O período pós-colisional do Ciclo Brasiliano/Pan-africano é marcado no sul do Brasil pela ocorrência de granitos metaluminosos e peraluminosos, controlados por um sistema transcorrente de zonas de cisalhamento (ZC). No Rio Grande do Sul (RS), a Zona de Cisalhamento Transcorrente Dorsal de Canguçu (ZCTDC), de cinemática sinistral e direção NE, é a principal estrutura que condicionou o posicionamento desses granitos (ca. 634 – 610 Ma). Entretanto, o Granito Butiá (GB – 629 Ma), localizado a noroeste da ZCTDC, ocorre como um corpo alongado de direção NNW que intrude rochas de alto grau metamórfico do Complexo Várzea do Capivarita (ca. 650 Ma). O GB possui trama planar bem desenvolvida (S>L), cuja foliação mergulha com alto ângulo para NNW; apesar de raramente apresentar lineação, seu posicionamento é interpretado como sintectônico a uma ZC transcorrente de cinemática destral. Dessa forma, um estudo de anisotropia de susceptibilidade magnética (ASM) foi realizado no GB, com o objetivo de melhor delimitar os mecanismos de seu posicionamento e relacioná-los com o sistema regional de zonas de cisalhamento. No total, 492 espécimes (180 cilindros) foram coletadas em 16 sítios, distribuídos no corpo principal do GB. A mineralogia magnética foi investigada através de curvas termomagnéticas, curvas de histereses e de aquisição de magnetização remanente isotermal, e detalhada com microscopia eletrônica de varredura em amostras representativas. Essas análises demonstram o domínio de fases paramagnéticas e uma pequena contribuição de minerais de baixa coercividade (e.g., magnetita, titanomagnetita) e alta coercividade (e.g., hematita). Apesar disso, a trama magnética é controlada exclusivamente por cristais paramagnéticos de biotita. A susceptibilidade magnética total é baixa e varia entre 0,1 e 8x10-5 SI. O parâmetro de forma (T) varia de 0,272 a 0,908 e o grau de anisotropia (P) varia de 1,073 a 1,266, aumentando do centro em direção as margens do GB. A presença de par S-C destral de origem magmática e microestruturas de deformação em alta temperatura (~650°C) confirmam que a deformação atuava durante o processo de cristalização. Esses elementos, junto à análise da trama magnética, sugerem que a ascensão e o posicionamento do magma foram controlados por uma ZC transcorrente de direção NNW e cinemática destral. Próximo as rochas encaixantes, os elipsoides magnéticos são fortemente oblatos, a foliação mergulha com alto ângulo para W ou E, e a lineação têm alto a moderado caimento, sugerindo significante achatamento e domínio de uma componente de cisalhamento puro de deformação. Longe das margens, a lineação tem baixos caimentos, paralelos a direção da foliação (NW-NNW), sugerindo um transporte horizontal e domínio de uma componente de cisalhamento simples de deformação, que promoveu o estiramento. No nordeste do corpo, a presença de roof pendants e menores ângulos de mergulho da foliação sugerem proximidade com a cúpula. A combinanção de bouyoancy forces e da partição da deformação regional, em cisalhamento puro e simples durante o posicionamento do GB, está de acordo com um regime transpressivo. Esses resultados também sugerem uma relação no tempo-espaço entre a ZC que controlou o posicionamento do GB e a ZCTDC. Possivelmente, elas formavam um par conjugado do mesmo sistema transcorrente durante o estágio pós-colisional do Ciclo Brasiliano/Pan-africano no sul do Brasil. / The post-collisional stage of the Brasiliano/Pan-African Orogenic Cycle in Southern Brazil is marked by metaluminous and peraluminous granites controlled by a transcurrent shear zone system. In the Rio Grande do Sul State, southernmost Brazil, the sinistral, NE-trending Dorsal de Canguçu Transcurrent Shear Zone (DCTSZ) is the best known structure that conditioned these peraluminous granites (ca. 634 – 610 Ma). However, the NNW-elongate Butiá Granite (BG – 629 Ma) is emplaced to the northwest of the DCTSZ, intrusive in the high-grade Várzea do Capivarita Complex (ca. 650 Ma). The BG has a S>L fabric, which foliation steeply dips towards NNW. Despite its poorly-developed linear fabric, BG emplacement is interpreted to have been controlled by a dextral transcurrent shear zone. Thus, anisotropy of magnetic susceptibility (AMS) study was performed in the BG aiming to constrain its emplacement mechanism and the relation of the granite with the regional shear zone system. A total of 492 specimens (180 drill cores) were obtained through 16 sites distributed along the BG main body. Magnetic mineralogy was investigated by hysteresis loops, thermomagnetic and IRM acquisition curves, and a complementary SEM analysis in representative samples. These experiments show a dominant