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Quaternary volcanism of the Rockeskyll Complex, West Eifel, Germany and the carbonatite-nephelinite-phonolite associationRiley, Teal Richard January 1994 (has links)
No description available.
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Volcanisme alcalin associé à l'initiation de la rupture continentale : Rift Est Africain, Tanzanie, bassin de Manyara / Alkaline volcanism associated with early stage of rifting : East African Rift, Tanzania, Manyara basinBaudouin, Céline 25 November 2016 (has links)
Le rift Est africain (REA) est une frontière de plaque en extension. Ce rift présente plusieurs stades d’extension, de l’initiation du rift en Tanzanie jusqu’à l’accrétion océanique en Afar. Le bassin de Manyara se situe le plus au sud de branche Est du REA. Il est caractérisé par la présence de volcanisme récent (< 1,5 Ma) et d’un essaim sismique dans la croûte inférieure (20 – 40 km). De par sa localisation et son contexte tectonique, le bassin de Manyara offre l’opportunité d’étudier le stade le plus précoce de l’initiation du rift. Le bassin de Manyara est composé de plusieurs types de laves hyperalcalines, les néphélinites magnésiennes (Mg# > 55) (Labait, Kwaraha), de calciocarbonatite (Kwaraha) et des néphélinites différenciées (Mg# < 35) (Hanang).Les néphélinites magnésiennes (Labait et Kwaraha) sont des laves primaires composées d’olivines et de clinopyroxènes (cpx). La modélisation géochimique des éléments en trace suggère que ces magmas primaires résultent d'un degré de fusion partielle ≤ 1 % à partir d'une péridotite à grenat et phlogopite. Ces magmas proviennent d’une profondeur > 120 km (présence de xénolites avec des conditions d’équilibre > 4 GPa). Les minéraux ont cristallisés à partir d’un magma pauvre en eau (0,1 et 0,5 pds % H2O). La calciocarbonatite et les néphélinites différenciés sont issues des néphélinites magnésiennes par cristallisation fractionnée et processus d’immiscibilité. Les néphélinites du Hanang sont riches en éléments alcalins (9,5 – 12,1 pds % Na2O+K2O) et en silice (44,2 – 46,7 pds% SiO2) et sont composés de cpx, grenat, néphéline, titanite et apatite. La zonation complexe dans les cpx (par exemple, changement brusque de Mg#, Nb/Ta, et H2O) implique une différenciation magmatique en système ouvert avec immiscibilité de liquide carbonaté et silicaté ainsi qu’un remplissage de la chambre magmatique avec des liquides primaires. La faible teneur en eau des cpx (3 – 25 ppm H2O) indique la présence d’un magma pauvre en eau (0,3 pds % H2O) lors de la cristallisation des cpx à des conditions crustales (340 – 640 MPa et 1050 – 1100 °C). L’étude des inclusions vitreuses dans les néphélines de Hanang permet de contraindre l'évolution magmatique tardive des néphélinites et le comportement des éléments volatils (CO2, H2O, S, F, Cl) lors du stockage et de la remontée du magma. Les inclusions vitreuses sont composées d’un verre trachytique, d’une phase carbonatée et d’une bulle de rétraction. Le verre trachytique contient du CO2 (0,43 pds % CO2, analyses SIMS), du soufre (0,21 à 0,92 pds% S), du chlore (0,28 – 0,84 pds % Cl) et très peu d’H2O (< 0,1 pds % H2O, analyses Raman). Le processus d’immiscibilité conduisant à la formation du carbonate se produit dans un système fermé pendant l'ascension rapide du magma, entre 200 – 500 MPa. La phase carbonatée est un carbonate anhydre et riche en Ca-Na-K-S (33 pds % CaO, 20 pds % Na2O, 3 pds % K2O, et 3 pds % S). Le liquide pré-immiscible a une composition phonolitique avec 6 ± 1,5 pds % CO2 à une pression de 700 MPa. Une étude préliminaire des inclusions par spectroscopie XANES et des roches par spectroscopie Mössbauer a permis de déterminer que les laves de Manyara se sont formées à conditions oxydantes (~ ∆FMQ +1,5).À l’initiation du rift, le volcanisme dans le bassin de Manyara est caractérisé par des magmas riches en CO2 et pauvres en H2O issus d’au moins 120 km de profondeur sous l'escarpement du rift. La présence de ces magmas riches en CO2 et la faible quantité de roches volcaniques émises à la surface peuvent indiquer que le piégeage et la percolation de ces magmas en profondeur est un déclencheur potentiel des essaims sismiques profonds. / East African Rift (EAR) is the divergent plate boundary. EAR exposes different stages of extension, from early stage rifting in Tanzania to oceanic accretion in Afar (Ethiopia). Manyara basin is the southernmost rift system of the east branch of EAR with recent volcanism (< 1.5 Ma) and a seismic swarm in the lower crust (20 – 40 km). Due to its location and tectonic setting, the Manyara basin