Nearly 100 chondrules were extracted from -8.6g of the Mokoia (CV3) meteorite and have been analyzed by sequential instrumental neutron activation analysis (INAA). The resulting data were utilized in a comprehensive statistical characterization of these objects and, unlike similar investigations, virtually no loss of relevant data was incurred due to the use of inadequate or inappropriate software. Mass and elemental frequency distributions, correlation analysis and sorting coefficients support a "nebular" setting for chondrule genesis, and a scenario in which interstellar "dust-balls" (= chondrule precursors) are subject to some transient (short duration) high-energy process(es) followed by gravitationally or aerodynamically induced sorting, while it appears that an enhanced oxygen fugacity due to particle/gas fractionation may also be a factor. Conversely, a "planetary" setting for chondrule formation which requires the melting of pre-existing rocks (e.g., incompatible with the observed data. Factor analysis has led to the identification of the following precursor assemblages (i.e., factors) in the Mokoia chondrite: a refractory lithophile phase, a siderophile/chalcophile phase, a Mg-rich (silicate ?) phase, a refractory siderophile phase and a common lithophile phase. Previous studies of the Allende (CV3), Ornans (C03), Semarkona (LL3) and Chainpur (L3) meteorites are compared with these findings and interchondrite relationships are discussed (e.g., do these objects share similar parental materials, or are their compositions somehow complementary? were they formed in proximity with each other? etc.). A very unique oxide-sulfide-phosphate opaque assemblage was found in Mokoia and analyzed by INAA/electron-probe microanalysis, and may eventually serve to place constraints on the low-temperature thermal histories of chondrules or chondrites as well as provide information concerning the oxygen and sulfur fugacities within the Mokoia chondrite parent body. / Graduation date: 1991

Undergraduate honors paper--Mount Holyoke College, 2006. Dept. of Astronomy. / Includes bibliographical references (42-44 leaves ).

The Abee enstatite chondrite breccia was studied using two methods: measurement of noble gases, and, analyses of the clast size-distribution and the overall texture of Abee. These studies were made in order to understand the formation of the Abee breccia and the formation of the enstatite chondrites. Noble gases were measured as a part of the consortium effort. Noble gases were measured in 17 samples from 10 regions within Abee. Radiogenic ages are 4.5 aeons. Cosmic ray exposure ages average 8 Myr. No evidence for pre-irradiation was found except for a chondrule which may have been neutron pre-irradiated. Abee has at least 2 iodine bearing minerals, both of which are silicate minerals. This suggests that iodine had refractory behavior in the E-chondrites. Two trapped components were found: one having planetary-type elemental and isotopic composition (termed "Kenna-type"), the second with a high argon to xenon ratio (termed "argon-rich") but isotopically similar to the first. Both components appear to be carried in silicate phases, probably enstatite. The Kenna-type component may be carried by small inclusions within silicate minerals. The argon-rich component may have originated from solar wind implantation before accretion of the E-chondrite parent body requiring an inner solar system origin or by noble gas trapping during high temperature mineral condensation requiring high nebular pressures. The clast size-distribution of Abee and 2 other meteorites from the Antarctic meteorite collection (BTNA 78004, ALHA 78113) were measured. The 3 meteorites appear to have formed during single, low energy impacts and that Abee was part of an ejecta blanket which mixed with surrounding regolith. From the textural study, a formation model for the Abee breccia is discussed. The breccia formed during a single impact. Clast metal rims were vapor deposited and partially metamorphosed during impact-generated heating. Greater heating formed dark and metal inclusions. Maximum temperatures were less than 1200 C and heating was brief. Later, the material was disturbed but not brecciated. Abee did not reside on an asteroidal regolith surface for a significant period of time due to the lack of pre-irradiation. This model suggests that the E-chondrite groups formed by metamorphic heating and metal to silicate fractionation on a single parent body.

