The modern foreland basin straddling the eastern margin of the Andean orogen is the prime example of a retro-arc foreland basin system adjacent to a subduction orogen. While widely studied in the central and southern Andes, the spatial and temporal evolution of the Cenozoic foreland basin system in the northern Andes has received considerably less attention. This is in part due to the complex geodynamic boundary conditions, such as the oblique subduction and accretion of the Caribbean plates to the already complex interaction between the Nazca and the South American plates. In the Colombian Andes, for example, a foreland basin system has been forming since ~80 Ma over an area previously affected by rift tectonics during the Mesozoic. This setting of Cenozoic contractile deformation superposed on continental crust pre-strained by extensional processes thus represents a natural, yet poorly studied experimental set-up, where the role of tectonic inheritance on the development of foreland basin systems can be evaluated. However, a detailed documentation of the early foreland basin evolution in this part of the Andes has thus far only been accomplished in the more internal sectors of the orogen. In this study, I integrate new structural, sedimentological and biostratigraphic data with low-temperature thermochronology from the eastern sector of the Colombian Andes, in order to provide the first comprehensive account of mountain building and related foreland basin sedimentation in this part of the orogen, and to assess as to what extent pre-existent basement anisotropies have conditioned the locus of foreland deformation in space and time. In the Medina Basin, along the eastern flank of the Eastern Cordillera, I integrated detailed structural mapping and new sedimentological data with a new chronostratigraphic framework based on detailed palynology that links an eastward-thinning early Oligocene to early Miocene syntectonic wedge containing rapid facies changes with an episode of fast tectonic subsidence starting at ~30 Ma. This record represents the first evidence of topographic loading generated by slip along the principal basement-bounding thrusts in the Eastern Cordillera to the west of the basin and thus constrains the onset of mountain building in this area. A comprehensive assessment of exhumation patterns based on zircon fission-track (ZFT), apatite fission-track (AFT) analysis and thermal modelling reveals the location of these thrust loads to have been located along the contractionally reactivated Soapaga Fault in the axial sector of the Eastern Cordillera. Farther to the east, AFT and ZFT data also document the onset of thrust-induced exhumation associated with contractional reactivation of the main range-bounding Servita Fault at ~20 Ma. Associated with this episode of orogenic growth, peak burial temperature estimates based on vitrinite reflectance data in the Cenozoic sedimentary record of the adjacent Medina Basin documents earlier incorporation of the western sector of the basin into the advancing fold and thrust belt. I combined these new thermochronological data with published AFT analyses and known chronologic indicators of brittle deformation in order to evaluate the patterns of orogenic-front migration in the Andes of central Colombia. This spatiotemporal analysis of deformation reveals an episodic pattern of eastward migration of the orogenic front at an average rate of 2.5-2.7 mm/yr during the Late Cretaceous-Cenozoic. I identified three major stages of orogen propagation. First, following initiation of mountain building in the Central Cordillera during the Late Cretaceous, the orogenic front propagate eastward at slow rates (0.5-3.1 mm/yr) until early Eocene times. Such slow orogenic advance would have resulted from limited accretionary flux related to slow and oblique (SW-NE-oriented) convergence of the Farallon and South American plates during that time. A second stage of rapid orogenic advance (4.0-18.0 mm/yr) during the middle-late Eocene, and locally of at least 100 mm/yr in the middle Eocene, resulted from initial tectonic