自2010年9月以來,中國大陸限制對日稀土出口所造成影響，在全球演然以成為熱門話題，亦為我所探究本論文鵠的。當時中國大陸在一片撻伐聲中，似成麻煩製造者，因影響片及整體稀土元素供需市場，特別是那些缺乏稀土元素生產卻又非常依賴中國大陸稀土的進口廠商所發出來的抗議。然事實上，稀土這元素在地球上並不匱乏，但因為它的開採上的成本高利潤卻不高，相對存量卻一直減少造成許多國家並不願去開採它，漸漸全球高逹95%以上的生產量由中國取代，卻也間接造成中國在稀土市場上的獨佔市場地位，但中國卻又是整個稀土市場價格的接受者，供需不均衡所造成的結果卻是相反地。因此中國政府當局大力支持與整合稀土產業進行一連串的體制改造及革新計畫整體架構十分迅速進行中。 此篇論文藉由所蒐集匱乏資料分析瞭解中國大陸稀土元素的發展，並透過經濟、政治分析中國不宜過度依賴稀土短期優勢，事實上，應可加強其稀土整體計劃在國際發展空間、提升稀土產業效能及加速其產業整合與技術提煉上改進，並同時兼顧環保及降低開採上污染等多個面向的思考，再者更瞭解稀土資源不但可增進人類的生活品質，其根本是歸屬大地之母-地球所擁有。 / The objective of this paper is to explore the hot issues of China’s Rare Earths Elements (REEs) on the global. Using a commonly-accepted methods and materials to research of China’s REEs, On the whole, the impact of China’s REEs restriction is almost regarded as mainstream troublemaker who become overshadows influence the REEs market in the world. However it’s not, On the contrary, the Earth is not in shortage of rare earth resources. The problem is in the worldwide supply and demand structure of REEs unbalance and the price is not reasonable for China’s REEs. China’s REEs growing forcefulness regards as a new strength called attention to foreign powers claim China stops exports of rare earth is completely groundless. REEs are as a new symbol of strength and high value metals in upcoming century changed China’s REEs racial policies turn into aggressively to enhance its national level security and pursing its welfare and hegemony in REEs. China is devoted to manage its REEs output quota reduced reliance on demand countries as strategic policies but so to the foreign countries changed their policies. Analysis of the paper indicated basic findings. China holds a main of capturing a larger portion of the global supply but couldn’t depend on its superiority of REEs’ reserves. In other words, China should be devoted to develop its REEs policies as a way to promote and engage China’s REEs grow space agenda with the rest of the world. Find ways to deals with the rough harsh international reality, strive to streamline its rare earth industry, accelerate industrial upgrading, technological innovation in accordance to protect its domestic REEs industries, the environment, reserve REEs resources and learn how to get along with other countries. Extremely, the China government should recognize the resources of REEs are belonging to human-beings and the Earth, not only to China has.

