The overarching science question being addressed by this research project was the geological history of the nakhlite group of Martian meteorites as representative of a young Amazonian Martian crust. This included the magmatic processes and mechanism of emplacement at the origin of the meteorites but also the nature of a young Amazonian Martian aquifer that circulated throughout the nakhlites bedrock from its chemistry, origin and longevity. Answering these questions are fundamental to understand the physical and chemical properties and chronological evolution of Mars sub-surface environment over the last billion year with implication for astrobiology and current and future Mars exploration. For this project, a large set of nakhlite meteorites (probably the most comprehensible) have been assembled. It included NWA 5790, NWA 817, NWA 998, MIL 03346, Y 000593/000749, Lafayette and Nakhla. The mineralogy and mineral texture and chemistry of each meteorite have been fully characterized at the �m- and nm-scale using Electron Microscopy techniques (SEM and TEM) and Raman Spectroscopy at the University of Glasgow and Mass Spectroscopy (LA ICP-MS) at the University of Durham. The nakhlites are differentiated basaltic rocks formed by accumulation of augite in a sub-surface environment. The chemical composition of both cumulus augites (the liquidus phase) and their multiphase and glass inclusions representing trapped magma during augite growth indicate that the parent magmas at the origin of the meteorites were not primitive but residua of progenitors that experienced cryptic fractional crystallization processes in the deep basaltic plumbing system. The nakhlites have similar mineralogy but each meteorite has mineral phases with distinct properties which indicates that the rocks experienced each their own crystallization history. The nakhlites probably crystallized within separate igneous bodies/batches. Compositional variability of the nakhlites' parent magmas cannot be explained by a differentiation of a single pulse of magma that solidified through continuous fractional crystallization of augite and olivine alone in a shallow magma chamber. Aqueous alteration of the nakhlites is limited but the presence of small quanti- ties of clay minerals from the smectite family with carbonate, sulphate, halite and Fe-oxide demonstrate the existence of briny crustal water in the young Martian basaltic crust at least at the site sampled by the nakhlites. Variations in mineral assemblages provide evidences for contrasting conditions in the aqueous environments ranging from neutral-to-acidic (with a deposition of sulfate and halite) to near neutral-to-alkaline (with a precipitation of carbonate) apparently associated with a temporal evolution of the brines' property. The texture and chemistry of the secondary mineral assemblages are consistent with a deposition from discrete aqueous events fading away over time.

Evidence exists for great volumes of water on early Mars. Liquid surface water requires a much denser atmosphere than modern Mars possesses, probably predominantly composed of CO2. Such significant volumes of CO2 and water in the presence of basalt should have produced vast concentrations of carbonate minerals, yet little carbonate has been discovered thus far. These ‘missing carbonates’ comprise the Mars carbonate conundrum. This thesis provides insight to the conundrum via three distinct lines of investigation. Firstly, using engineering to expand our ability to locate carbonates on the Martian surface. A Micro-Optic UltraSonic Exfoliator (MOUSE) was designed and built that was tested on a range of rock types and wavelengths. Using ultrasonics demonstrates many advantages over the rock abrasion tool currently used on Mars rovers, including a smoother grind finish and a lower rate of tool tip wear when using tungsten carbide. Secondly, carbonates present in our only samples of the Martian regolith on Earth, meteorites, were studied. Carbonates found in Martian meteorites can provide a record of aqueous and atmospheric conditions extending back over 4.5 billion years. This thesis observes carbonates in two meteorites, ALH 84001 and Lafayette, representing early Mars and more recent Mars respectively, and finds evidence for two types of carbonate replacing glass in ALH 84001. The aqueously altered minerals of these two meteorites were compared with those found in the terrestrial ophiolites of Leka (Norway), and Semail (United Arab Emirates), and these ophiolites were assessed for suitability as Mars analogues. Chemically zoned carbonate rosettes similar to those in ALH 84001 are found in the Semail ophiolite samples. No carbonates were identified in Leka samples, but extensive serpentinisation was present. Finally, this thesis sought to replicate alteration processes and products that are recorded by Martian meteorites within a Mars analogue laboratory environment. The effects of differing initial atmospheric and mineral compositions were explored, specifically the comparison of CO2 and SO2 with basalt versus CO2 with olivine. These three interdisciplinary strands of investigation provide some novel tools, ideas and evidence to help solve the Mars carbonate conundrum.