inversion of the Eastern Cordillera. I correlate this episode of rapid orogen-front migration with an increase in the accretionary flux triggered by acceleration in convergence and a rotation of the convergence vector to a more orogen-perpendicular direction. Finally, stagnation of the Miocene deformation front along former rift-bounding reactivated faults in the eastern flank of the Eastern Cordillera led to a decrease in the rates of orogenic advance. Post-late Miocene-Pliocene thrusting along the actively deforming front of the Eastern Cordillera at this latitude suggests averaged Miocene-Holocene orogen propagation rates of 1.2-2.1 mm/yr. In addition, ZFT data suggest that exhumation along the eastern flank of the orogen occurred at moderate rates of ~0.3 mm/yr during the Miocene, prior to an acceleration of exhumation since the Pliocene, as suggested by recently published AFT data. In order to evaluate the relations between thrust loading and sedimentary facies evolution in the foreland, I analyzed gravel progradation in the foreland basin system. In particular, I compared one-dimensional Eocene to Pliocene sediment accumulation rates in the Medina basin with a three-dimensional sedimentary budget based on the interpretation of ~1800 km of industry-style seismic reflection profiles and borehole data tied to the new chronostratigraphic framework. The sedimentological data from the Medina Basin reveal rapid accumulation of fluvial and lacustrine sediments at rates of up to ~ 0.5 mm/yr during the Miocene. Provenance data based on gravel petrography and paleocurrents reveal that these Miocene fluvial systems were sourced by Upper Cretaceous and Paleocene sedimentary units exposed to the west, in the Eastern Cordillera. Peak sediment-accumulation rates in the upper Carbonera Formation and the Guayabo Group occur during episodes of gravel progradation in the proximal foredeep in the Early and Late Miocene. I interpreted this positive correlation between sediment accumulation and gravel deposition as the direct consequence of thrust activity in the Servita-Lengupá Fault. This contrasts with current models relating gravel progradation to episodes of tectonic quiescence in more distal portions of foreland basin systems and calls for a re-evaluation of tectonic history interpretations inferred from sedimentary units in other mountain belts. In summary, my results document a late Eocene-early Miocene eastward advance of the topographic loads associated with the leading edge of deformation in the northern Andes of Colombia. Crustal thickening of the Eastern Cordillera associated with initiation of thrusting along the Servitá Fault illustrates that this sector of the Andean orogen acquired ~90% of its present width already by the early Miocene (~20 Ma). My data thus demonstrate that inherited crustal anisotropies, such as the former rift-bounding faults of the Eastern Cordillera, favour a non-systematic progression of foreland basin deformation through time by preferentially concentrating accommodation of slip and thrust-loading. These new chronology of exhumation and deformation associated with specific structures in the Colombian Andes also constitutes an important advance towards the understanding of models for hydrocarbon maturation, migration and trap formation along the prolific petroleum province of the Llanos Basin in the modern foredeep area. / Das Vorlandbecken, das sich an der östlichen Flanke der Anden erstreckt, ist ein prototypisches Beispiel für ein Retro-Arc-Vorlandbecken eines Subduktionszonenorogens. Im Gegensatz zu den südlichen und zentralen Anden, wurde die zeitliche und räumliche Entwicklung dieses känozoischen Systems im nördlichen Teil des Orogens weit weniger untersucht. Dies liegt unter anderem an den komplexen geodynamischen Randbedingungen, wie der schrägen Subduktion und Anlagerung der karibischen Plattengrenzen an die südamerikanische und Nazca-Platte, deren Interaktion ebenfalls komplex ist und durch unterschiedliche Konvergenzrichtungen und –geschwindigkeiten gekennzeichnet ist. Aufgrund dieser Verhältnisse hat auch