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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.
11

Identifying and quantifying sediment sources and sinks in the Root River, Southeastern Minnesota

Stout, Justin Collin 01 May 2012 (has links)
Currently, our ability to predict the flux of fine sediment at the watershed scale is limited by the precision of erosion rate estimates for the many potential sources distributed throughout a landscape as well as our understanding of the connectivity of sediment pathways during transport. In absence of a robust predictive model which can be validated by measurements of sediment fluxes and use of geochemical tracers. Predicting fine sediment yield at the watershed scale requires multiple redundant lines of information. This thesis outlines the methods used, and the data sets collected in the Root River watershed in Southeastern Minnesota, all of which are multiple lines of evidence to the sediment dynamics in the Root River. The research indicates that the Root River is a very dynamic watershed. The hydrologic regime of the watershed has shifted over the last half century. Due to this shift sediment fluxes are very dependent of the magnitude and sequence of events. Geomorphic analysis of the landforms and the use of a developed tool, TerEx, indicate that many reaches of the river have easily accessible near-channel sources of sediment. Sediment fingerprinting results illustrate that source tracer concentrations are variable across the landscape, that as a whole, upland sources are still a major contributor to the suspended sediment load, and that in some sub-watersheds near-channel sources are dominate in the suspended load. Over all the channel-floodplain exchange exerts strong control on the flux of sediment through this river system.
12

Meteoric 10Be as a Tracer for Subglacial Chemical Weathering in East Antarctica

Arnardóttir, Eiríka Ösp 12 1900 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Subglacial chemical processes in Antarctica are potentially significant contributors to global geochemical cycles, but current understanding of their scale and nature is limited. A sequential chemical extraction procedure was developed and tested to investigate the utility of meteoric 10Be as a tracer for chemical weathering processes beneath the East Antarctic Ice Sheet. Subglacial meltwater is widely available under the Antarctic Ice Sheet and chemical constituents within it have the potential to drive geochemical weathering processes in the subglacial environment. Meteoric 10Be is a cosmogenic nuclide with a half-life of 1.39×106 years that is incorporated into glacier ice, therefore its abundance in the subglacial environment in Antarctica is meltwater dependent. It is known to adsorb to fine-grained particles in aqueous solution, precipitate with amorphous oxides, and/or be incorporated into authigenic clay structures during chemical weathering. The presence of 10Be in weathering products derived from beneath the ice therefore indicates chemical weathering processes in the subglacial environment. Freshly emerging subglacial sediments from the Mt. Achernar blue ice moraine were subject to chemical extractions where these weathering phases were isolated and 10Be concentrations therein quantified. Optimization of the phase isolation was developed by examining the effects of each extraction on the sample mineralogy and chemical composition. Experiments on 10Be desorption revealed that pH 3.2-3.5 was optimal for the extraction of adsorbed 10Be. Vigorous disaggregation of the samples before grain size separations and acid extractions is crucial due to the preferential fractionation of the nuclide with clay-sized particles. 10Be concentrations of 2-22×107 atoms g-1 measured in oxides and clay minerals in freshly emerging sediments strongly indicate subglacial chemical weathering in the catchment of the Mt. Achernar moraine. Sediment-meltwater contact in the system was calculated to be on the order of thousands of years, based on total 10Be sample concentrations, local basal melt rates, and 10Be ice concentrations. Strong correlation (R = 0.96) between 10Be and smectite abundance in the sediments indicate authigenic clay formation in the subglacial environment. This study shows that meteoric 10Be is a useful tool to characterize subglacial geochemical weathering processes under the Antarctic Ice Sheet.
13

Σταθερά ισότοπα (δ2Η, δ18Ο) στον υετό : ανάλυση των ισοτοπικών υπογραφών στην Ελλάδα και κλιματολογική ανάλυση στην περιοχή της Κεντρικής και Ανατολικής Μεσογείου

