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<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>

The Southern Brittany Migmatite Belt developed during the Ligerian Orogeny within a narrow time interval 403 Ma to 372 Ma. Detailed field mapping of several key localities within the belt (Port Navalo, Port Blanc and Roguedas, around the Golfe du Morbihan, and Ville-es-Martin at St. Nazaire) has revealed a heterogeneous suite of high grade gneisses, Al-silicate rich gneisses (morbihannites), low to high melt fraction metatexites and diatexites. Careful petrography and mineralogy has allowed the establishment of reaction histories for each rock type which have been utilised in constructing segments along a P-T path. Reverse zoned rims and the replacement of garnet by Crd and/or Bt + PI suggests the following generalised reactions have occurred: Grt + Bt + S11 + Qtz~ Crd + He + Um + Kfs + H 0 and Grt --=;>Bt + PI + Qtz. tarnet-cordierite gneisses record an early prograde event. Growth zoned garnet cores and a sequence of inclusions, from the garnet core to the garnet rim, of Qtz + 11m + Ky, PI + St + Rt + Ky + Bt and PI + St + Rt + Sil + Bt constrain the prograde evolution and suggest the crossing of the simplified reactions Ms + Chl~ St + Bt + Qtz and St + Qtz ~Grt + Ky + vap. A detailed evaluation of the available thermometers and barometers, equilibrium considerations, the stability relations of biotite, and petrographic analysis have enabled the construction of a tightly constrained P-T path. It is suggested that the prograde P-T path is the result of a series of sediments deposited in an ensialic marginal basin with a higher than normal geothermal gradient which has been tectonically buried by overthrusting during basin closure. The retrograde near isothermal decompression path is interpreted to be the result of the development of a rising anatectic granite diapir which has dragged its thermal envelope, the migmatites, to shallow crustal levels during its ascent.

<p>The Sierra Blanca metamorphic core complex (SBMCC), located 90 miles west of Tucson, is part of the southern belt of metamorphic core complexes that stretches across southern Arizona. The SBMCC exposes Jurassic age sedimentary rocks that have been metamorphosed by intruding Late Cretaceous peraluminous granites and pegmatites. Evidence of this magmatic episode includes polysythetic twinning in plagioclase, albite exsolution of alkali feldspar resulting in myrmekitic texture, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary (Miocene?) tectonic fabric, associated with the exhumation of the Sierra Blanca metamorphic core along a low-angle detachment fault, forming the SBMCC. The NW-SE elongated dome of metamorphic rocks forms the footwall of the detachment shear zone, and is separated from the hanging wall, composed of Paleozoic and Mesozoic metasedimentary rocks, by a low-angle detachment shear zone. Foliation is defined by gneissic layering and aligned muscovite, and is generally sub-horizontal, defining the dome. The NNW-SSE mineral stretching lineation is expressed by plagioclase and K-feldspar porphyroclasts, and various shear sense indicators consistent with a top-to the-NNW shear sense. Lineation trends in a NNW-SSE orientation; however, plunge changes across the domiform shape of the MCC. Much of the deformation is preserved in the blastomylonitic gneiss derived from the peraluminous granite, including epidote porphyroclasts, grain boundary migration in quartz, lozenged amphiboles, mica fish, and retrograde mineral alterations. Detailed petrologic observation and microstructural analysis indicate deformation temperatures of 450-575 ? ?C presented here provide thermomechanical constraints on the evolution of the SBMCC.

