The Seiland Igneous Province, of which 5400 km2 is exposed, is hosted within a discrete terrane within the northernmost part of the Caledonian orogenic belt. The Province consists of numerous mafic and ultramafic plutons emplaced into a sedimentary succession indicative of a continental setting. Accompanying this mafic magmatism is a significant volume of intermediate monzonitic and dioritic rock (10% of the total exposed igneous rock), as well as numerous nepheline syenite and carbonatitic intrusions. This study reports ID-TIMS U-Pb analyses on magmatic zircons from a range of intrusions, which indicate that the bulk of the Seiland magmatism took place between 560 Ma and 570 Ma, whereas previous studies had produced a range of ages between 420 Ma and 830 Ma. The data indicate that only one magmatic episode is represented in the rocks of the Seiland Igneous Province, invalidating previous models involving multiple rifting events over a period of 300 m.y. Detailed geochemical investigation of several plutons from an evolved high alkali suite of gabbroic intrusions in the Seiland Igneous Province has shown that these plutons are generally enriched in trace elements compared to layered intrusions from other areas across the globe, but that geochemically the gabbros are relatively homogenous. The rocks yield εHf and εNd values for the gabbroic rocks ranging from +8 to -6 and from +4 to -4, respectively, indicative of the contamination of mantlederived material with crustal material. The most primitive isotopic values are similar to those obtained from the carbonatites and nepheline syenites, indicating the same mantle source gave rise to the magmas that were subsequently emplaced as the Seiland Igneous Province. The homogeneous trace element content of the different mafic rocks most likely indicates a relatively homogeneous mantle source for the original magmas of the province, which has subsequently been affected by processes of assimilation and crustal contamination. The monzonitic and dioritic bodies in the Seiland Igneous Province are not derived from melted silicic crustal material and may have been formed by the melting of pre-existing mafic material. The new geochronology invalidates the metamorphic framework previously proposed for the Seiland Igneous Province, which postulated several orogenic events between the emplacement of the magmas and the Caledonian Orogeny. There is no evidence for metamorphic activity in the period between 570 Ma and 420 Ma, and there are monazites in gneissic rocks hosted within mafic rocks of Seiland age that preserve an age of 640 Ma. This leads to the conclusion that only one metamorphic event, the 420 Ma Caledonian Orogeny caused by the collision of Baltica and Laurentia, affected the Seiland terrane after the emplacement of the Seiland magmas. The new data obtained lead to a model for the evolution of the Seiland Province in which a number of heavily modified and contaminated mantle-derived mafic magmas derived from the mantle were emplaced into the continental crust of the Seiland nappe between 560 and 570 Ma. This magmatism was accompanied by the injection of alkaline magmas into the same area of the crust, and the melting of mafic rock emplaced earlier. This magmatic event is considered to have occurred in an extensional stress regime, possibly during intracontinental rifting or back-arc spreading. This event took place well before the 420 Ma Caledonian Orogeny, and thus the Seiland Igneous Province can be considered a remnant of an older geological terrane that was emplaced onto the margin of Baltica during the Caledonian Orogeny.

We analyzed detrital zircons in Lower-Middle Pennsylvanian strata collected from seven sandstones in the Forest City Basin and seven sandstones in the Illinois Basin. In these basins, Lower-Middle Pennsylvanian strata unconformably overlie Mississippian and Devonian strata and reflect a renewed influx of detritus after a significant depositional hiatus. In the total combined dataset (n=3,106), U-Pb ages of approximately 66% of zircons match ages interpreted to be derived from the Appalachian region, including Grenville (1.3-1.0 Ga), Pan-African (530-620 Ma and 750 Ma), Taconic (440-490 Ma), Acadian (350-420 Ma), and Alleghenian (330-270 Ma) ages. Subordinate populations of grains consist of Granite-Rhyolite (1300 -1500 Ma), Yavapai and Mazatzal Terrane (1600- 1800 Ma), Penokean and Trans-Hudson orogens (1800-1900 Ma), and Superior Province (>2.0 Ga) ages. Proportions of grains matching Appalachian sources increased in the Illinois Basin from ~46% to ~79% between our stratigraphically lowest and highest samples, respectively. The Forest City Basin exhibited a similar upsection increase in Appalachian derived grains, which increased from ~52% in our stratigraphically lowest sample to ~70% in our stratigraphically highest sample. Proportions of grains from northern sources (the Canadian Shield and Penokean Province) diminished upsection as these source areas and recycled sediments containing associated grains become covered with Appalachian-derived sediments. Overall, these shifts are interpreted to reflect an increased flux of Alleghenian erosional detritus across the Laurentian craton as a result of the overfilling of the Appalachian foreland region. These results supplement our understanding of the stratigraphic and provenance records left by fluvially dominated large-scale sedimentation events that occur during the formation of supercontinents.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