Λυκούδης, Σπυρίδων 20 April 2011 (has links)
Η διατριβή αυτή μελετά τα σταθερά ισότοπα στον υετό της Ελλάδας. η γεωγραφική κατανομή τους είναι η θεωρητικά αναμενόμενη, ενώ οι βαθμίδες με τη θερμοκρασία και το υψόμετρο και η τοπική μετεωρική γραμμή συμφωνούν με τη βιβλιογραφία για την ευρύτερη περιοχή. Η επίδραση της πορείας της αέριας μάζας, δεν είναι ευδιάκριτη λόγω της επίδρασης τοπικών διεργασιών κλασμάτωσης. Επίσης, η ισοτοπική σύσταση των πηγών ακολουθεί την κατανομή της σύστασης του υετού και είναι γενικά απεμπλουτισμένη σε σχέση με αυτόν. Ελέγχεται η καταλληλότητα των δεδομένων για κλιματολογική θεώρηση των ισότοπων του υετού στην κεντρική και ανατολική Μεσόγειο. Οι υπάρχουσες τάσεις σπανίως είναι σημαντικές και δεν έχουν χωρικά οργανωμένες μορφές. Επομένως, έχει νόημα ο υπολογισμός κλιματικών τιμών και η ανάπτυξη, με χρήση συνδυασμού προτύπων παλινδρόμησης και γεωστατιστικών μεθόδων, πλεγματικών κλιματικών ισοτοπικών δεδομένων και πλεγματικών ισοτοπικών χρονοσειρών. Τέλος, ερευνάται η ικανότητα των συνοπτικών ταξινομήσεων να οδηγούν σε ισοτοπικά διακριτές κλάσεις, αναπαράγοντας, ταυτόχρονα, σημαντικό μέρος της παρατηρούμενης ισοτοπικής μεταβλητότητας. Γενικά οι ταξινομήσεις βελτιστοποίησης με σχετικά μεγάλο αριθμό κλάσεων ικανοποιούν τα ανωτέρω. επιχειρείται η ανασύσταση ισοτοπικών χρονοσειρών χρησιμοποιώντας μέσες τιμές, σταθμισμένες βάσει των συχνοτήτων εμφάνισης των συνοπτικών κλάσεων και των υψών υετού. Η βέλτιστη επίδοση επιτυγχάνεται από εποχικές ταξινομήσεις με κλάσεις που αναπαράγουν τις βασικές ατμοσφαιρικές κυκλοφορίες, ακόμα και αν αυτό δεν συνεπάγεται βέλτιστους στατιστικούς δείκτες. / this thesis studies the stable isotpes in precipitation over greece. the geographical distribution is the one theoreticaly expected, while the temperature and altitude gradients, and the local meteoric line are onstistent with the literature for the area. the influence of air mass trajectory is not clear due to the effect of local fractionation processes. also, the composition of springs follows that of rain and is generaly depleted compared to it. the suitability of existing central and eastern mediterranean data, for climatological purposes is examined. existing trends are spatially inconsistent and rarely significant. thus, it is possible to calculate climatic values and obtain, using a combination of regression models and geostatistical methods, gridded isotopic climatologies and time series. finally, the ability of synoptic classifications to provide isotopicaly distinct classes, while at the same time reproducing the observed isotopic variability, is assessed. optimization classifications with a relatively large number of classes fulfill these criteria. reconstruction of isotope time series using mean values weighted according to synoptic class frequency and rain amount is possible. the best results are obtained from seasonal classifications with classes representing the basic atmospheric circulations, even if this does not lead to optimized statistical indices.
14

Evaluation of Paleo-climate for the Boise Area, Idaho, from the last Glacial Maximum to the Present Based on delta 2H and delta 18O Groundwater Composition

Schlegel, Melissa Eileen 18 May 2005 (has links) (PDF)
There are four distinguishable groundwater systems in the Boise area, Idaho, U.S.A., identified as modern batholith, thermal batholith, Boise frontal fault, and Nampa-Caldwell systems (Figure 1). Modern batholith and thermal batholith groundwaters are located in Tertiary to Cretaceous aged granites and granodiorites of the Atlanta lobe of the Idaho Batholith. The frontal fault system near Boise, ID defines the southeastern edge of the Idaho Batholith, and divides the batholith from the western Snake River Plain. The Nampa-Caldwell system is in the volcanic, fluvial and pluvial sediments of the western Snake River Plain. Groundwater ages for these systems are modern, 5-15 ka, 10-20 ka, and 20-40 ka respectively. Local meteoric water lines (LMWL) using the delta 2H and delta 18O composition of the groundwater were defined for each system using linear regression techniques. LMWL had variable and defined single slopes of 6.94 and 8. Deuterium excess values (d) were found for each system for each linear regression method. Relative differences of the deuterium excess value assuming the two single slope methods were similar. Changes in moisture source humidity and temperature, and Boise area recharge temperatures calculated from stable isotopic data and the deuterium excess factor agree with other published data. At the moisture source there was a 9% humidity increase and a 7-6 °C decrease of sea surface temperature between the present and the last glacial maximum (LGM). The local temperature decreased 4-5 °C from the present to the LGM for the Boise area.
15