The earth's core consists of a solid metallic center surrounded by a liquid metallic outer layer. Understanding the compositions of the inner and outer cores allows us to better understand the dynamics of the earth's core, as well as the dynamics of the cores of other terrestrial planets and moons. The density and size of the earth's core indicate that it is approximately 90% metallic, predominantly iron, with about 10% light elements. Iron meteorites, believed to be the remnants of planetary cores, provide further constraints on the composition of the earth's core, indicating a composition of 86% iron, 4% nickel, and 10% light elements. Any potential candidate for the major light element core component must meet two criteria: first, it must have high cosmic abundances and second, it must be compatible with Fe. Given these two constraints there are five plausible elements that could be the major light element in the core: H, O, C, S, and Si. Of these five possible candidates this thesis focuses on S and C as well exploring the effect of minor amounts of O and H on the eutectic temperature in a Fe-FeS core. We look at two specific aspects of the Fe-FeS system: first, the shape of the liquidus as a function of pressure, second, a possible cause for the reported variations in the eutectic temperature, which draws on the effect of H and O. Finally we look at the effect of S and C on partitioning behavior of Ni, Pt, Re,Co, Os and W between cohenite and metallic liquid. We are interested in constraining the shape of the Fe-FeS liquidus because as a planet with a S-enriched core cools, the thermal and compositional evolution of its core is constrained by this liquidus. In Chapter 1 I present an equation that allows for calculation of the temperature along the liquidus as a function of pressure and composition for Fe-rich compositions and pressures from 1 bar to 10 GPa. One particularly interesting feature of the Fe -rich side of the Fe-FeS eutectic is the sigmoidal shape of the liquidus. This morphology indicates non-ideal liquid solution behavior and suggests the presence of a metastable solvus beneath the liquidus. An important consequence of such curved liquidi is that isobaric, uniform cooling requires substantial variations in the solidification rate of the core. Additionally, in bodies large enough for P variation within the core to be significant, solidification behavior is further complicated by the P dependence of the liquidus shape. Brett and Bell (1969) show that at 3 GPa, the liquidus curvature relaxes, implying that the liquid solution becomes more ideal. By 10 GPa, the liquidus approaches nearly ideal behavior (Chen et al., 2008b). However, at 14 GPa, the liquidus again assumes a sigmoidal curvature (Chen et al., 2008a; Chen et al., 2008b), suggesting a fundamental change in the thermodynamic behavior of the liquid. Chapter 1 of this thesis accounts for the observed complexity in the liquidus up to 10 GPa thus enabling more accurate modeling of the evolution of the cores of small planets (Buono and Walker, 2011). Accurately knowing the eutectic temperature for the Fe-FeS system is important because it places a minimum bound on the temperature of a S-enriched core that has a solid and liquid component which are in equilibrium. Unfortunately literature values for the 1 bar to 10 GPa eutectic temperature in the Fe-FeS system are highly variable making the estimation of core temperature, an important geodynamic parameter, very difficult. In Chapter 2 we look at a possible cause of this observed variation by experimentally investigating the effects of H on the eutectic temperature in the Fe-FeS system at 6 and 8 GPa. We find that H causes a decrease in the eutectic temperature (but that O does not) and that this decrease can explain some of the observed scatter in the available data. The effect of H on the eutectic temperature increases with increasing pressure (i.e. the eutectic temperature is more depressed at higher pressures), matching the trend reported for the Fe-FeS system (Fei et al., 1997). Our work suggests a significantly higher eutectic temperature than is commonly used in the Fe-S system and explains the lower observed eutectic temperatures by employing the ternary Fe-S-H system. Additionally, we report an equation which allows for accurate prediction of the composition of the eutectic in the Fe-FeS system. The constraints presented here (eutectic temperature in the Fe-FeS system are 990 °C up to at least 8 GPa in conjunction with the equation presented in Chapter 1, allows for complete prediction of the Fe-rich liquidus in the Fe-FeS system to 8 GPa. It is important