The generation of electricity in light water nuclear power plants uses zirconium alloys as the primary containment and cladding of the nuclear fuel. The environmental impacts of the production of zirconium alloys have been analyzed form a lifecycle perspective. From the mining of the zirconium-bearing mineral zircon to the finished zirconium alloy tube. A qualitative study indentifying the production processes and their potential environmental impacts have been performed. A quantitative study to perform a lifecycle analysis of the zircon mining and mineral separation was carried out. The life cycle analysis for the zircon mining was compared to the current lifecycle analysis (LCA) in Vattenfall's Forsmark nuclear power plant environmental product declaration (EPD). The results showed that the additional impact on Forsmark's EPD, when including the mining of zircon, is below 0.1% of the current levels for all parameters analyzed. A lifecycle analysis for the production of zirconium metal and zirconium alloy tube could not be performed due to lack of data from the zirconium metal industry. The major direct emissions from the zircon mining industry are related to the use of fossile fuels in machinery. The major direct emissions from the zirconium metal manufactoring industry are related to the use of acids.

Thèse doctorat : Génie des Matériaux : Villeurbanne, INSA : 1997. / Titre provenant de l'écran-titre. Bibliogr. p. 144-151.

The Tibetan plateau is arguably the most important geological feature on Earth, yet its formation and evolution are poorly understood. This investigation utilizes Cretaceous sedimentary strata exposed in the Lhasa terrane of southern Tibet in order to constrain the paleogeography and tectonic setting of the region prior to the Indo-Asian collision. Lower Cretaceous strata consist of clastic sedimentary units that were deposited in shallow marine and fluvial environments. In northern Lhasa these sediments were deposited in a peripheral foreland basin that formed in response to the Lhasa-Qiangtang collision. The lower Cretaceous sediments in southern Lhasa are quartzose and were derived from cover strata exposed by local uplifts. A marine limestone of Aptian-Albian age overlies the lower Cretaceous clastic strata and was deposited in a shallow continental seaway. The paleogeography of the Lhasa terrane during deposition of the carbonate units was dominated by the effects of the Lhasa-Qiangtang collision, although other conditions, such as a high eustatic sea-level, influenced sedimentation as well. The Upper Cretaceous Takena Formation is composed of a basal member of marine limestone and an overlying member of fluvial red beds. The arkosic strata of the Takena Formation were deposited in a retro-arc foreland basin that formed to the north of the Gangdese magmatic arc. Collectively, the Cretaceous sedimentary strata indicate significant tectonic activity occurred in southern Tibet prior to the Indo-Asian collision. Moreover, the data suggest the crust of southern Tibet was thickened and possibly at high elevations before the Cenozoic.

Thesis (M.S.)--Ohio University, August, 2008. / Title from PDF t.p. Includes bibliographical references.

Thesis (M.S. in Earth and Environmental Sciences)--Vanderbilt University, May 2006. / Title from title screen. Includes bibliographical references.

