Invasive tufa deposits on Foel Fawr, South Wales are forming from lime kiln waste deposited from the 18th century until the 1950s. The tufa deposits are unusual in their anthropogenic origin and form the largest site of this type in the UK. At emergence pH is extreme (>11) and this consequently generates significant pressure on organisms living in and around the system. Morphologically, the calcium carbonate tufa deposits are similar to those formed in other extreme environments (e.g. hot springs, caves), forming many of the same features (e.g. terraces, rimpools, pisoids, stalactites). By identifying and mapping tufa facies at Foel Fawr, the spatial distribution of these facies has been directly compared to these potentially analogous environments. Analysis of the fabrics associated with each facies highlights the importance of physico-chemical precipitation in the system; proximal facies are dominated by abiotic fabrics, while distal and marginal facies show an increasing degree of biological influence. This process is comparable to the partitioning of fabrics and facies observed in hot spring systems, however, the role of microbes in precipitation is apparently less important on Foel Fawr. The present day extreme chemistry of the site selectively excludes organisms and generates a partitioning of biology. Hydrochemical monitoring of the site reveals that the extreme pH of the system is in decline. The recession of the extreme hydrochemistry is confirmed by colonisation of previously excluded organisms and allowed the physical decay of the site. Fabrics preserved within the deposits support the suggestion that the extreme environments were previously much more widespread.

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Chemical, textural, and isotopic heterogeneity within granitic magmas/rocks, and their extrusive equivalents, are common phenomena. This is to be expected since the source materials, from which the granitic magmas were created by partial melting, are themselves heterogeneous. Micro-sampling of feldspar crystals within granites has revealed complex internal Sr and Nd isotope variations thought to reveal subtle variations in the isotopic composition of the melt from which particular zones crystallised. These previous studies provide evidence of both macro-scale (regional) and micro-scale isotopic variation within granitic magmas. What is unknown is the scale and nature of chemical and isotopic variation occurring on the meso-scale (metre, decametre, hectometre). In this study, high-precision geochemical and isotopic (Sr, Nd, and O) data is obtained for spatially well-constrained samples, from three granitic intrusions from the UK, to study the scales over which isotope heterogeneities are preserved, and the maximum volumes of magma over which isotope and elemental homogenisation may have been achieved. This information provides important constraints on the physical and chemical characteristics of processes that occur during magma genesis, ascent, and emplacement. The regional-scale geochemical and isotopic heterogeneity in the Criffell pluton (SW Scotland) has been well documented and ascribed to 'incomplete hybridisation' between magmas derived from the melting of mantle and/or 'new' basic crust and metasediments. Sampling on the 10 to 100 m scale in this study demonstrates major-, trace- and rare earth element homogeneity between samples of similar petrography. Within the Dalbeattie Quarry granodiorite, subtle heterogeneity in initial ([sup]87Sr/[sup]86Sr)[sub]397 Ma compositions exist (0.70582 to 0.70615), between samples collected ~ 150 m apart. The small-scale heterogeneity is outside of analytical error (± 0.0001). [delta][sup]18O heterogeneity also occurs on similar small scales (~ 120 m), with values ranging from 8.9 to 10.7 %. The larger error on the [epsilon][sub]Nd(397 Ma) values do not allow any small-scale heterogeneity to be resolved. The geochemical and isotopic heterogeneity of the Cairnsmore of Fleet pluton, another Southern Upland granite, is also well known, and considered to be a result of similar processes to that of Criffell. This study demonstrates that the Cairnsmore granite is more petrographically variable in terms of grain-size, mafic/felsic mineral proportions, and accessory mineral assemblages over scales ranging between 100 and 350 m. The existence of more petrographic and geochemical heterogeneities on smaller scales suggests that homogenisation processes were less effective in this pluton compared to Criffell. On scales < 1 km, ([sup]87Sr/[sup]86Sr)[sub]392 Ma compositions and [epsilon][sub]Nd(397 Ma) values are essentially homogeneous. Forest Track samples PAHCF23 (0.70796) and PAHCF25A (0.70672) are ~ 1 km apart and can only just be distinguished outside of analytical error. However, [delta][sup]18O data demonstrate the existence of both regional-scale and locality-scale [delta][sup]18O heterogeneity on the 100 m, decametre and even cm-scale (8.3 to 9.7%0, error ± 0.1%0). The two