The complete consumption of the oceanic domain of a tectonic plate by subduction into the upper mantle results in continent subduction, although continental crust is typically of lower density than the upper mantle. Thus, the sites of former oceanic domains (named suture zones) are generally decorated with stratigraphic sequences deposited along continental passive margins that were metamorphosed under low-grade, high-pressure conditions, i.e., low temperature/depth ratios (< 15°C/km) with respect to geothermal gradients in tectonically stable regions. Throughout the Mesozoic and Cenozoic (i.e., since ca. 250 Ma), the Mediterranean realm was shaped by the closure of the Tethyan Ocean, which likely consisted in numerous oceanic domains and microcontinents. However, the exact number and position of Tethyan oceans and continents (i.e., the Tethyan palaeogeography) remains debated. This is particularly the case of Western and Central Anatolia, where a continental fragment was accreted to the southern composite margin of the Eurasia sometime between the Late Cretaceous and the early Cenozoic. The most frontal part of this microcontinent experienced subduction-related metamorphism around 85-80 Ma, and collision-related metamorphism affected more external parts around 35 Ma. This unsually-long period between subduction- and collision-related metamorphisms (ca. 50 Ma) in units ascribed to the same continental edge constitutes a crucial issue to address in order to unravel how Anatolia was assembled. The Afyon Zone is a tectono-sedimentary unit exposed south and structurally below the front high-pressure belt. It is composed of a Mesozoic sedimentary sequence deposited on top of a Precambrian to Palaeozoic continental substratum, which can be traced from Northwestern to southern Central Anatolia, along a possible Tethyan suture. Whereas the Afyon Zone was defined as a low-pressure metamorphic unit, high-pressure minerals (mainly Fe-Mg-carpholite in metasediments) were recently reported from its central part. These findings shattered previous conceptions on the tectono-metamorphic evolution of the Afyon Zone in particular, and of the entire region in general, and shed light on the necessity to revise the regional extent of subduction-related metamorphism by re-inspecting the petrology of poorly-studied metasediments. In this purpose, I re-evaluated the metamorphic evolution of the entire Afyon Zone starting from field observations. Low-grade, high-pressure mineral assemblages (Fe-Mg-carpholite and glaucophane) are reported throughout the unit. Well-preserved carpholite-chloritoid assemblages are useful to improve our understanding of mineral relations and transitions in the FeO-MgO-Al2O3-SiO2-H2O system during rocks’ travel down to depth (prograde metamorphism). Inspection of petrographic textures, minute variations in mineral composition and Mg-Fe distribution among carpholite-chloritoid assemblages documents multistage mineral growth, accompanied by a progressive enrichment in Mg, and strong element partitioning. Using an updated database of mineral thermodynamic properties, I modelled the pressure and temperature conditions that are consistent with textural and chemical observations. Carpholite-bearing assemblages in the Afyon Zone account for a temperature increase from 280 to 380°C between 0.9 and 1.1 GPa (equivalent to a depth of 30-35 km). In order to further constrain regional geodynamics, first radiometric ages were determined in close association with pressure-temperature estimates for the Afyon Zone, as well as two other tectono-sedimentary units from the same continental passive margin (the Ören and Kurudere-Nebiler Units from SW Anatolia). For age determination, I employed 40Ar-39Ar geochronology on white mica in carpholite-bearing rocks. For thermobarometry, a multi-equilibrium approach was used based on quartz-chlorite-mica and quartz-chlorite-chloritoid associations formed at the expense of carpholite-bearing assemblages, i.e., during the exhumation from the subduction zone. This combination allows deciphering the significance of the calculated radiometric ages in terms of metamorphic