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Pendant l'Eocène Moyen, dans la région du désert d'Atacama, Nord Chili, la mise en place de porphyres et la déformation synchrone de la Précordillère aboutissent à la formation de clusters importants de dépôts de cuivre supergènes et exotiques, actuellement en cours d'exploitation. La formation de ces dépôts métallifères résulte de l'interaction entre la tectonique, l'érosion et le climat. La nature et la chronologie de ces interactions sont encore débattues. Ce travail de doctorat se concentre sur la quantification des processus géomorphologiques, tectoniques et érosifs, sur le versant ouest des Andes, autour de 23°S dans le District minier Centinela situé dans la Précordillère. Vingt-neuf nouvelles données thermochronologiques basse-température et leur modélisation indiquent que les porphyres cuprifères mis en place à faible profondeur durant l'Eocène moyen étaient déjà exhumés près de la surface à l'Oligocène moyen. Il existe un intervalle de temps de cinq millions d'années entre l'exhumation du porphyre qui constitue la source primaire de cuivre et le dépôt secondaire de cuivre dans le district de Centinela daté par les méthodes 40Ar/39Ar et K/Ar. Cette relation suggère que les dépôts de cuivre secondaires ont eu lieu lorsque les reliefs étaient déjà aplanis. Un dépôt exotique cuprifère syn-sédimentaire s'est formé dans le bassin continental du district Centinela. Des échantillons de sable ont été prélevés entre 135 et 13 mètres de profondeur dans les mines El Tesoro et Mirador. Les concentrations en 10Be et 21Ne de quatorze nouveaux échantillons ont permis de déterminer l'âge du dépôt et de contraindre les paléo taux de sédimentation des derniers 14 Ma. L'étude permet de dater le dépôt exotique à ~12 Ma et suggère qu'il a eu lieu lors d'une quiescence des taux d'érosion, confirmant l'idée que les dépôts supergènes de cuivre en milieu aride ont lieu après l'aplanissement des reliefs. Ces résultats confirment aussi que les taux d'érosion ont drastiquement chuté après 10-12 Ma, quand l'hyperaridité s'est établie. Ce travail de thèse illustre la balance nécessaire entre l'exhumation et les taux de précipitation pour former des minéralisations secondaires de cuivre et les conserver. / During the Middle Eocene in the Atacama Desert region (northern Chile), the intrusion of porphyries and the synchronous deformation of the Precordillera resulted in the formation of important clusters of supergene and exotic copper ore deposits that are currently exploited. Such metal ore deposits result of the interaction of tectonics, erosion and climate, for which both timing and relations remain debated. This PhD study focuses on the quantification of geomorphological, tectonic and erosive processes to understand their relationship in the Andean western slope around 23°S in the Centinela district in the Precordillera. Twenty-nine new low-temperature thermochronological data and their modelling indicate that shallow porphyry copper emplaced during mid-Eocene were quickly exhumed near the surface by the early Oligocene. There is a five million years-long time gap between the exhumation of primary source of copper and the ~25-12 Ma range of existing 40Ar/39Ar and K/Ar ages of secondary mineralization in the District. This suggests that supergene copper related deposits occurred when the reliefs where already flattened. A syn-sedimentary exotic copper mineralization was deposited in an intra-mountainous basin in the Centinela District. We sampled sand at different depths between 135 and 13 meters in the Tesoro and Mirador open-pit mines, one of them including this exotic deposit. The 10Be and 21Ne concentrations of fourteen new samples were used to determine the exotic deposit age and to constrain the paleo-sedimentation rate for the last 14 Ma. The study dates the exotic deposit at ~12 Ma and suggests that this mid-Miocene exotic layer occurred during an erosive quiescence, confirming the view that supergene copper mineralization occurs during a stage of slower geomorphic activity in arid environments. The results also confirm that the erosion rates drastically dropped after 10-12 Ma, when the hyperaridity was established. This study highlights the necessary balance between exhumation and precipitation rates required to form secondary copper.

A new apatite (U-Th)/He (AHe) dataset from subvertical transects collected in the Teton and Gallatin Ranges in the Teton-Yellowstone region provides insight for the slip history and length of the Teton fault. Along the northernmost segment of the Teton fault, inverse thermal history modeling of AHe data from Eagles Rest Peak yield a ~9 Ma age for onset of fault slip. This age supports previous interpretations that Mount Moran may be the true center of the Teton fault. This refined interpretation coupled with lengthdisplacement fault scaling analysis and previous estimates of total fault displacement (~6 km) indicates that the Teton fault may extend 50-90 km north of Mount Moran. However, this new data precludes the possibility that the Teton and East Gallatin faults represent the same structure. Yet, because these systems share a similar structure trend and initial slip ages (13 Ma and 16 Ma, respectively), they may still be related at a larger scale. To the south, the Teewinot transect yields the oldest onset age of ~32 Ma, however a >500 m vertical data gap in this transect leads us to cautiously interpret the results of this model, particularly as this age conflicts with four other transects along-strike.