Orientadores: Julio Cesar Hadler Neto, Peter Christian Hackspacher / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T05:57:37Z (GMT). No. of bitstreams: 1 Palissari_Rosane_D.pdf: 15939989 bytes, checksum: f455fc1254ec2dd67bb39d1df46cce88 (MD5) Previous issue date: 2007 / Resumo: O Método dos Traços de Fissão (MTF)é uma das técnicas mais poderosas usadas para descrever as histórias térmicas de rochas presentes na camada da superfície terrestre,sob condições de baixa temperatura.Se a rocha hospedeira teve a temperatura elevada em um dado período,os traços de fissão que se formaram desde então,são encurtados irreversivelmente ou apagados (os traços sofrem annealing ),como conseqüência de um processo de difusão termicamente ativada. Os minerais mais comumente utilizados no MTF são a apatita e o zircão,sendo este último o objetivo deste trabalho.O zircão é sensível ao annealing térmico sob temperaturas mais altas que a temperatura de fechamento da apatita,que é aproximadamente 120 o C . As características do annealing dos traços de fissão em zircão têm sido obtidas utilizando-se dados de experimentos de laboratório,que são executados em tempos menores que 1 ano,e comumente em tempos ainda menores.Estes dados são usados para calibrar modelos de annealing empíricos,que descrevem a dependência do encurtamento dos traços com o tempo e a temperatura.No entanto,um problema de ordem prática é a incerteza introduzida na extrapolação para tempos geológicos (10 6 ¿ 10 8 anos),através dos modelos calibrados pelos dados de laboratório (<1 ano). Um dos objetivos deste estudo é fornecer condições de contorno adicionais para a faixa de tempo-temperatura da zona de annealing do zircão,através de dados de zircões de poços, cujas amostras foram expostas a temperaturas estáveis por ~1 milhão de anos.Desta forma, o problema da extrapolação é abordado explicitamente ajustando-se os modelos a dados geológicos. Vários modelos de annealing foram propostos na literatura de traços de fissão.A formulação básica destes modelos baseia-se na equação de Arrhenius e foi apresentada por Laslett et al.(1987).Existem outros modelos de annealing que são baseados no mesmo princípio:Crowley et al.(1991);Laslett e Galbraith (1996);Rahn et al.(2004)e Yamada et al. (2007).Estes modelos têm sido usados preferencialmente,uma vez que inúmeros fenômenos, desde a formação dos traços até o ataque químico,não são bem entendidos ainda.orém,dois outros modelos calibrados no presente trabalho (Carlson,1990;Guedes et al.,2005a), procuram estabelecer uma correlação direta entre seus parâmetros e os fenômenos envolvidos.Os ajustes dos vários modelos foram comparados entre si,levando-se em conta considerações estatísticas. Além das calibrações efetuadas ajustando-se os modelos a dados geológicos, foram abordadas comparações de previsões dos modelos (relacionadas com as fronteiras da Zona de Annealing Parcial)com outros dados geológicos baseados em densidades de traços de fissão / Abstract: Fission-track (FT)analysis has developed into one of the most useful technique used to constrain the low-temperature thermal history of rocks in the upper part of the Earth's crust.If a host rock is subjected to elevated temperatures,fission tracks that have formed up to that point in time are shortened irreversibly or annealed,as a consequence of a thermally activated diffusion process. The most commonly analysed minerals are apatite and zircon and the latter is the focus of this work,since this mineral is sensitive to thermal annealing at higher temperatures,while the close temperature for apatite is around 120 o C. Short-term annealing characteristics of FT in zircon are generally based on laboratory experiments which are performed on timescales of less than 1 year,and typically much less. These data have been used to calibrate annealing empirical models,that describe the temperature and time dependence of fission track shortening.However,a practical problem is the uncertainty introduced through the extrapolation of laboratory calibrated models (<1 year)to geological timescales (10 6 ¿ 10 8 years). One of the purpose of this study is to give further constraints on the temperature range of the zircon annealing zone over a geological time scale using zircons data from boreholes,which samples have been exposed to a stable temperature for ~1 Ma.In this way,the extrapolation problem is explicity adressed by fit the zircon annealing models with geological timescale data. Several empirical models formulations have been proposed to perform these calibrations and have been compared in this work.The basic formulation is an Arrhenius-type model and is given by Laslett et al.(1987).There are other annealing models which are based on the same general formulation:Crowley et al.(1991);Laslett and Galbraith (1996);Rahn et al.(2004)and Yamada et al.(2007).These models equations have been preferred due to the great number of fenomena from track formation to chemical etching that are not well understood.However,two other calibrated models in this work (Carlson,1990;Guedes et al.,2005a)try to stablish a direct correlation between their parameters and the related fenomena.Several model fits are compared by themselves,considering statistical data. Besides calibrating annealing models with geological timescale data,model predictions (related with Parcial Annealing Zone boundaries)were compared with another geological data / Doutorado / Geofísica Nuclear / Doutor em Ciências

The Old Hickory mine is a world class placer titanium deposit located at the boundary of the Coastal Plain and the Piedmont in Virginia, astride the Sussex-Dinwiddie county line (77°34' W Long, 36°55'N Lat., Cherry Hill Quad). The Old Hickory deposit, discovered in 1987 by C. R. Berquist, was opened as a commercial mine in 1997, and is presently operated by Iluka Resources. Heavy minerals constitute an average of 8% of the sediment, but locally reach concentrations as rich as 60%. The ore minerals, in order of decreasing concentrations, are ilmenite, rutile, and zircon, which are believed to have been derived from weathering of Piedmont and Blue Ridge sources. After fluvial transport to the coast, the ore minerals were redistributed laterally along the coast by longshore currents, and ultimately concentrated by intense wave action, probably generated by large storms. The ores occur over an area of 8 km x 3 km, with ore minerals being found from the surface to up to depths of 12 meters, and appear to occur in at least two distinct ore horizons. This study examines the general ore mineralogy and differences in the mineralogy, grain sizes, secondary textures, and geochemistry of the ore minerals in the two distinct ore zones. Distinguishable differences between the two zones include a slightly coarser grain size, more angular grains of rutile, and a higher percentage of accessory minerals (epidote, garnet, etc) in the younger zone. Approximately 40% of all the ilmenite grains contain exsolution lamellae of hematite, a residual texture from the time of original ilmenite crystallization. Weathering of these ilmenite grains has preferentially dissolved out the hematite while preserving the original texture; thus the weathering increases the titanium content of the ore by removing some of the iron. The weathering also affects the distribution of minor elements such as aluminum, manganese, and chromium. At Old Hickory, the zircon population can be divided into two main types (thin, elongate rounded pink prisms, and short, thicker white to clear prisms) that may represent either multiple source regions or multiple generations of heavy mineral deposition. The variations in grain size, angularity, and rutile content are likely to be mappable and may prove useful in continuing stratigraphic studies, and in distinguishing separate ore zones. / Master of Science