conditions. Results show that the Afyon Zone and the Ören Unit represent a latest Cretaceous high-pressure metamorphic belt, and the Kurudere-Nebiler Unit was affected by subduction-related metamorphism around 45 Ma and cooled down after collision-related metamorphism around 26 Ma. The results provided in the present thesis and from the literature allow better understanding continental amalgamation in Western Anatolia. It is shown that at least two distinct oceanic branches, whereas only one was previously considered, have closed during continuous north-dipping subduction between 92 and 45 Ma. Between 85-80 and 70-65 Ma, a narrow continental domain (including the Afyon Zone) was buried into a subduction zone within the northern oceanic strand. Parts of the subducted continent crust were exhumed while the upper oceanic plate was transported southwards. Subduction of underlying lithosphere persisted, leading to the closure of the southern oceanic branch and to subduct the front of a second continental domain (including the Kurudere-Nebiler Unit). This followed by a continental collisional stage characterized by the cease of subduction, crustal thicknening and the detachment of the subducting oceanic slab from the accreted continent lithosphere. The present study supports that in the late Mesozoic the East Mediterranean realm had a complex tectonic configuration similar to present Southeast Asia or the Caribbean, with multiple, coexisting oceanic basins, microcontinents and subduction zones. / Kontinentale Subduktion resultiert aus dem Abtauchen des ozenanischen Gebiets einer tektonischen Platte in den Oberen Erdmantel. Dies geschieht obwohl die kontinentale Erdkruste normalerweise eine geringere Dichte besitzt als der Obere Erdmantel. Die Lage ehemaliger ozeanischer Gebiete (auch als Suturzonen bezeichnet) ist dementsprechend durch stratigraphische, sedimentäre Gesteinsabfolgen gekennzeichnet, die entlang des passiven Kontinentalrandes abgelagert wurden. Anschließend wurden diese Gesteine unter niedrigen Temperaturen und hohem Druck umgewandelt, auch niedrig-gradige Hochdruckmetamorphose genannt. Während der gesamten Zeitspanne des Mesozoikums und Känozoikums (seit etwa 250 Millionen Jahren bis heute) wurde der mediterrane Raum durch die kontinuierliche Schließung des Tethyschen Ozeans (dem heutigen Mittelmeer) geprägt, der vermutlich in zahlreichen kleineren Ozeanen und Mikrokontinenten aufgeteilt war. Dennoch bleiben die genaue Anzahl und Lage der tethyschen Ozeane und Kontinente (die Paläogeographie der Tethys) bis heute umstritten. Das ist insbesondere der Fall in West- und Zentral-Anatolien, wo im Zeitraum zwischen der Oberen Kreide (vor 98 bis 65 Mio. J.) und dem unteren Känozoikum (vor 65 bis 40 Mio. J.) ein kontinentales Fragment am südlichen Kontinentalrand der Eurasischen Platte angelagert wurde (auch als Akkretion bezeichnet). Der vorderste Bereich von diesem Fragment erfuhr vor etwa 85-80 Millionen Jahren eine metamorphe Umwandlung, die mit den Prozessen der fortschreitenden Subduktion assoziiert werden können. Hingegen wurden die hinteren Bereiche erst später vor ca. 40-30 Mio. J. durch die Kollison der zwei Platten metamorph überprägt. Die ungewöhnlich lange Zeitspanne von etwa 40-50 Mio. J. zwischen den metamorphen Prozessen der Subduktion und der Kollision, stellt eine entscheidende Frage zum Verständnis der Entstehung von Anatolien dar. Die Afyon Zone repräsentiert hierbei eine tektonisch-beanspruchte sedimentäre Gesteinseinheit, die in einer strukturell tieferen Position bezüglich des frontalen metamorphen Hochdruckgürtels liegt und südlich von ihm anzutreffen ist. Die Afyon Zone besteht aus mesozoischen sedimentären Einheiten (250 bis 65 Mio. J. alt), die auf präkambrischem (älter als 545 Mio. J.) bis paläozoischem Untergrund (bis vor 250 Mio J.) abgelagert wurden, und vom nordwestlichen bis zentralen Anatolien, entlang der vermutlichen Tethys-Suturzone, verfolgt werden können. Obwohl die Afyon-Zone als eine niedrig-temperierte metamorphe Gesteinseinheit bezeichnet wird, wurde in letzter Zeit von Vorkommen von Hochdruckmineralen (v.a. Eisen(Fe)-Magnesium(Mg)-Karpholith in metamorphen