The results reveal that: (a) the Late Jurassic eastern Pacific region consisted of an E-dipping Andean/Cordilleran arc-back-arc system which rifted prior to inception of the Greater Antilles arc; (b) the end of E-dipping subduction and the initiation of the SW-dipping Greater Antilles island arc took place at ∼135–125 Ma and involved the transform motion of suites of Andean/Cordilleran arc rocks into the N and S ends of the Antillean arc; (c) the rocks of the present-day Dutch-Venezuelan Antilles and Aves Ridge record a different tectonic story involving a separate long-lived E-dipping Andean arc system with a polarity reversal event related to the collision of the ∼90 Ma Caribbean-Colombian Oceanic Plateau (CCOP) and (d) at ∼90 Ma, plume-related rocks were also formed on the proto-Caribbean plate between the Americas as part of an oceanic plateau distinct from the CCOP.

This study reconstructs the explosive volcanic history of Pantelleria, a peralkaline caldera volcano situated in a rift zone in the central Mediterranean Sea, from the earliest exposed eruption products (~324 ka) to the 46 ka Green Tuff Formation which forms a marker horizon blanketing the entire island. The pre‐Green Tuff stratigraphy has been revised by tracing and logging eruption‐units around the island, making extensive use of coastal cliff sections not reported before. Eight widespread ignimbrite formations have been defined and for the first time have been given type localities. Most ignimbrites are welded and contain lithic breccias. Caldera collapse is thought to have occurred during five of the eight major eruptions and is thought to have re‐used the same scarps multiple times. In interignimbrite repose periods, which last between ~3 and ~52 ka, nearly twenty localised cone or shield‐shaped eruptions have occurred producing mostly pumice falls and lavas of dominantly rhyolitic composition. In contrast, ignimbrites are commonly trachytic but some are strongly zoned and include rhyolitic end‐members. The chemical zonation is more pronounced after longer repose periods. Petrogenetically, the volcano has followed the same liquid line of descent, dominated by fractional crystallisation, throughout its >300 ka history and no recurring chemical cycles have been detected. Calculation of accurate volumes is hindered by the island’s small size, with most eruption products deposited under water. To help constrain eruption volumes, distal ash layers found across the Mediterranean Sea (at up to 1300 km distance: Lesvos, Greece) have been chemically correlated with the proximal eruptions and their volumes calculated to 0.1‐18 km3. Distal ash volumes are up to 45 times larger than onshore volumes for the same formation (0.1‐0.8 km3) and are a powerful tool to complement the proximal record, thereby significantly improving previous volume estimates.

Remote sensing data and image processing techniques are used increasingly to aid scientific investigation and address geological problems in areas that are difficult to map by conventional methods. This thesis explores how multi spectral satellite data, supported by traditional geological techniques, facilitate a study of lateritic palaeosols. The work centres on laterites, which are thin but important elements of the Phanerozoic stratigraphy of NE Africa. They immediately pre-date midOligocene flood basalts and, if mapped, can be used to delineate a flood basalt-Iaterite contact and define the pre-30 Ma African Surface and uplift patterns. They have important engineering properties and are key to understanding basement alteration and its associated mineralization. They affect agriculture and groundwater quality and retention - essential in Sub-Saharan Aflica where access to safe water is limited. They dominate the landscape, yet are unmapped and marginalised in the literature. Their geological context supports a laterite-focused remote sensing mapping strategy. A strategy for geologic mapping of laterites based on their simple mineralogy and spectral characteristics that distinguish them from other rocks is developed. Methods for mapping are presented using Earth Observation data. The outcome is a series of regional geological maps of Eritrea and Ethiopia. These reveal that laterite cover is more extensive than previously thought and enable further lines of research. The maps provide a means of regional dating of laterites, which, together with ages obtained for overlying flood basalts and new basement cooling ages, indicate a major planation during the Palaeozoic and constrain the timing of associated uplift and erosion. A regional review of Mesozoic-Cenozoic climatic, strati graphic and structural evolution is presented and a model of Neogene deformation of the lateriteflood basalt datum is produced. Finally, laterite maps, petrographic and geochemical evidence are used to access basic essentials of life: clean water, a safe environment and a sustainable economy.

No description available.

The idea of a rigid lithosphere that supports loads through flexural isostasy was first postulated in the late 19th century. Since then, there has been much effort to investigate the spatial and temporal variation of the lithosphere's flexural rigidity, and to understand how these variations are linked to its rheology. In this thesis, flexural modelling is used to first re-assess the variation in the rigidity of oceanic lithosphere with its age at the time of loading, and then to constrain mantle rheology by testing the predictions of laboratory-derived flow laws. A broken elastic plate model was used to model trench-normal, ensemble-averaged profiles of satellite-derived gravity at the trench-outer rise system of circum-Pacific subduction zones, where an inverse procedure was used to find the best-fit Te and loading conditions. The results show a first-order increase in Te with plate age, which is best fit by the depth to the 400 ± 35 °C plate-cooling isotherm. Fits to the observed gravity are significantly improved by an elastic plate that weakens landward of the outer rise, which suggests that bending-induced plate weakening is a ubiquitous feature of circum-Pacific subduction zones. Two methods were used to constrain mantle rheology. In the first, the Te derived by modelling flexural observations was compared to the Te predicted by laboratory-derived yield strength envelopes. In the second, flexural observations were modelled using elastic-plastic plates with laboratory-derived, depth-dependent yield strength. The results show that flow laws for low-temperature plasticity of dry olivine provide a good fit to the observations at circum-Pacific subduction zones, but are much too strong to fit observations of flexure in the Hawaiian Islands region. We suggest that this discrepancy can be explained by differences in the timescale of loading combined with moderate thermal rejuvenation of the Hawaiian lithosphere.

No description available.

Magnetic surveys are an important method of understanding subsurface geology, however there are several reasons why correction by remote referencing may fail, including local induced effects, activity levels of the field, and simple distance between survey and base station. We look for ways to improve correction by remote referencing using insights from global field models and comparisons of data from a wide range of observatories. We investigate the conditions in which the behaviour of nearby observatories differ from each other, and where the CM4 comprehensive model fails to match the observed behaviour of the local geomagnetic field. The misfits are separated by cause: those due to the activity level of the geomagnetic field, and the location of the observatory. We see that CM4 is a good match to observatories in the conditions it was designed for (mid-latitudes and Kp up to 2), but also that it can produce a good fit to stations out of this range (up to Kp of 3 or 4). The correlation of misfits to CM4 allows us to separate effects due to latitude, and location on the coast. Further investigation allows us to suggest some corrections that may improve the quality and extent of magnetic data gained by surveys in these locations. High latitude stations show changes in behaviour which fall into latitudinally split groups, most likely due to the presence of induced fields from ionospheric currents. Ensuring base station and survey fall into the same grouping would eliminate many of the problems this causes. Geomagnetic storms often lead to survey data being unusable due to their effects. We find that while X component data contains mostly storm signal, the Y and Z components at many stations contain retrievable data. The recovery period of the storm can, for most stations, be used after a regression is applied. We also consider the effects of induced fields due to the tides and the coast effect -well-known effects that can be seen at many stations. We find a correction for the dominant M2 tidal effect using cosine waves. We also find an approximate correction for the coast effect, using cosine or sine waves of the Sq period as appropriate for the station pair chosen. It is also noted that small differences in location can have a large effect on the induced fields, as seen at GUI and TAM, where storms seem to have a smaller than expected effect.

No description available.

No description available.

No description available.