The role of feedback between erosional unloading and tectonics controlling the development of the Himalaya is a matter of current debate. The distribution of precipitation is thought to control surface erosion, which in turn results in tectonic exhumation as an isostatic compensation process. Alternatively, subsurface structures can have significant influence in the evolution of this actively growing orogen. <br><br>Along the southern Himalayan front new 40Ar/39Ar white mica and apatite fission track (AFT) thermochronologic data provide the opportunity to determine the history of rock-uplift and exhumation paths along an approximately 120-km-wide NE-SW transect spanning the greater Sutlej region of the northwest Himalaya, India. 40Ar/39Ar data indicate, consistent with earlier studies that first the High Himalayan Crystalline, and subsequently the Lesser Himalayan Crystalline nappes were exhumed rapidly during Miocene time, while the deformation front propagated to the south. In contrast, new AFT data delineate synchronous exhumation of an elliptically shaped, NE-SW-oriented ~80 x 40 km region spanning both crystalline nappes during Pliocene-Quaternary time. The AFT ages correlate with elevation, but show within the resolution of the method no spatial relationship to preexisting major tectonic structures, such as the Main Central Thrust or the Southern Tibetan Fault System. Assuming constant exhumation rates and geothermal gradient, the rocks of two age vs. elevation transects were exhumed at ~1.4 &#177;0.2 and ~1.1 &#177;0.4 mm/a with an average cooling rate of ~50-60 &#176;C/Ma during Pliocene-Quaternary time. The locus of pronounced exhumation defined by the AFT data coincides with a region of enhanced precipitation, high discharge, and sediment flux rates under present conditions. We therefore hypothesize that the distribution of AFT cooling ages might reflect the efficiency of surface processes and fluvial erosion, and thus demonstrate the influence of erosion in localizing rock-uplift and exhumation along southern Himalayan front, rather than encompassing the entire orogen.<br><br>Despite a possible feedback between erosion and exhumation along the southern Himalayan front, we observe tectonically driven, crustal exhumation within the arid region behind the orographic barrier of the High Himalaya, which might be related to and driven by internal plateau forces. Several metamorphic-igneous gneiss dome complexes have been exhumed between the High Himalaya to the south and Indus-Tsangpo suture zone to the north since the onset of Indian-Eurasian collision ~50 Ma ago. Although the overall tectonic setting is characterized by convergence the exhumation of these domes is accommodated by extensional fault systems.<br><br>Along the Indian-Tibetan border the poorly described Leo Pargil metamorphic-igneous gneiss dome (31-34&#176;N/77-78&#176;E) is located within the Tethyan Himalaya. New field mapping, structural, and geochronologic data document that the western flank of the Leo Pargil dome was formed by extension along temporally linked normal fault systems. Motion on a major detachment system, referred to as the Leo Pargil detachment zone (LPDZ) has led to the juxtaposition of low-grade metamorphic, sedimentary rocks in the hanging wall and high-grade metamorphic gneisses in the footwall. However, the distribution of new 40Ar/39Ar white mica data indicate a regional cooling event during middle Miocene time. New apatite fission track (AFT) data demonstrate that subsequently more of the footwall was extruded along the LPDZ in a brittle stage between 10 and 2 Ma with a minimum displacement of ~9 km. Additionally, AFT-data indicate a regional accelerated cooling and exhumation episode starting at ~4 Ma. <br><br>Thus, tectonic processes can affect the entire orogenic system, while potential feedbacks between erosion and tectonics appear to be limited to the windward sides of an orogenic systems. / Welche Rolle Wechselwirkungen zwischen der Verteilung des Niederschlags, Erosion und Tektonik während der Entwicklung des Himalayas über geologische Zeiträume gespielt haben bzw. heute spielen, ist umstritten. Dabei ist von besonderem Interesse, ob Erosion ausschliesslich in Folge tiefkrustaler Hebungsprozesse entsteht und gesteuert wird, oder ob Regionen besonders effektiver Erosion, bedingt durch isostatische Kompensation, die Lokation tektonischer Deformation innerhalb aktiver Orogene beeinflussen können. <br><br>Entlang der südlichen Himalayafront ermöglichen neue thermochronologische 40Ar/39Ar-Hellglimmer- und Apatite-Spaltspur-Alter die Bestimmung der Exhumationspfade entlang eines 120-km-langen NE-SW-gerichteten Profils, dass quer durch die gesamte Sutlej-Region des nordwestlichen, indischen Himalayas verläuft. Dabei deuten die 40Ar/39Ar-Daten in übereinstimmung mit früheren Studien darauf hin, dass zuerst das Kristallin des Hohen Himalayas und anschliessend, südwärts propagierend, das Kristallin des Niederen Himalayas während des Miozäns exhumiert worden ist. Im Gegensatz