Löslighet och transport av sällsynta jordartsmetaller i Källfallsfältets gruvsandsmagasin Hugo de Campos Pereira Syftet med detta arbete har varit att kartlägga vilka mekanismer som styr lösligheten av sällsynta jordartsmetaller (eng. rare earth elements, REE) i sulfidhaltig anrikningssand vid den föredetta gruvan Källfallsfältet i Västmanland. För syftet har markvatten- och grundvattenprovtagning utförts, tillsammans med laktester och geokemisk modellering med Visual MINTEQ ver. 3.0. Resultaten visade att sulfidvittring är den främsta processen som styr pH i anrikningssanden, och därmed också indirekt REEs löslighet. Däremot är sulfidvittring ingen källa till REE i sig då ämnena inte föreligger sulfidbundna, något som oxiderat tillgänglighetstest NT ENVIR 006 visade. Istället går REE ut i lösning i anrikningssanden genom vittring av lättvittrade silikatmineral. Vanligtvis betraktas metall bunden i silikatform inte som geokemiskt aktiv. Jämförelser mellan laktester med olika jämviktstid visade att en kinetisk (tidsberoende) faktor föreligger, kopplad till nämnda silikatvittring, som påverkar pH och således också metallöslighet vid laktester på anrikningssanden. Vid jämförelse mellan laktester och halter i anrikningssandens mark- och grundvatten bör denna därmed vägas in. Det pH-statiska laktestet SIS-CEN/TS 14997 visade begränsad möjlighet att undersöka kinetik med anledning av att det utförs under förhållandevis kort tid, 48 timmar. REE- och Cu-halter vid syratitrering (de behandlingar med lägst syratillsatser) och enstegslakning (SIS-CEN ISO/TS 21268-2:2010) visade god, respektive förhållandevis god, överensstämmelse med uppmätta markvattenhalter. Detta visade att syratitrering och enstegslakning är laktest som är tillämpbara, respektive förhållandevis väl tillämpbara, för att uppskatta markvattenhalter i anrikningssanden. Specieringsmodellering med Visual MINTEQ ver. 3.0 visade att pH och DOC är de viktigaste parametrarna som styr REEs speciering i anrikningssandens mark-, grund och ytvatten. Samtliga REE bildar starka komplex med löst organiskt material, men koncentrationerna av DOC var generellt sett låga. I sura sulfatrika mark-, grund och ytvatten domineras specieringen av lösta sulfatkomplex, huvudsakligen (REE)SO4+, följt av fria hydratiserade joner som näst vanligaste förekomstform. Dessa resultat överensstämmer väl med tidigare modelleringsstudier av REEs speciering i sura sulfatrika vatten resulterande från gruvavfall. Med bakgrund av detta och av att REEs ekotoxicitet verkar överensstämma med den fria jon-modellen (eng. free ion model) förväntas REE uppvisa högre toxicitet vid låga pH-värden. / Solubility and transport of rare earth elements in the mine tailings of Källfallsfältet Hugo de Campos Pereira The mechanisms which govern the solubility of rare earth elements (REEs) in sulfide-containing tailings at the former mine site of Källfallsfältet (Västmanland, Sweden) were studied by the means of soil water and ground water sampling, leaching tests and geochemical modeling using Visual MINTEQ ver. 3.0. The results showed that weathering of sulfides is the primary process governing pH in the tailings, and thus also REE solubility. However, weathering of sulfides is no source for REE in itself since the elements are not bound in sulfides, which the oxidized availability test NT ENVIR 006 showed. Instead REE are released into solution by weathering of easily weathered silicates. Usually, metal bound in silicate form is not considered geochemically active. A kinetic (time dependent) factor, associated with the weathering of silicates, was found to affect pH and thus also metal solubility in leaching tests performed on the tailings. The standardized pH static leaching test (SIS-CEN/TS 14997) showed limitations in observing kinetic effects because of its relatively short equilibration time (48 h). Thus, in future studies with similar materials, leaching test kinetics should be taken into account when comparing leached concentrations with field measured concentrations. Acid titration and one step batch test (SIS-CEN ISO/TS 21268-2:2010) proved to be applicable and relatively well applicable to the tailings, respectively, in order to estimate soil solution concentrations. Speciation calculations using Visual MINTEQ ver. 3.0 showed that pH and DOC concentration are the most important factors which affect REE speciation in soil solution, ground water and surface water associated with the tailings. In acid sulfate rich solutions, low in DOC, speciation is dominated by sulfate complexes, mainly (REE)SO4+, followed by free dissolved ions as the second most common form. These results are in accordance with previous modeling studies of REE speciation in acid sulfate rich waters resulting from tailings. This, together with previous results showing that REE ecotoxicity seems to follow the free ion model, implies that the toxicity of the elements is expected to increase with decreasing pH value.