EVENTOS DE PRECIPITAÇÃO EXTREMA ASSOCIADOS ÀS INUNDAÇÕES NA ÁREA URBANA DE BRAGANÇA/PA. / EXTREME PRECIPITATION EVENTS ASSOCIATED WITH FLOODS IN URBAN AREA OF BRAGANÇA/PA.

Costa, Tarcísio Oliveira da 24 November 2014 (has links)
The study of urban climate has a great importance in regard to the understanding of the human-nature relationship and the interaction between the local climate and the city. This expectation motivated this study on the Urban Climate in the city of Bragança, Pará State, a city that has undergone urban impacts from the rains that cause floods and flooding that hit several areas of the city, especially along the course from the Cereja stream, that is cutting the urban mesh. The Floods are one of the most serious problems which affects the cities when there is an occurrence of extreme precipitation events, generating impacts that affect the daily routine of the people. In this way, the choice for the study of meteoric impact of the channel, the third channel among the subsystems of the Urban Climate System (SCU), it is justified by the study of floods and flooding that happened in the city and the need to understanding the environmental conditions that originate. In this context, this study aimed to analyze the urban climate and extreme expectation events associated with the occurrence of floods and flooding in the urban area of Bragança. Therewith, we analyzed the occurrence of floods in Cereja stream and flooding in Bragança in 2004-2013 period; It was analyzed the variability of precipitation in urban areas from January to May, in 2014; we identified the atmospheric systems linked to extreme expectation events in the urban area of the city; however, the balance of participation of climate systems during the Amazon winter 2014 and it was made a map of climate risk in areas of extreme rainfall situations with sight to urban land use planning in the city. Therefore, the research was based on the SCU theory developed by Monteiro (1976). In the historic flood (2004-2013) were found 32 extreme events, that only 07 were classified as episodes of relevance for this study due to the impact of records in the urban area. The weather data analyzed was collected of the Weather Station Conventional of Tracuateua city (EMT) and Automatic Weather Station of Bragança (EMB) that belongs to INMET and a network of 07 rain gauges installed in the urban area of the city in 2014 which allowed a development of variability maps precipitation during the Amazon winter. Were also it was developed participation swing charts of atmospheric systems with satellite images from GOES 13 aid provided by INPE and Letters daily Synoptic of 00h and 12h provided by the Navy of Brazil. With the results, it was observed that the ZCIT has increased the participation in the occurrence of extreme events and urban impacts, and it was noted that there is a great variability of expectation in the study of the area, up to 161 mm between the northnortheast sector (Rainier) and the South-southwest sector (less rain). Finally we prepared a risk map as a tool for urban land in use planning, considering the local climate variable. / O estudo do clima urbano é de grande importância no que se refere à compreensão da relação homem-natureza e da interação entre o clima local e a cidade. Essa perspectiva motivou este estudo sobre o Clima Urbano de Bragança/PA, cidade que tem sofrido impactos urbanos oriundos das chuvas que provocam inundações e alagamentos que atingem diversas áreas da cidade, principalmente, ao longo do curso do Igarapé Cereja, que corta a malha urbana. As inundações são um dos graves problemas que afetam as cidades quando há ocorrência de eventos de precipitação extrema, gerando impactos que influenciam no cotidiano das populações. Nesse sentido, a escolha pelo estudo do canal do Impacto Meteórico, terceiro canal dentre os subsistemas do Sistema Clima Urbano (SCU), justifica-se pelo estudo das inundações e alagamentos que tem ocorrido em Bragança e pela necessidade de entendimento das condições climáticas que as originam. Nesse contexto, este trabalho teve como objetivo geral analisar o clima urbano e os eventos de precipitação extrema associados à ocorrência de inundações e alagamentos na área urbana de Bragança-PA. Com isso, analisou-se a ocorrência de inundações no Igarapé Cereja e alagamentos em Bragança no período de 2004-2013; analisou-se a variabilidade da precipitação na área urbana no período de janeiro à maio do ano de 2014; identificou-se os sistemas atmosféricos ligados aos eventos de precipitação extrema na área urbana de Bragança-PA; realizou-se o balanço de participação dos sistemas atmosféricos durante o inverno amazônico de 2014 e elaborou-se um mapa de áreas de risco climático em situações de extrema precipitação com vistas ao ordenamento territorial urbano do município. Para tanto, a pesquisa baseou-se na teoria do SCU elaborada por Monteiro (1976). No histórico de inundações (2004-2013) foram encontrados 32 eventos extremos, dos quais apenas 07 foram classificados como episódios de relevância para este estudo, devido aos registros de repercussão na área urbana. Os dados meteorológicos analisados foram coletados da Estação Meteorológica Convencional de Tracuateua (EMT) e Estação Meteorológica Automática de Bragança (EMB), pertencente ao INMET e por uma rede de 07 pluviômetros instalados na área urbana de Bragança/PA em 2014, que possibilitou elaboração de mapas da variabilidade da precipitação durante o inverno amazônico. Foram também elaborados gráficos de balanço de participação mensal dos sistemas atmosféricos, com auxílio de imagens do satélite GOES 13 disponibilizadas pelo INPE e Cartas Sinóticas diárias das 00h e 12h disponibilizadas pela Marinha do Brasil. Com os resultados, observou-se que a ZCIT tem maior participação na ocorrência de eventos extremos e impactos urbanos, além de observar-se que há uma grande variabilidade da precipitação na área de estudo, de até 161 mm entre o setor norte-nordeste (mais chuvoso) e o setor Sul-sudoeste (menos chuvoso). Por fim foi elaborado um mapa de riscos como instrumento para o ordenamento territorial urbano, considerando a variável climática local.
16

