<p> This dissertation examines the influence which a geophysical process (giant impacts) has on a geochemical marker (composition) during terrestrial planet formation. Simultaneously studying all planets maximizes the available constraints and permits examination of controls on the overall composition of the Earth. I also examine the Galilean satellite system to determine the universality of the terrestrial conclusions. </p><p> The late stages of planetary accretion involve stochastic, large collisions. Impact-related erosion and fragmentation can have profound consequences for the rate and style of accretion and the bulk chemistries of terrestrial planets. However, the previous predominate assumption in computer models of accretion was that all collisions resulted in perfect merging despite the likelihood of these collisions producing a range of outcomes (e.g., hit-and-run, removal of material from target, or production of several post-collision bodies). In this work, I investigate the effects of late-stage accretion with multiple collision types and the consequences on the bulk (mantle/core) and isotopic (Hf&ndash;W) composition. </p><p> My model is composed of two parts: (1) N-body accretion code tracks orbital and collisional evolution of the bodies and (2) geochemical post-processing evolves composition in light of impact-related mixing, partial equilibration and radioactive decay. For terrestrial planets, Part (1) is Chambers (2013, Icarus) and incorporates multiple collisional outcomes. For Galilean satellites, Part (1) is Ogihara &amp; Ida (2012, Icarus) and assumes perfect merging for all collisions thus the model is not self-consistent (it likely overestimates compositional changes). </p><p> For the terrestrial planets, the results are consistent with observed mantle/core ratios and tungsten isotopic anomalies. A moderate (approx. 0.4) core equilibration factor is preferred due to protracted accretion time. It is important to include multi-modal collisions when modeling planet formation if composition, timescales, or spatial distribution of mass are being investigated. </p><p> I could not reproduce the observed ice fraction gradient of the Galilean satellites, even with an initial compositional gradient and vaporization of water ice. Some other physical process(es) are needed, perhaps tidally-driven volatile loss at Io and Europa. Extensive inward radial migration smooths out initial compositional gradients.</p>

<p> Chondritic meteorites are undifferentiated fragments of asteroids that contain the oldest solids formed in our Solar System. Their primitive, solar-like chemical compositions indicate that they experienced very little processing following accretion to their parent bodies. As such, they retain the best records of chemical and physical processes active in the protoplanetary disk during planet formation. Chondritic meteorites are depleted relative to the sun in volatile elements such as S and O. In addition to being important components of organic material, these elements exert a strong influence on the behavior of other more refractory species and the composition of planets. Understanding their distribution is therefore of key interest to the scientific community. While the bulk abundance of volatile elements in solid phases present in meteorites is below solar values, some meteorites record volatile-rich gas phases. The Rumuruti (R) chondrites record environments rich in both S and O, making them ideal probes for volatile enhancement in the early Solar System. </p><p> Disentangling the effects of parent-body processing on pre-accretionary signatures requires unequilibrated meteorite samples. These samples are rare in the R chondrites. Here, I report analyses of unequilibrated clasts in two thin sections from the same meteorite, PRE 95404 (R3.2 to R4). Data include high resolution element maps, EMP chemical analyses from silicate, sulfide, phosphate, and spinel phases, SIMS oxygen isotope ratios of chondrules, and electron diffraction patterns from Cu-bearing phases. Oxygen isotope ratios and chondrule fO2 levels are consistent with type II chondrules in LL chondrites. Chondrule-sized, rounded sulfide nodules are ubiquitous in both thin sections. There are multiple instances of sulfide-silicate relationships that are petrologically similar to compound chondrules, suggesting that sulfide nodules and silicate chondrules formed as coexisting melts. This hypothesis is supported by the presence of phosphate inclusions and Cu-rich lamellae in both sulfide nodules and sulfide assemblages within silicate chondrules. Thermodynamic analyses indicate that sulfide melts reached temperatures up to 1138 &deg;C and fS₂ of 2 x 10^-3 atm. These conditions require total pressures on the order of 1 atm, and a dust- or ice-rich environment. Comparison with current models suggest that either the environmental parameters used to model chondrule formation prior to planetesimal formation should be adjusted to meet this pressure constraint, or R chondrite chondrules may have formed through planetesimal bow shocks or impacts. The pre-accretionary environment recorded by unequilibrated R chondrites was therefore highly sulfidizing, and had fO₂ higher than solar composition, but lower than the equilibrated R chondrites. </p><p> Chalcopyrite is rare in meteorites, but forms terrestrially in hydrothermal sulfide deposits. It was previously reported in the R chondrites. I studied thin sections from PRE 95411 (R3 or R4), PCA 91002 (R3.8 to R5), and NWA 7514 (R6) using Cu X-ray maps and EMP chemical analyses of sulfide phases. I found chalcopyrite in all three samples. TEM electron diffraction data from a representative assemblage in PRE 95411 are consistent with this mineral identification. TEM images and X-ray maps reveal the presence of an oxide vein. A cubanite-like phase was identified in PCA 91002. Electron diffraction patterns are consistent with isocubanite. Cu-rich lamellae in the unequilibrated clasts of PRE 95404 are the presumed precursor materials for chalcopyrite and isocubanite. Diffraction patterns from these precursor phases index to bornite. I hypothesize that bornite formed during melt crystallization prior to accretion. Hydrothermal alteration on the parent body by an Fe-rich aqueous phase between 200 and 300 &deg;C resulted in the formation of isocubanite and chalcopyrite. In most instances, isocubanite may have transformed to chalcopyrite and pyrrhotite at temperatures below 210 &deg;C. This environment was both oxidizing and sulfidizing, suggesting that the R chondrites record an extended history of volatile-rich interaction. These results indicate that hydrothermal alteration of sulfides on the R chondrite parent body was pervasive and occurred even in low petrologic types. This high temperature aqueous activity is distinct from both the low temperature aqueous alteration of the carbonaceous chondrites and the high temperature, anhydrous alteration of the ordinary chondrites. </p>