dazu weisen die neuen Apatit-Spaltspur-Alter auf eine gleichmässige und zeitgleiche Exhumation beider kristallinen Decken entlang des Sutlejflusses. Dieser 80x40 km weite Bereich formt einen elliptischen, nordost-südwest orientierten Sektor erhöhter Exhumationsraten während des Pliozäns und Quartärs. Innerhalb des Fehlerbereichs der Spaltspurmethode zeigen die Alter eine gute Korrelation mit der Höhe, zeigen aber gleichzeitig keine Abhängigkeit zu bedeutenden tektonischen Störungen, wie die "Main Central Thrust" oder dem "Southern Tibetan Fault System". Unter der vereinfachten Annahme konstanter Exhumationsraten deuten zwei verschiedene Höhenprofile auf Exhumationraten in der Grössenordnung von ~1,4 &#177;0,2 und ~1,1 &#177;0,4 mm/a bei einer durchschnittlichen Abkühlrate von ~50-60 &#176;C/m.y. während des Pliozäns bzw. Quartärs hin. Der anhand von Spaltspuraltern bestimmte Sektor verstärkter Exhumation korreliert mit dem Gebiet, das während des Holozäns hohen Niederschlags-, Erosion- bzw. Sedimenttransportraten ausgesetzt ist. Daher vermuten wir, dass die Verteilung von jungen Spaltspuraltern den regionalen Grad der Effiziens von Oberflächenprozessen und fluviatiler Erosion wiederspiegelt. Dies deutet auf einen Zusammenhang zwischen Erosion und der Lokalisierung von Hebung und Exhumation entlang der südlichen Front des Himalayas hin, und zeigt gleichzeitig, dass die Exhumation nicht einfach über die gesamte Front gleichmässig verteilt ist.<br><br>Trotz der Wechselwirkungen zwischen Exhumation und Erosion, die möglicherweise die Entwicklung der südlichen Himalayafront beeinflussen, beobachten wir auch tiefkrustale tektonische Exhumation in ariden Gebieten nördlich des Hohen Himalayas, die vermutlich im Zusammenhang mit plateauinternenen Deformationsprozessen steht. So haben sich zum Beispiel mehrere metaplutonische Gneissdomkomplexe zwischen dem Hohen Himalaya im Süden und der Indus-Tsangpo Suturzone im Norden seit der Indien-Asien Kollision vor ca. 50 Millionen Jahren entwickelt. Obwohl die Dome sich grossräumig in einem kommpressiven Spannungsfeld befinden, werden sie lokal entlang von Extensionsstrukturen exhumiert. Bis heute sind die Ursachen für die Entstehung dieser Prozesse umstritten.<br><br>Entlang der Indisch-Tibetischen Grenze erstreckt sich der fast vollkommen unbeschriebene Leo-Pargil-Gneissdomkomplex (31-34&#176;N/77-78&#176;E) innerhalb des Tethyschen Himalayas. Neue Geländekartierungen, strukturelle und geochronologische Daten der westliche Flanke des Leo Pargil Domes dokumentieren, dass dieser sich entlang zeitlich verbundener Abschiebungssysteme in einem extensionalen Regime entwickelt hat. Im Gelände wird der Dome von einem mächtigen Störungssystem begrenzt, die "Leo Pargil Detachment Zone" (LPDZ). Durch den tektonischen Versatz entlang der LPDZ liegen heute niedriggradig metamorphe Sedimentgesteine im Hangenden neben hochgradigen Gneisen in Liegenden. Unabhängig von der Probenlokation entlang des aufgeschlossenen Störungssystemes ergeben alle neuen 40Ar/39Ar-Hellglimmeralter um die 15 Ma und deuten auf ein regional wichtiges Abkühlungsereignis hin. Im Gegensatz dazu deuten die neuen Apatit-Spaltspuralter (AFT) auf eine kontinuierliche Exhumation der hochmetamorphen Einheiten im Liegenden der LPDZ unter sprödtektonischen Bedingungen zwischen 10 und 2 Ma hin, bei einem minimalen Versatz von ungefähr 9 km. Desweiteren deuten die Apatit-Spaltspur-Daten auf überregionale beschleunigte Abkülhlungs- bzw Exhumationsphase seit 4 Ma.<br><br>Daraus kann gefolgert werden, dass die tektonischen Prozesse die Entwicklung des gesamten Gebirges beflussen können, während potenzielle Wechselwirkungen zwischen Erosion und Tektonik auf die luvwärtigen Gebirgsflanken beschränkt zu bleiben scheinen.

A evolução da margem continental do sudeste do Brasil tem sido discutida por diversos autores desde meados do século passado até os dias atuais, especialmente no contexto da origem e evolução dos escarpamentos e das bacias tafrogênicas. Buscou-se contribuir com novos dados sobre a evolução da área a partir da aplicação da termocronologia de baixa temperatura (U-Th)/He em apatita, que oferece uma sensibilidade significativa para registrar movimentações tectônicas na crosta superior. Foi possível obter idades em 107 cristais de apatita de 18 amostras do embasamento coletadas no perfil com orientação NW-SE, numa seção entre a Serra da Mantiqueira e o Gráben da Guanabara. As idades corrigidas variam entre 250,1 8,7 Ma e 43,5 1,9 Ma (2 &#963;) e as não corrigidas entre 174,13 3,03 Ma e 27,07 0,60 Ma (1 &#963;). O Neocretáceo, o Eocretáceo e o Paleoceno são os principais registros no conjunto de dados, em ordem de importância. No Neocretáceo, o intervalo entre 83,6 e 72,1 Ma (Campaniano) representa o maior destaque nos registros termocronológicos, embora os outros registros (Maastrichtiano e Santoniano) também estejam presentes e sejam importantes. As idades do Neocretáceo destacam a importância dos eventos tectonomagmáticos e soerguimento regional na história térmica dessa