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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Polyorogenic evolution of the western Pays de Leon, Finistere, France

Roper, H. January 1980 (has links)
A completely new 11thological classification is made of the Lannilis Metamorphic Complex and the Plouguerneau Mi~atites, which lie south and North respectively of the Porspoder Lineament in the north-west Pays de Leon. The sequence of metamorphic, magmatic and tectonic episodes is analysed and a correlation between the two complexes is suggested. The metasedimentary Iithologies are thought to be derived from Brioverian semi-peli tes, and the meta-igneous rocks from post-Brioverian intrusions. The later granitic rocks associated with the Plouguerneau Migmatites are described and classified in detail for the first time. The structures which define the Porspoder Lineament itself are also described. This feature may have originally been an intra-continental fault of transform type. Existing geochronological data and new K-Ar mineral dates are used to fit the geological evidence from the NW Pays de Leon to the absolute time scale. The importance of the Hercynian orogeny is emphasised; the main metamorphism and migmatisation are attributed to the Bretonic (Devono-Carboniferous) phase. A study has also been made of the Le Conquet Metamorphic Complex in the SW Pays de Leon. An entirely new interpretation of the field relations and geochronology of the lithologies previously known as 'Gneiss de Brest', 'Gneiss de Lesneven', and 'Granodiorite des Renards' is presented. A single major intrusion, the Granodiorite de Brest, is recognised. It was emplaced into the already deformed and metamorphosed Briverian during the latter stage~ stages of the late-Precambrian/Cambrian Cadomian orogeny, probably at about 550 my. Other intrusions (Granodiorite de Pont-Cabioc ~ and doleritic Filons de Kermorvan) were also emplced prior to the main regional metamarphism (the Bretonic phase of the Hercynian orogeny) which produce~taurolite- and sillimanite-bearing assemblages in the associated (originally Br1over1an) metasediments. This sequence of events, and later phases of folding and granite emplacement, are tentatively correlated with events in the NW Pays de Leon and in the supracrustal terrain of central Finistere. A special study has also been made of the Bretonic regional metamorphism of the whole of the western Pays de Leon. Observed assemblages suggest a geothermal gradient intermediate between the Barrovian and Abukuma types. Attention is drawn to the long and complex history (Lower Proterozoic or Pentevrian, Cadomian and Hercynian) represented by the rocks of the western Pays de Leon.

The geology of the Ribkwo area, Baringo district, Kenya

McClenaghan, Marcus Patrick January 1971 (has links)
The Ribkwo area is divided into two contrasting east and west parts by the Kito Pass fault system, This has upfaulted the area to the west of the Chepanda Hills and Sigatgat Hill exposing 6,000 to 7,000 feet of phonolite and tuffaceous sediments with subordinate basaltic lavas (the Tugen Hills Group of Miocene to middle Pliocene age) resting on metamorphic basemento The phonolites in the Chepanda Hills form the flanks of a large dominantly phonolite volcano with its centre in the Sigatgat Hill area. The Barpelo Basalts followed the Tugen Hills Group and were erupted from several minor centres in the area to the east of the Kito Pass fault system c 1 came after its first major movement in the middle Pliocene. Flood trachytes followed the basalts and occur on both sides of the fault system in tho south of the area. They are overlain by fossiliferous sediments of upper Pliocene age which were deposited in a tectonic basin to the east of the Chepanda Hills, Further movements on the Kito Pass fault system preceded the build up of Ribkwo, a large dome shaped upper Pliocene volcano of phonolitic trachyte, which covers most of the eastern part of the area. Its south-eastern flank is overlain by thin formations of basalt, mugearite, and tuff which range from upper Pliocene to Pleistocene age. A tectonic history, consisting of major and minor faulting episodes, is described and is broadly similar to other areas in the northern part of the Rift Valley. The faulting is entirely of the normal type and is consistent with tensional tectonics. The petrography of the lavas is described and their chemistry and mode of evolution is discussed.

The strucuture and metamorphism of the Carn Chuinneag area, Ross-shire

Shephered, J. January 1971 (has links)
No description available.

The northern boundary of the Ikertoq shear belt, west Greenland

Grocott, John January 1977 (has links)
No description available.

The geology of the Bovey basin

Edwards, R. A. January 1971 (has links)
No description available.

Palaeomagnetic studies on rock formations in the High Atlas and Anti-Atlas regions of Morocco

