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This research is an exploration both of the Precambrian metamorphic geology of south-western Montana and the Wlaser ablation microprobe ^4OAt-³⁹At geochronological technique. Using the high spatial resolution of the UV laser microprobe it has been possible to produce systematic ^4OAt-³⁹Ar ages within individual mica grains. Further, the UV laser has been used to drill into biotite inclusions within garnet to look at the shielding effect of the garnet lattice, and to drill depth profiles into garnet to measure helium diffusion in laboratory experiments. The south-western Montana region of the Precambrian Wyoming Province was believed to have undergone at least three separate periods of metamorphism: M1- granulite facies in the Archaean, M2 - amphibolite facies in the Early Proterozoic, and M3 - greenschist to epidote-amphibolite facies in the Mid-Proterozoic. Because of the relatively low blocking temperature of the 40Ar- 39Ar geochronological system in mica (c.300-350 °C), it is readily reset by regional metamorphic events and previous K-Ar and 4OAr_38 Atgeochronology had found that the Early Proterozoic event dominated the ages obtained. UV laser 40Ar-39At dating of the matrix mica constrained the timing of cooling from the Early Proterozoic metamorphic event to between 1780 to 1740 Ma with a cooling rate between 1 and 8 °C/m.y. 4OAr_39Ar analyses of individual biotite inclusions in garnet also produced similar ages. However, Pb-Pb step leach dating of a small subset of garnet yielded ages between 1808 and 1765 Ma, demonstrating that the garnet did not grow during an Archaean event but, rather, during the Early Proterozoic metamorphic event. Thus, the shielding properties of garnet on biotite inclusions could not be easily assessed in these samples. However, where matrix biotite had been partially reset by the Cretaceous plutons, there was some evidence to suggest that a minority of the biotite inclusions in the same sample had been shielded from resetting. The influence of fractures, defects and other fast diffusion paths is believed to have prevented most of the inclusions from being shielded. No evidence was found to show that the rocks in south-western Montana were metamorphosed during the Archaean and it seems likely that the M1 and M2 events were not greatly separated in time and were both Early ProterozoiC in age. The high spatial resolution of the UV laser microprobe was used in order to date highly altered biotite within rocks that had undergone later (M3) greenschist metamorphism. Biotite was interlayered with chlorite, clinozoisite and prehnite but using the UV laser it was possible to separately analyse areas of unaltered biotite and areas of alteration within a single mineral and produce ages from both. It was thus possible to measure two ages from one sample: an unaltered age consistent with the timing of the Early Proterozoic metamorphism, and a younger age that could be linked to the c.1500-1360 Ma timing of Belt basin formation to the north and west of the region. This technique therefore was able to overcome the difficulties associated with producing meaningful ages from altered samples whilst constraining the timing of the M3 metamorphic event.

This research characterizes the nature of fractures in Paleozoic and Mesozoic caprock seal analogs exposed in central and south-eastern Utah. The results of this research show evidence for fluid flow and mineralization in the subsurface as well as reactivation of fractures suggesting that the fractures act as a loci for fluid flow through time. The heterolithic nature of the caprock seals and meso-scale (cm to m) variability in fracture distributions and morphology highlight the strong link between the variation in material properties and the response to changing stress conditions. The variable connectivity of fractures and the changes in fracture density at the meso-scale plays a critical role in subsurface fluid flow. The presence or formation of new fractures can result in seal bypass systems, which can cause failure of hydrocarbon traps, CO2 geosequestration sites, waste and subsurface fluid repositories. An integrated approach of field, borehole geophysical, burial and stress history modeling, rock strength testing, and numerical modeling are used to understand the effects changing material properties, rock strength, and stress history have on sealing capacity. Simplified stress history models derived from burial history curves are combined with laboratory derived rock properties to understand the importance variations in rock properties and differential and effective mean stress have on the mechanical failure of fine-grained clastic sedimentary rocks. Burial history and rock strength data show that in units that experience similar burial depths and changing mechanical property exert a control on deformation type. Geomechanical models reveal changes in local strain magnitudes at locked mechanical interfaces, suggesting that elastic mismatch between layers results in differential strain distribution. Characterization of fracture patterns, rock strength variability and the modeled changes in subsurface strain distribution is especially important for understanding the response of low-­‐permeability rocks to changing stress in the subsurface, and is applicable to multiple geo-engineering scenarios such as exploitation of natural resources, waste disposal, and management of fluids in the subsurface. The analyses presented in this dissertation provide analog fracture data for fine-grained clastic rocks and a dataset for better understanding the importance of heterogeneity in low permeability rocks.

