Dissertations / Theses on the topic 'Basement Complex'

1-, 2- and 3-dimensional fracture network characteristics of the mainland Lewisian Gneiss Complex (LGC) have been used assess if the LGC is a suitable onshore analogue for the fracture networks within the offshore Clair basement. Faults that cut the Clair basement rocks are becoming increasingly recognised as important structural conduits that connect (oil & gas bearing) sedimentary packages across the main basement structure. The basement of the Clair field is poorly understood, with limited seismic and well datasets; so using an onshore fracture analogue, of the mainland LGC, will hopefully improve the understanding of the Clair basement fracture systems. To determine the suitability of the mainland LGC as an analogue for the Clair basement four main research questions are asked in this thesis: What is the offshore Clair basement? What are the geological characteristics and attributes of the fracture networks in the mainland LGC? What are the dominant controls on these fracture network characteristics? How can the mainland Lewisian be used as an analogue for the Clair basement? Onshore datasets (outcrop, terrestrial laser scans & NEXTMap® DEM) exhibit prominent NE-SW and/or NW-SE fault and fracture trends. The Clair basement seismic dataset exhibits comparable NE-SW & NW-SE trending faults, but the basement core samples exhibit a strongly aligned NNE-SSW fracture trend that is not so clearly represented in the onshore datasets. Fracture spacing distributions from the mainland LGC have strong power-law relationships over at least three orders of magnitude. Power-law relationships are also present from Clair basement datasets but the lack of large datasets means that these relationships are considered fairly weak. Qualitative and Quantitative onshore and offshore analyses suggest that the mainland LGC is a suitable analogue for the Clair basement to some degree, but that their relationship is not a simple one. The results presented in this thesis do not provide a unique solution for the Clair basement fracture networks. Instead the onshore data provide model types that can be used in sensitivity models to ultimately assess which onshore dataset provides the best geological and statistical analogue for the Clair basement.

Geophysical, hydrochemical and hydrogeological investigations were undenaken to evaluate the groundwater prospects in the study area. The factors which affect/determine the spatial development of ground water in the area was also examined. The results show that the essential conditions for groundwater availability in hard rock terrains are satisfied. The average weathering depth is 34 m, rainfall is high and seasonal and the geological evolutionary sequence included tectonic phases during which suitable geological structures are expected to have been developed. Analysis of borehole drilling records revealed that each borehole encountered at least one water strike. The clay mineral stable in the prevailing physico-chemical conditions is kaolinite, an evidence that weathering sites are being flushed presumably by flowing groundwater. Available results of isotope analysis also show that the stable isotope concentration in the groundwater is similar to that of current meteoric water. It is therefore concluded that the ground water is receiving current recharge. Infact water balance calculations and results of baseflow analysis indicate that this recharge is substantial. The yields of the boreholes varied greatly spatially ranging between 0.7 and 10.9 I/s. This may be low compared with values quoted for sedimentary rock terrains, but in view of the present low level of water supply in the area, it is considered that exploitation of this resource would represent a significant improvement on the present situation. A physical catchment hydrogeological model is presented to explain the observed spatial variation in yields. In this model, a threshold elevation is considered to exist in each catchment. At elevations below this threshold, borehole yield is sustained entirely by fracture flow. At elevations above this threshold, borehole yield is sustained by storage in the weathered rocks. Pumping tests on large diameter wells show that groundwater abstration using these wells would be greatly improved by repeated pumping after every 60 - 80 minutes recovery. An equation is presented for calculating the number of times a well can be repeatedly pumped in an operating day. The drawdown of the boreholes contained a large well loss component. This well loss was incurred during the early stages of pumping when water had to be withdrawn from well storage to supplement the aquifer flow in order to meet the pumping capacity. Field results presented indicated that the drawdown can be minimised by stepping the discharge rather than imposing it all at once at the onset of pumping. Field results indicate that the use of well water levels for mapping the water table may not be valid in weathered hard rocks.