contribution of paramagnetic phases and a small content of low-coercivity (e.g., magnetite and titanomagnetite) and highcoercivity (e.g., hematite) remanence-carrying minerals. In spite of the presence of minor ferromagnetic grains, the BG magnetic anisotropy fabric is interpreted as dominantly controlled by paramagnetic biotite crystals. The bulk magnetic susceptibility ranges between 0.1 and 8.0×10−5 SI. Shape parameter (T) ranges from 0.272 to 0.908, and anisotropy degree (P) ranges from 1.073 to 1.266, increasing from the inner portion of the pluton to its margins. The presence of dextral S-C magmatic fabric and high temperature (ca. 650 °C), solid-state deformation at the margins confirms that the pluton was deformed during its cooling process. Such features, together the magnetic fabric analysis, suggest that magma ascent and emplacement were controlled by a NNW-trending dextral transcurrent shear zone. Close to the host-rocks, magnetic foliation dips steeply towards W or E, and magnetic lineation plunges steeply to moderate, displaying strongly-oblate ellipsoids. This is interpreted as a result of shortening and the significantly pure-shear component of deformation operating close to the host-rocks. Shallow-plunging lineation parallel to the NWto NNW-striking foliation is found away from the pluton margins, which is related to the horizontal displacement, where the simple-shear component of deformation was more effective, resulting stretching. Foliation becomes less steep towards the BG northeastern portion and the presence of roof pendants in this area suggests the proximity to the roof zone. The combination of buoyancy forces and the partitioning of regional strain into simple and pure shear are in accordance with a transpressive regime. These results also suggest a time-space relationship between the NNW-dextral shear zone that controlled the emplacement of the Butiá Granite and the sinistral, NE-trending DCTSZ, responsible for the emplacement of peraluminous granites. Possibly, these zones formed a conjugate pair during the transcurrent deformation of the early post-collisional stage of the Brasiliano/PanAfrican Cycle in southernmost Brazil.

A Faixa Araçuaí foi formada no Neoproterozóico a partir da colisão E-W entre os continentes Sul-Americano e Africano. Sua porção leste compreende uma extensa área migmatítica (~300 km de comprimento por 50-100 km de largura) onde afloram anatexitos e leucogranitos (unidade Carlos Chagas), kinzigitos e granulitos migmatizados, que provavelmente são o registro de uma ampla fusão parcial da crosta intermediária a inferior. Observações de campo associadas com evidências micro-estruturais indicam que a deformação ocorreu quando as rochas estavam incompletamente solidificadas. Estimativas de temperaturas sincinemáticas realizadas a partir do geotermômetro TitaniQ (titânio-em-quartzo) indicam que a temperatura mínima para a cristalização de cristais de quartzo é ~750°C. Tais temperaturas combinadas com composição química de leucossomas dos anatexitos sugerem que a viscosidade das rochas crustais foi reduzida para pelo menos 108 Pa s. Baixo valor de viscosidade associado às evidências de campo e de micro-estruturas são consistentes com a geração de no mínimo 30% de volume de magma durante a orogênese. Grandes quantidades de magma promovem um drástico enfraquecimento da resistência mecânica das rochas à deformação, e atestam que a crosta anatética do extremo leste da Faixa Araçuaí representa um análogo de litosferas quentes (hot orogen), tal como a Himalaiana. Investigação mineralógica detalhada permitiu caracterizar um comportamento dominantemente paramagnético para os anatexitos e ferromagnético para os granulitos. Medidas de orientação preferencial cristalográfica (OPC) a partir da técnica de EBSD (electron backscatter diffraction) revelam que a foliação magnética surge, sobretudo, a partir da orientação preferencial dos eixos [001] da biotita orientados perpendicularmente ao plano de fluxo. Contudo, dada a fraca anisotropia linear desse mineral, apenas uma secundária contribuição de sua subtrama foi observada para a origem da lineação magnética (k1). A correspondência entre os eixos [001] de feldspatos e k1 ocorre devido a OPC de pequenas inclusões de ilmenita que imitam a OPC de seus minerais hospedeiros. Correlação entre k1 da Anisotropia de Remanência Anistéretica (ARA) e k1 da Anisotropia de Suscetibilidade Magnética (ASM) demonstra que, na escala do espécime, a lineação magnética tem uma contribuição da anisotropia dos minerais ferromagnéticos. Assim sendo, a lineação magnética nos anatexitos é o resultado da combinação da trama cristalográfica de feldspatos e de biotita com