Sedimenten) im zentralen Bereich berichtet. Diese neuen Erkenntnisse stellen die bisherigen Interpretationen zur tektonisch-metamorphen Entstehung der gesamten Region in Frage, insbesondere der der Afyon-Zone. Deshalb war eine erneute gründliche Überarbeitung und Untersuchung der wenig studierten metamorph-überprägten Sedimentgesteine in diesem Gebiet notwendig. Deshalb, überarbeitete ich die metamorphe Entwicklung der gesamten Afyon Zone, beginnend mit intensiver Geländearbeit und -beobachtungen. Mineralvergesellschaftungen aus Karpholith und Glaukophan, die unter niedrigen Temperaturen und hohem Druck entstanden sind, wurden in der gesamten Gesteinseinheit gefunden. Guterhaltene Mineralvergesellschaftungen aus Karpholith und Chloritoid sind nützlich für das Verständnis unter welchen Temperatur- und Druck-Bedingungen die Gesteine in die Tiefe gelangen (prograde Metamorphose). Durch die Untersuchungen von Gesteinsgefügen und der Eisen-Magnesium-Verteilung zwischen den Mineralien Karpholith und Chloritoid lassen sich Aussagen zu der Bildungstemperatur und dem Druck dieser Minerale machen. Dafür benutzte ich eine verbesserte Datenbank mit Mineraleigenschaften, die mir die Modellierung von Temperatur und Druck erlaubte und im Einklang mit den chemischen und mikroskopischen Beobachtungen steht. Es ergab sich, dass die Karpholith-haltigen Gesteine in der Afyon-Zone einen Temperaturanstieg von 280 zu 380°C (bei einer Tiefe von 30-35 km) erfahren haben. Um noch bessere Aussagen über die Entstehung zu treffen, wurden auch radiometrische Datierungen an Proben aus der Afyon-Zone, sowie an zwei weiteren Sedimentgesteinseinheiten (Ören- und Kurudere-Nebiler-Einheit aus SW Anatolien) gemacht. Für die Altersbestimmung benutzte ich die weitverbreitete 40Ar-39Ar Datierungsmethode an Hellglimmer-Mineralien in den Karpholith-haltigen Gesteinen. Temperatur und Druck können auch bestimmt werden, wenn man den Übergang von einer Mineralvergesellschaftung zu einer anderen Vergesellschaftung beobachtet. Dies gilt zum Beispiel für den Übergang von einer Karpholith-haltigen Zusammensetzung zu einer Quartz-Chlorit-Glimmer und Quartz-Chlorit-Chloritoid Mineralvergesellschaftung wenn tief subduzierte Gesteine wieder nach oben gelangen (Exhumation). Damit lassen sich die radiometrischen Alter den metamorphen Prozessen zu bestimmten Temperaturen und Drücken zuordnen. Mit diesen Erkenntnissen lassen sich die Afyon-Zone und die Ören-Einheit einem Hochdruck-Gebirgsgürtel in der späten Kreidezeit zuordnen, während die Kurudere-Nebiler Einheit durch die mit der Subduktion in Verbindung stehende Metamorphose vor ca. 45 Mio. J. beeinflusst wurde. Später wurde diese Einheit durch die Metamorphose, resultierend aus der Kollision vor 26 Mio. J., abgekühlt. Die Ergebnisse dieser und anderer Arbeiten erlauben es die Anlagerung von Kontinenten in West-Anatolien besser zu verstehen. Es wird gezeigt, dass mindestens zwei (im Gegensatz zu vorher einem) voneinander unabhängige Ozeanarme während der Subduktion von 92 bis 45 Millionen Jahren geschlossen wurden. Zwischen 85-80 und 70-65 Millionen Jahren, wurde ein schmales kontinentales Gebiet (welches die Afyon-Zone beinhaltet) in die Subduktionszone hineingzogen. Teile der subduzierten kontientalen Kruste kamen wieder an die Oberfläche (Exhumation), während die obere ozeanische Platte südwärts transportiert wurde. Die anhaltende Subduktion im oberen Bereich des Erdmantels (Lithosphäre) führte zu der Schließung des südlichen Ozeanarms und zu der Subduktion des zweiten kontinentalen Gebietes (welches die Kurudere-Nebiler-Einheit beinhaltete). Darauf folgte die kontinentale Kollisionsphase unter dem Ausklingen der Prozesse der Subduktion, der Krustenverdickung und der Abtrennung der subduzierten ozeanischen Platte von der akkretionierten kontientalen Lithosphäre (auch als Delamination bezeichnet). Die hier präsentierte Arbeit unterstüzt die Annahme das während der Oberen Kreidezeit das Ost-Mediterrane Gebiet tektonsich komplex angeordnet war, vergleichbar mit dem heutigen Südost-Asien oder der Karibik, mit ihren vielen gleichzeitig existierenden ozeanischen Becken, Mikrokontinenten und Subduktionszonen.