área, inclusive com idades (~86 Ma) atribuídas ao contexto de soerguimento da Serra do Mar. As idades do Eocretáceo indicam o registro de eventos térmicos mais antigos, vinculados à evolução pré-rifte. Já os dados do Paleoceno estariam associados ao evento de reativação responsável pela implantação do sistema de riftes continentais (~65 Ma) e as idades do Eoceno, restritas à borda de falha da bacia de Resende (49,7 Ma e 43,5 Ma), à reativação do sistema de riftes nessa área. A dispersão de idades foi interpretada como efeito dos danos de radiação já que muitos grãos apresentam correlação entre idade e concentração de urânio (eU). Os padrões de tempo-temperatura (t-T), definidos a partir dos modelos HeFTy calibrados para o modelo de difusão que considera os efeitos de danos de radiação nos cristais, registraram eventos de resfriamento rápido, os quais mostram correlação direta com episódios de reativação e soerguimento na margem continental e com registros nas bacias continentais e marginais. O padrão de aumento das idades com a elevação, assim como da costa em direção ao interior é observado, mas mostra-se alterado pela ocorrência de idades mais jovens associadas à complexa evolução dessa margem continental com desnivelamentos de blocos vinculados à tectônica pós-rift, numa situação que ressalta a influência dos episódios de reativação. As estimativas de denudação total variam entre 1,2 e 2,8 km. As taxas de erosão variam entre 15,2 e 35,3 m/Ma. A evolução da área indica não apenas a influência de um evento específico mas, possivelmente, uma combinação de episódios que se alternaram e/ou atuaram em conjunto em determinados períodos. Os eventos de reativação mais antigos, combinados com os mais recentes, exibem os seus remanescentes na paisagem (serras da Mantiqueira e do Mar e os grábens e bacias sedimentares) e assumem papel fundamental na evolução da área. Os registros de tais episódios podem ser observados nas histórias térmicas das rochas e nos depósitos correlativos nas bacias sedimentares marginais e intracontinentais. / This doctoral dissertation involves low-temperature thermochronologic investigations to constrain the Mesozoic and Cenozoic tectonic reactivation of the continental margin of southeast Brazil. The study area is located in a segment of the Neoproterozoic Ribeira belt in southeastern Brazil, which occupied a central position in Western Gondwana. Lately, during the Mesozoic and Cenozoic, fault zones related to the development of the continental rifts in southeast Brazil reactivated. Using apatite (U-Th)/He thermochronology (AHe), we have presented the results of analysis on 107 apatite crystals of basement samples collected from a NWSE transect in the Mantiqueira Mountains to the Guanabara Graben, as well as from the NESE transverse faults. The data range from 27.07 0.60 Ma to 174.13 3.03 Ma (1 &#963;) for uncorrected ages, and from 43.5 1.9 Ma to 250.1 8.7 Ma (2 &#963;) for corrected ages. The Neo-Cretaceous, Eo-Cretaceous, and Paleocene are the main recorded AHe ages, in order of importance. The Eo-Cretaceous ages indicate the occurrence of older thermal events related to a pre-rifting phase (~121 Ma). The Neo-Cretaceous ages signify the importance of tectonic and magmatic events, and regional uplifting for the thermal history of the study area, including ages related to the Serra do Mar Mountains uplift (~86 Ma). Paleocene ages seem to be related to the reactivation (~65 Ma), which was responsible for the continental rifts in the southeastern Brazil. Finally, the Eocene ages (49.7 Ma and 43.5 Ma), which are from samples restricted to the Resende Basin border faults, indicate a continental rift reactivation. We investigated the age dispersion data, which were interpreted as an effect of radiation damage. Several samples show correlations between apatite (U-Th)/He age and effective U concentration (eU). We have applied HeFTy thermal modeling to obtain timetemperature (t T) paths using a radiation damage diffusion model. Inverse modeling of (U-Th)/He age data suggests rapid cooling episodes for all samples. The main thermal events recorded by the HeFTy models show a direct correlation with the timing of regional tectonic events: reactivation phases, continental margin uplift, and the sedimentary record. Apatite (U-Th)/He ages increase with distance from the coast and with elevation. However, these patterns are discontinued by samples of younger ages as a result of the reactivation process of pre-existing structures in the Brazilian continental margin. The total estimated denudation range from 1.2 to 2.8 km. The erosion rates range from 15.2 to 35.3 m/My. Thus, the multi-episodic thermal events, which led to the formation of important regional tectonic and geomorphological features (Mantiqueira Mountains, Serra do Mar Mountains, grabens, and sedimentary basins), seem to play a fundamental role in the evolution of the Brazilian continental margin. The records can be found in the thermal history of rocks and its correlated deposits in the continental margin.