o alinhamento preferencial de grãos ferromagnéticos. Medidas de ASM realizadas para recuperar a trama mineral e investigar o fluxo nos migmatitos revela um padrão de deformação complexo, no qual, em função das direções de lineação, especialmente, é possível caracterizar três setores estruturais. A porção norte (região estrutural 1) com foliações dominantemente sub-horizontais e lineação fortemente orientada na direção NW-SE representa uma região de escape tectônico que ocorre através de um fluxo horizontal de canal (channel flow). Fluxos de canais possivelmente resultam da atuação de forças gravitacionais (gravity-driven flow). O setor sul (regiões estruturais 2 e 3) com variadas direções de foliação (NE-SW, E-W e NW-SE) e lineações com caimentos para Norte e Oeste, provavelmente refletem um regime de fluxo influenciado, sobretudo, pela tectônica de convergência E-W (collision-driven flow). Ambos os setores sugerem que na escala regional o fluxo crustal registrado pelos migmatitos resulta de um regime de deformação que envolve forças gravitacionais, devido a carga topográfica da crosta superior sobreposta à crosta intermediária parcialmente fundida, com viscosidade baixa, e forças tectônicas, associadas à colisão entre os continentes Sul-Americano e Africano. / The Araçuaí belt was formed by the collision between South American and African protocontinents during the Neoproterozoic. Its eastern part consists of an extensive migmatitic area (~300 km long x 50-100 km wide) where crop out anatexites and leucogranites (Carlos Chagas unit), migmatitic kinzigites and granulites that probably are the record of a widespread partial melting of the middle to lower crust. Field observations associated with microstructural evidences indicate that the deformation occurred when the rocks were incompletely solidified. Synkinematic temperature estimates realized using the TitaniQ (titaniun-in-quartz) geotermomether suggest that the minimum temperature for the quartz crystallization is ~750°C. Such temperatures combined with bulk rock composition of leucosome in the anatexites suggest that the viscosity of crustal rocks was dropped to at least 108 Pa s. Low viscosity values associated with field and microstructural evidences are consistent with the generation of at least 30% volume of melt during the orogeny. The presence of large volumes of melt promotes a drastic weakening of the mechanical strength of rocks and suggests that the anatectic crust of the eastern Araçuaí belt represents an analogue of present day hot orogen such the Himalayas. Detailed mineralogy investigation permitted to characterize the paramagnetic behaviour of the anatexites and the ferromagnetic behaviour of the granulites. Crystallographic preferred orientation (CPO) measurements using the EBSD (Electron Backscatter Diffraction) technique reveal that the magnetic foliation results from the preferred orientation of the biotite [001] oriented normal to the flow plane. However, given the feeble linear anisotropy of this mineral, only a subsidiary contribution of its subfabric to the origin of the magnetic lineation (k1) was observed. Correspondence between [001] of feldspars and k1 is due to the CPO of small inclusions of ilmenite that mimic the CPO of their host minerals. Correlation between k1 of the Anisotropy of Anhysteretic Remanent Magnetization (AARM) and k1 of the Anisotropy of Magnetic Susceptibility (AMS) demonstrate that, at the specimen scale, the magnetic lineation has a contribution of the anisotropy of the ferromagnetic minerals. AMS measurements realized to recover the mineral fabric and investigate the migmatitic flow field revealed a complex strain pattern in which, considering the lineation trends, especially, it is possible to characterize three structural sectors. The north region (structural sector 1) with foliations dominantly sub-horizontal and lineation trending NW-SE is interpreted as a region of tectonic escape that may represent a horizontal channel flow. This oblique tectonic escape probably results from gravity forces (gravity-driven flow). The Southern region (structural sectors 2 and 3) with variable trending foliations (NE-SW, E-W and NW-SE) and lineation plunging to North and West, probably reflect a flow regime dominantly influenced by the E-W convergence of the African and South-American continents (collision-driven flow). Altogether, the characteristics of the various domains suggest that the deformation of the partially molten middle crust of the Araçuaí belt was the result of the combination of gravity forces due to the topographic load and tectonic forces due to the convergence between the African and South-American continents.

