Robust interpretations of rock thermal histories are critical for resolving the timing and rates of geologic processes, especially as low-temperature thermochronology has become a common tool for investigating the evolution of landscapes and mountain belts and the feedbacks between geodynamic processes. Most interpretations of thermochronologic cooling ages, however, attribute rock cooling entirely to rock exhumation - a common but tenuous assumption in many settings where thermochronology is used to investigate links between tectonics, climate, and landscape evolution, because these places often have history of magmatism. Exploring the complexities - and advantages - of interpreting low-temperature thermochronologic data in magmatic terranes is the principal theme of this work. Using simple analytical approximations as well as the finite-element code Pecube, we characterize the cooling age patterns inside and around plutons emplaced at upper and middle crustal levels and identify the advective and conductive scaling relationships that govern these patterns. We find that the resetting aureole width, the difference between reset and unreset cooling ages in country rocks, and the lag time between pluton crystallization age and pluton cooling age all scale with exhumation rate because this rate sets the advective timescale of cooling. Cooling age-elevation relationships in these steadily exhuming models have changes in slope that would masquerade as changes in exhumation or erosion rates in real datasets, if the thermal effects of the plutons were not accounted for. This is the case both in the country rocks immediately next to upper crustal plutons and, surprisingly, in the country rocks kilometers above mid-crustal plutons with no surface expression. Together with a lag-time analysis useful for the practical question of when it is appropriate to interpret a cooling age as an exhumation rate in crystalline rocks, this work improves our framework for evaluating the effects of magmatism on thermochronologic datasets. We also demonstrate the importance of considering the magmatic history of a region in field studies of the Colorado Plateau, where interpreting apatite (U-Th)/He data requires diagnosing significant inter- and intra-sample age variability. Prior to considering the thermal history of the region, we develop a new model for a common source of this age variability: excess He implantation from U and Th (i.e., eU) hosted in secondary grain boundary phases (GBPs), which can make very low eU apatites hundreds of percent 'too old'. Samples significantly affected by He implantation are not useful for thermal history interpretations, but this model does provide a diagnostic tool for discriminating these samples from those with useful age trends. Once the effects of GBPs have been accounted for, the remaining data from two different thermochronologic archives in the central Colorado Plateau provide a new perspective on the Cenozoic history of the region, which has a multiphase - and enigmatic - history of magmatism and erosion. We find that sandstones in the thermal aureoles around the Henry, La Sal, and Abajo mountains intrusive complexes were usefully primed by magmatic heating in the Oligocene to document the subsequent late Cenozoic history of the region more clearly than any other thermochronologic archive on the Plateau. These data document a stable Miocene landscape (erosion rates<30 m/Ma) that rapidly exhumed ~1.5-2 km in the Plio-Pleistocene (~250-700 m/Ma no earlier than 5 Ma) in the Henry and Abajo mountains, and strongly suggest most of this erosion occurred in the last 3-2 Ma. The integration of the Colorado River ca. 6 Ma, which dropped regional base-level, is the principal driver of this erosion. It is likely, however, that a component of the rapid Pleistocene rock cooling is unique to the high mountains of the Colorado Plateau and reflects an increase in spring snow-melt discharge during glacial periods. Although apatite thermochronology results far from the Oligocene intrusive complexes cannot resolve this detailed Plio-Pleistocene history, they do constrain the onset of late Cenozoic erosion to no earlier than ~6 Ma. Moreover, apatite cooling ages from these rocks also document Oligocene cooling (ca. 25 Ma) that is contemporaneous with the emplacement of the laccoliths and the waning of the vigorous magmatic flare-up that swept through the southwestern USA ca. 40-25 Ma. Although the cooling ages are consistent with ~1 km of exhumation in the late Oligocene and early Miocene, as previous workers have suggested in the eastern Grand Canyon region, we demonstrate that a transient change in the geothermal gradient (peaking at ~50˚C/Ma in the late Oligocene) driven by moderate mid-crustal magmatism can produce identical age patterns. Therefore, we re-interpret the mid-Cenozoic erosion event on the Colorado Plateau as primarily a change in the crustal thermal field, rather than an erosional event. This requires a more significant Laramide-age unroofing in parts of the central Plateau and perhaps a re-evaluation of the interpretations of Oligocene canyon cutting in the Grand Canyon region