Sn-Pb solder has long been used in the Electronics industry. But, due to its toxic nature and environmental effects, certain restrictions are made on its use and therefore many researchers are looking to replace it. Sn-3.0Ag-0.5Cu (SAC) solders are suggested as lead-free replacements but their coarse microstructure and formation of hard and brittle Inter-Metallic Compounds (IMCs) like Ag₃Sn and Cu₆Sn₅ have limited their use in high temperature applications. In this research work, RE elements, mostly lanthanum (La), are used as potential additives to SAC alloys. They reduce the surface free energy, refine the grain size and improve the mechanical and wetting properties of SAC alloys. An extensive experimental work has been performed on the microstructure evolution, bulk mechanical properties, individual phase (matrix and IMCs) mechanical properties, creep behavior and wettability performance of the SAC and SAC-La alloys, with different (La) doping. SEM and EDS have been used to follow the continuous growth of the IMCs at 150°C and 200°C and thus provide a quantitative measure in terms of their size, spacing and volume fraction. Grain size is measured at regular intervals starting from 10 hours up to 200 hours of thermal aging using Optical Microscope with cross polarized light. Bulk mechanical properties are evaluated using tensile tests at low strain rates. Individual phase mechanical properties like Young's modulus, hardness, strain rate sensitivity index and bulge effects are characterized with nanoindentation from 100 µN up to 5000 µN loadings at different temperatures of 25°C, 45°C, 65°C and 85°C. Creep experiments are performed at elevated temperatures with good fitting of Dorn creep and back-stress creep models. Activation energy measurements are made at 40°C, 80°C and 120°C. Wettability testing on copper substrates is used for surface tension, wetting force and contact angle measurements of SAC and SAC-La doped alloys at 250°C and 260°C.

Foram determinadas as concentrações de terras raras (La, Ce, Nd, Sm, Eu, Tb, Yb e Lu) e outros elementos-traço (Cs, Rb, Ba, U, Th, Ta, Hf, Co e Sc) em 51 amostras representativas de derrames e soleiras das regiões norte e nordeste da Província Magmática do Paraná, que ocorrem no norte do estado de São Paulo e no sul de Minas Gerais. O método utilizado para estas determinações foi a técnica de ativação com nêutrons térmicos e epitérmicos, seguida de espectrometria gama de alta resolução, que forneceu resultados com elevados níveis de precisão e de exatidão (geralmente com valores inferiores a 10%), conforme atestado pelas concentrações determinadas no material geológico de referência JB-1. Os dados obtidos foram analisados conjuntamente com determinações de elementos maiores, menores e dos traços Sr, Y, Zr, Nb, Cr e Ni, realizadas por fluorescência de raios ? X. As rochas investigadas são quimicamente representadas por basaltos toleíticos, andesi-basaltos toleíticos e lati-basaltos, enquanto as mais evoluídas (MgO < 3%), que ocorrem de modo muito subordinado, são representadas por latitos e lati-andesitos, além de um riodacito. As rochas básicas (SiO2 < 55% e/ou MgO > 3%) são caracterizadas por apresentarem conteúdos de TiO2 maiores que 3%, sendo que grande maioria possui fortes semelhanças com os magmas-tipo Pitanga, embora tenham sido encontrados alguns derrames, localizados no norte do estado de São Paulo, geoquimicamente semelhantes aos magmas-tipo Urubici (típicos do sul da província). Rochas básicas com concentrações de TiO2 entre 2% e 3% foram também raramente encontradas, as quais representam equivalentes intrusivos de derrames Paranapanema. As rochas mais evoluídas só foram encontradas em soleiras e possuem características geoquímicas que indicam diferenciação a partir de magmas do tipo Pitanga. O comportamento de elementos maiores, menores e traços nas rochas intrusivas e extrusivas do tipo Pitanga, incluindo as mais diferenciadas, é compatível com um processo de evolução por cristalização fracionada envolvendo plagioclásios, clinopiroxênios e titano-magnetitas. A comparação entre derrames e soleiras do tipo Pitanga indica a atuação significativa de processos de diferenciação in situ nas rochas intrusivas, que causaram uma maior variabilidade composicional (soleiras: MgO entre 2,3% e 6,4%; derrames: MgO entre 3,2% e 5,5%). As rochas mais diferenciadas são também caracterizadas por anomalias positivas de európio, que sugerem o acúmulo de plagioclásio devido a esse processo de fracionamento. Os dados obtidos também reforçam que não houve participação significativa de componentes astenosféricos do tipo N-MORB, E-MORB e OIB na gênese das rochas básicas investigadas, as quais possuem grande similaridade geoquímica com os basaltos da Cadeia Rio Grande (sítio 