Recent work suggests an emerging new paradigm for the Scandinavian ice sheet (SIS); one of a dynamically fluctuating ice sheet. This doctoral research project explicitly examines the history and dynamics of the SIS at four sites within Sweden and Norway, and provides results covering different time periods of glacial history. Two relatively new dating techniques are used to constrain the ice sheet history: the optically stimulated luminescence (OSL) dating technique and the terrestrial cosmogenic nuclide (TCN) exposure dating technique. OSL dating of interstadial sediments in central Sweden and central Norway indicate ice-free conditions during times when it was previously inferred the sites were occupied by the SIS. Specifically, the SIS was absent or restricted to the mountains for at least part of Marine Isotope Stage 3 around 52 to 36 kyr ago. Inland portions of Norway were ice-free during part of the Last Glacial Maximum around 25 to 20 kyr ago. Consistent TCN exposure ages of boulders from the Vimmerby moraine in southern Sweden, and their compatibility with previous estimates for the timing of deglaciation based on radiocarbon dating and varve chronology, indicate that the southern margin of the SIS was at the Vimmerby moraine ~14 kyr ago. In central Sweden, consistent TCN ages for boulders on the summit of Mt. Åreskutan and for the earlier deglaciated highest elevation moraine related to the SIS in Sweden agree with previous estimates for the timing of deglaciation around 10 ka ago. These results indicate rapid decay of the SIS during deglaciation. Unusually old radiocarbon ages of tree remains previously studied from Mt. Åreskutan are rejected on the basis of incompatibility with consistent TCN ages for deglaciation, and incompatibility with established paleoecological and paleoglaciological reconstructions. Altogether this research conducted in different areas, covering different time periods, and using comparative geochronological methods demonstrates that the SIS was highly dynamic and sensitive to environmental change. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.

第22回名古屋大学年代測定総合研究センターシンポジウム平成21(2009)年度報告

The Egrigoz, Koyunoba, and Alacam plutons are located in the Northern Menderes Massif of western Turkey between the Simav normal fault to the south and the Izmir-Ankara-Erzincan suture to the north. Although much attention has focused on their geochemical and geochronological history, their relationship to each other and other major structures in the region is still debated. Some geologic maps show the Egrigoz and Koyunoba pluton bounded to the west by the low-angle Simav detachment fault. In contrast, other regional maps show no offsets between the plutons and surrounding metamorphic rocks. Yet other studies indicate thrust faults may be present near the Egrigoz pluton, between Menderes metamorphic rocks and a meta-rhyolite unit. To gain a better understanding of the history of the Egrigoz, Koyunoba, and Alacam plutons, ArcGIS digital elevation data from the region, geochronological data, geochemical analyses, and cathodoluminescence (CL) images were acquired to search for effects of micro- to macro-scales of deformation. Numerous ~E-W trending extension lineations that parallel the Simav graben and cut the plutons were observed in relief images. These lineations, likely due to large-scale ~N-S extension, continue across plutons inferring that extension continued after the exhumation of these rocks. The Simav graben and its associated high-angle fault are evident in the elevation data, but no other significant detachment-related basins or structures are shown, including the low-angle Simav detachment. U-Pb zircon ages, ranging from 29.9±3.9 Ma to 14.6±2.6 Ma, suggest the plutons crystallized over a ~15 m.y. time frame. Samples from the plutons are peraluminous S-type granite to granodiorites. The plutons were emplaced in a post-collisional volcanic-arc setting and range from magnesian to ferroan with increasing silica contents. Geochemical analyses show little difference between the three plutons, consistent with the rocks arising from a similar source. To document microstructures that might help explain these heterogeneities, CL images were obtained. CL images document a complicated tectonic history including magma mixing, multiple episodes of brittle deformation, and fluid alteration. The CL images constitute evidence of a complex multi-stage tectonic history for the region that includes water-mediated brittle deformation. / text