Hailwood, E. A. January 1972 (has links)
The first part of this thesis (Chapters I to 8) describes the results of palaeomagnetic studies on samples collected from the High- Atlas and Anti-Atlas regions of Morocco. New palaeomagnetic pole positions are described from formations of Late Precambrian, Lower Cambrian, Devonian, Triassic, Jurassic and Cretaceous ages. The new Moroccan Late Precambrian and Lower Cambrian poles are shownto be more consistent with reliable Lower Palaeozoic poles of the same age from North America than ones from Southeast Africa, when the two continents are plotted on a Bullard-type reconstruction. It is concluded that a small part of Northwest Africa, including Morocco, may originally have been attached to North America, and that the rest of Africa was widely separated from North America at that time. Collision between Africa and Eastern North America probably occurred during the Carboniferous period, resulting in the formation of the Hercynian fold-belts along the present-day North Atlantic margins of the two continents and the welding of extreme Northwest Africa to the rest of the continent. Subsequent separation probably took place along a slightly different line, so that Morocco was left attached to Africa. Radiometric dating results from Moroccan igneous intrusions paralleling the local coastline yielded a mean age of 183 my, i. e. Lower Juraszic. other evidence suggests that the Mesozoic rifting between North America and Northwest Africa began at this time, and it is considered likely that the intrusion of the Moroccan Lower Jurassic igneous bodies was directly related to this event. Palaeomagnetic results from the Moroccan Cretaceous sediments indicate a gradual widening of the North Atlantic Ocean during the course of the Mesozoic. There are no significant differences between mean Triassic, Jurassic and Cretaceous poles from Morocco, and corresponding poles from South-east and Central Africa, and it is concluded that no significant post-Triassic relative tectonic movement has occurrcd between North-west and South-east Africa. The second part of the thesis (Chapters 9 and 10) describes an attempt at the AF demagnetisation of sediments by means of alternating fields of strangths up to 5000 Oe. Experiments were performed to investigate the effects of small asymmetries (up to 5%) in waveform of the applied alternating field, and it was shown that asymmetrics present in 'the natural AC mains supply at the Close House Laboratory at certain times, of the day are sufficiently high to produce appreciable AMM's in rock samples, if no sample rotation system is used during the demao-natisation process

Interpretation of Project MAGNET data (1959 to 1966) for Africa and the Mozambique Channel (Part I) ; Seismic ray tracing with applications to Africa (Part II)

Green, Alan G. January 1973 (has links)
Part I: This part of the thesis is concerned with the interpretation of Project MAGNET profiles over the African continent and Mozambique Channel. The paths of the continental profiles lie between latitudes 5°N. and 22°S., while the paths of the profiles which cross the Mozambique Channel lie between latitudes 0° and 35°S. (figure (1)). The geology and geochronology of 'equatorial' Africa are described briefly in chapter (1). In chapter (2) a new method of magnetic profile analysis is introduced and applied to a number of simulated profiles. This method forms the basis of the interpretation of the continental Project MAGNET profiles (chapter (4)). In chapter (3) the various details of the reduction of the Project MAGNET data (e.g. the interpolation of the data, removal of the regional magnetic field, removal of the diurnal magnetic field) are described. The continental Project MAGNET data are interpreted in chapter (4) while the 'oceanic' data are interpreted in chapter (5). Part II: Until recently most seismological data have been explained in terms of spherically symmetric Earth models. Improved recording techniques (e.g. seismic arrays) and the increased number of recording stations have resulted in the discovery of large lateral variations of the seismic velocity in the crust and mantle which are closely correlated with major tectonic features (e.g. ocean ridges and trenches). It has therefore become increasingly necessary to consider laterally. heterogeneous Earth models when inverting seismological data. This part of the thesis is concerned with the development and application of some computer programs to trace seismic rays through laterally heterogeneous velocity media. In the first chapter the basic principles of seismic wave theory and the ray approximation are outlined. This will include: (i) A derivation of the ray path equations for a seismic ray travelling through structures in which the velocity is a function of three dimensions and two dimensions respectively. The velocity structures may be continuously varying and/or defined in discrete units bounded by velocity discontinuities. (ii) A derivation of the equations describing the geometrical spreading effect in velocity structures which are a function of two coordinates. The equations which represent the energy partitioning of a seismic ray at a finite velocity boundary (Zoeppritz's equations) are stated. (iiI) The method of interpolation of the velocity data and the integration procedure. (iv) A brief description of the computer programs. In chapter (2) the two dimensional computer program (i.e. the computer program which traces seismic rays through velocity structures which are a function of two dimensions) is applied to some 'standard' Earth models and in the final chapter this program is used (a) to derive a spherically symmetric velocity depth model from body wave data, which represents the average velocity beneath east and southern Africa, and (b) to test some models of the East African Rift obtained from interpretations of gravity data.

Aspects of the palaeoecology of large predators, including man, during the British Upper Pleistocene, with particular emphisis on predator-prey relationships