516F) e Cadeia Walvis (sítio 525A), especialmente com os desta última, indicando o envolvimento do componente mantélico EMI. / It is presented the determination of rare earth (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) and other trace (Cs, Rb, Ba, U, Th, Ta, Hf, Co and Sc) element concentrations in 51 representative samples of flows and sills from northern and northeastern Paraná Magmatic Province, particularly those located at north of São Paulo State and south of Minas Gerais. The employed analytical method to those determinations was thermal and epithermal neutron activation analysis, followed by high resolution gamma ray spectrometry, which provided high precision and accuracy results (in general better than 10%), as verified by determinations in the international geological reference material JB-1. The obtained results were integrated with major, minor and trace (Sr, Y, Zr, Nb, Cr and Ni) elements determined by X-ray fluorescence. The investigated rocks are mainly represented by tholeiitic basalts, tholeiitic andesi-basalts and lati-basalts, with subordinate relatively evolved (MgO < 3wt%) lithotypes, which are represented by latites and lati-andesites, besides one rhyodacite. The basic rocks (SiO2 < 55% and/or MgO > 3%) are characterized by presenting TiO2 contents higher than 3wt%, very similar to Pitanga magma-type, although some flows, located at northern São Paulo State, geochemically similar to Urubici magma-type (typical of southern Paraná) were also found. Basic rocks having TiO2 contents between 2 and 3 wt% were rarely encountered and represent intrusive equivalents of Paranapanema flows. The more evolved rocks were just found in sills and have geochemical characteristics that indicate differentiation from Pitanga magma-types. Major, minor and trace element behaviour of intrusive and extrusive rocks of Pitanga type, including those differentiated ones, is compatible with evolution by fractional crystallization of plagioclases, clinopyroxenes and titanium magnetites. The comparison between flows and sills of Pitanga type indicates the significant role of in situ differentiation in the genesis intrusive rocks, causing its larger compositional variability (sills: MgO between 2.3 and 6.4wt%; flows: MgO between 3.2 and 5.5wt%). The most evolved rocks are also characterized by positive europium anomalies, which suggest plagioclase accumulation caused by such fractionation process. The obtained data also corroborate the lack of significant participation of N-MORB, E-MORB and OIB asthenospheric mantle components in the genesis of basic rocks, which present very close geochemical similarity with Rio Grande Rise (site 516F) and Walvis Ridge (site 525A) basalts, particularly with the last ones, indicating the involvement of EMI mantle component.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-04-03T16:44:03Z No. of bitstreams: 1 THIAGO ANDRADE DE SOUSA .pdf: 5768772 bytes, checksum: b3c4e1c52ed521e2c3772627711af6fa (MD5) / Made available in DSpace on 2017-04-03T16:44:03Z (GMT). No. of bitstreams: 1 THIAGO ANDRADE DE SOUSA .pdf: 5768772 bytes, checksum: b3c4e1c52ed521e2c3772627711af6fa (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências- Geoquímica Ambiental. Niterói, RJ / Os sedimentos continentais depositados no fundo oceânico estão condicionados, majoritariamente, a evolução do clima, ao substrato geológico e ao tipo de transporte, sendo o transporte fluvial o de maior magnitude. Uma vez depositado, os sedimentos tornam-se registros do passado e carregam informações sob a forma de assinatura geoquímica. Os Elementos Terras Raras (ETR) apresentam um comportamento coerente ao longo de uma coluna sedimentar tornando-os útil nos estudos de proveniência sedimentar. Razões entre elementos maiores (Fe/Ca, por exemplo) são descritos na literatura como indicadores de reconstrução do aporto terrígeno. A geoquímica dos ETR e elementos maiores são determinados neste trabalho para o entendimento da dinâmica paleoclimática sobre o aporte e proveniência dos sedimentos da margem leste (Bacia de Santos) do Brasil, e as anomalias do Ce e Eu, confrontando técnicas analíticas distintas (ICP-MS e XRF core scanner) nos principais eventos abruptos (Younger Dryas e Heinrich events) ao longo dos últimos 45.000 anos. Igualmente é discutido a proveniência do material sedimentar por meio de razões entre Elementos Terras Raras leve (ETRL) e Elementos Terras Raras pesado (ETRP) comparando possíveis fontes disponíveis na literatura. O padrão de distribuição indica enriquecimento em ETRM sobre ETRL e ETRP em todos os eventos. Isso significa que a proveniência deste material, provavelmente, deve-se a uma única fonte. As concentrações dos ETRL são sempre maiores que ETRM e ETRP. Esse padrão é outro