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Granitic magmatism in collision belts is widely regarded as a major mechanism for generating continental crust. This hypothesis can be tested by identifying the source rocks of granitic magmas, and in particular the contribution by pristine mantle material. The complexity of granites, and their susceptibility to post-crystallisation alteration, has until recently provided a major obstacle to progress. Zircon, a common and chemically robust accessory mineral in granitoid rocks, retains a record of the composition of the magma it grew from. Recent developments in microanalysis (ion microprobe and laser ablation ICP-MS) now enable in-situ analysis of zircon crystals at high spatial resolution and precision, providing access to this record at the previously inaccessible intra-crystal scale. The resulting data have enormous potential to provide new insights into the nature and age of source rocks and the processes driving magma evolution. This project used an integrated in-situ O, U-Pb and Hf isotope, trace and rare earth element study of zircon to identify the sources and chart the evolution of two ‘I-type’ (igneous/infracrustal precursor) Scottish late Caledonian (~430-400 Ma) granite plutons. I have constrained models of magma generation, the relative contributions of mantle and crust, the ages and identities of their lower crustal sources, and have shown that the plutons played, at most, a minor role in crustal growth. In addition, I have been able to resolve the extent to which open-system changes like magma mixing affected the magma compositions. The same approach was used in a pilot study of three Caledonian (~460 Ma) ‘S-type’ (sedimentary/supracrustal precursor) granite plutons, which theoretically represent magmas formed by melting of a purely supracrustal source. The data confirm that Dalradian country rocks were the primary source, but reveal remarkable isotopic diversity within and amongst the three plutons. The most important general conclusion from this PhD study is that the complexity and scale of isotopic heterogeneity between plutons, amongst samples of the same pluton, in single samples and within individual crystals is far greater than previously recognised, consistent with the incremental assembly of plutons from multiple melt batches of differing composition, sources and petrogenetic evolution.

<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>

A study has been made of a 2 km2 catchment at Peatfold, Glenbuchat in north-east Scotland. The catchment is underlain by basic igneous rock, predominantly quartz-biotite-norite, which has been deeply weathered in Tertiary times and subsequently affected by glacial and periglacial processes such as solifluction of glacial drift. Vegetation is predominantly heather moorland. The chemistry and mineralogy of the soils and parent material was investigated in detail. Precipitation and river water chemistries were studied through a one year period, which involved collection of weekly and monthly precipitation samples and regular weekly and storm river water samples. River samples were analysed for pH, sodium, potassium, calcium, magnesium, chloride, sulphate, phosphate, nitrate, nitrite, ammonia, bicarbonate, iron, aluminium, manganese, silicate and total organic carbon. Precipitation was acidic (mean pH 4.3), dilute (mean total dissolved solids 13-7 mg 1-1) and dominated by hydrogen ion, sodium, chloride and sulphate. Its composition varied greatly, but distinct seasonal trends as a result of varying influence from oceanic, industrial and terrestrial sources were observed. River water was neutral (mean pH 7.0), more concentrated (mean total dissolved solids 70 mg 1-1) and less variable in composition. The latter was dependent upon hydrology with calcium, magnesium, silicate and bicarbonate increasing in concentration at low discharges and hydrogen ion, potassium, transition metals and total organic carbon increasing in concentration at higher discharges. Since hydrology has influenced soil type, variations in river composition related to soil type being drained could be detected. Seasonal trends in composition were also observed. Inputs in precipitation and outputs in river water were calculated for all species for one year. All species had a net output except hydrogen ion, nitrate, nitrite, ammonia, sulphate and phosphate. Outputs of silicon (32 kg ha-1), calcium (22 kg ha-1) and bicarbonate (114kg ha-1) were large. The large net output of chloride (35 kg ha -1) indicates the importance of dry deposition of aerosols of oceanic spray. When this is allowed for, the calculated rate of outputs of elements due to weathering in kg ha-1 is: Si > Ca > Mg > Na > K > Fe > Al.