die Oberplatte eine sehr differenzierte tektonische Entwicklung erfahrens. In den kolumbianischen Anden hat sich zum Beispiel seit ca. 80 Milllionen Jahren ein Vorlandbeckensystem in einem Gebiet gebildet, das während des Mesozoikums durch Rifttektonik geprägt war. Dieses Gebiet, in dem kompressive Deformation die Strukturen vorheriger extensionaler Prozesse z.T. reaktiviert und überlagert, ist daher ein natürliches, wenn auch bisher wenig erforschtes Naturlabor, um zu untersuchen, wie sich tektonische bedingte Anisotropien auf die Entwicklung von Vorlandbeckensystemen auswirken können und Änderungen in den Ablagerungsräumen und in der Faziesverteilung von Sedimenten hervorrufen. In dieser Arbeit präsentiere ich neue strukturelle, sedimentologische und biostratigraphische Daten zusammen mit neuen Informationen zur Exhumationsgeschichte mit Hilfe von Niedrigtemperatur-Thermochronologie aus dem östlichen Teil der kolumbianischen Anden, um zum ersten Mal eine vollständige Darstellung der Gebirgsbildung und zugehöriger Vorlandbeckensedimentation in diesem Teil der Anden zu liefern. Zusätzlich wird untersucht, zu welchem Ausmaß bereits existierende krustale Anisotropien den Ort der Vorlanddeformation in Raum und Zeit bestimmt haben. Im Medina Becken, an der östlichen Flanke der östlichen Kordillere, habe ich detaillierte strukturelle Kartierungen und neue sedimentologische Daten mit einem neuen chronostratigraphischen Rahmen, der auf detaillierter Palynologie basiert, verknüpft. Dieser Bezugsrahmen verbindet einen nach Osten hin ausdünnenden, syntektonischen früholigozänen bis frühmiozänen Keil, welcher rasche Faziesänderungen enthält, mit einer Phase schneller tektonischer Subsidenz, die vor ca. 30 Millionen Jahren beginnt. Dieser hier erarbeitete Datensatz stellt den ersten Beweis einer tektonisch bedingten Subsidenz dar, die durch Bewegungen entlang der Haupüberschiebungen an der Westgrenze des Vorlandes stattfanden. Dadurch wird das Einsetzen der Gebirgsbildung in diesem Gebiet zeitlich eingegrenzt. Eine umfassende Auswertung von Exhumationsmustern, die auf Zirkon- (ZFT) und Apatit-Spaltspuraltern (AFT) sowie thermischen Modellierungen beruhen, zeigt, daß diese Überschiebungsbahnen und die bedeutende Aufschiebungstätigkeit und tektonische Auflast entlang der reakivierten, vormals extensionalen Servita-Störung, im zentralen Bereich der östlichen Kordillere liegen. Weiter östlich dokumentieren AFT und ZFT Daten den Einsatz einer durch Überschiebungen hervorgerufenen Exhumation, die mit einer kompressiven Reaktivierung der großen Servita-Störung vor ca. 20 Millionen Jahren zusammenhängt. Vitrinitreflexionsdaten aus dem känozoischen Sedimentationsdatensatz des benachbarten Medina Beckens zeigen eine bedeutende Absenkung in dieser Region, bei der der westliche Sektor des Beckens schon im Anfangsstadium der orogenen Entwicklung in den nach Osten wandernden Falten- und Überschiebungsgürtel einbezogen wurde. Ich verbinde diese neuen thermochronologischen Daten mit veröffentlichten AFT Analysen und bekannten chronologischen Indikatoren für Spröddeformation, um die räumlich-zeitlichen Muster in der Entwicklung der Gebirgsfront in den Anden Zentralkolumbiens zu charakterisieren. Diese Analyse der Deformation zeigt ein episodisches Muster in der östlich gerichteten Migration der Gebirgsfront, mit einer durchschnittlichen Rate von 1.8-3.4 mm/a am Übergang von der späten Kreide zum frühen Känozoikum. Ich habe dabei drei Hauptabschnitte des lateralen Orogenwachstums identifiziert. Zuerst wandert die Gebirsfront, nach dem Beginn der Gebirgsbildung in den Zentralkordilleren während der späten Kreidezeit, ostwärts mit niedrigen Raten (0.3-3.3 mm/a) bis ins frühe Eozän. Ein solches langsames laterales Wachstum des Orogens resultiert aus Akkretionsprozessen im Zuge einer langsamen und schrägen (SW-NO orientiert) Konvergenz der Farallon- mit der südamerikanischen Platte. Eine zweite Phase schnellen Fortschreitens der Gebirgsfront mit Raten von 5.3-13.3 mm/a, lokal sogar bis zu 100 mm/a, fand während des mittleren/späten Eozäns statt und resultierte aus einer