main granite varieties of the Dartmoor pluton (SW England) are generally, homogeneous in terms of their petrography and geochemistry on 100 m, decametre, meter and even cm scale. However, isotope heterogeneity, outside of analytical error is shown to exist on even the cm-scale. The samples PAHD34A and P AHD34B, from Blackenstone Quarry, have ([sup]87Sr/[sup]86Sr)[sub]280Ma compositions of O.70949 and 0.71292 respectively, and were collected 50 cm apart. Samples PAHD35A and PAHD35B have ([sup]87Sr/[sup]86Sr)[sub]280 Ma compositions of 0.70960 and 0.71205, and were collected 100 cm apart. Variation in [delta][sup]18O and [epsilon][sub]Nd(280 Ma) values also exist. PAHD34A and PAHD34B have [delta][sup]180 compositions of 10.01 and 10.98 %0 (± 0.1%0), and SNd(280 Ma) values of -3.8 and -3.3 (± 0.2), respectively. Either the distinct magma batches, that coalesced to form the pluton, were much smaller in Dartmoor (compared to the Criffell and Cairnsmore plutons), or these heterogeneities may represent volumes of magma, within larger domains, that escaped homogenisation by mixing and diffusion. The existence of discrete, isotopically distinct batches of magma within the Criffell, Cairnsmore and Dartmoor plutons favours the dyke model for granitoid magma ascent through a pulsed magma delivery, in which separate magma batches (or pulses) coalesce to form plutons at or near their final emplacement levels. The scale over which such magma pulses can still be recognised varies within each pluton. The magma pulses are likely to have been larger in size, but subsequent homogenisation processes in the chambers led to a reduction in their size. However, homogenisation was not complete. In all three plutons, it is generally only the isotope ratios that display significant small-scale heterogeneity. Processes such as fractional crystallisation, are considered to be secondary, overprinting geochemical and isotopic heterogeneity from much deeper regions.

Understanding how faults initiate and fault architecture evolves is central to predicting bulk fault zone properties such as fault zone permeability and mechanical strength. The study of faults at the Earth’s surface and at near-surface levels is significant for the development of high level nuclear waste repositories, and CO2 sequestration facilities. Additionally, with growing concern over water resources, understanding the impact faults have on contaminant transport between the unsaturated and saturated zone has become increasingly important. The proposal of a high-level nuclear waste repository in the tuffs of Yucca Mountain, Nevada has stimulated interest into research on the characterisation of brittle deformation in non-welded to densely welded tuffs and the nature of fluid flow in these faults and fractures. The majority of research on the initiation and development of faults has focussed on shear faults in overall compressional stress regimes. Dilational structures have been examined in compressional settings e.g. overlapping faults generating extensional oversteps, or in normal faults cutting mechanical layered stratigraphy. Previous work has shown the affect mechanical stratigraphy has on fault dip angle; competent layers have steeply dipping segments and less competent layers have shallowly dipping segments. Displacement is accommodated by shear failure of the shallow segments and hybrid failure of the steeply dipping segments. As the fault walls of the shear failure segment slip past each other the walls of the hybrid failure segment are displaced horizontally as well as vertically thus forming dilation structures such as pull-aparts or extensional bends. Work on truly extensional faults has been at the kilometre scale of fissure swarms in rift systems where the focus is on fault geometry and direction of fault propagation. This study examines dilational faults with offsets of centimetres to 10’s of meters within moderately and densely welded ignimbrite units on the caldera island of Gran Canaria, Spain. Through the investigation of fault populations within different ignimbrite units I have examined how the fault architecture changes with accumulated displacement, identified the factors controlling fault core evolution and using these observations developed a new model for the initiation and growth of dilational faults in ignimbrites. The faults in this study do not have a linear correlation of increasing fault core thickness with displacement. Fault core width varies along fault dip and the largest offset faults have the narrowest fault cores. Furthermore, the damage zone joint frequency shows a limited increase with increasing displacement and faults and joints are sub-parallel. From these observations I have developed a new model for fault initiation and evolution in which the petrophysical properties of the host rock are the primary control on fault architecture. Faults initiate on existing sub-parallel joints and grow by the incorporation of material from joint surfaces and joint bound