Le but de ce travail a été de réaliser des études téphrostratigraphiques sur des environnements sédimentaires variés dans le but de définir, dans un premier temps, le degré d'efficacité des techniques de détection des téphras classiquement utilisées. Le travail d'analyse des cendres volcaniques a tout d'abord été ciblé sur des téphras clés et anciennement étudiés sur des sites reconnus, en Belgique et dans le Massif du Jura, dans le but d'actualiser des données avec les techniques d'analyses performantes actuelles. Le travail a ensuite été étendu à des sites de l'Est du Massif Central, dont le potentiel téphrostratigraphique n'avait jamais été exploité, offrant ainsi la possibilité de s'assurer sans ambiguïté de la source de cryptotéphras repérés dans le Jura et en Suisse, dont l'origine était incertaine. Ce travail d'échantillonnage a été réalisé dans des milieux lœssiques, carbonatés et tourbeux permettant également de discuter des conditions de conservation des dépôts volcaniques et de leurs constituants. Les études téphro-chrono-stratigraphiques s'inscrivent fréquemment dans une réflexion sur l'impact écologique et environnemental des éruptions volcaniques. Un nombre croissant d'études tendent à montrer un impact écologique des téphras, en étant la cause de bloom de diatomées. Ce travail de thèse a permis de discuter de cet aspect environnemental qui a été mené dans le Jura, dans un environnement défavorable à la préservation des diatomées. / The challenge of this work was to carry out several tephrostratigraphic studies in various sedimentary environments in order to test the efficiency of classical detection methods of tephra layers. First, analysis has been focused on tephra keys, previously studied in known sites, in Belgium and in the Jura Mountains, in order to update data with current analytical techniques. This work was later expanded to sites from eastern French Massif Central, an area with unexploited tephrostratigraphic potential, which offers the possibility to precise the source of cryptotephras identified in the Jura and Switzerland whose origin was uncertain. This work has been carried out in tephras sampled in loess, carbonate maris and peat allowing to discuss conservation conditions of volcanic deposits. Sorne tephro-chrono-stratigraphic studies show ecological and environmental impacts of volcanic deposits in lakes and peatlands, such as diatom blooms. This thesis allows to discuss this environmental aspect in carbonate maris, i.e. an unfavorable environment for preservation of diatoms.

Un des enjeux majeurs dans le domaine du magnétisme moléculaire est de mieux comprendre et prévoir, dans les composés à base moléculaire, les corrélations qui existent entre les propriétés structurales (modulables à partir de méthodes de synthèse de type « bottom-up ») et les propriétés magnétiques. En particulier, la compréhension et la maîtrise de l’anisotropie magnétique à l’échelle locale est primordiale, notamment en vue de concevoir des molécules-aimants avec de plus hautes températures de blocage. Dans ce contexte, ce travail de thèse s’organise autour de deux grands axes. La première partie se concentre sur la détermination et la caractérisation de l’anisotropie magnétique locale dans des complexes moléculaires d’ions de transition de faible nucléarité. La diffraction de neutrons polarisés (PND) nous a permis, pour la première fois, de mettre clairement en évidence le tenseur de susceptibilité magnétique locale dans un complexe moléculaire mononucléaire de Fe3+ Bas-Spin ainsi que dans deux complexes, mononucléaire et dinucléaire, de Co2+ Haut-Spin. Cette approche novatrice mène à l’établissement de relations magnéto-structurales claires et directes, en reliant les directions magnétiques locales propres à l’environnement de coordination des ions métalliques et en particulier aux axes locaux de distorsion. Nous avons également mené l’étude originale d’un complexe à transition de spin thermo-induite de Mn3+ par diffusion inélastique de neutrons (INS) dans les deux phases Haut-Spin (HS) et Bas-Spin (BS). Cette étude nous a conduits à la proposition d’un modèle d’hamiltonien de spin anisotrope dans les deux états HS et BS, en relation avec la structure du complexe. Dans une seconde partie plus exploratoire de la thèse, nous avons mené une étude complète des propriétés structurales et magnétiques de nanoparticules ferromagnétiques d’analogue du bleu de Prusse CsNiCr, par diffusion de neutrons aux petits angles (SANS). Les effets de taille, d’organisation et de concentration sur leurs propriétés superparamagnétiques ont ainsi été clairement mis en évidence. En particulier, nous avons mis en exergue, pour les particules de plus petite taille (5 nm de diamètre), une contribution magnétique qui résulte de la manifestation d’un phénomène collectif, tandis que celles de plus grande taille (28 nm de diamètre) apparaissent être dans un état complètement multidomaine. / One of the major issues in the field of molecular magnetism is to better understand and predict the correlations between