La marge sud péruvienne est située au niveau d’une zone majeure de subduction océan continent depuis au moins le Paleozoique inférieur. C’est dans ce cadre que s’est formé l’un des plus importants orogènes du monde : les Andes Centrales. En effet, l’épaisseur crustale y est >60 km et ce sur une importante surface. Cependant, on considère actuellement que ce surrépaississement a été acquis incrémentalement seulement depuis ~30 Ma. Dans le but de comprendre comment et quand ce surrépaississement est apparu, la majeure partie des études précédentes s’est focalisée sur l’évolution de l’arc magmatique et sur l’histoire de la déformation, du soulèvement et de l’érosion de la zone d’arrière arc. Cependant, l’évolution tectonique et thermique de l’avant arc reste mal connue bien que cette zone soit susceptible de bien enregistrer les changements liés à la dynamique de subduction.Cette thèse à pour objectif de mieux contraindre l’évolution thermique et les couplages entre les processus magmatiques, tectoniques et sédimentaires depuis 200 Ma dans l’avant-arcactuel du sud du Pérou. De nouvelles données géo-thermochronologiques couplées à une nouvelle carte tecto-stratigraphique éclaircissent l’évolution de la marge péruvienne depuis le Jurassique. Trois périodes clefs sont analysées dans ce mémoire : le début de l’épaississement crustal, les déformations de l’avant-arc associées à la formation de l’Orocline bolivien et l’épaississement crustal de l’orogène des Andes Centrales pendant le Néogène.Nous montrons que l’épaississement crustal a probablement commencé entre 90 et 50Ma après plus de 200 Ma d’amincissement, et ce a la faveur d’une évolution en trois étapes :croissance initiale (90-74 Ma), « flare-up » (74-62 Ma) et effondrement extensionnel (62-50Ma). L’extension a ensuite prédominé dans l’avant-arc tout en diminuant progressivement jusqu’à ~30 Ma. Par ailleurs, nous mettons en évidence d’importantes zones de faillesnormales orientées perpendiculairement à la marge sud-péruvienne et qui délimitent de grands blocs basculés vers le nord-ouest. Ces déformations révèlent une extension parallèle à l’orogène dans l’avant arc pendant le Paléogène, probablement due à la formation de l’Orocline bolivien par rotation antihoraire de blocs rigides. Enfin, les traits géomorphiques visibles dans la zone cotiere du sud du Pérou permettent de définir deux périodes de soulèvement de la surface (entre 23 et 10 Ma et depuis ~4.5 Ma), séparées par une période de subsidence (entre ~10 et ~4.5 Ma). La même chronologie ayant été décrite sur le versant Amazonien de l’orogène, nous proposons que cette évolution soit due à des variations à grande échelle de l’épaisseur crustale ; le soulèvement de la surface étant provoqué par addition à la croûte de magma d’origine mantellique et la subsidence par un flux de matériel crustal ductile depuis les zones précédemment sur-épaissies. / The southern Peruvian margin has been located above a major ocean-continentsubduction zone since at least the Early Paleozoic, resulting in the formation of one of thelargest orogens in the world: the Central Andes, where crustal thickness is >60 km over a largearea. This overthickening is currently thought to have occurred incrementally only during thelast 30 Ma. To understand how and when crustal overthickening was acquired, most of theprevious studies have focused on the magmatic arc evolution and on deformation, uplift anderosion history of the backarc. The tectono-thermal Cenozoic evolution of the forearc remainspoorly known, whereas it is a zone prone to recording changes in subduction dynamics.The objective of this dissertation is to address the thermal evolution and the couplingbetween magmatic, tectonic and sedimentary processes over the past 200 Ma in the presentdayforearc of southern Peru where the crust thickens from ~30 km along the coastline tomore than 60 km under the present-day volcanic arc. New geo- and thermochronological datacoupled to a novel geological map illuminate the evolution of the south Peruvian margin sincethe Jurassic. Three key periods of the margin evolution are addressed in this dissertation: theonset of crustal thickening, the deformations associated in the forearc with the formation ofthe Bolivian Orocline and the Neogene crustal thickening of the Central Andean orogen.We show that crustal thickening likely began between 90 and ~50 Ma after more than200 My of lithospheric thinning during a three step evolution of the magmatic arc as follows:growth (90-74 Ma), flare-up (74-62 Ma), extensional collapse (62-50 Ma). Extension prevailedin the forearc since then and waned until ~30 Ma. In addition, we evidence important normalfault zones striking perpendicular to the southern Peruvian margin that delineate largenorthwestward tilted blocks. This deformation reveals orogen parallel extension in the forearcduring the Paleogene likely due to the formation of the Bolivian Orocline by counterclockwiserotation of rigid blocks. Finally, geomorphic features in the coastal area of southern Perureveal two periods of surface uplift (~23 to 10 Ma and since ~4.5 Ma), separated by a period ofsurface subsidence (from ~10 to ~4.5 Ma). The same chronology has been described on theAmazonian side of the Central Andean orogen. We thus propose that this evolution is due tolarge-scale crustal thickness variations; surface uplift being triggered by addition of mantlederivedmagmas to the crust and subsidence by ductile flow away from the previouslyoverthickened crust.