Young rifts such as the Malawi Rift System, located at the southern end of the East African Rift System, are a natural laboratory for how continents begin to break apart. Extension is typically accommodated by earthquakes within the upper crust. However, where extension occurs at a slow rate, the small number of historically recorded earthquakes likely provides an incomplete view of the potential magnitude range of events, limiting seismic hazard knowledge and the understanding of rift dynamics. Geological and geomorphological studies of faults scarps may help understand how faults develop, structurally evolve and accommodate displacement. Thus, in this thesis, using field and satellite observations of fault scarps, alongside numerical models, I develop a number of new methodologies in order to better understand young rift evolution. I show that the coseismic stress change between two active parallel faults influences whether the faults link, and the linkage style is determined by the distance between the faults. I also show that the orientation of a major border fault in a young rift can be influenced by local stresses and/or weakness at depth, forming faults oblique to what is expected by the regional stress field. Lastly, I identify segmentation on several Malawi Rift System faults from variations in scarp height and steps in the fault traces, and show that the morphology of each can be used to infer the number of prehistoric earthquake events. My work may suggest that large, normal faults in young rifts develop through a specific growth model, and that they can host earthquakes larger in magnitude than historically recorded. This research can help better understand rift evolution and earthquake hazard in the Malawi Rift System, as well as other regions where normal faults have the potential to cause large magnitude earthquakes, such as the Rukwa rift, Baikal rift and the Basin and Range Province.

Fault zones are ubiquitous structures throughout the Earth’s crust and as a fault evolves it can significantly influence the rheological and hydrological properties of the crust. Fluid flow through fault zones is typically associated with fault-fluid-rock interactions and these interactions can affect the mineralogy, strength and evolution of a fault zone. In this study, field mapping is combined with petro-physical and stable isotopic analyses of the fault rock to evaluate the fault-fluid-rock interactions that occur within different fault zones, and the effects of these reactions on fault zone and fault population evolution. At Passo Moro in the NW Itilian Alps, there are three sets of joints cross-cutting the granite gneiss and numerous faults have formed by reactivation of pre-existing joints. The distribution of faults at Passo Moro is ultimately controlled by the variability of joint density within the host rock and the pre-existing joint distribution also affects the likelihood of whether a fault will grow into a mature fault zone or not. Where the joint density is high, strain is unable to accumulate to significant levels to enable joint reactivation into faults, whereas where joint density is low, fault zones are isolated and thus there are no structures nearby to facilitate fault linkage. At Passo Moro the fault population has evolved in a similar way as that described by Martel (1990) whereby small faults link to form simple faults which connect to form compound fault zones. The Virgin Fault and Spaghetti Fault would be considered as small fault zones and The Ciao Ciao Fault is equivalent to a compound fault zone. All three fault zones have different fault architectures and the small faults have been affected by different fluid-rock reactions compared to the larger fault. The small faults have experienced fault zone strengthening by K-feldspar precipitation, whereas the large fault has been weakened by muscovite precipitation. The different reactions between the fault zones are primarily controlled by the water-rock ratio which in turn is governed by permeability and the volume of fluid that infiltrates the fault zone. The Virgin Fault is considered as a rock-dominated system (K-feldspar-rich) whereas The Ciao Ciao fault is a fluid-dominated system (muscovite-rich). However, stable isotopes from both fault zones record a low water-rock ratio signifying rock-dominated conditions. Therefore the mineralogy of the fault rock is not solely controlled by the permeability defined water-rock ratio. The fluid dominated conditions promoting muscovitization in the Ciao Ciao Fault were probably enabled by an open fluid system and large volumes of fluid flowing through the fault during its lifetime. Stable isotopes indicate that water-rock ratios got lower with time in the Virgin Fault implying a limited open system, whereas muscovitization and stable water-rock ratios in the Ciao Ciao Fault point towards open system behaviour. In the Ciao Ciao Fault quartz precipitation only occurs in the foliated cataclasite within the fault core. Quartz precipitation is typically associated with closed system behaviour and suggests that the foliated cataclasite periodically ceased to be open to fluids and hence experienced cycles of higher and lower permeability. Stable isotopes show that the Virgin Fault records mineral precipitation from a metamorphic-like fluid, but after fault deactivation, the fault periodically transmitted progressively more meteoric-like fluids via a micro-fracture network. The Ciao Ciao Fault records mineral precipitation from a more meteoric-like fluid compared to the Virgin Fault, and flow through micro-fracture networks is dominated by an essentially meteoric fluid. The Ciao Ciao Fault therefore does not preserve evidence of fluids from its early history. This study indicates that the geochemical reactions that occur within a fault are controlled in part by the evolutionary stage of the fault, the fault rock permeability and the volume of fluids that pass through the fault. These results have been used to propose models for how the hydraulic properties and strength of a fault (population) evolve with time. The models produced from this study help advance our understanding of the processes that occur during the timescale of the seismic cycle, and how a population of faults will evolve in terms of mineralogy, strength and fluid flow. Such information will be of use to those involved in mineralization and mining studies, the storage of nuclear waste in crystalline rock, and earthquake prediction studies.