New and existing U–Pb and 40Ar/39Ar geochronological data, and oxygen and hydrogen stable isotope data, are combined with structural and metamorphic data from Thor–Odin, the southern culmination of the Monashee Complex. This leads to a new interpretation of the timing of deformation and metamorphism. Amphibolites in Thor–Odin with hornblende 40Ar/39Ar dates between ~75–70 and ~51 Ma experienced more 18O- and D-depletion than amphibolites with older dates. The younger dates that were previously interpreted as cooling ages, may have resulted from complete or partial Ar loss in the presence of meteoric fluids that were introduced into the rock during extension. <br><br> Monazite crystals in pelitic schist, quartzite and orthogneiss, which have U–Pb ages younger than 40Ar/39Ar hornblende ages in amphibolite in northwest Thor–Odin, may have grown during tension in the presence of fluids. Titanite, xenotime and zircon dates may be interpreted in the same way. Thus, the U–Pb dates that were previously interpreted as representing peak of metamorphism and the hornblende 40Ar/39Ar dates that were previously interpreted as representing cooling ages, may be interpreted as reflecting meteoric fluid penetration of the crust during regional extension. This implies that the age of the thermal peak of metamorphism is older than ~75–70 Ma. Migmatisation in a basement orthogneiss in Thor–Odin occurred at ~1.8 Ga. Dissolution rims are preserved in zircon between ~1.8 Ga domains and 52 Ma overgrowths. Because growth of new zircon (and possibly other U–Pb accessory phases) did not take place, any geological event that occurred during the ~1.8 Ga to 52 Ma time interval is not recorded. Cordilleran deformation and metamorphism may have taken place within that time interval, e.g. in the Middle Jurassic and/or mid- to Late Cretaceous, the time of Cordilleran deformation and metamorphism in the rocks overlying the Monashee Complex. <br><br> The Joss Mountain orthogneiss, west of the Monashee Complex in the Selkirk Allochthon, is dated at 362 +/– 13 Ma. F3 folding in pelitic schist at Joss Mountain is constrained between ~73 and ~70 Ma. Existing structural, metamorphic and geochronological data in, and close to, the Shuswap Metamorphic Complex in the southern Canadian Cordillera are shown to be consistent with a channel flow model.

No description available.

L'évolution d'une chaîne de montagne résulte des rétroactions entre le climat et la tectonique via l'érosion. La chaîne Himalayenne, soumise à des processus climatiques et tectoniques très actifs est un chantier d'étude idéal pour comprendre ces interactions. Dans cette étude nous nous sommes intéressés à l'évolution topographique de la région du Sikkim (Inde) ainsi qu'aux processus de formation et de développement du mégafan Quaternaire de la Tista, dépôt fluviatile situés au pieds de ces reliefs. Nos résultats indiquent qu'à l'échelle géologique, les taux d'exhumation (obtenus par les traces de fission sur apatite) les plus forts sont concentrés dans le Sud-Ouest du Sikkim (1.2 ± 0.6 mm/an) suggérant un contrôle tectonique lié à la formation du duplex du Moyen-Pays (« Rangit Duplex »). Les taux d'érosion à l'échelle millénaire (obtenus par 10Be) les plus forts (≈ 5 mm/an) sont enregistrés au niveau de la « Main Central Thrust Zone », mais les zones sources de ces échantillons semblent affectées par des glissements de terrain menant à une surestimation de ces taux. Des taux d'érosion importants sont également enregistrés au Nord du Sikkim (1 à 2 mm/an) et coïncident avec les fortes valeurs de l'indice ksn, localisées au niveau de l'altitude d'avancée maximale des glaciers durant le Dernier Maximum Glaciaire. Nous en concluons que l'érosion millénaire au Sikkim soit en partie liée à l'héritage géomorphologique glaciaire. Le mégafan de la Tista stocke les produits d'érosion du Sikkim et s'étend sur plus de 16 000 km2 depuis le front de la chaîne, où il est fortement incisé, jusqu'à la confluence de la Tista avec le Brahmapoutre. Nous présentons un scénario de développement du mégafan avec le développement successifs de deux lobes distaux en aval d'un lobe proximal commun, développé au front de la chaine depuis au moins 50 000 ans et incisé par la Tista depuis 4000+600/-400 ans. Le lobe distal occidental a été formé tôt dans l'histoire du mégafan, par des rivières drainant le Sikkim et se jettant dans le Gange, et a été abandonné au début de l'Holocène (10 000 – 11000 ans). Le lobe distal oriental, très peu incisé et plus récent (< 1000 ans), s'est construit quand le réseau de drainage principal du Sikkim a migré vers l'Est grâce à d'importantes avulsions. Les périodes d'aggradation et d'incision des rivières sont compatibles avec un guidage climatique, où les périodes de forte intensité de mousson et de forts flux sédimentaires associés coïncident avec des phases d'aggradation dans l'avant-pays. Les phases initiales et terminales de ces périodes de fortes moussons sont caractérisées par de l'incision dans l'avant pays. En revanche, le rôle de l'activité tectonique sur l'alluvionnement et l'incision du mégafan semble mineur. Les résultats pétrographiques et isotopiques (Sr et Nd) utilisés pour contraindre les sources des sédiments du mégafan indiquent une forte différence avec les sédiments actuellement transportés par la Tista qui pourrait