L'évolution topographique des chaînes de montagne résulte d'interactions complexes entre la tectonique et le climat via l'action des processus de surface. La quantification de l'évolution du relief passe par le développement d'outils méthodologiques permettant d'identifier les processus mis en jeu pour des échelles de temps (103-106 années) et d'espace (1-100 km) caractéristiques de contextes orogéniques. Dans cette étude, l'évolution Néogène et Quaternaire du relief des Alpes Européennes est abordée à partir d'une approche couplant la thermochronométrie basse-température in-situ (essentiellement (U-Th-Sm)/He et 4He/3He sur apatite) et la modélisation numérique. Le développement d'une méthode numérique associant la modélisation thermo-cinématique (Pecube) à un algorithme d'inversion (Neighbourhood Algorithm) permet l'interprétation quantitative de données thermochronologiques en termes d'histoires d'exhumation et d'évolution du relief. La quantification de l'évolution du relief reste néanmoins problématique et fortement dépendante du contexte géomorphologique étudié. Cette étude implique la nécessité de repenser a priori la stratégie d'échantillonnage et d'interprétation des données suivant le contexte géomorphologique considéré et le signal d'exhumation que l'on cherche à quantifier via la thermochronologie. Enfin, l'application de cette approche à un jeu de données thermochronologiques échantillonnées dans le massif des Ecrins-Pelvoux (Alpes françaises) révèle l'existence d'un épisode d'exhumation rapide cessant autour de ~5-6 Ma, encadré par des taux d'exhumation plus modérés. Cependant, les données ne permettent pas de conclure quant à l'évolution tardi-Néogène du relief dans le massif des Ecrins-Pelvoux. L'application de la thermochronométrie 4He/3He dans la vallée du Rhône (Alpes suisses), couplée à des données thermochronologiques issues de la littérature, confirme un épisode d'exhumation rapide jusqu'à ~5-7 Ma, et révèle une augmentation majeure du relief local (~1-1.5 km) associée au creusement des vallées par d'importants appareils glaciaires. Le début de cette phase de creusement correspond à la transition climatique Mi-Pléistocène (~1 Ma) depuis des cycles glaciaires symétriques de 40 ka vers des cycles asymétriques (100 ka) de plus forte amplitude. Ces données permettent également de reconstruire la topographie pré-glaciaire du bassin versant du Rhône, et ainsi d'évaluer, à une échelle plus globale, l'impact des glaciations Pléistocènes sur l'évolution du relief. Des résultats préliminaires issus de la modélisation numérique des processus glaciaires mettent en évidence le potentiel d'une telle approche afin de tester quantitativement l'influence de la transition climatique Mi-Pléistocène sur le développement du relief alpin, ouvrant de nouvelles perspectives de recherche. Enfin, l'étude de l'évolution topographique post-glaciaire dans le massif des Ecrins-Pelvoux (modélisation numérique et utilisation du 10Be cosmogénique produit in-situ) met en évidence une dynamique d'érosion fluviale pouvant atteindre localement des vitesses de l'ordre du cm an-1, illustrant l'évolution géomorphologique rapide en réponse à la transition climatique entre le tardi-Pléistocène et l'Holocène. / The topographic evolution of mountain belts results from complex couplings between tectonics, climate and surface processes. Quantifying landscape evolution requires methodological tools to constrain forcing processes over temporal (103-106 years) and spatial (1-100 km) scales characteristic of orogenic systems. This thesis investigates the Neogene and Quaternary relief evolution of the European Alps using in situ low-temperature thermochronometry (mostly apatite (U-Th-Sm)/He and 4He/3He) and numerical modeling. A novel numerical approach combining thermal-kinematic modeling (Pecube) with an inversion scheme (Neighbourhood Algorithm) allows extracting quantitative information on exhumation and relief histories from thermochronological datasets. Quantifying relief evolution remains problematic, however, and strongly depends on the geomorphic setting. Our results show that both thermochronology data sampling and modeling strategies have to be considered a priori, in function of the geomorphic setting and the spatial/temporal scale of the exhumation signal to be constrained. This approach has been applied on a thermochronological dataset collected in the Ecrins-Pelvoux massif (French Alps). The results show a pulse of rapid exhumation until ~5-6 Ma, preceded and followed by more moderate rates of exhumation. However, the data cannot resolve the late-Neogene relief evolution in the Ecrins-Pelvoux massif. New 4He/3He thermochronometry data from the Rhône valley (Swiss Alps), combined with thermochronological data from the literature, also point out an episode of rapid exhumation until ~5-7 Ma, and reveal a major increase in local topographic relief (~1-1.5 km) linked to valley carving by large mountain glaciers. The onset of this phase of relief carving corresponds to the Mid-Pleistocene transition from symmetric 40-ka to asymmetric and high amplitude 100-ka glacial/interglacial oscillations. The new data also permit to reconstruct the pre-glacial topography of the Rhône basin, and to evaluate the net effect of Pleistocene glaciations on relief evolution at the basin scale. Preliminary results from numerical modeling of glacial dynamics highlight the potential opportunity of using such an approach to quantitatively assess the impact of the Mid-Pleistocene climate transition on Alpine relief development, leading to new research avenues. Finally, the post-glacial topographic evolution of the Ecrins-Pelvoux massif has been studied using numerical modeling and in situ cosmogenic 10Be analyses. The results suggest efficient fluvial incision at rates of cm yr-1, illustrating the efficient landscape response to late-Pleistocene/Holocene climate change.