The uniquely low temperature sensitivity of the apatite (U-Th)/He system makes it an invaluable tool for studying shallow crustal processes which are not accessible through other techniques. Major advancements in both the theoretical and practical aspects of the technique have taken place over the past decade or so, however the routine application of the process is often held back by the perceived problem of single grain age ‘over dispersion’, particularly when applied to old, slowly cooled geological settings. There persists a misconception that age dispersion is indicative of a problem with the apatite (U-Th)/He system. A significant component of single grain age dispersion is inherent to the natural system, and therefore beneficial to reconstructing robust thermal histories. Variations in crystal grain size, accumulated amounts of radiation damage and changes to the helium concentration gradient within a grain due to fragmentation all contribute positively to age dispersion. Other, imposed factors such as crystal zoning and 4He implantation (which are undesirable) can also contribute to dispersion, however in the vast majority of cases their effects are negligible and only contribute noise to the inherent natural dispersion signal. The Ballachulish Igneous complex (BIC) in western Scotland has been used as a case study to demonstrate the range of age dispersion which should be expected when analysing large numbers of single grain aliquots per sample. Where 20+ grains are analysed, total dispersion will often be well in excess of 100% for old, slowly cooled samples, indeed dispersion in excess of 200% is possible. Such dispersion will often be as a consequence of outlying or apparently anomalous ages, however such ages should not be discounted unless there is sound analytical justification to do so. Apparent anomalous ages will often be ‘swallowed up’ by the data if more, or even different sized/shaped grains are analysed. Due to the competing effects of the three main causes of inherent natural dispersion, it should not be expected that large, well dispersed data sets will show any significant correlation between single grain age and either grain size or eU concentration. However a lack of correlation does not indicate poor quality data. Brown, Beucher and co-workers (Brown et al., 2013; Beucher et al., 2013) proposed a new modelling approach to account for the common occurrence of broken crystals in apatite separates, demonstrating that the additional inherent natural age dispersion arising from analysing fragments can be exploited when reconstructing thermal histories. A new inversion technique – HelFRAG was developed, based on a finite length cylinder diffusion model. The model is computationally demanding, therefore sampling based inversion methods requiring many forward model simulations become less practical. Consequently, an approximation of the finite cylinder diffusion model has been incorporated into the modelling software QTQt (Gallagher, 2012). Here, the approximation – QFrag has been demonstrated capable of returning comparable results to the full HelFRAG inversion technique when given the same synthetic data set, enabling the more routine application of the fragment model. Both QFrag and HelFRAG modelling techniques have been used to model the new BIC AHe dataset. The purpose is twofold: to demonstrate the importance of the fragment model with a real dataset, and to provide a new thermochronological interpretation for the BIC. When using this dataset, modelling samples individually shows only subtle differences (if any) between modelling broken grains correctly as fragments, verses modelling them incorrectly as whole grains. A far greater difference in the model output is seen when only modelling 3-6 grains compared to 20+, irrespective of whether fragments are treated correctly or not. When multiple samples are modelled together in a vertical profile, the fragment effect becomes much more important. A very different thermal history interpretation arises when any broken grains are modelled incorrectly as whole grains compared to when modelled as fragments. The new thermal history interpretation for the BIC involves a four stage cooling history from the time of intrusion (c. 424Ma). Very rapid cooling and uplift occurred immediately after intrusion over the first c. 20Myrs of the history (Phase 1). This brought the complex from c. 10km depths to within 2-3km of the surface. There followed much slower continued uplift between c. 404Ma and c. 300Ma, resulting in up to 1km of denudation (Phase 2). Over the next c. 150Myrs only a small volume of uplift occurred, however the geothermal gradient increased towards the end of this time period, suggesting crustal thinning (Phase 3). A final, rapid period of cooling and uplift occurred at c. 140Ma, bringing the top of the profile very near to the surface (Phase 4). No significant denudation has occurred since the end of this rapid uplift phase (10’s to 100’s of meters at most). The first two phases of cooling are interpreted as the final stages of the Caledonian orogeny, with erosion driven isostatic uplift causing continued denudation after the cessation of collisional tectonics. The end of phase three and the subsequent rapid uplift (Phase 4) are interpreted as the beginnings of crustal thinning and continental rifting which ultimately led to the opening of the North Atlantic Ocean.