s'expliquer par l'influence de roches sédimentaires téthysiennes crétacés exposées au nord du Sikkim, et actuellement drainées par la Kosi. Cela suggère que cette zone ait été récemment (4000 ans) capturée par la Kosi, provoquant l'incision récente et importante du mégafan, due au rééquilibrage du profil de la Tista. Cette hypothèse préliminaire permettrait d'expliquer également la taille disproportionnée du mégafan comparée à celle de son bassin versant actuel. Par ailleurs, nos résultats montrent que les variations de l'érosion et de l'altération chimique répondent à des variations climatiques globales et régionales. Les périodes de fortes intensités de précipitations de mousson se traduisent au Sikkim par une plus forte pénétration des précipitations dans la haute chaîne et une plus forte altération chimique des silicates. Depuis le dernier maximum glaciaire, la région du Sikkim est caractérisée par une augmentation de l'érosion et de l'altération chimique. / Understanding the relative strengths of tectonic and climatic forcing, as well as the interactions between these controls, at different spatial and temporal scales is important to understand the evolution of orogenic topography. The Himalayas, subjected to both tectonic and climatic phenomena very active, is one of the most popular sites for the study of these interactions. The focus of this project is to understand (1) the evolution of orogenic topography of Sikkim (India), (2)the processus of formation and development of th quaternary Tista megafan. Our results show that long-term exhumation rates obtained by thermochronology (apatite fission tracks) do not correlate with any geomorphic or climatic parameters. We suggest a tectonic control where high rates in southwest Sikkim (1.2±0.6 mm/yr) may be linked to the building of the lesser Himalaya Rangit Duplex. The highest erosion rates recorded at millennial timescales (10Be ∼5 mm/yr) occur in catchments spanning the Main Central Thrust Zone but appear to be strongly influenced by recent landsliding. High erosion rates (1-2 mm/yr) also occur in north Sikkim and may be linked to a strong glacial inheritance on the landscape, as attested by high channel-steepness values close to the maximum extent of glaciers during the Last Glacial Maximum. In contrast, variations in precipitation rate do not seem to strongly influence either short-term erosion or long-term exhumation rates in Sikkim. The Tista megafan spreads over more than 16 000 km2 form the mountain front, where it is strongly incised, to the confluence of the Tista River with the Brahmaputra River, and stores sediments produced in the Sikkim Himalaya. We propose a scenario for the formation and abandonment of the Tista megafan based on new Infra-Red Stimulated Luminescence (IRSL) and 10Be cosmogenic age constraints. We suggest that two distal lobes developed successively downstream from a common proximal lobe. Deposition took place since ~50 ka assuming a constant sedimentation rate of 0.88±0.10 mm.yr-1 and incision began at 〖4.0〗_(-0.4)^(+0.6) ka at an average rate of 〖10.5〗_(-1.8)^(+0.6) mm yr-1. The western distal lobe of the megafan was deposited early in the history of the megafan, possibly when the Sikkim Himalaya catchments were drained by rivers that where tributaries of the Ganga River, and was abandoned in the early Holocene (10-11 ka). The eastern poorly incised and recent (<1ka) may have been built when the main Tista drainage system had shifted eastward through possible nodal avulsions. Tectonic processes seem to play a minor role in guiding the Tista River course and driving incision of the megafan deposits. Abandonment and incision of megafan surfaces and hinterland terraces appears associated to both the onset and the ending of phases of strong monsoon precipitation, during which the balance between water and sediment discharge changes rapidly. Petrographic ans isotopic (Nd and Sr) used to constrain sources of the megafan deposits display a significant difference with sediments actually transported by the Tista River, which could be explained by the influenced of tethyan sedimentary rocks exposed North to Sikkim, and actually drained by the Kosi River. This suggests that this area has been recently (4000 years) captured by the Kosi River, inducing a recent and important incision of the megafan in its proximal part due to the balancing of the river profile. This preliminary hypothesis could also explain the higher size of the megafan comparing to the one of its catchment. Otherwise, our results show that the variations of erosion and chemical alteration respond to global and regional climatic variations. Periods of strong summer monsoon and heavy rainfall are traduced in Sikkim by the more penetration of precipitation into the relief and a strong chemical weathering. Since the Last Glacial maximum, the Sikkim Himalaya is characterised by an augmentation of erosion and chemical weathering.