A evolução da margem continental do sudeste do Brasil tem sido discutida por diversos autores desde meados do século passado até os dias atuais, especialmente no contexto da origem e evolução dos escarpamentos e das bacias tafrogênicas. Buscou-se contribuir com novos dados sobre a evolução da área a partir da aplicação da termocronologia de baixa temperatura (U-Th)/He em apatita, que oferece uma sensibilidade significativa para registrar movimentações tectônicas na crosta superior. Foi possível obter idades em 107 cristais de apatita de 18 amostras do embasamento coletadas no perfil com orientação NW-SE, numa seção entre a Serra da Mantiqueira e o Gráben da Guanabara. As idades corrigidas variam entre 250,1 8,7 Ma e 43,5 1,9 Ma (2 &#963;) e as não corrigidas entre 174,13 3,03 Ma e 27,07 0,60 Ma (1 &#963;). O Neocretáceo, o Eocretáceo e o Paleoceno são os principais registros no conjunto de dados, em ordem de importância. No Neocretáceo, o intervalo entre 83,6 e 72,1 Ma (Campaniano) representa o maior destaque nos registros termocronológicos, embora os outros registros (Maastrichtiano e Santoniano) também estejam presentes e sejam importantes. As idades do Neocretáceo destacam a importância dos eventos tectonomagmáticos e soerguimento regional na história térmica dessa área, inclusive com idades (~86 Ma) atribuídas ao contexto de soerguimento da Serra do Mar. As idades do Eocretáceo indicam o registro de eventos térmicos mais antigos, vinculados à evolução pré-rifte. Já os dados do Paleoceno estariam associados ao evento de reativação responsável pela implantação do sistema de riftes continentais (~65 Ma) e as idades do Eoceno, restritas à borda de falha da bacia de Resende (49,7 Ma e 43,5 Ma), à reativação do sistema de riftes nessa área. A dispersão de idades foi interpretada como efeito dos danos de radiação já que muitos grãos apresentam correlação entre idade e concentração de urânio (eU). Os padrões de tempo-temperatura (t-T), definidos a partir dos modelos HeFTy calibrados para o modelo de difusão que considera os efeitos de danos de radiação nos cristais, registraram eventos de resfriamento rápido, os quais mostram correlação direta com episódios de reativação e soerguimento na margem continental e com registros nas bacias continentais e marginais. O padrão de aumento das idades com a elevação, assim como da costa em direção ao interior é observado, mas mostra-se alterado pela ocorrência de idades mais jovens associadas à complexa evolução dessa margem continental com desnivelamentos de blocos vinculados à tectônica pós-rift, numa situação que ressalta a influência dos episódios de reativação. As estimativas de denudação total variam entre 1,2 e 2,8 km. As taxas de erosão variam entre 15,2 e 35,3 m/Ma. A evolução da área indica não apenas a influência de um evento específico mas, possivelmente, uma combinação de episódios que se alternaram e/ou atuaram em conjunto em determinados períodos. Os eventos de reativação mais antigos, combinados com os mais recentes, exibem os seus remanescentes na paisagem (serras da Mantiqueira e do Mar e os grábens e bacias sedimentares) e assumem papel fundamental na evolução da área. Os registros de tais episódios podem ser observados nas histórias térmicas das rochas e nos depósitos correlativos nas bacias sedimentares marginais e intracontinentais. / This doctoral dissertation involves low-temperature thermochronologic investigations to constrain the Mesozoic and Cenozoic tectonic reactivation of the continental margin of southeast Brazil. The study area is located in a segment of the Neoproterozoic Ribeira belt in southeastern Brazil, which occupied a central position in Western Gondwana. Lately, during the Mesozoic and Cenozoic, fault zones related to the development of the continental rifts in southeast Brazil reactivated. Using apatite (U-Th)/He thermochronology (AHe), we have presented the results of analysis on 107 apatite crystals of basement samples collected from a NWSE transect in the Mantiqueira Mountains to the Guanabara Graben, as well as from the NESE transverse faults. The data range from 27.07 0.60 Ma to 174.13 3.03 Ma (1 &#963;) for uncorrected ages, and from 43.5 1.9 Ma to 250.1 8.7 Ma (2 &#963;) for corrected ages. The Neo-Cretaceous, Eo-Cretaceous, and Paleocene are the main recorded AHe ages, in order of importance. The Eo-Cretaceous ages indicate the occurrence of older thermal events related to a pre-rifting phase (~121 Ma). The Neo-Cretaceous ages signify the importance of tectonic and magmatic events, and regional uplifting for the thermal history of the study area, including ages related to the Serra do Mar Mountains uplift (~86 Ma). Paleocene ages seem to be related to the reactivation (~65 Ma), which was responsible for the continental rifts in the southeastern Brazil. Finally, the Eocene ages (49.7 Ma and 43.5 Ma), which are from samples restricted to the Resende Basin border faults, indicate a continental rift reactivation. We investigated the age dispersion data, which were interpreted as an effect of radiation damage. Several samples show correlations between apatite (U-Th)/He age and effective U concentration (eU). We have applied HeFTy thermal modeling to obtain timetemperature (t T) paths using a radiation damage diffusion model. Inverse modeling of (U-Th)/He age data suggests rapid cooling episodes for all samples. The main thermal events recorded by the HeFTy models show a direct correlation with the timing of regional tectonic events: reactivation phases, continental margin uplift, and the sedimentary record. Apatite (U-Th)/He ages increase with distance from the coast and with elevation. However, these patterns are discontinued by samples of younger ages as a result of the reactivation process of pre-existing structures in the Brazilian continental margin. The total estimated denudation range from 1.2 to 2.8 km. The erosion rates range from 15.2 to 35.3 m/My. Thus, the multi-episodic thermal events, which led to the formation of important regional tectonic and geomorphological features (Mantiqueira Mountains, Serra do Mar Mountains, grabens, and sedimentary basins), seem to play a fundamental role in the evolution of the Brazilian continental margin. The records can be found in the thermal history of rocks and its correlated deposits in the continental margin.