Turner, Alan January 1981 (has links)
This thesis discusses aspects of the palaeoecology of large predators, including man, during the Upper Pleistocene in Britain, with particular emphasis on predator-prey relationships. Upper Pleistocene is here taken as the Ipswichian (last) interglacial and the Devensian (last) glaciation. In addition to man, the term large predator includes lion, hyaena, wolf, leopard, bear, lynx and wolverine. The primary aim is to predict features of past predator and prey behaviour by integrating the results of modern ethological observations on similar or analogous species with the published evidence of Upper Pleistocene environments deduced from botanical, sedimentological and geomorphological investigations, and thus to extract information on trends in predator ecology and predator-prey relationships between the Ipswichian and Devensian. The study also examines the possibility that interpretations of human activity in Upper Pleistocene Britain have been founded largely on material accumulated by hyaenas, and discusses the value of examining past human behaviour from an ecological perspective in which man is regarded as one predator among many. The predictions of past behaviour are tested on vertebrate remains recovered from Upper Pleistocene deposits and how available in numerous museum collections. Much of the material derives from hyaena-accumulated bone assemblages in caves, and holds a potential wealth of information on the behaviour of this species and its predatory and scavenging activities. It is argued that the broad scope of the enquiry overcomes the shortcomings of this material which result from inadequate standards of recovery, recording and curation. The major conclusions reached in the study are: 1. That man and large mammals were seasonal occupants of Devensian Britain, on the evidence of reindeer antler remains, bear specimens in hyaena-accumulated assemblages and an analysis of tooth wear in horses. 2. That Ipswichian hyaenas found conditions more arduous than their Devensian counterparts, and may have died out at the end of Zone II of the interglacial, on the evidence of hyaena mortalities and the extent of bone consumption in hyaena-accumulated assemblages of the period. 3. That Devensian hyaenas did not tend to kill horses but instead scavenged their remains, most probably from lion kills, in view of the evidence for sexual parity in samples of horse teeth. 4. That much of the vertebrate material associated with Upper Palaeolithic industries and taken to show evidence of human economic activities is indeed the result of hyaena bone-accumulation, on the basis of comparisons with modern hyaena behaviour, and therefore inadmissable. 5. That an integration of present results with those from Europe and other parts of the world suggests that the importance of man as a member of the Pleistocene fauna may have been overemphasised.

Development of geoelectrical techniques for investigation and monitoring of landfills

George, Andrew January 2006 (has links)
A review of geophysical applications to investigation and monitoring of landfills identified that the geoelectrical methods, such as ERT, SP and EM, are ideally suited because much information can be inferred from the electrical characteristics of landfill waste. The review identified scope for further development due to constraints of geophysical surveying along the ground surface. In particular, the ERT method suffers a loss of data accuracy and resolution with increasing depth of investigation. These constraints have provided the main focus for interest during this research project. A field test site was examined on a reconnaissance basis using a multi- method geophysical approach to obtain the best possible sub-surface characterisation and interpretation in the absence of intrusive calibration data. On the basis of results obtained a model was produced showing combined geoelectrical response, which may be used to plan further detailed investigations including conventional intrusive site examination. It is further demonstrated that the effectiveness of ERT in a landfill setting lies with the arrangement of measurement electrodes and application of specialised electrode address configurations. In an active landfill setting, basal electrodes installed within the cell drainage medium prior to waste emplacement were used in conjunction with ground surface electrodes and the address configuration applied across the array pair. Delineation of basal leachate accumulation and differentiation from perched tables within the waste profile was possible. In a closed landfill setting, where restorative capping and leachate extraction was scheduled, a system for ERT monitoring was established by installing vertical electrode arrays during routine drilling and emplacement of gas wells. In this setting, baseline sub surface geoelectrical characteristics were identified against which the effects of landfill capping and leachate extraction were assessed through variance in model resistivities and percentage resistivity change. This research has provided recommendations for geophysical monitoring best practice, which may help site stakeholders to achieve a more effective management of leachate control systems, to assess the effectiveness of restorative strategies, and to demonstrate legislative compliance with a greater degree of certainty.

Propagation and early growth of normal faults

Baudon, Catherine January 2007 (has links)
This research project used 3D seismic data located in the Levant Basin, eastern Mediterranean and in the Espirito Santo Basin, offshore Brazil, in order to investigate the early propagation of small normal faults and develop criteria to reconstruct fault kinematics. Detailed interpretation of the 3D geometry of faults, extensive mapping of the throw distribution and investigation of the ductile deformation in the volume surrounding the fault planes provided new insights into the propagation and early growth of normal faults. The Levant survey was used to investigate a unique array of small blind normal faults that were then compared to neighbouring small growth faults in order to better understand their early growth history. Criteria for the recognition of blind faults were defined. Unrestricted blind faults were compared to those that underwent a subsequent mechanical interaction with a major lithological boundary or another structure. The results show that such restrictions affect the throw distribution on most of the fault plane and is not only limited to the proximal zone of interaction. An analysis of growth faults that have recently made the transition from a blind stage to a syn-sedimentary stage suggests that most of the fault surface area formed during the blind propagation phase. A large proportion of the displacement was added during the syn-sedimentary phase as a result of interaction with the free surface. This led to a change in the position of the point of maximum displacement, as well as a shift of the entire vertical throw distribution. These results suggest that the dimensions of the faults were established early in the growth history and that displacement on and surrounding fault planes was added for a near constant dimension. Crestal extensional faults that grew by blind propagation before reaching the surface were investigated from the Espirito-Santo survey. These faults were reactivated by blind propagation after a significant period of quiescence. A reconstruction of the 3D geometry of the fault network and detailed analysis of the throw distribution provided new insights into the kinematics of reactivation. Two distinct modes of reactivation are recognised: a typical reactivation by upward propagation and a reactivation by dip linkage. These are selective processes and factors controlling preferential reactivation are discussed. All these results have wide implications for fault growth models and are applicable to many petroleum systems.

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