Les principaux gisements d’uranium connus du Niger (Arlit, Akouta et Imouraren) sont tous localisés dans le bassin de Tim Mersoï, à l’Est de la faille d’Arlit. Les gisements d’Arlit et d’Akouta sont encaissés dans des formations Carbonifères et présentent une minéralisation à uranium essentiellement réduite, alors que le gisement d’Imouraren est contenu dans une formation d’âge Jurassique sous forme de minéralisation uranifère majoritairement oxydée avec quelques poches de minéralisation réduite. La découverte de nouvelles concentrations d’uranium à l’Ouest de la faille d’Arlit et les différences entre les gisements dans le Carbonifère et le Jurassique, ont encouragé une réévaluation des modèles métallogéniques antérieurs. L’objectif est de déterminer si les différentes minéralisations uranifères ont été formées durant un même évènement diagénétique/hydrothermal en lien avec un épisode géotectonique majeur, ou si celles-ci sont polyphasées dans le temps, afin de proposer un modèle métallogénique global. Une approche multi-technique regroupant une étude détaillée de la diagenèse, des fluides, de la minéralisation, de la géochronologie et de la géothermométrie, a été appliquée afin de retracer l’histoire d’enfouissement du bassin et d’appréhender les conditions de dépôt de l’uranium. Deux phases principales de minéralisation uranifère se distinguent: (i) un épisode diagénétique/hydrothermal principal entre 100 et 135 Ma au cours duquel les minéraux primaires d’uranium et de cuivre précipitent en milieu réduit dans des conditions proches de l’enfouissement maximal (P : 80-120 bars, T : 115-150 °C), en relation avec les périodes de rift atlantique au Crétacé. (ii) une série de remaniement des minéraux primaires en milieu oxydant pour former des minéraux secondaires d’uranium, de vanadium et de cuivre en conditions supergènes liée à l’exhumation des séries depuis 50 Ma, lors des grandes phases d’oxydation connues en Afrique de l’Ouest. / The main U-deposits of Niger (Arlit, Akouta, and Imouraren) are all located in the Tim Mersoï Basin, east of the Arlit Fault. The deposits of Arlit and Akouta are hosted in Carboniferous formations and have a substantially reduced uranium mineralization, while the Imouraren deposit is contained in a Jurassic formation in the form of predominantly oxidized uranium mineralization with some pockets of reduced mineralization. New ore bodies discoveries west of the Arlit Fault in the regions of Arlit and Akouta and the differences between the U-deposits in the Carboniferous and Jurassic, have encouraged a reevaluation of the previous metallogenic models. The objective is to determine whether the uranium mineralizations of Tim Mersoï Basin were formed during the same diagenetic/hydrothermal event in relation with a major geotectonic event, or if they are polyphase over time, in order to propose a general metallogenic model. A multi-technique approach involving a detailed study of diagenesis, fluid circulations, mineralization, geochronology and geothermometry was applied to trace the burial history of the basin and constrain the P-T conditions of uranium deposition. Two main phases of uranium mineralization are distinguished: (i) A diagenetic/hydrothermal episode between 100 and 135 Ma in which primary uranium and copper minerals precipitate in reduced environment under conditions close to maximum burial (P : 80-120 bars, T : 115-150 °C), in relation with Atlantic rift periods during Cretaceous. (ii) A serie of remobilizations of primary uranium minerals in oxidizing environment to form secondary uranium, vanadium and copper minerals under supergene conditions related to uplift since 50 Ma, during the major events of oxidation in western Africa.