indicativo de fonte única do material sedimentar. O somatório das concentrações dos ETR durante o MIS 2 é sempre maior do que o MIS 1. O comportamento dos ETR durante os eventos Heinrich são bem similares. A média das concentrações dos ETR nestes eventos são superiores aos encontrados no MIS 1 – Interglacial. As análises das razões Fe/Ca e Ti/Ca pelas duas técnicas mostram-se coerentes e indicam maiores durante o MIS 2. Isto é devido ao aumento de chuvas na região (intensificação do SMAS), nível do mar regressivo (plataforma continental exposta) e por efeitos de diluição do carbonato marinho estimulada pela entrada de matéria orgânica. As razões Al/Si e Fe/K apresentam sinais distintos ao longo do testemunho deste estudo. O aumento de Si durante o MIS 2, em relação aos outros períodos, indica que o glacial foi menos úmido que o interglacial. O aumento de K dentro dos eventos Heinrich indica mudança no padrão de intemperismo continental devido aos episódios de chuvas e aumento no intemperismo químico nas bacias de drenagens. A anomalia do Ce é negativa em todos os períodos e indica condições oxidantes no ambiente deposicional ou oriundas de uma porção detrítica continental. A anomalia do Eu é ligeiramente positiva para todos os períodos. Isto é um indicativo de assimilação ou acúmulo de feldspato. Dados de cinco possíveis fontes para a proveniência do material foram extraídos da literatura. Os sedimentos de Cabo Frio apresentam fracionamento entre ETRL e ETRP próximos aos dados deste estudo. Entretanto, para a razão (Eu/Sm) observa-se boa correlação com fontes vindas da Patagônia e do Rio da Prata. Alguns autores apontam a pluma do Rio da Prata na contribuição sedimentar na região da Bacia de Santos. / The continental sediments deposited in the ocean floor are conditioned, mainly, to the evolution of the climate, the geological substrate and the type of transport, being the fluvial transport of the greater magnitude. Once deposited, the sediments become records of the past and carry information in a form of geochemical signature. Rare Earth Elements (REE) present a coercive behavior along a sedimentary column making them useful for studies of sedimentary origin. Ratios for larger elements (Fe/Ca, for example) are indicators of the reconstruction of the terrigenous port. The geochemistry of the ETR and major elements are determined in this work to understand the paleoclimatic dynamics on the contribution and provenance of the sediments of the eastern margin (Santos Basin) of Brazil, and the anomalies of the Ce and Eu, confronting different analytical techniques (ICP- MS and XRF core scanner) in the main abrupt events (Younger Dryas and Heinrich events) over the last 45,000 years. The origin of the sedimentary material is also discussed by means of ratios between Light Rare Earth Elements (LREE) and Heavy Rare Earth Elements (HREE) comparing possible sources available in the literature. The distribution pattern indicates MREE enrichment over LREE and HREE in all events. This means that the origin of this material, probably, is related to a single source. LREE concentrations are always higher than MREE and HREE. This pattern is another indicative of a single source of sedimentary material. The sum of REE concentrations during MIS 2 is always greater than MIS 1. The behavior of REE during Heinrich events is very similar. The mean REE concentrations in these events are higher than those found in MIS 1 - Interglacial. The analyses of Fe/Ca and Ti/Ca ratios are stronger than those observed during the investigation period (MIS) due to the regressive margin level (continental shelf exposed), and the effects of dilution of the marine carbonate stimulated by imput of organic matter. The Al/Si and Fe/K ratios show distinct signals over time during this study. The increase of Si during MIS 2, in relation to the other periods, indicates that the glacial was less humid than the interglacial. The increase of K within the Heinrich events indicates a change in the continental weather pattern due to rainfall episodes and increase in chemical weathering in the drainage basins. The Ce anomaly is negative at all periods and indicates oxidizing conditions in the depositional environment or from a continental detrital portion. The Eu anomaly is slightly positive for all periods. This is an indicative of assimilation or accumulation of feldspar. Data from five possible sources for a sample of the material was extracted from the literature. The Cabo Frio sediments show the fractionation between LREE and HREE. However, for a (Eu / Sm) ratio a good correlation is observed with sources coming from Patagonia and Rio de la Plata. Some authors point out a region of the River Plate and a sedimentary region in the region of the Santos Basin.