the structural properties of molecule-based compounds and their magnetic properties, all of which may be tunable using “bottom-up” synthesis methods. In particular, the understanding and control of the magnetic anisotropy at the atomic scale is essential, especially with the aim to design Single-Molecule Magnets (SMM) with higher blocking temperatures. In this context, this thesis work is focused on two mains subjects. The first part deals with the determination and the characterization of the local magnetic anisotropy in low-nuclearity molecular complexes based on transition ions. Polarised neutron diffraction (PND) allows us, for the first time, to directly access the local susceptibility tensor in a Low-Spin Fe3+ mononuclear complex as well as in two, mononuclear and dinuclear, High-Spin Co2+ complexes. This innovative approach leads to the establishment of unique and direct magneto-structural correlations, by relating the local magnetic principal directions with the coordination environment of the metallic ions and, in particular, with the local distortion axes. We have also carried out an original investigation by inelastic neutron scattering (INS) of a Mn3+ thermo-induced spin-transition compound in both High-Spin (HS) and Low-Spin (LS) states. On the basis of this study, we were able to propose an anisotropic spin-Hamiltonian model in both HS and LS phases, and their relationships with the structure of the molecule are discussed. In a second more exploratory part of the thesis, we have carried out by small-angle neutron scattering (SANS) a complete study of the structural and magnetic properties of Prussian blue analogues (PBA) ferromagnetic nanoparticles CsNiCr. The effects of size, organization and concentration on their superparamagnetic properties have been clearly highlighted. In particular, a strong magnetic contribution has been observed for the smallest particles (5 nm diameter) which results from the manifestation of a collective process, while the biggest (28 nm diameter) appear to be in a multi-domain state.

Os sistemas estuarinos são ambientes de transição entre o continente e o oceano, onde atividades humanas são intensivamente desenvolvidas. O Sistema Estuarino de Santos e São Vicente, localizado na porção central do Litoral do Estado de São Paulo, tem se destacado como um dos principais pólos econômicos do Brasil, devido ao complexo petroquímico e siderúrgico, ao Porto de Santos e à aptidão turística da região. O rápido e intenso desenvolvimento, a partir da década de 40, resultou na degradação do ecossistema local devido à introdução de esgotos e efluentes não-tratados, bem como ao aporte atmosférico de substâncias nocivas. O objetivo principal deste trabalho foi determinar as concentrações de hidrocarbonetos marcadores geoquímicos em sedimentos de testemunhos, para traçar o histórico da contribuição destes compostos ao longo dos últimos 100 anos, relacionando os resultados com a ocupação urbano-industrial da região. Paralelamente, procurou-se determinar a origem da matéria orgânica sedimentar (C, N e S) assim como verificar a existência de correlação estatística entre os hidrocarbonetos e a susceptibilidade magnética, ou seja, indicadores de poluição de natureza distinta. Quatro testemunhos foram coletados em áreas de mangue e próximas à fontes pontuais de poluição, como o lixão do Alemoa, o terminal petrolífero do Alemoa e próximo ao acesso do Pólo Industrial de Cubatão. A identificação e quantificação dos hidrocarbonetos foram feitas por um cromatográfo a gás acoplado a um detector de ionização de chama (GC-FID) para os hidrocarbonetos alifáticos e a um espectrômetro de massa (GC-MS) para os hidrocarbonetos policíclicos aromáticos (PAHs). A análise granulométrica mostrou o predomínio de sedimentos lamosos nos sedimentos mais recentes, devido a progradação das áreas de mangue e às atividades antrópicas como o escorregamento de morros adjacentes e a dragagem de canais. A aumento no teor do nitrogênio (Ntot.) nas secções próximas ao topo dos testemunhos é proveniente das indústrias de fertilizantes e do lançamento de esgotos não-tratados. Embora tenha ocorrido um aumento na concentração de n-alcanos de fontes antrópicas ao longo dos últimos anos, a introdução biogênica aparece como um importante componente no total dos n-alcanos, sendo atribuída à contribuição dos múltiplos rios que deságuam no estuário e do mangue adjacente. A distribuição da concentração dos hidrocarbonetos alifáticos, em particular a mistura complexa não resolvida, foi relacionada com o desenvolvimento do Pólo Industrial de Cubatão e do Porto de Santos, à deposição de resíduos sólidos no morro do Alemoa e à adoção de medidas de controle de poluição por parte das indústrias da região. Em relação aos PAHs, foi possível estabelecer as principais fontes (petrogênica ou pirolítica) destes compostos ao longo dos testemunhos. O predomínio de PAHs de maior peso molecular (4 – 6 anéis), indicou contribuição antrópica da queima de biomassa, carvão, óleo bruto e combustíveis fósseis. A correlação