Carbonaceous chondrites have an approximately solar bulk composition, with some exceptions (e.g. H), and exhibit a range of parent body alteration. Investigations of both pristine and altered chondrites yield valuable insight into the processes and conditions of the early Solar System prior to and resulting in the planets we observe today. Such insight and the dynamic models developed by astrophysicists are constrained by chemical, mineralogical, and textural characteristics of chondrite components (chondrules, refractory inclusions, metal, and matrix). This dissertation uses a variety of chondritic components to address the following: 1) what do correlations within a population of refractory inclusions reveal about early Solar System conditions; 2) what is the distribution of trace elements among chondrite components and how does this affect component formation from precursor aggregation to chondrite accretion; and 3) can metal associated with chondrules further our understanding of chondrule formation and/or deformation? The first two objectives were investigated using suite of carbonaceous Ornans-group (CO) chondrites of varying petrologic grades (Colony CO3.0, Kainsaz CO3.2, Felix CO3.3, Moss CO3.6, and Isna CO3.8). These chondrites were analyzed using several analytical techniques including: electron microprobe element mapping, a modal phase analysis algorithm, and laser ablation inductively coupled plasma mass spectrometry. Within the comprehensive dataset of refractory inclusion characteristics (area, major mineralogy, bulk major chemistry, texture, and rare Earth element (REE) patterns and abundances) there is an overwhelming lack of correlations implying that thermal processing prior to accretion was stochastic and that sorting was minimal. Only two CO chondrites were analyzed for REE abundances (Colony and Moss). While refractory inclusions exhibit the greatest enrichments in REE relative to CI, after modal recombination chondrule glass contributes most significantly to the bulk REE budget in both chondrites. The bulk mean REE patterns for both Colony and Moss are flat and approximately CI in abundance while the mean REE patterns for components are nearly flat with relative enrichments (~10x CI for both chondrule glass and refractory inclusions) or depletions (chondrule olivine) relative to CI. Lack of correlations between REE and other characteristics, nearly flat REE patterns and nearly equivalent enrichment factors relative to CI across chondrite groups, including the CO chondrites analyzed here, implies that REE were equilibrated in precursor material prior to chondrite component formation. We propose a scenario for the equilibration of REE with vapor-solid or solid-solid reactions with subsequent accretion of chondrite components. Metal-rich chondrules in Acfer 139, a carbonaceous Renazzo-group (CR) chondrite were used to address the final objective. Chemical information was obtained using electron microprobe quantitative analysis and element mapping, electron backscatter diffraction was used to analyze the crystal structure of the metal nodules, and computed tomography provided insight into the 3D relationships of the metal. Eight chondrules with abundant metal nodules, both as rims and within the chondrule interior, were analyzed in detail. Chondrule A is of particular interest as it contains three concentric metal layers. A majority of the metal nodules fall on the calculated condensation trajectory of Co/Ni in a vapor of solar composition with the interior metal nodules containing higher Ni wt% and Co wt% than the rim nodules. Twinning is evident in many of the metal nodules and could indicate a ubiquitous parent body deformation process. Chemical inhomogeneity of Ni only occurs within the metal nodules of chondrule A and implies these metal nodules were reheated to high temperatures. The combination of chemical inhomogeneity, multiple sets of twins, and other evidence of strain imply that the formation of these chondrules was not straightforward and involved multiple iterations of heating, and potentially addition of material. A plausible model of chondrule formation in the early Solar System must be able to account for this more complicated thermal and alteration history and produce the chemical and textural variety of chondrules present in the region of chondrite accretion.

Thesis (Ph. D.) -- University of Tennessee, Knoxville, 2005. / Vita. Includes bibliographical references (p. 57-76). Also available via World Wide Web.

To constrain the thermal histories of two complex L chondrite melt breccia samples (NWA 5964 and NWA 6580) we compare textures and chemical compositions of metal and sulfide to L melt rock (NWA 6454 and NWA 6579) and strongly shocked (shock stage S6) (NWA 4860) samples. The inferred thermal histories can be used to evaluate formation settings on the L chondrite parent body. The L melt samples probably formed as different melt units within warm but largely unmelted material relatively close to the surface of the parent body, and the same is true for the S6 sample, except it experienced less melting. The breccia samples likely formed deeper, below different impact craters, by the injection of shock melt into a cooler chondritic basement. Carbide grains in the melt breccias could have formed by a contact metamorphic process caused by heating of the chondritic basement in proximity to the melt. Within the melt regions of the various samples, inferred cooling rates are on the order of 1-10 °C/sec, whereas in the chondritic portions of the melt breccias, the inferred cooling rates are many orders of magnitude slower, ~1-100 °C/My. The complex intergrowths of metal and FeS (hereafter referred to as dendritic grains) within the melt are recording cooling rates above the metal-sulfide eutectic, while the metal grains outside of the melt regions are recording cooling rates at much lower temperatures. It is likely the melt regions in the breccias cooled substantially prior to coming to rest against the chondritic basement, and thereafter the melt-chondrite rocks cooled more slowly.