Understanding crystallisation in magma chambers is a key challenge for igneous petrology. It is particularly important to understand the origins of layering in peralkaline rocks, e.g. the kakortokite (nepheline syenite), Ilímaussaq Complex, S. Greenland, as these are commonly associated with high value multi-element economic deposits. The kakortokite is a spectacular example of macrorhythmic (>5 m) layering. Each unit consists of three layers comprising arfvedsonite-rich (sodic-amphibole) black kakortokite at the base, grading into eudialyte-rich (sodic-zirconosilicate) red kakortokite, then alkali feldspar- and nepheline-rich white kakortokite. Each unit is numbered -19 to +17 relative to a characteristic well-developed horizon (Unit 0), however there is little consensus on their development. This project applies a multidisciplinary approach through field observations combined with petrography, crystal size distributions (CSDs), mineral and whole rock chemistries on Units 0, -8 to -11 and a phonolite/micro-nephelinolite (“hybrid”) sequence that crosscuts the layered kakortokite. Textures and compositions are laterally consistent across outcrop and indicators of current activity are rare. CSDs indicate in situ crystallisation with gravitational settling as a minor process. Chemical discontinuities occur across unit boundaries. The layering developed through large-scale processes under exceptionally quiescent conditions. The discontinuities reflect open-system behaviour; units were formed by an influx of volatile-rich magma that initiated crystallisation in a bottom layer. Nucleation was initially suppressed by high volatile element concentrations, which decreased to allow for crystallisation of arfvedsonite, followed by eudialyte, then alkali feldspar and nepheline to form each tripartite unit. The chemistry of the hybrid indicates mixing between a primitive (sub-alkaline) magma and kakortokite. Thus injections of magmas of varying compositions occurred, indicating a complex plumbing system below current exposure. The lessons learned at Ilímaussaq, which is extremely well exposed and preserved, are relevant to understanding magma chamber dynamics in the more common instances of pervasively altered peralkaline rocks.

This report has investigated the ethical issues associated with mining or processing of materials that make them considered as controversial. For each material, the main areas of use and the top producing countries are analysed, followed by social and/or environmental issues as well as potential problems in the future. In total, 13 materials are discussed, of which most are minerals. The overall issues, that are recurring throughout the report and are important to be aware of are: child labor, low safety standards, mining activity resulting in deforestation or harming biodiversity, mining processes that affect communities (e.g. because of large water consumption) and the risks associated with widespread illegal mining. The report also provides research about organisations and initiatives that aim to affect the problems, and gives a brief view over tools that can be used to increase awareness of these issues.