Understanding water balances is essential for sustainable water resource management, especially in semi-arid basement complex areas where there are large demands for water supplies, but the complex hydrogeological conditions limit groundwater development. This research presents an approach for water balance estimation based on the conceptual and computational modelling of six major landscape unit’s which have been classified on the basis of their differing hydrological responses. Detailed conceptual models of the hydrological processes operating in each of the different landscapes in a catchment and the processes that control water movement between the different landscapes are developed based on data analysis, fieldwork and literature. Two computational models (the WaSim soil water balance model and a new water balance model for bare rock) are used to estimate the daily water balance of each of the landscape units taking cognisance of their interconnectivity which includes runoff becoming run-on. Water balance simulations were run for the individual landscapes using input data from the semi-arid Sokoto Basin in Northwest Nigeria, and outputs for representative wet and dry years are used to demonstrate the reliability of model responses. The individual landscapes outputs were subsequently integrated, taking account of their area weighted contributions, to give a catchment-scale water balance which compares favourably with the observed river discharge at Fokku. The catchment water balance results reveal that AET accounts for the largest loss in the catchment at 72 % of the average rainfall for 37 years. This is followed by the groundwater flow to rivers, then runoff to rivers, representing 16% and 11 % of the average rainfall. This research has provided valuable insights into hydrological behaviour of the basement complex system and the effect of landscape variability on the water balance of these areas. The research suggested a rational approach to groundwater resource management in the basement complex areas that takes cognizance of the hydrological behaviour of different landscape units, focussing on areas with deep weathered material within the catchment identified in this research. The research specifically stresses the need to apply methods of water conservation during excess rainfall for future use in the dry season.

Bibliography: leaves 112-120.
Metamorphism observed in the Vredefort structure increases in grade on a regional scale from lower greenschist facies in the outer perimeter of the Potchefstroom syncline, throughupper greenschist and amphibolite grades within rocks of the Witwatersrand Supergroupand Dominion Group in the collar of the Vredefort dome, to granulite grades in the core ofthe dome. In the collar, two metamorphic assemblages have been identified, one representing a peak metamorphic event pre-impact in age and constrained to temperatures >420-620°C at 3.0-4.0 kbar, and a younger retrograde event, constrained to 500-540 ± 15°C, which overprints the latter assemblage and overgrows pseudotachylite in a small number of samples.

The topic of the master thesis is new medico-social facility hospice St. Michaela. The purpose of the object is the maximizing of improvement in the quality of life of dying, severely ill and incurable patients, with the use of palliative care. The construction follows the Complex of Regional Hospital Náchod. Together with as a retirement home Náchod completes a support network of health and social care. The building is designed as a four-building storey and is partially embedded into the sloping terrain. Floors are divided into individual facilities and together constitute a functional unit. In the basement is the technical room, warehouses, garages and kitchen facilities. On the ground floor are then socio-public rooms and facilities. On the second floor is located hedmaster of hospice and accommodation area. The third floor is devoted to the accommodation area. The proposed structure made of brick longitudinal system, supplemented by concrete basement walls. The horizontal structure is made of filigree ceiling panels. Stairs are designed as a precast concrete and steel. Individual roof structures is made from unwalkable, walkable and vegetation compositions. The cladding consists of ventilated facade of glass and wooden panels. Foundations are designed from the lineal foundation.

Depuis la mise en place en 2010, d’une nouvelle tarification française sur le tarif de l’énergie géothermique, l’Alsace est la région de France la plus dynamique quant à la réalisation de forages géothermiques profonds à haute température (>150°C). Ainsi, l’approche géologique, qui a été primordiale pour les forages de Rittershoffen, le sera encore davantage pour les projets à venir compte tenu de la méconnaissance géologique de certaines zones profondes du bassin rhénan. Cette étude propose d’appréhender la compréhension de l’architecture stratigraphique et séquentielle des formations de la couverture sédimentaire rhénane. 15 puits profonds ont été réinterprétés et corrélés à travers l’ensemble du bassin, permettant l’élaboration d’une colonne stratigraphique complète incluant le sommet et la base de chaque formation. Ces réinterprétations ont également mis en lumière le signal caractéristique de la diagraphie gamma-ray (GR) de chacune des formations de la colonne stratigraphique rhénane. De plus, la caractérisation lithostratigraphique du passage entre le socle et la couverture sédimentaire a fait l’objet d’un axe important de recherche
Since the introduction of a new French pricing system for geothermal energy in 2010, Alsace has been the most dynamic region in France for deep geothermal drilling at high temperatures (>150°C). Thus, the geological approach, which has been essential for the Rittershoffen boreholes, will be even more for future projects given the lack of geological knowledge of some deep parts of the URG. This study aims at understanding the stratigraphic and sequential architecture of the formations of the URG sedimentary cover. 15 deep wells were reinterpreted and correlated throughout the basin, allowing the development of a complete stratigraphic column including the top and base of each formation. These reinterpretations also highlighted the characteristic gamma-ray signal (GR) of each of the formations in the URG stratigraphic column. In addition, the lithostratigraphic characterization of the transition between the basement and the sedimentary cover was the subject of an important research focus