slabs. The growth of the fault depends on the joint spacing and the competency of the host rock. In densely welded ignimbrites, joint spacing is controlled by sub-layers within the ignimbrite unit which are formed by flattening and stretching of fiamme. In moderately welded ignimbrites, fiamme and lithic inclusions in the ash matrix act as sites of joint initiation; the greater the abundance of such flaws the higher the joint frequency. Whether fault growth is promoted or inhibited depends to some extent on the competency of the material. Faults cutting ash-rich friable units have narrow fault cores regardless of displacement. This suggests that the material is easily abraded in the fault core inhibiting fracturing of the host rock and incorporation of new material. Hence host rock fabric and composition have an important influence on fault architecture in these ignimbrite units. The other influence on fault evolution is the tensile stress regime in which faulting occurs. The faults in this study form by hybrid failure and so have both vertical and horizontal displacements. The dilation of existing joints causes slip on the joints and allows material to fall into the joint forming a fault core. This work identifies distinct differences between the mechanism of dilational fault initiation and resultant fault architecture compared to that of shear faults. The observations made in this study indicate that the host rock petrophysical properties, stress regime at time of faulting (tensile or compressive) and confining pressure are primary influences on fault architecture and not displacement; contradicting the widely accepted fault thickness-displacement scaling relationship. I suggest that the architecture of dilational faults can be predicted by examining the host rock properties and using the data from this study have developed a framework that illustrates how ignimbrite host rock properties may affect deformation structures. Such frameworks for individual lithologies may be more useful in predicting fault zone properties as opposed to global scaling relationships. The results of this study have implications for conceptual models of fluid flow based on fault architectures predicted using the thickness-displacement relationship.

Many processes involved in the accretion of lower oceanic crust remain enigmatic. To investigate some of these processes, the principal focus of this study is drill core 'CY-4', an unbroken 2.2km long section through sheeted dykes and mafic and ultramafic cumulates of the Troodos ophiolite lower crust, Cyprus. The generally accepted hypothesis states CY-4 intersected an axial magma chamber that was intruded by an off-axis pluton, based on a 'stepped' increase in clinopyroxene titanium content at 1331 m depth. This comprehensive structural, textual and trace element examination throughout CY-4 indicates a single, open system, plutonic sequence. It is comprised of high-level, varitextured gabbros, underlain by foliated gabbronorites and low-level, banded, gabbronorites and ultra mafic cumulates. Steeply inclined planar and linear fabrics were generated by upward migration of magma. Flow was predominantly channelised through the upper cumulates and diffuse through the lower cumulates, with corresponding differences in preserved structures and textures. Channelised flow and magma remobilisation in the rapidly cooled and poorly equilibrated upper cumulates is responsible for the decametre-scale textural and chemical variations. Syn-tectonic porous flow through the slower-cooled banded cumulates led to grain-scale textural and chemical interactions. Any initial mineral co-variations were erased during supra-solidus equilibration and efficient expulsion of incompatible element-rich melts. Any early-formed layering was transposed. A new model of CY-4 accretion is proposed in which a broad range of depleted and boninitic magma compositions were efficiently homogenised in the lower crust to yield the narrower ranges of extruded compositions. Correlations with Troodos Lower an Upper Pillow Lava series may indicate sources within the foliated gabbronorites, and the deeper ultramafic region respectively. The structural resemblance of the CY-4 cumulate series to fast-spreading lower crust can be reconciled with the slow spreading rate calculated for Troodos if CY-4 intersected a ridge axial node of magma upwelling