offers the opportunity to study the earliest stage of rift initiation. Manyara volcanism is composed of several types of hyper-alkaline lavas as Mg-nephelinites (Mg# > 55) (Labait, Kwaraha), calciocarbonatite (Kwaraha) and evolved nephelinites (Mg# < 35) (Hanang).Mg-nephelinites (Labait and Kwaraha) are primary lavas mainly composed of olivine and clinopyroxene (cpx). Geochemical modelling from trace elements suggests that these primary magmas result from a degree of partial melting < 1 % from a CO2-garnet-phlogopite-bearing peridotite. These magmas have an asthenospheric source at depth > 120 km (lava carries xenoliths with equilibrium conditions > 4 GPa). The minerals were crystallized from a magma with a low H2O content (0.1 and 0.5 wt% H2O). The calciocarbonatite and evolved nephelinites are derived from Mg-nephelinites by fractional crystallization and immiscibility processes. Hanang nephelinites are silica- and alkaline-rich lavas (44.2 – 46.7 wt % SiO2, 9.5 –12.1 wt % Na2O+K2O, respectively) composed by cpx, Ti-garnet, nepheline, apatite and titanite. Complex zonation of cpx (e.g. abrupt change of Mg#, Nb/Ta, and H2O) and trace element patterns of nephelinites record magmatic differentiation involving open system with carbonate-silicate immiscibility and primary melt replenishment. The low H2O content of cpx (3 – 25 ppm wt. H2O) indicates that at least 0.3 wt % H2O was present at depth during carbonate-rich nephelinite crystallization at 340 – 640 MPa and 1050 – 1100 °C. The study of hosted-nepheline melt inclusions from Hanang allows constraining the late magmatic evolution of nephelinites during storage and magma ascent. Melt inclusions are composed by a silicate trachytic glass, a carbonate phase and a shrinkage bubble. Trachytic glass contains high content in CO2 (0.43 wt %, SIMS analyses), sulfur (0.21 – 0.92 wt % S), chlorine (0.28 –0.84 wt % Cl) and H2O low content (< 0.1 wt %, Raman analyses). Immiscibility process leading to the formation of carbonate occurs in a closed system during rapid magma ascent between 200 – 500 MPa. The carbonate phase is a Ca-Na-K-S-rich and anhydrous carbonate (33 wt % CaO, 20 wt % Na2O, 3 wt % K2O, and 3 wt % S). The pre-immiscible liquid has a phonolitic composition with 6 ± 1.5 wt % CO2 at 700 MPa. A preliminary study of melt inclusions by XANES spectroscopy and whole rocks by Mössbauer spectroscopy was used to determine these Manyara lavas were formed at oxidizing conditions (~ ΔFMQ +1.5).The early stage rifting volcanism (Manyara Basin) is characterized by CO2-rich and H2O-poor magmas from at least 120 km below the rift escarpment. The presence of CO2-rich magmas and the small amount of volcanic rocks erupted at the surface may indicate that the storage and percolation of these magmas at depth is a potential trigger for deep seismic swarms.
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The geology of the Londiani area of the Kenya Rift ValleyJones, William Barry January 1975 (has links)
An area of about 900 square miles (2300 km² ) at the junction of the Kenya and Kavirondo Rift Valleys was studied and a map of it on a scale of 1 : 50,000 is presented. The fonmations present are alkaline lavas and tuffs ranging in age from 12 m.y. b.p. to recent and can be divided into a basanite to phonolite series older than 7 m.y. and a basalt to trachyte series younger than 7 m.y. The fonna.tions are grouped into four assemblages, each .consisting of rocks derived fr.om sources in about the same area. A series of trachytio ash flows about 4m.y. old, the Eldama Ravine Tuff; and two trachyte volcanoes, Londiani of 3 m.y. b.p. and Kilornbe of 2 m.y. b.p., together with their associated syenite bombs are described in detail. The structure of the area is dominated by the Equator and Mau Monoclines which form the western margin of the Kenya Rift Valley. Faults are relatively unimportant but show three distinct trends which can be related to structures in the basement. Chemical analysis was carried out on about 200 rocks, particularly concentrating on the Eldama Ravine Tuff and the Londiani and Kilambe Trachytes. This, with the petrography, showed that the. rocks within the ba.sa·ni te to phonolite series and the basalt to trachyte series are related in general but not in detail by fractional crystallisation. It is also shown that in the trachytic rocks Na, Fe, Y and the Lanthanides are very mobile.
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Flow fabric determination of two Mesoproterozoic midcontinent rift dike swarms, northeastern MinnesotaFein, Elizabeth May 16 January 2009 (has links)
No description available.