The Andean Cordilleran orogenic system stretches over 7,000 km along the western margin of South America and serves as a useful laboratory to evaluate the causes of spatial and temporal variations in orogenic processes. Although the geology of the Andean margin is fundamentally controlled by the subduction of the Nazca plate beneath the South American plate, the style of deformation, basin morphology, exhumation history, and volcanic activity along this margin are remarkably heterogeneous in both time and space. My Ph.D. work presents new data from the Miocene – Pliocene along-strike depocenters bounding the basement block uplifts of the Sierras Pampeanas and the fold and thrust belt of the Andean Precordilleran in the south Central Andes between ca. 27.5°S and 30.5°S. I use new observations from sedimentology, detrital zircon U-Pb data, and low-temperature thermochronology to evaluate the mechanisms driving basin organization, sedimentation, and exhumation. Geohistory analysis supports flexurally controlled basins between ca. 18 and 6 Ma with detritus derived exclusively from the active Precodillera to the west. Accelerated deformation in the Precordillera produced accelerated sedimentation from ca. 10 – 8.5 Ma. A deceleration of sedimentation from ca. 6 – 5 Ma was most likely controlled by heightened aridity. Around the same time, low-temperature thermochronometers record the widespread exhumation of the foreland basin system for over 300 km along strike, this may be driven by dynamically controlled uplift related to Miocene flat-slab subduction. Low-temperature thermochronometers suggest that the geothermal gradient throughout the late Miocene was ca. 35°C/km – 25°C/km and had not been significantly depressed as previously proposed. Granite-cored ranges in the Sierras Pampeanas were sampled for low-temperature thermochronology to constrain the exhumation history of the region. Modeling of both apatite fission track and apatite (U-Th-Sm)/He thermochronometers demonstrates that these rocks have been close to the surface since the late Paleozoic. Reheating during the Cretaceous is attributed to elevated geothermal gradients due to back-arc rifting. Final exhumation (1- 2 km) occurred in the mid to late Miocene and may have been controlled by the onset of flat-slab subduction. These results suggest that the Sierras Pampeanas may have had inherited positive topography that has controlled basin organization and sediment distribution patterns since the Paleozoic.

River incision into a widespread, upland low-relief landscape, and related patterns of exhumation recorded by low-temperature thermochronology, together underpin geodynamic interpretations for crustal thickening and uplift of the eastern Tibetan Plateau. We report results from a suite of 11 (U-Th-Sm)/He cooling-age samples. Eight samples comprise a 1.2 km relief section collected from elevations up to 4800 m in the Jiulong Shan, an elevated, rugged region located in the hinterland of the Yalong-Longmen Shan Thrust Belt, and surrounded on three sides by upland low-relief landscape surfaces. Zircon and apatite cooling ages record two episodes of rapid exhumation in the early Oligocene and late Miocene, that were separated by a period of stability from similar to 30 to 15 Ma. The first episode is consistent with a similar pulse evident from the Longmen Shan. The second episode is ongoing, and when integrated with adjacent cooling-age data sets, shows that doming of the Jiulong Shan has resulted in 2 to 4 km of differential exhumation of the plateau interior. We show from a compilation of glacial landform-mapping that the elevation of the plateau surface closely tracks global last glacial maximum equilibrium line altitude. We hypothesize that smoothing of highlands by efficient glacial and periglacial erosion, coupled with potential river captures and conveyance of sediments via external drainage, can yield an apparently continuous low-relief plateau landscape formed diachronously at high elevation. (C) 2016 Elsevier B.V. All rights reserved.