Terrestrial Archives of Meteoric 10Be

Adrian A Singleton (11814842) 19 December 2021 (has links)
<div><div><div><p>The radionuclide 10Be is produced in the atmosphere and is delivered to Earth’s surface in meteoric rain and aerosols. The stable nuclide 9Be is present in trace concentrations within rocks in Earth’s crust and is released via chemical weathering. Together, these two isotopes have been employed to study a wide range of Earth processes. Here I explore new terrestrial archives of Be isotopes: cave speleothems and terrestrial Mn-oxides. Until this point, these archives have barely been studied. Only one published dataset of Be isotopes in cave speleothems exists (Lundblad, 2006), and to my knowledge, terrestrial manganese oxides are yet to be explored. However, since speleothems and Mn-oxides precipitate from groundwater, they have the potential to encode temporal variations in the 10Be/9Be ratio of water and colloids in the vadose zone.</p><p>I develop a framework for using the 10Be/9Be ratio in the dissolved phase and/or secondary weathering products as a metric of chemical weathering rate. I am motivated by several over-arching questions:</p><ol><li><p>1) Which factor, or factors, is/are dominant in controlling Be isotopes in speleothems and terrestrial Mn-oxides?</p></li><li><p>2) Can Be isotopes in speleothems be used as a metric of weathering rate over time, particularly across glacial/interglacial cycles?</p></li><li><p>3) Can Be isotopes be used to date the formation of terrestrial Mn-oxides?</p></li></ol><p>I measure Be-isotope concentrations in speleothems from Soreq Cave, Israel. By applying an equation that I derive in this thesis, I use the temporal variation in the speleothem10Be/9Be ratio to calculate chemical weathering rates over the last 168 ka. Chemical weathering varies with independent proxies for temperature. The weathering-temperature relationship can be fit to an Arrhenius relationship, and the calculated activation energy (Ea) matches other field-based estimates for feldspar, an abundant mineral in the soil above the cave. In the Appendices I present additional results of Be-isotope measurements in a flowstone from Buffalo Cave in South Africa, as well as Mn-oxides from the Appalachians.</p></div></div></div>
17

Kinetic quantification of vertical solid matter transfers in soils by a multi-isotopic approach / Quantification de la cinétique des transferts verticaux de matière solide dans les sols par une approche multi-isotopique