Made available in DSpace on 2014-06-11T19:32:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-11-19Bitstream added on 2014-06-13T19:21:56Z : No. of bitstreams: 1 francomagalhaes_aob_dr_rcla.pdf: 5041816 bytes, checksum: 4e36d86919b2c22df4f361432ee24c8f (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A evolução do Arco de Ponta Grossa relaciona-se aos diversos eventos de reativação da Plataforma Sul-americana no sudeste brasileiro a partir do Cretáceo Inferior. A análise multi-métodos dos traços de fissão em apatita e zircão no eixo central do Arco de Ponta Grossa permitiu identificar períodos de exumação nas seguintes épocas: (1) Cretáceo Inferior (idades de traços de fissão em zircão entre 138 ± 51 Ma e 107 ± 22), relacionado aos processos tectônicos, magmáticos e de exumação do evento de ruptura do Gondwana Sul-Ocidental; (2) Cretáceo Superior (idades de traços de fissão em zircão entre 90 ± 14 Ma e 69 ± 21 Ma; e idades de traços de fissão em apatitas entre 74 ± 14 Ma e 66 ± 2 Ma), relacionado ao alçamento do embasamento cristalino como resposta à uma anomalia térmica causada pela passagem da Pluma de Trindade sob o sudeste brasileiro, e conseqüente geração tectônica de relevo e erosão que forneceu sedimentos para as bacias de Santos e do Paraná; (3) Cretáceo Superior – Paleoceno Inferior, evento tectônico relacionado a um soerguimento regional que resultou no alçamento e erosão das bordas das bacias da Plataforma Sul-americana, em especial a Bacia do Paraná. Este evento também é associado ao tectonismo gerador das bacias do Rifte Continental Sudeste do Brasil, no segmento central; (4) Oligoceno-Mioceno (idades de traços de fissão em apatitas entre 26 ± 3 Ma e 14 ± 2 Ma) há o registro da mais recente reativação das zonas de falha NW, em especial a Zona de Falha de São Jerônimo-Curiúva, associada ao rearranjo do campo de tensões neste período, e conseqüente erosão das porções de rocha, que marca o início da sedimentação no segmento sul do Rifte Continental Sudeste do Brasil, composto pela Bacia de Curitiba, grábens de Guaraqueçaba, Sete Barras e Cananéia; e as formações Pariqüera- Açu e Alexandra... / The evolution of Ponta Grossa Arch is genetically related to the post-rift reactivation of the South American Platform since Early Cretaceous. Apatite and Zircon lowtemperature thermochronology analysis in Ponta Grossa Arch provided the following interpretations: (1) Zircon fission-track ages between 138 ± 51 Ma and 107 ± 22are related to the tectonic, magmatic and exhumation processes occurred during the Gondwana breakup in Early Cretaceous; (2) Zircon fission-track ages between 90 ± 14 Ma and 69 ± 21 Ma, and apatite fission-track ages between 74 ± 14 Ma and 66 ± 2 Ma are evidenced the basement uplift as a response of thermal anomaly induced by Trindade plume since this time, as also evidenced in other areas of SE-Brazil during Late Cretaceous. The resulting highlands were the main source-area for the Coniacian-Maastrichian sediments of the Santos (Santos formation) and Paraná (Bauru Group) basins; (3) Between Late Cretaceous and Early Paleocene, the tectonic processes caused uplift and erosion of the Paleozoic interior basins, specially the Paraná Basin. At this time, preexisting shear zones were reactivated, formed the Continental Rift Basins of SE Brazil and continental sediments were deposited in these basins at the northern part of the study-area during this time; (4) During Oligocene to Miocene, apatite fission-track ages between 26 ± 3 Ma and 14 ± 2 Ma indicate the youngest reactivation of the NE-SW Precambrian shear zones and consequent exhumation of high elevated area. The origin of the Continental Rift Basins of SE Brazil in the study area (Curitiba basin, Guaraqueçaba, Sete Barras and Cananéia Grabens, and Pariquera-Açu and Alexandra formations) is probably related to the movement along NWSE trending fault zones (São Jerônimo-Curiúva Fault Zone). Thermal histories evidenced local and sea base-level stability and peneplanation processes caused dissection in highelevated areas.

Cette thèse cible l'étude de la structure thermique de la croûte supérieure (<10km) dans les arcs magmatiques continentaux, et son influence sur l'enregistrement thermochronologique de leur exhumation et de leur évolution topographique. Nous portons notre regard sur deux chaînes de montagne appartenant aux Cordillères Américaines : Les Cascades Nord (USA) et la zone de faille Motagua (Guatemala). L'approche utilisée est axée sur l'utilisation de la thermochronologie (U-Th-Sm)/He sur apatite et zircon, couplée avec la modélisation numérique de la structure thermique de la croûte. Nous mettons en évidence la variabilité à la fois spatiale et temporelle du gradient géothermique, et attirons l'attention du lecteur sur l'importance de prendre en compte la multitude des processus géologiques perturbant la structure thermique dans les chaînes de type cordillère, c'est à dire formées lors de la subduction océanique sous un continent. / This thesis focuses on the influence of the dynamic thermal structure of the upper crust (<10km) on the thermochronologic record of the exhumational and topographic history of magmatic continental arcs. Two mountain belts from the American Cordillera are studied: the North Cascades (USA) and the Motagua fault zone (Guatemala). I use a combined approach coupling apatite and zircon (U-Th-Sm)/He thermochronology and thermo-kinematic numerical modelling. This study highlights the temporal and spatial variability of the geothermal gradient and the importance to take into account the different geological processes that perturb the thermal structure of Cordilleran-type mountain belts (i.e. mountain belts related to oceanic subduction underneath a continent).