Variations in major, minor, and trace elements compositions and ratios, as well as isotope ratios are all useful tools in studying the composition of the Earth’s mantle, and heterogeneities present therein. Since the mantle itself doesn’t easily lend itself to study, ocean island basalt (OIBs) are commonly used as a proxy due to compositional differences combined with the range of origination depth, a combination that allows them to represent the heterogeneity of the mantle, sampling everything from the core mantle boundary to the old or recent additions of recycled oceanic crust. Fogo, being one of the most active volcanoes in the world, continuously samples the interior of our planet, and as such is a prime location for studies of mantle geochemistry. This study aims to determine the origin of the mantle lithologies present at Fogo. The study is a continuation and extension of the studies conducted by Barker et al. (2014) and Magnusson (2016). This study utilises major, minor, and trace element geochemistry in clinopyroxene and olivine phenocrysts, as well as Ni-isotopes from whole rock samples. Using the relative values of Ni, Mn, and trace elements and their ratios in olivine and clinopyroxene phenocrysts we aim to further unravel the mechanics of the creation of ocean islands and provide additional constraints regarding the mechanics of the formation of heterogeneities in the Earth’s mantle. This study will focus on Ni* and Mn* in olivine phenocrysts, trace element composition and ratios of olivine phenocrysts and clinopyroxene phenocrysts, and Ni-isotope data.  This study found evidence for both pyroxenite, carbonatite, and carbonated eclogite source lithologies at Fogo. A correlation between La/Sm and δ60Ni was also found, indicating a control on the δ60Ni by source pyroxenite. This study suggests a carbonated eclogite origin for the lithologies present at Fogo, which would have hosted the majority of the olivine phenocrysts. The phenocrysts then resided within a separated carbonatite melt fraction that either contaminated or metasomatized a pyroxenite melt where the clinopyroxene phenocrysts nucleated. The melt then evolved to an alkali basalt melt through melt-rock reactions, principally via the dissolution of orthopyroxenes and concomitant precipitation of clinopyroxene and olivine (Zhang, Chen, Jackson & Hofmann 2017).

The work for this thesis was conducted on the basement lithologies of the Limpopo Province in South Africa. An investigation into the correlation between structural geology and the flow/occurrence of groundwater was conducted on these lithologies. Field measurements of geological structures were recorded and compared graphically and statistically to existing groundwater borehole data. Data analysis revealed that the structural geology in the basement lithologies of the Limpopo Province of South-Africa does not have a clearly identifiable influence in terms of spatial patterns in groundwater flow and occurrence at a regional scale. Groundwater targets created through weathering rather than tectonics were evidently more easily recognized. Structural controls on groundwater in the granitic aquifers from this specific area are not totally negligible, although it is believed that such influences will be better identified through intensive local scale investigations. As drilling for groundwater is an expensive practice, the knowledge gained through this study and the possibility of a correlation between groundwater flow/occurrence compared to structural geology might improve the odds of finding groundwater for the communities and farmers in the area. / Dissertation (MSc)--University of Pretoria, 2009. / Geology / unrestricted

Southern Star Valley is a structural and physiographic basin bounded on the east by the southern Star Valley fault, an active normal fault associated with Basin and Range extension. The southern Star Valley fault separates southern Star Valley from the Salt River Range and forms a dramatic north-south trending topographic escarpment. Statistical analysis of relative-age dating (RD) parameters taken from glacial deposits in the Salt River Range defined distinctive age groups for the deposits, and comparison of RD data allowed correlations with late Pleistocene and Holocene glacial deposits elsewhere in the Rocky Mountains. However, the sedimentary lithologies in the glacial deposits in the study area and inherent variability of RD data limited definitive regional correlations. The southern Star Valley fault (SSVF) lies in a parabola-shaped zone of large, seismogenic normal faults. The zone trails to the west of the eastward-migrating Yellowstone hot spot. Basin-facing fault scarps up to 11 meters high created by recurrent late Quaternary faulting along the southern Star Valley fault are preserved in late-Pleistocene and Holocene alluvial fans along the Salt River Range front. Radiocarbon ages from faulted deposits exposed in a trench provide age estimates of ca. 8,090 ± 80 and 5,540 ± 70 yrs. B. P. for the two most recent paleoearthquakes. The magnitudes of the paleoearthquakes, based on surface rupture height and length and estimates, were between Ms6.9 and Ms7.1. The tectonic geomorphology of river alluvium and alluvial fans near the SSVF suggests that recurrent faulting has downdropped the northern end of southern Star Valley more in relationship to the southern part of the valley and created a deep depocenter in the northern part.