Jagercikova, Marianna 18 March 2014 (has links)
Le lessivage du lutum (0-2 µm) est un de processus majeurs de la pédogenèse, qui a néanmoins été peu quantifié et modélisé. Ce processus ainsi que la bioturbation ont été quantifiés ici en couplant des différents systèmes isotopiques (137Cs, 210Pb (xs), 10Be atmosphérique, 206/207Pb, δ13C, 14C) à une modélisation numérique par une équation de diffusion-convection à paramètres variables avec la profondeur. Cette méthode originale a été appliquée sur des anthroposéquences de Luvisols développées sur du loess et différantes de par leur utilisation (culture, prairie ou forêt) et leurs pratiques agricoles (travail du sol, apport du fumier). Nos résultats montrent que 91 ± 9 % du 137Cs et 80 ± 9 % du 10Be sont associés au lutum et ainsi peuvent effectivement tracer des transferts verticaux de matière solide dans les sols à pH > 5 et à teneur en carbone organique faible. Le partage du plomb entre les différentes phases solides est plus complexe. En considérant deux compartiments pour les isotopes (macropores ou la matrice de sol), nous avons conçu un modèle multi-isotopique permettant de quantifier la contribution des transferts de matière solide à la distribution verticale de la fraction 0-2 µm actuelle. Le lessivage est responsable de 9 à 66 % de l'accumulation de lutum dans l'horizon Bt. Le coefficient de diffusion permet de quantifier le taux de mélange par la bioturbation. La modélisation multi-isotopique est une méthode de prédilection pour les études modernes de la pédogenèse et des processus de la zone critique. / Clay translocation is one of the major soil forming processes, howeverit is poorly quantified and modeled. We propose to quantify it togetherwith bioturbation by combining different isotopic systems (137Cs , 210Pb (xs),meteoric 10Be, 206/207Pb, δ13C, 14C) with numerical modeling based on a nonlineardiffusion-convection equation with depth dependent parameters. Thisnovel method has been applied on Luvisol anthroposequences developed onloess, differing by their land use (cropping versus grassland or forest) andtheir agricultural practices (reduced tillage, no tillage and manure input).Our results show that as much as 91 ± 9 % and 80 ± 9 % of 137Cs and10Be, respectively, are associated to the clay size fraction (0-2 µm) and canthus effectively trace vertical solid matter transfers in soils with pH > 5 andlow organic carbon. Lead partitioning between different solid phases is morecomplex. Considering two spatial distributions of isotopes (macropores or soilmatrix), we built up a multi-isotopic modelling approach that simulates theexperimental data with the common set of transfer parameters and allowedus to quantify the relative contributions of vertical solid matter transfers topresent-day 0-2 µm vertical distributions. Clay translocation is responsiblefor 9 to 66 % of the clay accumulations in the Bt-horizon. The diffusion coefficientalso quantifies the rate of soil mixing by bioturbation. Modeling of thekinetics of solid matter transfer at multiple spatio-temporal scales should becomea method of predilection in modern pedogenic and critical zone studies.
18

The Occurrence of Thermal Groundwater in the Basin and Range Province of Arizona

Wright, Jerome J. 23 April 1971 (has links)
From the Proceedings of the 1971 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 22-23, 1971, Tempe, Arizona / The distribution of groundwater having temperature considered to be higher than normal is examined on a regional basis. Much of the work was done by searching the literature and examining USGS records. The geographic distribution of the thermal waters is reviewed; relation to structure, geothermal gradients and water quality are discussed. Current and past utilization of thermal water from both springs and wells of the state has never been very extensive. Conclusions were: (1) the occurrence of thermal water in the state is closely allied to major structural elements, especially major fault zones; (2) geothermal gradients vary widely from place to place; (3) the extent of 'bedrock' influence on thermal water occurrence is difficult to ascertain; (4) most thermal water in southern Arizona is derived from meteoric water.
19

Tertiary limestones and sedimentary dykes on Chatham Islands, southwest Pacific Ocean, New Zealand