Ordinary chondrites are the most common type of meteorite to fall to Earth and are composed of lithified primitive nebular materials which have experienced variable extents of thermal metamorphism and shock processing. They were subjected to radiogenic heating by incorporation of unstable short lived radionuclides such as 26Al in the early solar system. The relationship between metamorphism and impact processing in ordinary chondrites is not fully understood. An unresolved issue in the study of ordinary chondrites is whether their original parent bodies were fragmented by impacts into rubble-pile bodies while they were still hot, or whether they retained their onion-shell structures until they had shed their radiogenic heat. Heat is lost more quickly due to catastrophic impacts because warm material from the interior is exposed directly to the space environment until the impact debris re-accretes into a rubble-pile body, and is then distributed evenly between the surface and the interior of the new rubble-pile body. The extent of retrograde metamorphism possible in ordinary chondrites would therefore largely be dictated by the extent to which their parent bodies were broken up by impacts. Disaggregation caused by an impact would record fast cooling between the temperature at the time of breakup and the temperature at the time of re-accretion. In this thesis project, five H6 chondrites (Butsura, Estacado, Kernouve, Portales Valley, Queen's Mercy) and five L6 chondrites (Bruderheim, Holbrook, Leedey, Morrow County, Park) were subjected to three different thermometry analyses (pyroxene, olivine spinel, and metallographic) to determine their cooling profiles and evaluate same set of samples. Cooling rates for pyroxene and olivine--spinel thermometry systems are determined using the formulation of Dodson (1973) as modified by Ganguly & Tirone (1999). Cooling rates for the metallographic system are determined using the method developed by Wood (1967) as modified by Willis & Goldstein (1981). At temperatures higher than ~600 degrees C, all samples experienced cooling rates which are orders of magnitude faster (100's to 1000's of degrees C/kyr) than what is predicted for onion--shell thermal evolution (10's of degrees C/Myr) by e.g. Monnereau et al. (2013). At temperatures below ~600 degrees C, i.e. those recorded by the metals, cooling rates are much slower in comparison to the silicate/oxide systems, with the exception of Park, which continued to cool quickly. The discrepancy between high-- and low--temperature cooling rates for both H-- and L--chondrites can best be accounted for by a catastrophic impact which occurred while each body was still near its peak metamorphic temperature, followed by re--accretion into a rubble--pile, which would then cool slowly due to the poor thermal conductivity of rubble--piles. Shock heating does not appear to affect silicate--oxide thermometers.

Analyzing the constituents of meteorites has played an important role in forming the contemporary theories of solar system evolution, planets formation, and stellar evolution. Meteorites are often a complex mixture of common rock forming silicates, such as olivines and pyroxenes, with a range of exotic species including hydrated silicates, and in some cases organic compounds. We used Micro-Raman spectroscopy to analyze the compositions of three carbonaceous chondrites: NWA852, Murchison and Allende. Raman spectra were measured using laser sources with different excitation wavelengths: HeNe 633 nm and Nd:YAG 532 nm. We were able to detect 9 minerals in NWA852, 3 minerals in Murchison and 4 minerals in Allende. Some of these minerals like pyrite in NWA852 and magnetite in NWA852 and Murchison provide evidence for potential previous organic life. Other minerals like ringwoodite in Allende and lizardite in NWA852 reveal information about previous astrophysical and geological events experienced by the meteorites. The detection of graphite in the Murchison and Allende reveals information about the microstructure of these meteorites.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 77-80. / by Dushan Stephen Bukvic. / M.S.

The solid-metal/silicate-melt partition coefficient for W has been determined experimentally for the temperature and oxygen fugacity conditions at which eucritic basalts formed. The partition coefficient for W is 25 ± 5 at 1190°C and an oxygen fugacity of 10⁻¹³∙⁴. The solid-metal/silicate-melt partition coefficient for P, D(P), has been determined experimentally at 1190°C and 1300°C. The dependence of the partition coefficient on oxygen fugacity is consistent with a valence state of 5 for P in the silicate melt. The experimental partition coefficients are given by: (1) log D(P) = -1.21 log fO₂ -15.95 at 1190°C (2) log D(P) = -1.53 log fO₂ -17.73 at 1300°C The partition coefficients may be used to interpret the depletion of W/La and P/La ratios in the Earth, Moon, and eucrites relative to Cl chondrites. The depletion of the W/La ratios in the eucrites may be explained by partitioning of W into 2% to 10% solid metal assuming equilibration and separation of the metal from the silicates at low degrees of partial melting of the silicates. The depletion of P/La ratios requires an additional 5% to 25% sulfur-bearing metallic liquid. The depletion of both P/La and W/La ratios in the Moon can be explained by partitioning of P and W into liquid metal during formation of a small lunar core by metal-silicate separation at low degrees of partial melting of the silicates. The W/La ratios in the Earth and Moon are virtually indistinguishable, while P/La ratios differ by a factor of two. The concentrations of FeO also appear to be different. These observations are difficult to reconcile with the hypothesis of a terrestrial origin of the Moon following formation of the Earth's core, but are consistent with an independent formation of the Earth and Moon. In contrast to the Moon and eucrites, the depletion of P/La and W/La ratios in the Earth cannot be explained by an internally consistent model involving equilibrium between metal and silicate at low pressures.