This thesis compiles the results of a 3D seismic-based study of the geometry and emplacement mechanics of igneous sills and sill complexes intruded into basins along the NE Atlantic Margin. Dolerite sills were intruded into the Upper Cretaceous and Paleocene mud-dominated sediments of these basins during the Paleocene and Early Eocene, approximately synchronous with the onset of seafloor spreading between NW Europe and Greenland. Detailed interpretation of igneous intrusions in four case-study areas has revealed that sills adopt a wide range of geometries, ranging from near-concordant sheet-like forms to complex discordant forms. Detailed mapping illustrates that the traditional definition of a sill as 'a tabular igneous intrusion with concordant surfaces of contact' is inadequate when describing the fully three-dimensional geometry of sills. This has encouraged the development of a new classification scheme for igneous sills that considers their detailed three-dimensional geometry. Many sills have been found to adopt a saucer-shaped geometry and these are interpreted to form through a three-step model involving lateral propagation, inflation and overburden deformation, and intrusion along deformation-related peripheral fractures. 3D seismic mapping has allowed for igneous sill complexes to be imaged in three dimensions for the first time. These complexes are found to form highly interconnected networks that cover many kilometres of vertical section (&sim;8 km). Based on the interpretation a new model for the construction of sill complexes is proposed. In this model a sill complex builds up from deeper to shallower levels with sills intruded at one stratigraphic level acting as feeders for sills intruded at shallower levels. Interpretation of hydrothermal mounds and jack-up structures formed during sill intrusion has allowed for the timing of sill emplacement to be constrained in the four case-study areas. This has revealed that several discrete phases of intrusion took place during the Paleocene and earliest Eocene

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.

Aeolianites and palaeosols on the Meditcrranean coastal plains of Israel were investigated with luminescence dating in order to explore the sedimentological evidence for climate change in the area and the response to it. The dated samples were taken from sites between the towns of Haifa and Netanya South, which are located in a quarry near the town of Habonim and further towards the coast, in a quarry North of the town of Hadera and further towards the coast as well as at the coastal cliff and in a sewage gully by the town of Netanya South. The aims of this study were to correlate aeolianite and palaeosol exposures along the Mediterranean coast, to establish a chronology for a climatological interpretation, and also whether aeolianite formation and palaeosol development could be correlated with major climate events of the Late Pleistocene in the Eastern Mediterranean. Over 80 samples were collected from various sites, covering exposures from North to South and also from East to West. They were dated with infrared optical stimulated luminescence (IR-OSL) and thermoluminescence (TL). In addition radio fluorescence spectra were obtained from some of the samples and also their equivalent doses were determined with infrared radiofluorescence (IR-RF) The chronology established through the luminescence dating results showed that aeolianite formation and palaeosol development in the Carmel and Sharon coastal plains are connected with the cyclical occurrence of enhanced rainfall over the Mediterranean. These conditions, which also cause the Mediterranean sapropels to form, are characterised by a sudden increase of precipitation. The rainfall lessens over the time of the episode but temperatures increase. It is likely that most of the soils in the coastal plains developed during the humid conditions of the rainfall episodes, while sand accumulation and aeolianite formation took place during the arid conditions at the end of the rainfall episodes or shortly afterwards. A new climate-event-stratigraphical model for the correlation of the deposits is suggested.

Carbonatite magmas characteristically expel fluids into the surrounding country rock, creating metasomatised alkali-rich fenite aureoles. This thesis examines evidence for the mobility ofhigh field strength elements (HFSE), including the rare earth elements (REE), niobium and zirconium into these fenite aureoles in order to provide a better understanding of element mobilisation, transportation and precipitation. The study is timely because the REE and Nb are recognised as critical metals. The REE, in particular, are used in green technologies, and have grown in importance in recent years. The combination of the concentration of REE mines in China, associated export restrictions and a severely limited scope for substitution of these elements, has highlighted the challenges of securing adequate supplies and of a better management of resources, together with the need for an improved knowledge of the processes by which mineral deposits are enriched to economic grade. The approach used here was to study fenite aureoles around two Cretaceous carbonatite complexes at Chilwa Island and Kangankunde in the Chilwa Alkaline Province of southern Malawi by re-examining samples held in the collections of the Natural History Museum, London (BM1968 P37 and BM1957 1056). The geology of the complexes had already been well described by M. Garson and A. Woolley but the results of recent studies elsewhere suggested that it should now be possible to explore