to understand the partitioning behavior of trace elements between the solid and liquid components of a system because it fundamentally informs our understanding of that systems chemical evolution. In light of this, we investigate partitioning behavior in the context of the Fe-S-Ni-C system in Chapter 3. Choice of this system was motivated by work outside the scope of this thesis investigating the liquidus relationships in the Fe-S-C system (Dasgupta et al., 2009). In these experiments, cohenite (Fe₃C) is the stable solid phase, instead of Fe-metal and we find that the partition coefficients between cohenite and Fe-C-S liquids are significantly lower than those between Fe-metal and Fe-S liquids. There are two potential situations to which this work can be applied. With respect to core formation, although it is unlikely that any planets entire inner core is carbide, it is possible that in a C-rich planet, as the Fe core crystallizes, C in the liquid phase could be enriched to the point where cohenite is a stable crystalizing phase. Under these circumstances, we would predict smaller depletions of the elements studied in the outer core than would be the case for Fe-metal crystallization. This work can also be applied to the earth's upper mantle which is thought to become Fe-Ni metal-saturated as shallow as 250 km. Under these circumstances, the sub-system Fe-Ni-C (diamond) -S (sulfide) becomes relevant and Fe-Ni carbide rather than metallic Fe-Ni alloy could become the crystalline phase of interest. Our study implies that if cohenite and Fe-C-S melt are present in the mantle, the mantle budget of Ni, Co, and Pt may be dominated by Fe-C-S liquid. Additionally, in the case of a S-free system, W, Re, and Os will also be slightly enriched in Fe-Ni-C liquid over cohenite. In total this body of work better constrains several key aspects of the compositional and thermal evolution of cores in small planetary bodies and has potential implications for the earth's mantle.

X-ray diffraction (XRD) was used to measure the unit cell parameters of pyrope (Mg3Al2Si3O12), grossular (Ca3Al2Si3O12) and four intermediate solid solutions synthesized at ~6 GPa and 1400°C in multi-anvil (MA) apparatus. Intermediate garnet solid solutions on this join show regular asymmetric positive excess volumes, but roughly 2-3 times bigger than previous reports from garnet hydrothermally synthesized in piston cylinder apparatus. The binary Margules equation used to fit this excess volume data gives parameters = 2.0±0.1 cm3/mol, which is about half as big as = 4.3±0.1 cm3/mol. Garnets synthesized in diamond anvil cells (DAC) with wider XRD peaks than those synthesized in MA have more nearly symmetrical excess volumes about 3 times larger than those previous piston cylinder syntheses. The large size difference between divalent Mg and Ca is the key reason for the non-ideal mixing properties of pyrope-grossular garnet solid solution. Partial order/disorder of Ca-Mg in the X site may be responsible for the interesting, variable mixing phenomena among different synthesis methods. The large excess volumes we measured from MA-synthesized garnets imply that the solvus of pyrope-grossular garnet will become experimentally accessible at high pressures, perhaps less than 10 GPa, unlike the expectations derived from the much smaller excess volumes of hydrothermally grown garnets. X-ray diffraction (XRD) methods and diamond anvil cells were used to measure the unit cell parameters of multi-anvil (MA) grown garnets: pyrope, grossular, and four intermediate solid solutions up to ~600°C and ~10 GPa. The unit cell parameters of these synthetic garnets increase with temperature and decrease with pressure. Thermal expansion coefficients of garnets in this series were calculated from the unit cell volumes' change with temperature. They are all in the range from ~2.0-2.8*10-5 K-1, and uniformly increase with temperature but differ with garnet compositions. At high temperature, the calculated thermal expansion coefficients of end-member pyrope and grossular in this study are larger than those reported by Skinner (1956). The compressional properties of these MA-synthesized pyrope and grossular are comparable with previous reports (Finger 1978; O'Neill et al., 1989; Zhang et al., 1998 and 1999; Pavese et al., 2001; Jiang et al., 2004). The Birch-Murnaghan EOS yields Κ0=165.4±1.8GPa, with Κ0’ fixed to be 5.92 for grossular and Κ0=172.5±2.0GPa for pyrope, with Κ0’ fixed to be 4.4. The bulk moduli of garnet with intermediate composition are all 155~160GPa, smaller than the end-members, showing no significant compositional dependence, as is consistent with the fact that garnets on this join have large positive excess volume, which makes them more compressible at high pressure. Application of these results indicates that the excess volumes in the pyrope-grossular series remain high even at high P and T. Multi-anvil (MA) technique was used to study the grossular-pyrope garnet solid solution for conditions of pressure and temperature stability against exsolution. Two garnet phases Py90Gr10 and Py40Gr60 with wt.