The Gulf of California in western Mexico is a prime example of a young passive margin that is currently undergoing the transition from continental rifting to seafloor spreading. With less than ~25 km of the width of the original continental surface area submerged, the northern Gulf Extensional Province represents a key area to assess the history of strain localisation during the early stages of continental extension. Geological mapping revealed that the basins and ranges of the Sierra San Felipe, located in the hanging wall of the Main Gulf Escarpment, are bounded to the east by an en-echelon array of left-stepping moderate- to low-angle normal faults that represent the next dominant set of normal faults from the break-away fault in direction of transport. Structural displacement estimates suggest up to ~4.5–9 km of broadly east-directed extension on the Las Cuevitas, Santa Rosa and Huatamote detachments. Fault kinematics suggest a transtensional stress regime with NE- to SE-directed extension and permutating vertical and N–S subhorizontal shortening. Clockwise vertical-axis block rotations and constrictional folding of the detachments were an integral part of the late Miocene to Pleistocene deformation history of the San Felipe fault array. This overall constrictional strain regime is indistinguishable from the present-day deformation in the Gulf Extensional Province and indicates that the fault array formed during a single phase of integrated transtensional shearing since rifting began in the late Miocene. / Apatite fission track (AFT) and (U-Th)/He results of Cretaceous crystalline basement samples from the Sierra San Felipe record a three-stage Cenozoic cooling history. Moderate cooling (~4–7ºC/m.y.) during late Paleocene to Eocene times is attributed to progressive down-wearing and bevelling of the ancestral Peninsular Ranges. Beginning at ~45–35 Ma, a period of tectonic quiescence with cooling rates of ≤1ºC/m.y. marks final unroofing of the basement and the development of a regional Oligocene to Miocene peneplain. Thermal modelling of samples from the footwall of the Las Cuevitas and Santa Rosa fault systems indicates that accelerated cooling began at ~9–8 Ma. This cooling pulse is attributed to tectonic denudation of the footwall and implies that faulting initiated synchronously on both detachments at ~9–8 Ma. Late Miocene deformation occurred distributed throughout the Sierra San Felipe, but started waning after the Pacific-North America plate boundary had localised into the Gulf of California by ~4.7 Ma / During a late Pliocene structural reorganisation in the northern Gulf, the locus of extension shifted from the Tiburón to the Delfín basins, thereby initiating strike-slip faulting on the Ballenas fracture zone, a transform fault located approximately 1.5–4.5 km offshore in central Baja California. This is consistent with low-temperature thermochronometric data from two horizontal transects perpendicular to the strike of the transform, which document a pronounced late Pliocene to Pleistocene heating event that is related to the structural and/or magmatic evolution of the transform fault. During reheating, maximum paleotemperatures reached >100–120ºC near the coast, but did not exceed ~60ºC some 5–8 km further inland. Highly non-systematic overprinting patterns are best explained by circulating hydrothermal fluids, which are most likely associated with magmatic leaking along the transform fault. / AFT and (U-Th)/He ages from a vertical profile collected on the Libertad escarpment, which forms part of the Main Gulf Escarpment in central Baja, pre-date Neogene extension and indicate that rift-related denudation was insufficient to expose samples from temperatures higher than the sensitivity zones of the two systems. One sample from the base of the escarpment however, records a middle to late Miocene hydrothermal overprint and suggests that extension in central Baja California likely initiated before ~10–8 Ma.