the fenitising process in more detail. Kangankunde is a rare earth-rich ferroan dolomite carbonatite, subject to active exploration for the REE. Chilwa Island contains a wider range of carbonatites, including apatite-, magnetite-bearing calcitic carbonatite, and REE mineral-bearing ankeritic and sideritic carbonatites. The presence ofassociated silicate rocks is minor at both these complexes. Samples were selected from across the fenite aureoles to represent areas of differing intensity and style of metasomatism. Whole-rock analyses were made to assess compositional changes across the aureole. Mineralogical studies by SEM-EDS, EPMA, LA-ICP-MS and SEM cathodoluminescence permitted the identification of mineral assemblages, the establishment of paragenetic sequences and also the characterisation of the REE compositions in apatite, zircon and the RE-bearing minerals from zones of varying degrees of alteration within the aureole. Fluid properties were further explored by fluid inclusion studies of secondary inclusions in the country rock quartz. Apatite and zircon in the fenite were dated by fission track analysis and a U-Pb LA-lCP-MS method, respectively, to determine their relationships with the carbonatite. At both complexes, fenite rocks contain micro-assemblages of minerals visible by backscattered electron imaging but not reported in previous studies. Examples include the assemblages of zircon, ilmenite, rutile, apatite and monazite found in veins of up to 500 um width in the sodi-potassic outer fenite at Chilwa Island, and the associations of strontianite, RE-minerals and carbonates in mm-sized veins in the more highly metasomatised parts of the aureole at Kangankunde. Alteration and dissolution-precipitation reactions seen in these micro-assemblages suggest that multiple fluid events occurred in the fenite aureole. The presence of alkaline minerals (aegirine, albite, K-feldspar, arfvedsonite) indicates pervasive fenitisation by fluids expelled from the carbonatite over distances of more than a kilometre. The micro-assemblages provide evidence that fluids were able to mobilise, transport and precipitate the HFSE and REE outwards over a similar distance into the country rock but that for the REE this event followed an earlier fenitisation by alkaline fluids. It is likely that fluids from more than one carbonatite have contributed to the variation in mineralogy and mineral composition. Fenite rocks and minerals have lower light REE:heavy REE ratios than those of the carbonatites in the core of the complexes. This cannot be explained by simple mixing between carbonatite and country rock end members, and fractionation of the REE during fluid transport is therefore invoked with relative preferential mobilisation and deposition of the mid to heavy REE. Zircon and apatite in the mineral assemblages at Chilwa Island appear petrographically to be co-eval. However, although fission track dating confirmed a carbonatitic age of c.130 Ma for apatite, the U-Pb dating of associated zircon produced ages of between 520 and 770 Ma and so zircon must be part of the original country rock rather than having co-precipitated with apatite. In the less altered fenites, zircon is stable, and at Chilwa Island, appears to encourage the nucleation of carbonatite-derived mineral assemblages. In contrast, zircon is unstable in higher- grade fenite at both complexes where metasomatising fluids were most intense. Zirconium is thus released from highly altered rocks and, rather than forming alkali zirconosilicates as happens in alkaline complexes, it appears to be transported outwards and is re-precipitated as a secondary, sub-micron zircon population in low- grade fenite. Interpretative models require the ingress of multiple fluids at each complex. Early alkaline fluids were more extensive and predominantly sodic. Later potassic fluids produced more intensive alteration in the inner aureole. The mineral assemblages were precipitated in veins in the aureole by fluids carrying the REE, which were expelled in multiple episodes from the different carbonatites at each complex, both before and after alteration by potassic fluids. At Chilwa Island, modelling suggests that early REE mineralisation in the fenite rocks from the outer carbonatites of the complex occurred after pervasive initial alkaline alteration by sodic fluids. This was overprinted by intense potassic alteration in the innermost fenites. The subsequent relative MREE and HREE enrichment in the aureole is attributed to fluids from the late-stage carbonatites. At Kangankunde, fluid events produced the same pattern of alkaline alteration followed by HFSE mineralisation, but here enrichment in the MREE and HREE occurred early, after the sodic alteration, with later fluids precipitating minerals with higher LREE:HREE ratios and substantial carbonate. As at Chilwa Island, the distinct characteristics of each mineralising fluid show that it is likely they were expelled from different carbonatites in the complex.