Titjen, Jeremy Quentin January 2007 (has links)
The Chatham Islands are located in the SW Pacific Ocean, approximately 850 km to the east of the South Island of New Zealand. This small group of islands is situated near the eastern margin of the Chatham Rise, an elongated section of submerged continental crust that represents part of the Late Paleozoic-Mesozoic Gondwana accretionary margin. The location and much of the geology of the Chatham Islands are attributed to intra-plate basaltic volcanism, initiated during the Late Cretaceous, in association with development of a failed rifting system to the south of the Chatham Rise. Despite the volcanic nature of much of the geology, the majority of the Cenozoic sedimentary stratigraphic record on the islands comprises non-tropical skeletal carbonate deposits whose deposition was often coeval with submarine volcanics and volcaniclastic deposits. This has resulted in complex stratigraphic relationships, with the volcanic geology exerting a strong influence on the geometry and distribution of the carbonate deposits. These limestones, despite some general field descriptions, have been little studied and are especially poorly understood from a petrographic and diagenetic perspective. The carbonate geology in detail comprises eleven discrete limestone units of Late Cretaceous through to Pleistocene age which were studied during two consecutive field expeditions over the summers of 2005 and 2006. These limestone occurrences are best exposed in scattered coastal outcrops where they form prominent rugged bluffs. While many of the younger (Oligocene to Pliocene) outcrops comprise of poorly exposed, thin and eroded limestone remnants (it;5 m thick), older (Late Paleocene to Early Oligocene) exposures can be up to 100 m in thickness. The character of these limestones is highly variable. In outcrop they display a broad range of textures and skeletal compositions, often exhibit cross-bedding, display differing degrees of porosity occlusion by cementation, and may include rare silicified horizons and evidence of hardground formation. Petrographically the limestones are skeletal grainstones and packstones with a typical compositional makeup of about 70% skeletal material, 10% siliciclasts, and 20% cement/matrix. Localised increases in siliciclastics occur where the carbonates are diluted by locally-derived volcaniclastics. The spectrum of skeletal assemblages identified within the Chatham Island limestones is diverse and appears in many cases to be comparable to the bryozoan dominant types common in mainland New Zealand and mid-latitude Australian cool-water carbonates in general. However, some key departures from the expected cool-water carbonate skeletal makeup have been identified in this study. The occurrence of stromatolitic algal mats in Late Cretaceous and Early Eocene carbonate deposits indicates not cool-temperate, but certainly warm-temperate paleoclimatic conditions. A change to cool-temperate conditions is recorded in the limestone flora/fauna from the mid-Late Miocene times following the development and later northward movement of the Subtropical Front. An uncharacteristic mix of shallow-shelf (bryozoans) and deeper water fauna (planktic foraminifera), together with their highly fragmented and abraded nature, is indicative of the likely remobilisation and redistribution of carbonate, primarily during episodic storm events. The Chatham Islands limestones formed within the relative tectonic stability of an oceanic island setting, which was conducive to ongoing carbonate accumulation throughout much of the Cenozoic. This contrasts markedly with other mainland New Zealand shelf carbonates which formed over sporadic and short-lived geological periods, experiencing greater degrees of burial cementation controlled by a relatively more active tectonic setting. As a consequence of the tectonically stable setting, the Chatham Islands limestones have experienced little burial and exhibit a paucity of burial cementation effects. They remain commonly soft and friable. Detailed petrographic investigations have shown the limestones are variably cemented by rare uneven acicular spar fringes, poorly to well-developed syntaxial rim cements about echinoderm fragments, and equant/blocky microsparite. Staining of thin sections and cathodoluminescence petrography show these spar cement generations are non-ferroan and their very dull- to non-luminescent nature supports precipitation from Mn-poor oxygenated waters, likely of an either meteoric or combined marine/shallow burial origin. Micrite is the dominant intra- and inter-particle pore fill and occurs both as a microbioclastic matrix and as precipitated homogenous and/or micropeloidal cement. The rare fringing cements often seen in association with homogenous and/or micropeloidal micrite may be indicative of true early marine (seafloor) cement precipitation and localised hardground development. An interesting feature of the geology of the Chatham Islands is the occurrence of carbonate material within sedimentary dykes. The locations of the dykes are in association with volcanic and volcaniclastic deposits. Similarities between dyke characteristics at Red Bluff on Chatham Island with mainland occurrences from East Coast and Canterbury Basins (North and South Islands, respectively) on mainland New Zealand have been recognised. They show complex structures including sidewall striations, internal flow structures as revealed by grain sorting, and extra-clast inclusions of previous fill lithologies which are characteristic of carbonate injection. This is in contrast to other dykes which are known to be of a passive fill origin. Multiple phases of carbonate sediment injection can be recognised by crosscutting relationships enabling the determination of a parasequence of events. Possible injection mechanisms are most likely associated with sediment overloading or hydrothermal pressurisation associated with emplacement of submarine volcanics. The Chatham Islands provide an exciting example of a geologically unique and complex non-tropical carbonate depositional setting. The production of carbonates is controlled by volcanic and volcaniclastic sediment input with the types of carbonate deposits and water depth variations related to thermal uplift/subsidence in association with global eustatic sealevel and temperature changes associated with development of Southern Ocean water fronts from the Late Cretaceous-Cenozoic. Carbonate deposition on the Chatham Islands is considered to relate to a rather variable and small scale oceanic, high energy, cool-water carbonate ramp setting whose geometry was continually evolving/changing as a consequence of periodic volcanic episodes.
20