estatística entre hidrocarbonetos e susceptibilidade magnética mostrou a aplicabilidade deste parâmetro na avaliação preliminar do histórico da poluição de sedimentos marinhos. O aporte de metais magnéticos, caracterizado pela susceptibilidade magnética, foi associado a diferentes fontes antrópicas de hidrocarbonetos e aos principais eventos históricos relacionados com o desenvolvimento urbano-industrial da Baixada Santista. / Estuarine areas are environments between land and ocean, where human activities are intensively developed. The Santos and São Vicente Estuary, located on the central portion of the coast of São Paulo state, has one of the most important industrial areas of Brazil. The increasing of urbanization and industrialization near the margins of Estuary, in the 50’s, has been responsible for the degradation of the mangrove, for the discharge of sewage, and consequently, it affects the input of organic matter and sedimentary deposition. The main objective of this work was to determine the concentration of hydrocarbons biomarkers in sediment cores in order to investigate the input of these substances in the last 100 years, and to find a relation with the urban and industrial occupation in this area. The organic matter origins (C, N and S) are also studied. A possible statistical correlation between two different pollution indicators (hydrocarbons and magnetic susceptibility) was investigated. Four sediments cores are collected in mangrove areas and near polluted places, as Alemoa garbage disposal, Alemoa petroliferous terminal and Cubatão industrial complex. Hydrocarbons concentrations were determined by gas chromatograph with flame ionization detector (GC-FID) for aliphatic compounds and by gas chromatograph coupled with mass spectrometer for polycyclic aromatic hydrocarbons (PAHs). The grain-size analyses showed that in the recent sediments, mud was predominant. It was associated with the mangrove progradation and anthropogenic activities such as settlement, garbage disposal and sweep activities. High nitrogen concentrations were found in the sediments near the top of the cores and it was associated with inputs from untreated sewage and industries. Although a large anthropogenic input of n-alkanes was detected in the recent sediments, the biogenic contribution by rivers and direct input from mangrove vegetation is an important in the total n-alkanes. The distribution of aliphatic hydrocarbons in the cores, meanly concerning “Unresolved Complex Mixture”, was associated with the formation and development of Cubatão industrial complex and the Santos harbour, waste disposal in Alemoa hill and with the preservation program, that results in the improvement of waste treatment and decrease of organic pollutants input in this area. The PAHs analyses indicated multiplies sources of these compounds (petrogenic and pyrolitic). The predominance of higher molecular weight compounds (4 – 6 aromatic rings) showed anthropogenic contribution from biomass, coal, oil and fossil fuels combustion. Statistical correlation of magnetic susceptibility with hydrocarbons indicated that the input of magnetic metals could be associated with several sources of hydrocarbons, related with the urban and industrial development of Santos and São Vicente Estuary.

Loess is a silty material produced via glacial grinding and its deposition is usually associated with colder periods when there is a considerable increase in atmospheric dust transport. The magnetic susceptibility of loess-palaeosol sequences has been the subject of extensive research within palaeoclimatology as it has proven to be reliable climate proxy. Most research on magnetic susceptibility has been focused on thick deposits found in Europe and Asia, in particular the Chinese Loess Plateau where it is possible to discern more than 2.5 million years of climate variation in deposits several hundred meters thick. The climate development throughout the Quaternary has been characterized by glacials where there has been a significant ice growth, and interglacials where ice sheets have retreated. The Last Glacial Maximum was the most recent time of ice sheets reaching their maximum extent, occurring at some point between 26.5 and 18 ka BP. Aeolian reworking of material produced in conjunction with the Irish Sea Ice Stream (ISIS) occurred approximately 5000 years after the LGM. The ISIS limit were located just north of the Lizard Peninsula, and impinged on the Isles of Scilly. Loess deposits in SW England has largely been ignored in previous research in favour of the previously mentioned Chinese loess, but may be important climate archives in understanding the climate development of the North Atlantic. As such, the scope of this thesis is investigating the magnetic susceptibility of loess deposits in Cornwall and the Isles of Scilly in the far SW England. This is done by analyzing 36 samples from Lowland Point and 24 samples from Chynhalls Point, both located at the Lizard Peninsula in Cornwall, as well as 20 samples from Porthcressa and 14 samples from