% composition ratio 1:1, the expected consolute composition, were heated at 6GPa and different temperatures. XRD measurement results showed that these two garnet phases converged completely to one phase with composition ~Py65Gr35 at 1200°C, indicating that the critical temperature of pyrope-grossular garnet solvus is lower than 1200°C, lower than some literature modeling results (Haselton and Newton, 1980). At 8GPa, long term heating experiments for both convergence and divergence showed that two garnet phases with composition around ~Py82Gr18 and ~Py62Gr38 were equilibrated with each other at 1200°C. These garnet pairs represent the positions of the pyrope-grossular garnet solvus' two limbs at 1200°C and 8 GPa. Convergence experiments at 1100 °C and 8 GPa also showed changing composition of a widely-separated compositionally different garnet pair. However the equilibrium composition at 1100 °C and 8 GPa failed to be constrained by divergence heating experiments because the relatively low temperature and much slow diffusion rate of Mg/Ca cation exchange in garnet. Observations of garnet immiscibility at < 10 GPa reported here suggest that the MA-garnet excess volumes represent internal equilibrium values. Deduction from our new two phase equilibrium experiments shows that pyrope-grossular solvus has a higher critical temperature in the range 800-900°C at 1 bar compared to previous thermodynamic models (T < 600°C) (Ganguly et al., 1996), suggesting that at pressure as high as 2GPa, exsolution in garnet can happen at a higher temperature than previous thought, which is strongly supported by the high temperature (800-860ºC) exsolution in garnet samples found from natural metagabbro, South Harris (Cressey,1978), and an immiscible garnet pair in pyrope-rich garnet crystal collected from Garnet Ridge, Arizona was reported by Wang et al. (2000).

The structure and petrology of Upper Precambrian and Cambrian rocks have been studied in detail, in an area 38 miles north - east of Adelaide, South Australia. The rocks occur within a broad zone of high grade metamorphism on the eastern side of the Mt. Lofty Ranges. The Upper Precambrian succession consists predominantly of pelitic and semi - pelitic schists, quartzites, calc - silicate rocks and calc - schists, and the Cambrian sequence of quartzo - feldspathic schists, migmatites, granite gneiss, calc - silicate rocks and minor pelitic schists and quartzites. The rocks have reached the sillimanite grade of metamorphism and the metamorphism is of the low pressure - intermediate type. Dolerites, pegmatites, minor granodiorites and granites intrude the meta - sediments. Mineralogical and structural relationships of the granite gneiss, indicate that it has been formed by recrystalliaation of the quartzo - feldspathic schists. Small scale metamorphic differentiation, appears to have accompanied the recrystallization. The migmatites are believed to have been formed by metamorphic differentiation rather than by anatexis. Three phases of deformation are recognised in the Upper Precambrian rocks and two in the Cambrian. The second deformation recorded in the Upper Precambrian rocks does not appear in the Cambrian rocks. Each deformation has been accompanied by the formation of foliation. In the Proterozoic rocks deformed by the second and third phases of folding, the foliation is a crenulation cleavage. The deformations in both the Upper Proterozoic and Cambrian sequences are considered to be related. Petrofabric studies of quartz, scapolite and biotite are related to the respective macroscopic structures. An analysis of the chronology of crystallisation and deformation of these rocks indicates that crystallisation continued during and after each phase of deformation. Faulting commenced either prior to or during meta - morphism. Intense metasomatic activity followed a later phase of faulting resulting in the widespread development of albitites and in some cases talc ore bodies. The albitites formed in the fault zone were subsequently brecciated by further movement and later healed by the introduction of more metasoinatic fluid. / Thesis (Ph.D.) -- University of Adelaide, Department of Geology, 1966.