel and sulfur and that a 3:2 mixture of Allende bulk sample and calcium- and aluminum-rich agregates is closer in major element abundances than either of these components to the average composition of the moon.
Using vacuum pyrolysis and high resolution mass spectrometry, a study is made of the gas release patterns of representative lunar samples, meteorites, terrestrial samples, and synthetic samples doped with various sources of carbon and nitrogen. The pyrolytic gas evolution patterns were intercorrelated, allowing an assessment of the possible sources of the volatilizable material in the lunar samples to be made. Lightly surface adsorbed species and more strongly chemisorbed species are released from ambient to 300 C and from 300 to 500 C, respectively. The low-temperature volatiles (less than 500 C) derived from various chondrites correlate well with the gas evolution patterns of volatile-rich samples, as for example 74220 and 61221. Solar wind entrapped species and molecules derived from reactions probably in the grain surfaces are evolved from about 500 to 700 C, respectively. Solar wind implanted C, N, and S species are generated from 750 to 1150 C, probably by reaction with the mineral matrix during the annealing process. Possible indigenous and/or refractory carbide, nitride, and sulfide C, N, and S are released in the region from 1200 C to fusion.
The abundances of zirconium and hafnium have been determined in nine stony meteorites by a new, precise neutron-activation technique. The Zr/Hf abundance ratios for the chondrites vary in a rather narrow range, consistent with previously published observations from our group. Replicate analyses of new, carefully selected clean interior samples of the Cl chondrite Orgueil yield mean zirconium and hafnium abundances of 5.2 and 0.10 ppm, respectively. These abundances are lower than we reported earlier for two Cl chondrite samples which we now suspect may have suffered contamination. The new Cl zirconium and hafnium abundances are in closer agreement with predictions based on theories of nucleosynthesis than the earlier data.
Grossular garnet has been observed in several white inclusions in the Allende meteorite. Compositions range from Gro(95)Py(5) to Gro(88)Py(12) in five inclusions. Its mottled appearance indicates that it crystallized from a glass of near-grossular composition and not by a solid-state reaction between wollastonite, anorthite, and melilite. These grossular-bearing inclusions either condensed directly as metastable liquids from the solar nebula or, if initial solid condensates were liquefied, by some subsequent heating process. In either case, a prolonged residence time in a thermal blanket appears necessary to effect crystallization of the grossular.
The Nedagolla meteorite was recognized by Axon to be a rare example of an iron which has been preterrestrially reheated to the point of melting. The dendrite secondary arms are spaced 200 microns apart, implying that Nedagolla solidified and cooled at about 0.02 C/sec. The presence of (Fe, Cr)(1-x)S inclusions precipitated during cooling in the interdendritic regions, and evidence of solute redistribution of Ni, Cr, Co, Si, and P are consistent with this cooling rate. Such a rate indicates that Nedagolla cooled very near the surface of its parent 'body'. Secondary microstructural features including the presence of isothermal taenite and minute phosphide precipitates, which have formed from the dissolution of primary phosphide material, indicate a later reheating to about 750 C for a period of several hours.
Melilite and pyroxene were separated from a coarsely crystalline chondrule in the Allende meteorite and analyzed by microprobe and spark source mass spectrometer techniques. Elemental abundances in the bulk chondrule are consistent with a mixture of equal amounts of the two minerals, as observed microscopically. The lanthanide distributions are markedly different in the two minerals; relative to chondrite abundances, melilite shows progressive depletion of the lanthanides La-Sm, a positive Eu anomaly, and relatively constant abundances of the heavier lanthanides (Gd-Yb, and Y) whereas pyroxene shows progressive enrichment towards the heavier lanthanides, on which is superimposed a negative Eu anomaly. Both minerals, and the bulk chondrule, show unusual concentrations of the platinum metals, but the crystallographic site or sites of these metals remains to be determined.
The Allende samples analyzed include seven Ca, Al-rich aggregates, ten melilite chondrules, an olivine chondrule, and two olivine-rich aggregates. The Allende meteorite has been described as a type III carbonaceous chondrite. Major element abundances were determined with the electron microprobe technique reported by Reed and Ware (1972). An MS7 spark source mass spectrometer was used for the determination of trace element abundances.
Foreign inclusions in stony meteorites. II - Rare gases and oxygen isotopes in a carbonaceous chondritic xenolith in the Plainview gas-rich chondrite
The application of an analytical approach combining gas chromatography with mass spectrometry (GC-MS) has shown that the amino acid composition of meteorite extracts is quite complex. A computer was used in the evaluation of the data obtained in the investigations. The computer programs developed have been concerned solely with the mass spectra of amino acids. Specialized programs have been written to determine the number of carbon atoms in an amino acid which is a member of any of three subclasses.