In marine geological settings, pockmarks are evidence of highly focused fluid expulsion at the seabed. The modern seafloor of the Lower Congo Basin (LCB, offshore West Africa) is covered by densely packed arrays of thousands of pockmarks, whose distribution reflects in part the spatial organization of underlying seal bypass features. This study describes and analyses the variable distributions of seabed pockmarks using 3D seismic and spatial statistics, in order to infer subsurface processes that control the fluid migration routes and understand the overall shallow plumbing system of the area. The 3D seismic visualization of feeding conduits (pipes) allowed the identification of the source interval for the fluids expelled during pockmark formation. Pockmark formation may be linked to gas hydrate dissociation and/or expulsion of free gas beneath the GHSZ. Spatial statistics were used to show the relationship between underlying discontinuities and seabed pockmarks distributions, and revealed that pockmark occurrence is not considered to be random. Several different types of geo-mechanical controls were recognised and divided into 1) stratigraphic or depositional controls, 2) strati-structural controls, and 3) structural controls, corresponding to increasing stages of deformation affecting basin sediments. Furthermore, from the wide variability of pockmark sizes present in the area and the local geomorphology, it is possible to conclude that pockmark size is related 1) to the sub-surface depth at which the fluid source interval occurs and 2) to lateral variations of the degree of overpressure. The results of this study are relevant for the understanding of shallow fluid plumbing systems in offshore settings, with implications on our current knowledge of overall fluid flow systems in hydrocarbon-rich continental margins. This is relevant for the understanding of shallow fluid plumbing systems in offshore settings and overall fluid flow systems in hydrocarbon-rich continental margins.

This work is focused on carbonate-hosted base metal deposits in the Irish midlands with emphasis on the Navan ore deposit, County Meath, Ireland. The Irish ore deposits were created by the mixing of two fluids, a metal-bearing fluid and a sulfur-rich brine. Herein I aim to further the understanding of the creation, movement, and mixing of these two fluids and how they created the giant Zn and Pb deposit at Navan, as well as how post-ore genesis fluids are recorded in the rocks around Navan. The first chapter contains a summary of current knowledge and views of the deposit, local lithologies, structures, and mineralization. The second chapter is original work that examines how metal distribution patterns and 3D meshes of the paleo-surfaces can yield insights into the movement of mineralizing fluid during ore genesis. This work builds on previous work over the many years the mine has been operating. This new work shows the spatial variability in Pb and Zn concentrations and ratios and interprets these values with respect to vertical and horizontal fluid flow. It also builds on the work of others to interrogate the extent to which a major paleo-erosion event and surface has affected the mineralization found above and below this surface. This has significant bearing for the future of exploration in the area. The third chapter is original work that contains new noble gas data from Navan and deposits across Ireland that elucidate the temperature and tectonic setting that drove the metal bearing fluid that made the Irish midlands so well-endowed in base metals. Sulfides from every major carbonate-hosted base metal mine in Ireland were crushed to release noble gases trapped in fluid inclusions, which had retained 3He/4He signatures from the time of mineralization ca. 350 Ma. These 3He/4He ratios indicate a small but clear contribution of mantle-derived 3He, which reveals that mineralization occurred during an extensional event that introduced heat from the mantle. The fourth chapter is original work based on new 40Ar/39Ar geochronological results that constrain the timing of a later fluid flow event caused by the Variscan compression that inverted the local basin. This inversion event created large wrench and reverse faults and has greatly complicated the local lithology and metal extraction. The timing of this inversion event was interrogated by analyzing the 40Ar/39Ar systematics of disturbed feldspars along a large reverse fault. The 293 ± 3 Ma minimum age produced represent the first radiometric age of the Variscan compressional event in central Ireland and confirms the long held assumption that these faults are related to this large scale tectonic event. The fifth and final chapter is a combination of original and recently published work from others. It focuses on a newly discovered area of mineralization several km to the south of Navan. Mineralization, fluid inclusions, and the structural setting of this new area are evaluated and compared to ‘typical’ Navan mineralization. The new area was created by hotter hydrothermal fluid and did not mix with the surface fluid as effectively as the main deposit.