Gimble Porth, both located at the Isles of Scilly. The instruments used for analysis are the Bartington MS2B and the Agico MFK-1 FA Kappabridge, where all 96 samples were analyzed on the former while the 36 Lowland Points samples and the 20 Porthcressa samples were also analyzed on the latter. The Bartington MS2B operates at two frequencies, 465 Hz and 4650 Hz, while the Agico MFK-1 FA Kappabridge operates at three frequencies, 976 hz, 3904 Hz, and 15616 Hz. The results from this study suggest that the Lizard Peninsula sample sites exhibit signs of magnetic enhancement through pedogenic processes while the sample sites at the Isles of Scilly consist of mainly unaltered material, likely due to an overlying sollifluction unit inhibiting magnetic enhancement. As a consequence of the different frequencies, the results were lognormalized to permit a direct comparison between the instruments. While the variability in magnetic susceptibility was strikingly similar, the results of the Kappabridge were shifted to ~20% higher values than those of the Bartington which may be attributed to the Kappabridges higher precision when analyzing weakly magnetic material. A similar shift is not evident when measuring the calibration samples of each instrument. In determining the mean annual precipitation after deposition, the Lizard Peninsula samples sites suggest an exposure to an annual precipitation between 300-400 mm/yr, compared to modern rainfall between 900-1000 mm/yr. The data from the Isles of Scilly were insufficient for calculating the mean annual precipitation due to the lack of evidence for magnetic enhancement. / Loess är benämningen för material i siltstorlek som produceras då glacial aktivitet maler ned den underliggande berggrunden. Detta material är tillräckligt litet för att fångas upp av vindar och därefter transporteras i atmosfären, för att därefter avsättas då vindhastigheten minskar. Under kalla perioder i jordens historia ökar denna transport då vindhastigheten ofta varit högre än under varma perioder. Under de varmare perioderna och med tiden så utsätts loess för jordmånsbildande processer och bildar palaeosoler. Den magnetiska susceptibiliteten hos loess-palaeosol-sekvenser har under flera årtionden varit ämnet för utbredd forskning då detta har visat sig vara en tillförlitlig klimatproxy för att förstå klimatutvecklingen under jordens gångna historia. I synnerhet har loess-palaeosol-sekvenser i Kina varit av intresse då det går att utröna mer än 2,5 miljoner år av klimatutveckling i avlagringar som på sina platser är flera hundra meter tjocka. Under den senaste istidens maximala utbredning mellan 26500 och 18000 år sedan passerade en isström över den Irländska sjön (Irish Sea Ice Stream, sammankopplad med inlandsisen), förbi Cornwalls norra kust och stötte samman med Scillyöarna. Det tog sedan ungefär 5000 år tills vindtransport av avsatt material påbörjades. Loessavlagringar i sydvästra England har känts till under årtionden men har till stor del ignorerats till fördel för de tidigare nämnda avlagringarna i Kina, men de kan agera som viktiga klimatarkiv för tiden efter den senaste istiden och därmed klimatutvecklingen i Nordatlanten. Denna rapport undersöker således den magnetiska susceptibiliteten i loess från två platser på Lizard-halvön i Cornwall, och två platser på Scillyöarna. Totalt analyserades 96 prover, 36 av dem från Lowland Point, 24 av dem från Chynhalls Point, båda belägna på Lizard-halvön, samt 20 prover från Porthcressa och 14 prover från Gimble Porth, båda belägna på Scillyöarna. Resultaten från denna studie påvisar att provplatserna på Lizard-halvön visar tecken på magnetisk förstärkning på grund av jordmånsbildande processer, medan provplatserna på Scillyöarna huvudsakligen består av oförändrat material, troligen på grund av att dessa täckts av annat material under isens tillbakadragning, vilket förhindrat jordmånsbildning. Resultaten från Lizard-halvön möjliggör beräkning av årsmedelnederbörden sedan materialet först avsattes, vilket beräknades till mellan 300-400 mm/år jämfört med modern årsmedelnederbörd mellan 900-1000 mm/år. Dessvärre möjliggjorde inte resultaten från provplatserna på Scillyöarna en liknande beräkning.

Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...

Combined anisotropy of magnetic susceptibility (AMS) and crystallographic studies were applied on a neogenne lava flow, for which we know the supposed flow path. Samples were studied under microscope, the minerals were analysed on microprobe, the orientation of olivine crystals was determined via EBSD and magnetic properties were studied. AMS data acquired from samples collected from representative outcrops of lava flow show weak preferred orientation of magnetite-ulvöspinel. EBSD analysis suggests only slight orientation of plagioclase in one sample. Analysed composition of olivine corresponds with mathematical model for eruption temperature and crystallization succession. Rootless cone (disorderly breccia cone) in lava body was found and desribed in the abandoned Machův lom quarry.