The delimitation of the very fines lithologies from seismic data is a crucial problem in geophysics, indeed the presence of the noise in seismic traces can deteriorate information and hide important hydrocarbons accumulations. For that we have to try in this paper to use a recent technique developed by A.Arneodo and his collaborators which is the wavelet transform modulus maxima lines (WTMM) combined with the discrete wavelet transform (DWT), to denoising traces and characterize each amplitude in the seismic trace by an exponent of Holder. In order to separate information that is of a significant geological lithology variation with the various noises. Our application at VSP data shows that this technique is a powerful tool of processing.

Carbonate preservation in the oceans occurs at a depth called the carbonate compensation depth (CCD). The CCD is where the input rate of carbonate from the surface of the ocean is balanced by the dissolution rate. Factors controlling the CCD are the CO2 in the atmosphere, weathering, and productivity in the surface water, the depth of the lysocline and deep water currents (and their ocean circulation). Two previous studies have investigated the variation of the CCD through geologic time, one in the equatorial Pacific (Pälike et al., 2012) and the other compiled results from the Pacific, Atlantic and Indian Oceans (Van Andel, 1975). The project consisted of compiling a database of sediment lithologies for many more sites in the Atlantic since the compilation by Van Andel, 1975, and together with a subsidence model of the ocean crust the systematic variations of CCD could be investigated. The results show that the CCD varies both spatially and temporally in accordance with previous studies. The reconstruction of the CCD needs further analysis, and possibly data from the oldest drilling program, the Deep Sea Drilling Project (DSDP). One result that is very important is that this study includes a total of 91 sites in the Atlantic Ocean, far more than in any of the other two studies. Future work can build upon the already started database of sediment lithologies.

MESMEG / Department of Mining and Environmental Geology / Many recent studies have shown that some of the greatest water needs occur in areas underlain by crystalline rocks with complex hydrogeology. Crystalline basement rocks underlie over 60% of the South African surface, and the Limpopo Province of South Africa is no exception. Previous attempts to develop the lithologies of Limpopo for groundwater abstraction without the use of sound scientific methodologies resulted in low yielding boreholes and a higher rate of borehole failure. The complexity of the lithologies in the region necessitates the use of sound scientific methodologies for the delineation of promising groundwater potential zones. Therefore, the principal objective of the present study was to delineate groundwater potential zones through an integrated approach of remote sensing, geophysics, as well as the use of ancillary datasets. The area of focus is located in the northeastern section of Limpopo province, covering an area of about 16 800km2. Geologically, it is underlain by three Lithostratigraphic domains comprised of Archean-aged basement rocks, Soutpansberg volcano-sedimentary succession and subsidiary basins of the main Karoo young sedimentary cover. In general, the groundwater potential of a region is a function of factors such as lithology, lineaments, slope, climate and land use/ land cover. Thus, the present study used parameters such as lineaments, lithologies, slope, and land use/ land cover to produce a groundwater potential zone map. The thematic layers were prepared from raw datasets, which include; LANDSAT 8 OLI, ASTER-DEM, aeromagnetic data, geological maps, and land use/land cover data, which were overlaid in a GIS environment. The resultant groundwater map revealed the presence of five distinct classes of groundwater potential zones, which were categorised into excellent, good, moderate, low and very low. Interpretation of the results shows that the study area is dominated by areas that may be regarded as moderate water potential zones, covering about 52% of the total area. On the other hand, low and good groundwater potential zones occur in almost equal proportions of 19.52 % and 24 % respectively. The results obtained were validated using GRIP borehole dataset, and a number of follow-up geophysical surveys. iii Overlaying of the boreholes dataset on the map showed positive correlation between borehole yields groundwater potential zones. On the other hand, follow-up Vertical Electrical Sounding surveys revealed the presence of conductive layers in some selected target areas. The groundwater potential zone map and validation results provided a meaningful regional assessment of groundwater distribution in the study area. Thus, the results of this study can be used as a guideline for future groundwater exploration projects. / NRF