Stasis may be operationally defined as the occurrence of little or no evolutionary change during an interval of geological time, and is an important consequence of punctuated equilibria. Studies of stasis in the fossil record of necessity address only morphological stasis, and that only in the subset of phenotypic characters preservable in the fossil record. Stasis in single characters may be recognised in fossil taxa by lack of significant change in mean value through an interval of geological time; stasis in multiple characters may be recognised by overlap in morpho space occupation by taxa where morpho space occupation is calculated by multivariate techniques. No quantitative definition is placed on such stasis because of the lack of comparable data on non-static (i.e. rapidly evolving) taxa to provide the alternative. Proposed explanations for stasis include: developmental and genetic constraints; environment fidelity; selection of generalist phenotypes in fluctuating environments; stabilising selection (including stabilising species selection); developmental canalisation; effects due to population size and distribution. Mean generic and specific durations (in myr.) of trilobites originating In the stratigraphical systems Cambrian-Carboniferous of England, Scotland and Wales are, respectively: Cambrian (4.42, 2.13); Ordovician (10.89, 2.06); Silurian (10.34, 3.54), Devonian (4.19, 1.12), Carboniferous, (14.82,5.74). Distributions of both generic and specific durations are highly positively skewed. Study of the species composition of the longest duration genera (those whose durations exceed the 90% quantile value for the system in which they originated) suggests that species stasis played an important role in the Cambrian and Carboniferous; no clear pattern is revealed for the interval SilurianDevonian inclusive. Chronostratigraphical range charts are presented for species and genera from England, Scotland and Wales. Study of the durations of Ordovician Laurentian genera in relation to their position on the palaeoslope shows that longest duration genera are eurytopic; their wide geographical and environmental dispersal enabled them to avoid localised factors which caused extinction in more endemic genera. Taxonomy-independent phylogenetic and morphometric analysis of selected long duration shape conservative genera from the middle to upper Ordovician and Silurian shows that disassociated mosaic evolution in some characters is abundant in all three, superimposed on an almost invariant body plan. Achatella Delo, 1935 had a duration of about 22 myr. (upper Llanvirn - Hirnantian, time scale of Tucker et al. 1990). Nine species (three new) and one form under open nomenclature have been diagnosed. Calyptaulax Cooper, 1930 had a duration of about 25 myr. (lower Llanvirn - upper Rawtheyan, time scale of Tucker et al. 1990). Two subgenera are diagnosed, each of duration about 20 myr. (time scale of Tucker et al. 1990). The nominate subgenus is well resolved on the cladogram, and five species have been diagnosed. Calyptaulax Abstract. Page ii (Calliops) is unresolved on the cladogram because of a disassociated mosaic pattern of "peripheral" character evolution; ten species have been diagnosed. A sixteenth species could not be assigned to a subgenus. Acernaspis Campbell, 1967 had a duration of about 11 myr. (lower Llandovery - Wenlock, time scale of Harland et al. 1989). Eighteen species have been diagnosed, three of them new. Several stratigraphical samples of Ananaspis Campbell, 1967 have been studied and an hypothesis that this genus arose through neoteny from Acernaspis has been confirmed, although not a further hypothesis that progressive neoteny continued throughout the existence of Ananaspis. Four Ananaspis species have been diagnosed, one of which is new. This does not constitute a complete survey of Ananaspis. The disassociated mosaic pattern of peripheral character states probably reflects differing degrees of developmental canalisation at different levels of phenotypic organisation. The basic body plan is strongly canalised, whereas at "peripheral" levels, less strong canalisation allows emergence of superficial characteristics. This, combined with eurytopic distribution, may keep the taxa adapted to their (various) environments without need for more major evolutionary change.