beginnenden tektonischen Inversion der östlichen Kordillere. Ich verbinde diese Phase rascher Gebirgsfrontmigration mit einem erhöhten Akkretionsfluß, der durch eine Beschleunigung der Konvergenz sowie einer Rotation des Konvergenzvektors in eine mehr rechtwinklige Richtung ausgelöst wurde. Letztlich führte eine Stagnation der Deformationsfront im Miozän entlang von ehemals riftbegrenzenden, reaktivierten Störungen an der östlichen Flanke der östlichen Kordillere zu einer Abschwächung der Raten der Gebirgsfrontmigration. Aus Überschiebungen des späten Miozän/Pliozän entlang der aktiv deformierten Front der östlichen Kordillere kann man auf durchschnittliche Bewegungsraten der Gebirgsfront von etwa 1.5-2.1 mm/a im Zeitraum Miozän bis Holozän schließen. Außerdem deuten ZFT Daten darauf hin, daß Exhumation entlang der östlichen Flanke des Orogens mit mittleren Raten von ungefähr 0.3 mm/a während des Miozäns stattfand. Im Pliozän erfolgte daraufhin eine Beschleunigung der Exhumation, wie kürzlich veröffentlichte AFT Daten nahelegen. Um die Beziehung zwischen tektonischer Auflast aufgrund der Verkürzung im Orogen und Evolution der sedimentären Fazies im Vorland zu untersuchen, habe ich die Progradation von Konglomeraten im Vorlandbeckensystem detailliert analysiert. Insbesondere habe ich eindimensionale Raten von Sedimentakkumulation vom Eozän bis zum Pliozän im Medina Becken mit einem dreidimensionalen Sedimenthaushalt verglichen. Dieser wurde aus der Interpretationen mit einer Gesamtlänge von ~2500 km seismischer Reflexionsprofile sowie Bohrlochdaten, verbunden mit dem neuen chronostratigraphischen Bezugssystem der sedimentären Ablagerungen, gewonnen. Die sedimentologischen Daten aus dem Medina Becken zeugen von rascher Akkumulation von fluviatiler und lakustriner Sedimente mit Raten von bis zu 0.5 mm/a während des Miozäns. Provenienzanalysen mittels Konglomerat-Petrographie und Paläoströmungsmessungen belegen, daß diese miozänen fluviatilen Systeme des Miozäns durch die Erosion sedimentärer Einheiten aus der oberen Kreide und dem Paläozän generiert wurden, die im Westen der östlichen Kordillere aufgeschlossen sind. Die höchsten Sedimentationsraten in der oberen Carbonera Formation und der Guayabo Gruppe finden sich während Episoden von Konglomeratprogradation der proximalen Vortiefe im frühen und späten Miozän. Ich interpretiere diese positive Korrelation zwischen Sedimentakkumulation und Konglomeratablagerung als direkte Konsequenz von Überschiebungstektonik an der Servita-Lengupá-Störung. Diese Interpretation ist allerdings im Gegensatz zu gängigen Sedimentationsmodellen Modellen, die eher eine tektonische Ruhephase mit der Progradation grober Schüttungen in den distalen Bereichen der Vorlandbecken in Verbindung bringen. Dies bedeutet, daß Interpretationen der aus Faziesverteilungen gewonnenen tektonischen Entwiklungsschritte eines Orogens auch in andeen Regionen neu bewertet werden müssen. Zusammengefaßt dokumentieren meine Ergebnisse, daß die Überschiebungsfront sowie die durch Einengung generierte Topographie und Auflast der Überschiebungsblöcke in den nördlichen kolumbianischen Anden während des späten Miozäns bis zum frühen Miozän ostwärts gewandert ist. Einengung und Krustenverdickung der östlichen Kordillere, verbunden mit beginnender Aktivität entlang der Servitá Störung, deutet an, daß dieser Bereich der Anden schon nahezu 90% seiner derzeitigen Breite bereits im Miozän (20 Ma) erreicht hattte. Die hier vorgestellten Daten zeigen also, daß ererbte krustale Anisotropien ein diachrones Voranschreiten der Vorlandbeckendeformation begünstigen. Dies geschieht durch Konzentration der Bewegungsverteilung an ererbten Störungen sowie lokalen Spannungsänderung im Vorland durch tektonische induzierte Auflasten. Diese neue Charakterisierung der Deformationsabfolge im Vorland der Anden bedeutet auch einen großen Schritt vorwärts in Richtung des Verstehens von Modellen, die das Reifen und die Wanderung von Kohlenwasserstoffen sowie die Entstehung von Ölfallen entlang der produktiven Petroleumprovinz im Llanos Becken der rezenten Vortiefe beschreiben.