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THE OCULUS RIFT’S EFFECTS ON IMMERSION SURROUNDINGMORAL CHOICE : A study of modern VR technology and itseffects on a user’s spatial immersion in avirtual environment / OCULUS RIFTS PÅVERKAN PÅ IMMERSIONEN KRING MORALISKA VAL : En studie kring modern VR-teknologi och desspåverkan på en användares spatiala immersioni en virtuell miljöPereswetoff-Morath, Alexander January 2014 (has links)
This report is about VR and the effects the VR technology Oculus Rift may or may not have on the different kinds of immersion possible in virtual environments, or games. The report is based on the premise that modern games have evolved into more story based adventures with better graphics, often with moral choice as gameplay, and theories regarding new mediums and the dangers of not fully understanding them. It is also done in cooperation with a research team at Högskolan i Skövde, with a focus on moral dilemmas, and is using a virtual environment to test this combined effort. The game engine Unity is used to create a realistic environment and together with the Oculus Rift, is testing what kinds of effects the VR technology has on the users. 20 test participants have shared their experiences and the majority, independent of gaming experience, claims it has a positive effect.
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The geochemistry of fluid processes in the Eastern Branch of the East African Rift SystemDarling, William George January 1996 (has links)
The East African Rift System is the world's major continental rift. While much geophysical and petrological attention has been paid to it, at least in the eastern branch ("Eastern Rift"), comparatively little research has been carried out into the geochemistry of rift fluids, despite the potential benefits to theoretical and practical studies. Hydrothermal activity provides the opportunity to sample a very wide range of waters and gases in the Eastern Rift. This thesis combines data from the literature with the results of the author's major investigation into Eastern Rift fluids carried out chiefly in Kenya, though with subsidiary investigations in Ethiopia and Djibouti. A synthetic approach has been adopted, whereby relationships and interactions are cross-referenced as far as possible to illuminate problems, thus demonstrating the usefulness of considering a wide range of fluids in the rift context. After reviews of physiography, geology, geothermics and hydrology of the Eastern Rift, the following topics are considered in detail: (i) chemical and isotopic evidence for water origin, movement and evolution, (ii) chemical and isotopic evidence for gas origin, movement and evolution, and (iii) fluid geothermometry. Within this context some specific aims have been pursued. The strong possibility of longdistance axial flows of groundwater has been shown by use of stable isotopic techniques. Further insights into alkaline hydrological discharge areas have been obtained by a combination of chemical and isotopic approaches. While carbon isotope ratios indicate an apparently homogeneous source of carbon dioxide, the existence of distinct mantle sources for volcanic rocks beneath different parts of the Eastern Rift has been comprehensively demonstrated by use of helium isotope ratios. Following the rather unsatisfactory performance of various gas geothermometers for evaluating geothermal system temperatures, a new relationship based on hydrocarbon breakdown has been developed. The possible use of oxygen isotopes in hydrothermal sinters as indicators of palaeoconditions has been investigated. In conclusion, topics worthy of further research in the Eastern Rift are suggested where the study of fluids would be of benefit.
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A local earthquake study near Lake Bogoria in the Kenya RiftYoung, Philippa Anne Victoria January 1989 (has links)
A 20 X 30 km2, 15 station, seismic network operated for 3 months in 1985, near Lake Bogoria in the Kenya Rift. The array provided both continuous and triggered seismic data. This thesis is concerned with the local earthquakes which occurred within 30 km of the network, in a 50 X 80 km2 study area including parts of the Rift shoulder and the central trough. 572 small events (ML < 2.7) could be located accurately (+2 km) in 3 dimensions. Unexpectedly, most of the seismic activity is associated with the major faults of the Rift shoulder, rather than the younger, minor faults in the central trough. A linear group of events in the central trough do not correspond to any surface feature, and seem to indicate a buried fault. The depth distribution of the seismicity peaks at 9 km and diminishes below 12 km, and the "brittle-ductile" transition is inferrred to occur within a 12 - 16 km depth range. This distribution is similar to those in other young intracontinental regions, suggesting a normal crustal rheology. Only a few events provided well-constrained focal mechanisms. Normal, steeply dipping, N-S striking fault plane solutions could be fitted to almost all events in the central trough. 12 of the best solutions were used to determine the stress orientation, the results indicated near-horizontal E-W extension, but this direction was poorly constrained. Suitable seismograms displayed shear wave polarisation and splitting compatible with the predictions of Extensive Dilatancy Anisotropy (EDA) theory. Instrinsic anisotropy, due to the basement fabric, is probably present, but the EDA should dominate the observations, thus allowing a determination of present-day stress orientation. Suprisingly, two dominent polarisation directions were seen in different parts of the array, indicating a change from E-W to NW-SE "tension" within the network.
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Rift Valley fever development of diagnostics and vaccines /Näslund, Jonas, January 2010 (has links)
Diss. (sammanfattning) Umeå : Umeå universitet, 2010. / Härtill 4 uppsatser.
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Carbonate sedimentation and extensional tectonics in the Maltese graben systemsDart, Christopher James January 1991 (has links)
No description available.
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Integrated tectonics and sedimentation in extensional basinsOliveira, Luis Otavio Aguiar January 2000 (has links)
No description available.
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