Many passive margins experience pulsed exhumation events late in their history as a result of plate boundary distal geodynamic mechanisms or climatic events. The onset of late Cenozoic glaciation, often associated with enhanced rates of erosion, is one such possible cause of passive margin rejuvenation. However, along passive margins the effectiveness of Plio-Pleistocene glaciers at eroding the landscape may be limited by low tectonic rock uplift rates or as a result of erosionally inefficient cold based continental ice-sheets. In this dissertation the evolution of post-orogenic topography and the effect of glaciations on denuding landscapes along the North Atlantic Passive Margin, in the White Mountains of New Hampshire and the western Scottish Highlands, was investigated. Background exhumation rates averaged over 106-7 yr timescale were determined using apatite (U-Th)/He thermochronology. To resolve whether or not a change in exhumation rate occurred coincident with glaciation these background exhumation rates were compared to magnitudes of erosion averaged over the glacially relevant 103-4 yr timescale using the in situ terrestrial cosmogenic nuclide 10Be. In chapter two, 106-7 yr timescale exhumation and burial histories across the western Scottish Highlands were determined. The results show that post-orogenic burial and exhumation is mostly a result of plate margin distal tectonic and magmatic factors that are variable across short distances (i.e., <100 km). In chapter three, patterns and magnitudes of erosion during glaciation and following deglaciation in the Scottish Highlands were investigated. The results indicate that polythermal glacial erosion denuded low elevation portions of the Scottish Highlands and preserved summits. This produced relief but did not significantly lower the maximum elevation of the landscape. Following deglaciation Scotland's sediment budget remains dominated by glaciogenic sediment. In the fourth chapter, magnitudes of background exhumation in the Presidential and Carter Ranges of the White Mountains, New Hampshire were compared to magnitudes of glacial erosion. The results indicate that most relief was produced prior to glaciation and that background exhumation rates in the Cenozoic are low (<0.01 mm yr-1). In the late-Cenozoic, cold- based glaciation prevented an acceleration of erosion in the White Mountains. The post- glacial sediment budget is made up of dominantly glaciogenic sediment. Overall, the main findings of this dissertation are; (1) post-orogenic burial, exhumation, and relief production are mainly the result of spatially heterogeneous plate margin distal vertical crustal motions; across passive margins covered by large continental ice sheets; (2) cold-based ice limits the magnitudes of late Cenozoic glacial erosion sediment budgets continue to be dominated by glaciogenic sediment, >10 ka after and (3) post-glacial deglaciation. / Ph. D. / Far away from the edges of modern tectonic plates, old mountain ranges (~300 million years old) may experience changes in rates of erosion long after the forces that built those mountains have gone away. Tectonic forces that occur far away from the edges of tectonic plates could cause these changes in erosion rate or they could be a result of changes in climate that create conditions in which erosion rates could increase. One change in climate that could have caused faster rates of erosion in old mountain ranges is climatic cooling causing the repeated advance and retreat of glaciers in mid to high latitudes over the past ~2.6 million years. Glaciers are usually seen as having the ability to erode faster than non-glacial processes (e.g., rivers). However, not all glaciers have the ability to erode really fast. In old mountain ranges glacial erosion might be limited because the mountains are not being uplifted very fast supplying new land to be subjected to erosion. Also, big ice sheets that covered many old mountain ranges can be very cold, freezing ice to the ground and therefore acting to protect the underlying landscape rather than eroding it. In this dissertation the question of whether glaciation caused an acceleration in erosion rates in old mountain ranges far away from the edges of tectonic plates is investigated, specifically in White Mountains of New Hampshire and the western Scottish Highlands. To this end, erosion rates in these mountain ranges were determined prior to glaciation and then compared to erosion rates during glaciation and following deglaciation. The results of the research presented in this dissertation indicate that; (1) pre-glacial erosion resulting from tectonic forces far from the edges of tectonic plates was more important at producing relief and eroding the landscape than glaciers; (2) ice covering old mountain ranges was at least partially cold-based, inhibiting erosion; and (3) following deglaciation sediments in streams are mostly sourced from remobilized glacially produced sediments rather than direct bedrock erosion.

Orientador: Peter Christian Hackspacher / Banca: Antonio Roberto Saad / Banca: Francisco José Fonseca Ferreira / Banca: Gilmar Vital Bueno / Banca: Sandro Guedes de Oliveira / Acomapnah 4 mapas anexos / Resumo: 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... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: 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. / Doutor

No description available.

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.

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.

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.