The physical properties of the coarse fraction of the till (0.4 to 20 cm) and the surface boulders have been studied at two different sites in Sweden. The research work included: development of a new image analysis software for 3D size and shape measurements of particles; lithological analysis on multiple size fractions in till and magnetic susceptibility survey on coarse till clasts, surface boulders and local bedrock. The new 3D image analysis method provides an enormous amount of size and shape data for each particle in the coarse fraction (2 to 20 cm) in till. The method is suitable for field study, cost effective and the software is executable in Matlab. The field imaging method together with the image analysis software give non subjective results of size and shape of coarse particles and makes it feasible and easy to study representative sample size, which is one tonne for testing clasts of size up to 20 cm. The lithological analysis of the multiple size fraction of the till clasts has been investigated on six different size fractions of the till (0.4 to 20 cm); the result of the different samples from the two sites shows that this method can potentially be used as a stratigraphic tool in the areas where there is no unique indicator lithologies. The magnetic susceptibility has been made on the surface boulders, the 6-20 cm till fraction and on insitu bedrock outcrops near to the study sites. The method has good potential for determining stratigraphic relationships between different till units as well as for determining the provenance ofcoarse clasts and surface boulders. / QC 20110413

Numerous techniques are used to study the magnetic history and properties of rocks, which provides important data on the Earth’s interior. In this study we conducted a series of experiments on two different sample sets, comprising pure magnetite (Set1) and a mixture of magnetite-hemoilmenite-bearing quartzite (Set2), in order to gather information about their magnetic susceptibility and remanent magnetization. A miniature diamond anvil cell (mDAC) constructed from hardened non-magnetic alloy (40HNU) was used for high pressure experiments. With the help of high sensitivity susceptibility bridge (MFK1-FA Kappabridge, AGICO), we measured the susceptibility of three samples and of the mDAC. Consequently, we loaded one of the samples in the mDAC and acquired susceptibility measurements during the compression and decompression of the system. For remanence measurements we used a 2G Enterprises SQUID magnetometer. We measured the natural remanent magnetization (NRM) and performed alternating field (AF) demagnetization on ten samples and on the mDAC. Additionally, isothermal and anhysteretic remanent magnetization (IRM and ARM) acquisition were performed on nine and one samples, respectively and demagnetization on three and one samples, respectively. Results showed that Set1 samples consist of both SD and MD magnetite grains. Regarding Set2 samples, the main magnetic carriers are SD and MD magnetite or titanium bearing magnetite grains, while there are indications that hematite and ferrimagnetic titanohematite might be present as well. The presence of eddy currents, due to the conducting materials of the mDAC, resulted in masking the signal of the sample making it difficult to draw any safe conclusions regarding how the susceptibility of the sample changes with pressure. All in all, there was a satisfactory response of the instruments working with very small amounts of material and an adequate signal stability of both the samples and the mDAC. Our study provided us with an insight into high pressure experiments and showed possible directions for future studies. / Många metoder används för att studera magnetiska egenskaper i berg, vilket ger viktig information om Jordens inre. I denna studie genomförde vi en rad experiment på två olika uppsättningar prov, innefattande ren magnetit (Set1) och en blandning av magnetit-hemoilmenit-bärande kvartsit (Set2), för att samla information om deras magnetisk susceptibilitet och magnetiska remanens. En miniatyr diamantstädcell (mDAC) konstruerad av en härdad icke-magnetisk legering (40HNU) användes för högtrycksexperiment. Susceptibilitetet av tre prover och av mDAC mättes en MFK1-FA Kappabridge, AGICO. Följaktligen monterade vi ett av proverna i mDAC och vi genomförde susceptibilitetsmätningar under kompression och dekompression. Vi använde en 2G Enterprises SQUID magnetometer för remanensmätningar. Den naturlig remanentmagnetiseringen (NRM) mättes och vi utförde alternerande fält (AF) demagnetisering på tio prover och på mDAC. Dessutom genomfördes isotermisk och anhysteretisk remanentmagnetisering (IRM och ARM) på nio respektive ett prover, och demagnetisering på tre respektive ett prover. Resultaten visade att Set1-prover består av både enkeldomän (SD) och multidomän (MD) magnetit. SD och MD magnetit- och titanomagnetitkorn är de viktigaste magnetiska mineral av Set2-prover, medan finns det indikationer på att hematit och ferrimagnetisk titanohematit också bidrar till signal. Virvelströmmar, som skapats av mDACs ledande material, maskerade provets magnetiska susceptibilitet och det var svårt att kommentera på hur provets susceptibilitet förändras med tryck. Sammantaget var instrumentens prestanda tillfredsställande, även vid små mängder material. Prov och mDACs signalstabilitet var också adekvat. Vår studie gav oss en inblick i högtrycksexperiment och magnetiska egenskaper och den visade möjliga riktningar för framtida studier.