Les terres rares sont des éléments chimiques au comportement très proche. Elles regroupent deux systèmes radioactifs de longue vie: 138La-138Ce (T1/2 = 292.5 Ga) et 147Sm-143Nd (T1/2= 106 Ga). Le Ce présente la particularité de s’oxyder sous forme 4+ dans les milieux supergènes alors que les autres terres rares sont présentes sous forme trivalente (3+). Ce comportement particulier du cérium induit une forte anomalie négative en Ce dans l’eau de mer et dans les sédiments se formant en équilibre avec l’eau de mer (sédiments biogènes et authigènes). L’étude du rapport 138Ce/142Ce peut apporter des informations concernant la nature des sédiments recyclés au cours des processus de subduction, et plus particulièrement sur la participation de sédiments authigènes et biogènes puisque de nombreuses laves sont caractérisées par des anomalies négatives en cérium. L’étude du système 138La-138Ce a été développée dans les années 80. Le temps de demi-vie du système étant important, et l’abondance du 138La faible, les variations du rapport isotopique 138Ce/142Ce sont toujours faibles. Nous proposons donc de reconsidérer l’étude du système 138La-138Ce avec la nouvelle génération de spectromètre de masse. Les mesures isotopiques du Ce sont réalisées sous forme oxyde sur un spectromètre de masse à thermo-ionisation. La précision analytique obtenue, après correction du fractionnement de masse de l’oxygène et de l’effet de queue de pic du 140Ce, est de 40 ppm sur une même session analytique. Une grande quantité de données ont été obtenues sur les standards de Ce AMES et JMC-304, ainsi que sur les standards de roche BCR-2 et BHVO-2. Deux zones de subduction intra-océaniques présentant des contextes géodynamiques contrastés ont été étudiées: les Petites Antilles et les Mariannes. Nous avons analysé les rapports isotopiques 138Ce/142Ce des laves, des sédiments provenant des piles sédimentaires forées en amont des fosses ainsi que des MORB dans le but de mieux caractériser la nature des sédiments participants à la genèse des laves. Les laves de la Martinique (Petites Antilles) présentent de grandes variabilités isotopiques en Ce et corrèlent avec les isotopes du Nd. L’origine des anomalies en cérium des laves ne peut pas être attribuée uniquement au composant sédimentaire participant à la genèse des laves. Dans le cas des Mariannes, les rapports isotopiques en Ce et Nd sont très homogènes. Des mélanges binaires solide-fluide entre le coin de manteau et les sédiments potentiellement subduits nous permettent de déterminer que les anomalies négatives en Ce des laves proviennent de la participation de fluides issus de la fusion partielle des sédiments biosiliceux (entre 1.5 et 7%). / Elements from the Rare Earth Elements have very close chemical behavior. They include two long-lived isotope systems: 138La-138Ce (T1/2 = 292.5 Ga) and 147Sm-143Nd (T1/2 = 106 Ga). Ce displays a specific behavior in supergene environments. For example in seawater cerium is oxidized in Ce (IV) whereas other rare earth elements are present in a trivalent state (3+). Thus, seawater rare earth element patterns are characterized by strong negative Ce anomalies. The sediments formed in equilibrium with seawater (biogenic and authigenic sediments) present similar chemical characteristics. The study of the 138Ce/142Ce ratio in lavas formed in subduction settings is able to bring additional information regarding the nature of recycled sediments, and more particularly the participation of authigenic materials in the genesis of these lavas since negative Ce anomalies are commonly measured in these samples. 138Ce/142Ce variations are always small given the long half-life of the parent isotope and its small abundance. Although the study of 138La-138Ce systematics has been developed during the 80’s, we propose here to reinvestigate its use as a potential tracer of recycled sediment with the new generation of mass spectrometers. The Ce isotopic compositions are measured in oxide species on a thermal ionization mass spectrometer. The analytical precision defined on the same analytical session is about 40 ppm after correction of oxygen mass fractionation and considering the tailing effect of 140Ce on lower masses. A large amount of data has been obtained on two artificial Ce standards (AMES and JMC-304), and on two rock standards (BCR-2 and BHVO-2). Two intra-oceanic subduction zones with contrasting geodynamic settings have been studied: the Lesser Antilles and the Marianas. We have analyzed the 138Ce/142Ce ratio on lavas, sediments drilled in front of the trenches, and MORB, in order to better characterize the nature of the sediments incorporated in the mantle wedge. A large Ce isotopic variability and correlation with Nd isotopes is observed for the Martinique lavas (Lesser Antilles). The origin of Ce anomalies of lavas cannot only be attributed to the participation of sediments at the source of the lavas. Marianas lavas present very similar Ce and Nd isotopic ratios. Binary solid-fluid mixing between the mantle wedge and sediments potentially subducted permits to assess the origin of the Ce anomalies to the participation of fluids coming from the partial melting of biosiliceous sediments (1.5% to 7%).