The northeast African continental margin of the Western Desert of Egypt is host to a complexly deformed series of Phanerozoic basins. Substantial sedimentary deposition (~5 km) and basin formation resulted from regional deformation due to continental collision and repeated rifting and inversion cycles. Limited sedimentary exposure and exploration has prevented elucidation of Phanerozoic basin evolution, particularly in the Paleozoic. Previous studies of the region have largely relied upon sedimentary analysis, gravity, and 2D/3D seismic data. This study, in contrast, has employed extensive use of detrital zircon (U-Th)/He thermochronology (n=1004) from 17 wells in conjunction with 3D seismic, well log correlation, and heat flow data to elucidate a spatiotemporally comprehensive tectonic and stratigraphic model. The detrital zircon thermochronometric data provides new evidence that the lower Paleozoic, Carboniferous, and Mesozoic stratigraphic sequences of the Western Desert represent thermally distinct, tectonically controlled sequences with independent thermal evolutions. The lower Paleozoic sequence has been partially thermally reset, reaching temperatures of ~140-170 ̊C. Partial resetting is noted throughout the region and reached its thermal maximum in the Permo-Triassic, synchronous with onset of Neotethyan rifting. The Carboniferous sequence has not been thermally reset, with exposure to temperatures no greater than ~140 ̊C and reaching thermal maximum presently. Carboniferous (U-Th)/He ages have dominant input from short-lag-time zircons (exhumation to deposition) and indicate the stratigraphic sequence was proximally sourced. The proximal sourcing is likely from transmitted stress and fault reactivation in Egypt during the Hercynian Orogeny that caused fault block exhumation and erosional unroofing. Sediment was shed from uplifted fault blocks that formed the eastern boundary of the Carboniferous sequence. The Mesozoic sequence has not been thermally reset, reaching temperatures no greater than ~120 ̊C and presently reaching thermal maximum. Localized areas with stacking of lower Paleozoic, Carboniferous, and Mesozoic sequences likely bury the lower Paleozoic to abnormally deep depths (~7 km) and elevated temperatures of ~200 ̊C. Evidence from faulting relationships, basin controlling structures, and heat flow data indicate that N-S trending basement structures may define a region of crustal transition between the Archean-Paleoproterozoic Saharan Metacraton and the juvenile Arabian-Nubian Shield. / text

Zircon (U-Th)/He (zircon He) dating has become a widely used thermochronologic method in the geosciences. Practitioners have traditionally interpreted (U-Th)/He dates from zircons across a broad spectrum of chemical compositions with a single set of ⁴He diffusion kinetics derived from only a handful of crystals (Reiners et al., 2004). However, it has become increasingly clear that a "one-size-fits-all" approach to these kinetics is inadequate, leading to erroneous conclusions and incongruent data. This dissertation develops a more grain-specific approach by showing the fundamental role that intracrystalline radiation damage plays in determining the He diffusivity in a given zircon. I present three appendices that seek to quantify the radiation damage effect on He diffusion in zircon, explain how this effect manifests in zircon He dates, and show how to exploit such manifestations to better constrain sample thermal histories. Of particular importance, this dissertation represents the first comprehensive study to concentrate on the entire damage spectrum found in natural zircon and also the first to show that two different mechanisms affect He diffusion in zircon in different ways across this spectrum. In the first appendix, I and my fellow co-authors describe results from a series of step-heating experiments that show how the alpha dose of a given zircon, which we interpret to be correlated with accumulated radiation damage, influences its He diffusivity. From 1.2 × 10¹⁶ α/g to 1.4 × 10¹⁸ α/g, He diffusivity at a given temperature decreases by three orders of magnitude, but as alpha dose increases from ~2 × 10¹⁸ α/g to 8.2 × 10¹⁸ α/g, He diffusivity then increases by about nine orders of magnitude. We parameterize both the initial decrease and eventual increase in diffusivity with alpha dose with a function that describes these changes in terms of increasing abundance and size of intracrystalline radiation damage zones and resulting effects on the tortuosity of He migration pathways and dual-domain behavior. This is combined with another equation that describes damage annealing in zircon. The end result is a new model that constrains the coevolution of damage, He diffusivity, and He date in zircon as a function of its actinide content and thermal history. The second and third appendices use this new model to decipher zircon He datasets comprising many single grain dates that are correlated with effective uranium (eU, a proxy for the relative degree of radiation damage among grains from the same sample). The model is critical for proper interpretation of results from igneous settings that show date-eU correlations and were once considered spurious (appendix B). When applied to partially reset sedimentary rocks, other sources of date variability, such as damage and He inheritance, have to be considered as well (appendix C).