The aim of this study was to develop a stratigraphic framework for the ‘mid-Cretaceous’ (Aptian-Cenomanian) strata of the Tanzanian coastal basins and, in particular, attempt to identify and recover the Aptian/Albian boundary (the interval of ‘Oceanic Anoxic Event’ 1b) for detailed investigation. Six pre-existing industry boreholes were selected for detailed micropalaeontological study (planktonic and benthic foraminifera) using modern taxonomic and biostratigraphic concepts. These sites are arranged approximately along strike from one another, and their stratigraphy and palaeoenvironmental histories are established. Information from these boreholes and many additional surface outcrop samples was used to select a location for two new boreholes which were expected to penetrate through the Aptian/Albian boundary (Tanzania Drilling Project [TDP] Holes 40A and 40B). In total, twelve planktonic foraminiferal biozones and two subzones of the upper Aptian - upper Cenomanian from the coastal basin of Tanzania are illustrated and described for the first time. Intra- and inter-basinal correlations are achieved using a combination of lithostratigraphy, biostratigraphy and carbon isotope stratigraphy. The planktonic and benthic foraminiferal assemblages are found to be similar to those reported from the Atlantic and Europe, and hence can be correlated to global records. An assessment of relative sea level change is achieved through benthic foraminiferal biofacies and planktonic: benthic ratios. Biostratigraphy of TDP Holes 40A and 40B was developed from the foraminiferal assemblages. A tentative correlation of the carbon isotope stratigraphy is made to the isotope records from Ocean Drilling Program Site 1049 in the subtropical Western North Atlantic and Vocontian Basin, southeast France. These investigations show that lowermost part of the Albian is missing in TDP Holes 40A and 40B which may explain why no organic carbon-rich shales relating to Oceanic Anoxic Event 1b were encountered. More expanded and organic rich successions may exist in the northern part of Tanzania and offshore where the succession thickens.

The development of Polygonal Fault Systems (PFS) remains poorly understood despite extensive study for over two decades. These systems of exclusively normal faults are developed over wide areas of many basins worldwide and are believed to influence caprock integrity and hydrocarbon reservoir quality, whilst also potentially presenting shallow drilling hazards. A seemingly obvious conclusion from their layer-bound nature and significant lateral extent is that their origin must be governed by the constitutive behaviour of the host sediments. Establishing specific causative mechanisms has, however, proven difficult. The aim of this research project is to first assess some existing arguments for PFS genesis and this is complimented by a review of modification of structure in soft rocks and discussion of how this facilitates changes in both shear and compaction. The approach in this work is to utilise geomechanical forward modelling to demonstrate how such changes might lead to PFS formation. The concepts of this approach are discussed with focus on the adopted computational framework and selected constitutive model. An argument for polygonal fault genesis is presented that is founded on diagenetically induced shear failure, and the requirements for incorporating this into the constitutive model are described. Recovery of realistic PFS geometries is demonstrated as validation of the geomechanical argument and the competency of the computational approach. Conceptual sensitivity studies at the field scale are undertaken to better understand what processes, reactions and conditions might control fault genesis and propagation. When observed in mapview polygonal faults commonly intersect bedding planes at a wide variety of azimuths which reflects an inferred horizontally isotropic state of stress. Occasionally, this so-called 'planform geometry' is modified by the presence of tectonic faults, slopes or salt structures. Therefore, there is the possibility that polygonal faults may be useful paleostress indicators. This is explored using the characterised materials in simple models featuring anisotropic horizontal stress conditions.