Este trabalho baseou-se no estudo de xenólitos de rochas metamórficas na região de Piratini e Pinheiro Machado, sudeste do Escudo Sul-rio-grandense. Partindo de estudos de campo, microscopia ótica, geoquímica de elementos maiores e traços e geocronologia U-Pb em zircão, essa associação de rochas gnáissicas, denominada de Gnaisses Piratini, apresenta uma composição intermediária a ácida, predominantemente granodiorítica a tonalítica, subalcalina cálcio-alcalina médio-K, peraluminosa a levemente metaluminosa. Estes dados, juntamente com sua idade magmática de 784 ± 4 Ma, leva esta associação a ser interpretada como originada em um ambiente de arco magmático continental, e metamorfisada em fácies anfibolito em torno de 664 a 688 Ma. Nesta dissertação é apresentado um estado da arte dos estudos publicados sobre os Gnaisses Piratini, além de considerações sobre a importância desta unidade como um embasamento de sua região. Após, é apresentado o artigo denominado “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submetido para publicação no periódico Brazilian Journal of Geology, onde são descritos os dados e interpretações obtidos sobre os Gnaisses Piratini. / This work has based on the study of xenoliths of metamorphic rocks in the region of Piratini and Pinheiro Machado, southeastern Sul-rio-grandense Shield. Through field studies, optical microscopy, geochemistry of major and trace elements and U-Pb zircon geochronology, this association of gneissic rocks, named Piratini Gneisses, features an intermediate to felsic composition, predominantly granodioritic to tonalitic, medium-K calc-alkaline subalkaline, peraluminous to slightly metaluminous. These data, together with the magmatic age of 784 ± 4 Ma lead this rock association to be originated on an active magmatic arc environment, and metamorphosed at around 664 to 688 Ma in amphibolite facies. This dissertation presents a state-of-the-art of studies published about Piratini Gneisses, in addition to considerations about the importance of this unit as a basement of your region. After, it is featured the article entitled “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submitted for publication in the “Brazilian Journal of Geology”, where are described the data and interpretations obtained on the Piratini Gneisses.

Made available in DSpace on 2014-06-11T19:26:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-11Bitstream added on 2014-06-13T20:54:24Z : No. of bitstreams: 1 manzano_jc_me_rcla.pdf: 2131375 bytes, checksum: 271da965a4cf05561a50d88fd56bcfb8 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Esta qualificação traz os resultados de uma pesquisa realizada nos Estados do Mato Grosso e Mato Grosso do Sul, onde foram estudados e caracterizados quanto à composição mineralógica, comportamento geoquímico e idades isotópicas, sete corpos granitóides, intrusivos em rochas metassedimentares de baixo grau do Grupo Cuiabá. Estas rochas granitóides, conhecidas pelos nomes Taboco, Rio Negro, Coxim e Sonora no Estado do Mato Grosso do Sul e São Vicente, Lajinha e Araguaiana no Estado do Mato Grosso, representam um importante e pouco estudado capítulo na evolução geológica e tectônica do território brasileiro. Estes corpos representam um magmatismo sin a pós colisional, que ocorreu em dois eventos distintos, um ao redor de 500Ma e outro por volta de 540Ma. Geoquimicamente são caracterizados por uma tendência cálcio alcalina de alto potássio com caráter predominantemente peraluminoso. O quadro estrutural das rochas encaixantes mostra uma evolução polifásica, evidenciada pelo registro de três fases deformacionais, relacionadas à evolução da Faixa de Dobramentos Paraguai. / This qualification brings the results of a research accomplished in Mato Grosso and Mato Grosso do Sul States, where they were studied and characterized as for the mineralogical composition, geochemical behavior and isotopic ages, seven bodies, intrusives in low grade meta sedimentary rocks of the Cuiabá Group. These granitic rocks, known by the names Taboco, Rio Negro, Coxim and Sonora in the Mato Grosso do Sul State and São Vicente, Lajinha and Araguaiana in the Mato Grosso State, represents an important however poor studied chapter in the geological and tectonic evolution of the Brazilian territory. These bodies represent a magmatism sin to pos colisionall, that happened in two different events, one around of 500Ma and other around 540Ma. Geochemically, are characterized predominantly by calcium alkaline of high potassium tendency with peraluminous character. The structural settings of the country rocks shows a polyphasic evolution, evidenced by the registration of three deformational phases, related to the evolution of Paraguai Folded Belt.