Le massif de Combeynot, sur la bordure nord-orientale du massif du Haut-Dauphiné (massifs cristallins externes, Alpes Françaises) est constitué de deux unités fondamentales (1) un socle, déformé et métamorphisé, représenté par un ensemble migmatitique et un orthogneiss oeillé ; ce socle se rattache aux formations du noyau du massif du Haut-Dauphiné, (2) un complexe annulaire subvolcanique, intrusif dans le socle, composé de formations volcaniques et volcano-détritiques, d'un réseau filonien microgranitique et rhyolitique très dense, de deux unités granitiques disposées de manière concentrique et de filons doléritiques tardifs terminant l'épisode magmatique. Une étude comparative sur la pétrographie, la structure, la typologie des zircons et la géochimie des éléments majeurs, en traces (Y, Nb, Zr, Rb, Sr, U, Th, Hf, Sc, Cs et Ta) et Terres Rares du complexe de Combeynot ont permis de retracer l'histoire magmatique de la série et de tester sa signification géodynamique. Le magmatisme de Combeynot est de nature alcaline intraplaque et traduit un environnement géotectonique de distension. Il trouve son origine dans le manteau à partir duquel plusieurs magmas subcontemporains s'individualisent par des taux de fusion partielle différents et conduisent aux unités acides par cristallisation fractionnée. Leur mise en place superficielle dans une zone orogénique encore non consolidée, riche en fluides et la participation des phases fluides juvéniles et/ou des eaux météoriques conditionnent la nature pétrographique acide, sursaturée et subsolvus des unités granitiques du complexe ainsi que les processus d'altération hydrothermale post- et tardi- magmatiques.

Geologically complex crystalline aquifers are distributed extensively in Africa and also underlie large parts of the semi-arid Limpopo Province where some of the greatest groundwater needs in South Africa occur. The importance of these basement aquifers makes it vital to identify high yielding hydrogeological zones that can be targeted for water supply, to sustain areas of high population density with few or no alternative water sources. The biggest challenge is to understand the factors that determine the secondary permeability of these weathered-fractured rock aquifers. The focus of this study was therefore to systematically analyse regional factors that may influence borehole yields and aquifer transmissivities. The study covered four distinct geological and morpho-structural domains within the Limpopo Province, covering about 23 500 km2. The borehole dataset compiled for the study consisted of over 8 000 boreholes contained in the Groundwater Resources Information Project (GRIP) Limpopo database of the South African Department of Water Affairs. Approximately 3 000 of these boreholes have been hydraulically tested and the lithology has been recorded in 1 200 cases. A commonly encountered problem of pumping tests analysis in crystalline aquifers is in choosing an appropriate model that best fits the observed drawdown response. In this thesis modern methods are proposed for the analysis of pumping test data in weathered-fractured rock aquifers and highlight the importance of diagnostic plots, especially derivatives, for the detection of flow regimes and the choice of the correct ‘theoretical’ model. Based on the classification no single analytical method can be universally applied to crystalline basement aquifers when considering the analysis of pumping test data. The GRIP borehole dataset was analysed in conjunction with spatial information to identify the relationship of regional factors such as - geology, hydrology, weathering thickness, topography, geomorphology, neo-tectonic stresses, and structural lineaments - on groundwater occurrence. Geology has a clear influence, with boreholes exploiting alluvial aquifers composed of highly permeable material, and certain rock types such as pegmatite, showing generally higher borehole productivities. Favourable borehole locations from a topographical point of view are predictably along rivers and valleys. Other identified favourable groundwater targets are the metamorphic aureoles of younger granite intrusions. Despite the local importance of the regolith as a recharge and storage mechanism for the underlying fractured bedrock, no correlation between borehole yields and depth of weathering was found. The pattern of lineament and dyke orientations in the different morpho-structural domains led to a more complex conceptual model of groundwater occurrence. This model is inconsistent with the predicted regime based on regional stress field data and suggests that local variations have a strong influence on groundwater occurrence. Due to the complex geological history of the area, it is difficult to link open discontinuities to a distinct recent or past tectonic event. It can be concluded that regional stress field data, as in this case, may not account for local, possibly highly significant, stress field variations. The hydrogeological importance of several factors on groundwater occurrence presented in this study can be used as a working reference for future groundwater development programmes.
Thesis (PhD)--University of Pretoria, 2011.
Geology
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