Réservoirs fluides et transferts en contexte d'exhumation orogénique : implications sur la position structurale des minéralisations Cu-Pb-Zn-Fe-Ag dans la région Lavrion-Eubée (Grèce) / Stuctural position and geochemistry of fluids associated with Cu-Pb-Zn-Fe-Ag deposits in the Lavrion-Evia area (Greece)

Scheffer, Christophe 07 December 2016 (has links)
Cette thèse est centrée sur la ceinture orogénique Attico-Cycladique formée durant l'orogénèse Alpine. Par une approche multi-méthodes et multi-échelles combinant géologie structurale, pétrographie, thermobarométrie des assemblages minéraux, géochimie élémentaire et isotopique, et données PVTX des inclusions fluides associées, ce travail vise à caractériser et comprendre les relations entre circulations fluides, interactions fluides/roches, déformation, et mobilisation-transport-dépôt des métaux. Les marbres et schistes de la péninsule du Lavrion et de l'île d'Eubée témoignent d'une évolution orogénique complexe marquée par une phase d'enfouissement à l'Eocène suivie par deux phases d'exhumation successives syn-et post-orogéniques. Les minéralisations de type Cu-Pb-Zn-Fe-Ag de la région du Lavrion sont synchrones de l’activation du détachement post-orogénique et de la mise en place de plutons de granodiorite. Leurs positions structurales témoignent d’un piégeage depuis un régime de déformation ductile jusqu'à fragile. Les minéralisations mises en place durant le régime de déformation ductile à ductile-fragile (skarn et remplacement de carbonate) sont associées à la décarbonatation des niveaux de marbres et à la circulation des fluides magmatiques. L'exhumation progressive de la racine orogénique se traduit par la transition des roches depuis une déformation ductile vers un régime fragile associé à l’ouverture du système aux fluides de surface et notamment aux fluides météoriques. Cette circulation est responsable d’une remobilisation des métaux des minéralisations primaires permettant alors une seconde phase de précipitation dans un régime cassant (veines épithermales) / This thesis is focused on the Attico-Cycladic orogenic wedge formed during the Alpine orogeny. From a multi-method and multi-scale approach using structural geology, petrography, mineral thermobarometry, element and isotope geochemistry, and PVTX data of associated fluid inclusions, this study deciphers the relationships between fluid circulation, fluid-rock interactions and mobilisation-transport-deposits of metals. Marbles and schists from the Evia Island and the Lavrion peninsula testify to a complex orogenic history marked by an Eocene burial phase followed by syn- and post-orogenic exhumation. Cu-Pb-Zn-Fe-Ag mineralisations from the Lavrion area are synchronous with the formation of the low-angle post-orogenic detachment and the emplacement of granodioritic magmas. The structural position of the deposits attests of an emplacement during ductile to brittle deformation conditions. Deposits associated with ductile to ductile-brittle deformation (skarn, carbonate replacement) are related to a marble decarbonation and magmatic fluid circulation. The progressive exhumation of the orogenic wedge allows the transition toward brittle conditions and opens the system to surficial meteoritic fluids. This meteoritic fluid circulation is responsible to remobilisation of metals from primary deposits allowing thus a second phase of deposition in a pure brittle deformation (epithermal veins)

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