Cette thèse constitue une étude de référence sur la qualité des ressources hydriques du bassin versant du fleuve Ibrahim au Liban, notamment avant la construction d’un grand barrage (Jannah). Pour ce faire, 7 stations (NI7 à NI1) ont été sélectionnées de l’amont vers l’aval sur l’Ibrahim et ses sources karstiques. L’ensemble des sept sous bassins a été caractérisé d’un point de vue hydroclimatologie et états de surface (sols, végétation, cultures, géologie, relief). Les débits mesurés à l’amont (2 stations) et à l’aval (1 station) nous ont permis de reconstituer les débits des autres stations intermédiaires grâce à des relations débits-surfaces spécifiques. À partir de prélèvements et d’analyses chimiques de la composition des eaux tout au long d’un cycle hydrologique et avec une fréquence mensuelle, les flux de matières exportées en solution par l’Ibrahim ont été estimés à 122 372 t/an. 80% de ce tonnage est exporté durant la période des hautes eaux. À partir de ce tonnage, on a pu estimer que l’altération chimique des roches carbonatées sur l’ensemble du bassin s’effectue à la vitesse de 81 cm/10000 ans. Cette altération consomme un flux élevé de CO2 typique des régions carbonatées soumises à un drainage intense (1500 mm/an), soit 2,23 x106 moles/km2/an de CO2. L’analyse de la concentration en éléments traces dans les sédiments de fond des cours d’eau, intégrateurs des transports solides, en hautes eaux et en basses eaux, montre des concentrations élevées pour le Sc, V, Cr, Co, Ni, Ga et Cu en passant de NI5 jusqu’à NI2. L’évaluation du degré de cette contamination et de sa variation spatio-temporelle a été effectuée grâce au facteur d’enrichissement en normalisant par rapport à l’aluminium et en prenant les sédiments de la station amont NI7 (source karstique) considérés comme peu ou pas contaminés en ET, comme fond géochimique naturel. Des teneurs élevées en Zn, Pb, Cu et d’autres éléments traces montrent que dans cette région où les activités industrielles, agricoles, et urbaines sont développées, il existe un apport anthropique non négligeable en éléments métalliques. Mais cette contamination reste modérée / Throughout the study framework conducted on the quality of the water resources in the Ibrahim River watershed in Lebanon (notably before the construction of a large dam, Jannah), 7 stations (NI7 to NI1) were selected, from upstream to downstream, including its karst springs. Hydroclimatological and specific catchment characteristics (such as land cover use, geology, hydrology, soil and topography) where characterized for the whole seven sub-basins respectively. Discharge data from the sources (2 stations) and the basin outlet (1 station) enhanced our study to determine and further calculate the discharge of other stations. Sampling and analyzing the chemical composition of water collected monthly during one hydrological cycle allowed us to determine the amount of dissolved material carried by the Ibrahim River. The river flux of dissolved material was estimated at 122 372 tons / year of which 80% of is exported during high flow season. Therefore this flux allowed us to estimate the rate of chemical weathering of carbonate rocks across the basin at 81 cm / 10000 years. This alteration consumes a high flux of CO2 (around 2,23x106 moles/km2/year of CO2) typical for carbonate regions subject to intense drainage (1500 mm). The analysis for the concentration of trace elements in fluvial sediments for the Ibrahim River for the low and high flow periods shows high concentrations of Sc, V, Cr, Co, Ni, Cu and Ga in the from NI5 station up to NI2. The assessment of the extent of the contamination and its spatio-temporal variation was conducted using the enrichment factor by normalizing to aluminium concentration and using the element concentrations in the sediments of station NI7 (karstic sspring) considered as the natural geochemical background for this catchment. High levels of Zn, Pb, Cu and other traces of noticeable elements show that in this region where industrial, agricultural and urban activities are developed, there is a significant anthropogenic contribution for some metallic elements; thus the trace element contamination remains moderate.

No description available.