abstract: Meteorites and their components can be used to unravel the history of the early Solar System. Carbonaceous chondrites are meteorites that originated from undifferentiated parent bodies that formed within a few million years of the beginning of the Solar System. These meteorites contain calcium-aluminum-rich inclusions (CAIs), which are the oldest dated solids in the Solar System at ~4.567 billion years old and thus preserve a record of the earliest stage of Solar System formation. The isotopic compositions of CAIs and bulk carbonaceous chondrites can be used to identify the sources of material inherited by the protoplanetary disk, assess the degree of mixing in the disk, and evaluate sample origins and potential genetic relationships between parent bodies. In particular, mass-independent Cr and Ti isotopic compositions have proven to be especially useful for these purposes. In this work, I first developed new methods for the chemical separation of Cr and Ti, improving the reliability of existing methods to ensure consistent yields and accurate isotopic measurements. I then measured the Cr and Ti isotopic compositions of CAIs from CV and CK chondrites to determine the extent of isotopic heterogeneity in the CAI-forming region and assess the role of CAIs in the preservation of planetary-scale isotopic anomalies. My results show that all measured CAIs originated from a common isotopic reservoir that incorporated material from at least three distinct nucleosynthetic sources and preserved limited isotopic heterogeneity. These results also suggest that planetary-scale isotopic anomalies cannot be attributed solely to the transport of CAIs from one part of the solar nebula to another. I finally measured the Cr and Ti isotopic compositions of bulk CM, CO, and ungrouped chondrites to evaluate the relationship between CM and CO chondrites, which have been suggested to originate from either distinct but related parent bodies or a common compositionally heterogeneous parent body. My results suggest that CM, CO, and related ungrouped chondrites originated from distinct parent bodies that formed from similar precursor materials in nearby formation regions. These results may have implications for asteroid samples returned by the OSIRIS-REx and Hayabusa2 missions. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

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.

Relationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with stretching modes of aliphatic hydrocarbons in NWA 852 and Tagish Lake. The former is highly correlated with the hydration band in all meteorites. Negative correlation is observed between water+organics and carbonate bands in all meteorites. Two dimensional infrared maps for NWA 852 and Orgueil show that carbonates are spatially separated from water+organic combination, silicates, OH, and CH distributions. Overlapping of the latter three in NWA 852 and Tagish Lake suggests a possible catalytic role of phyllosilicates in the formation of organics. Additionally, spectroscopic analyses on Sutter's Mill meteorite fragments present multiple distinct mineralogies. Spatial and spectral evidences on this regolith breccia suggest mixing of multiple parent bodies. Ratios of asymmetric CH2 and CH3 band strengths for NWA 852, Tagish Lake, and Sutter's Mill are similar to the average ratio of interplanetary dust particles and Wild 2 cometary dust particles, however significantly exceeds that of interstellar medium objects and several aqueously altered carbonaceous chondrites such as Orgueil. This suggests distinct formation regions and/or parent body processing of organics for these meteorites. Our infrared spectro-microtomography measurements on Murchison meteorite, representing the first such measurement on any kind of meteorite, comprise of three-dimensional reconstructions of specific molecular functional groups for understanding the spatial distributions of these groups.

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.

The isotopic composition of meteorite sulphur and sea water sulphates was investigated by means of a simultaneous collection mass spectrometer. It was found that sixteen samples of meteorite sulphur possessed identical isotope abundances within the precision of the instrument. The sulphates from various depths in the Atlantic, Pacific and Arctic Oceans, were found to be enriched in s34 compared to the meteorite base level. The overall variation in s32/s34 content was 0.39 percent for the sea water samples. / Thesis / Master of Science (MS)

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.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 152-168. / by Melvin Bruce Fegley, Jr. / Ph.D.

The polymer-like organic material in the Orgueil (Cl) chondrite was analyzed by high vacuum pyrolysis/gas chromatography/mass spectrometry, a new technique specially developed for this type of polymer analysis. Orgueil powder, previously solvent-extracted to remove all soluble organic compounds, whether indigenous or contaminant, was pyrolyzed in temperature steps at 150°, 300°, 450°, and 600°C. Gas chromatographic/mass spectrometric analysis of the vacuum pyrolyzates revealed a series of alkenes to C₈, an extensive series of alkylbenzene isomers, thiophene, alkylthiophenes, and benzothiophene, and the nitrogen compounds acetonitrile, acrylonitrile, and benzonitrile. Comparison of the Orgueil polymer fragments with those reported in polymer analyses of the Murchison and Allende meteorites suggests that qualitatively and quantitatively the Orgueil and Allende polymeric materials are very similar. The presence of acetonitrile, acrylonitrile, and benzonitrile, typical breakdown products of amino acids, in Orgueil pyrolyzates suggests the presence of amino acids in an insoluble form in the meteorite polymer matrix. Changes in the distribution of polymer fragments occurred during high vacuum pyrolyses as the temperature was increased stepwise from 150° to 600°C. These changes imply a progressive alteration in the character of the polymeric material toward a condensed aromatic structure through the preferential loss of aliphatic and heteroaromatic portions at lower temperatures. A possible inference is that the polymeric material in Orgueil is a complex mixture of polymerized materials having different thermal stability. Comparison of vacuum pyrolyzates of the Orgueil polymeric material with pyrolyzates of terrestrial kerogen indicates similarities in composition and structure. These similarities suggest the possibility that meteorite polymers may have formed near the surfaces of meteorite parent bodies by low temperature processes similar to those by which terrestrial kerogen is formed.

ELEMENTAL AND ISOTOPIC STUDY OF DIFFERENTIATED METEORITES AND IMPLICATIONS FOR THE ORIGIN AND EVOLUTION OF THEIR PARENT BODIES Iron meteorites are differentiated meteorites composed largely of Fe-Ni alloys. The metallic phase of many iron meteorites shows a texture called the Widmanstätten pattern, which develops as a two-phase intergrowth of kamacite (α-bcc, ferrite) and taenite (γ-fcc, austenite), and forms by nucleation and growth of kamacite from taenite during slow cooling of the parent body. Selected iron meteorites - octahedrites of different structural and chemical groups (Canyon Diablo, Toluca, Bohumilitz, Horh Uul, Alt Biela, Nelson County, Gibeon and Joe Wright Mountain) were studied with intention to evaluate the scale and extent of Fe isotopic heterogeneities in iron meteorites and to find the possible link between the isotopic variations and thermal histories of the respective meteorite parent bodies. The Fe isotopic compositions of kamacite and taenite in the studied meteorites, obtained by three independent analytical techniques with different spatial resolution capabilities (laser ablation and solution MC ICP-MS and SIMS) show significant variations of up to ~4.5‰ in δ56 Fe. The taenite is isotopically heavier compared to kamacite in all studied meteorites. There is no correlation...

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.