The Paparoa Metamorphic Core Complex developed in the Mid-Cretaceous due to continental extension conditioning the crust for the eventual breakup of the Gondwana Pacific Margin, which separated Australia and New Zealand. It has two detachment systems: the top-NE-displacing Ohika Detachment at the northern end of the complex and the top-SW-displacing Pike Detachment at the southern end of the complex. The structure is rather unusual for core complexes worldwide, which are commonly characterised by a single detachment system. Few suggestions for the kinematics of the core complex development have been made so far. In this study structural-, micrographic- and fission track analyses were applied to investigate the bivergent character and to constrain the kinematics of the core complex. The new results combined with reinterpretations of previous workers’ observations reveal a detailed sequence of the core complex exhumation and the subsequent development. Knowledge about the influence and the timing of the two respective detachments is critical for understanding the structural evolution of the core complex. The syntectonic Buckland Granite plays a key role in the determination of the importance of the two detachment systems. Structural evidence shows that the Pike Detachment is responsible for most of the exhumation, while the Ohika Detachment is a mere complexity. In contrast to earlier opinions the southwestern normal fault system predates the northeastern one. The Buckland Pluton records the ceasing pervasive influence of the Pike Detachment, while activity on the Ohika Detachment had effect on the surface about ~8 Ma later. Most fission track ages are not related to the core complex stage, but reflect the younger late Cretaceous history. They show post core complex burial and renewed exhumation in two phases, which are regionally linked to the development of the adjacent Paparoa Basin and the Paparoa Coal Measures to the southwest and to the inception of seafloor spreading in the Tasman Sea in a larger context.

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.

abstract: The Byrd Glacier region of Antarctica is important for understanding the tectonic development and landscape evolution of the Transantarctic Mountains (TAM). This outlet glacier crossing the TAM marks a major discontinuity in the Neoproterozoic-early Paleozoic Ross orogen. The region has not been geologically mapped in detail, but previous studies have inferred a fault to exist beneath and parallel to the direction of flow of Byrd Glacier. Thermochronologic analysis has never been undertaken across Byrd Glacier, and little is known of the exhumation history of the region. The objectives of this study are to assess possible differential movement across the inferred Byrd Glacier fault, to measure the timing of exhumation, and to gain a better overall understanding of the structural architecture of the TAM. Apatites and zircons separated from rock samples collected from various locations north and south of Byrd Glacier were dated using single-crystal (U- Th)/He analysis. Similar cooling histories were revealed with comparable exhumation rates of 0.03 ± 0.003 and 0.04 ± 0.03 mm/yr north and south of Byrd Glacier from apatite data and somewhat similar rates of 0.06 ± 0.008 and 0.04 ± 0.01 mm/yr north and south of Byrd Glacier from zircon data. Age vs. elevation regressions indicate a vertical offset of 1379 ± 159 m and 4000 ± 3466 m from apatite and zircon data. To assess differential movement, the Kukri Peneplain (a regional unconformity) was utilized as a datum. On-site photographs, Landsat imagery, and Aster Global DEM data were combined to map Kukri Peneplain elevation points north and south of Byrd Glacier. The difference in elevation of the peneplain as projected across Byrd Glacier shows an offset of 1122 ± 4.7 m. This study suggests a model of relatively uniform exhumation followed by fault displacement that uplifted the south side of Byrd Glacier relative to the north side. Combining apatite and zircon (U-Th)/He analysis along with remote geomorphologic analysis has provided an understanding of the differential movement and exhumation history of crustal blocks in the Byrd Glacier region. The results complement thermochronologic and geomorphologic studies elsewhere within the TAM providing more information and a new approach. / Dissertation/Thesis / M.S. Geological Sciences 2011

Estudos termocronológicos por traços de fissão em apatita são utilizados para estabelecer os principais eventos de denudação, erosão e subsidência na margem continental emersa do sul do Brasil e Uruguai. Os dados obtidos permitem verificar que as idades aparentes de traços de fissão variam de 383,4 ± 40,9 a 9,7 ± 1,2 Ma, entre o Devoniano Superior e o Mioceno, com comprimento dos traços de fissão entre 14,02 a 8,87 μm. A correlação entre idade e distribuição do comprimento dos traços de fissão confinados evidencia que as amostras sofreram diferentes reduções no comprimento dos traços de fissão. Isto indica que as rochas foram submetidas a diferentes posições crustais, paleotemperaturas e tempo de residência na Zona de Apagamento Parcial. As histórias térmicas obtidas mostram que processos de resfriamento lentos e contínuos foram registrados nas regiões desde o final do Pensilvaniano (Neopaleozóico). Os padrões de denudação são complexos, mas foi possível caracterizar no Uruguai e Rio Grande do Sul reflexos do evento orgênico Gondwanides (ou São Rafaélico) atuantes nas margens do Gondwana SW. Nas regiões do norte do Rio Grande do Sul, Santa Catarina e Paraná foi possível documentar com detalhe o recuo da escarpa da margem continental associada a fragmentação e dispersão mesocenozóica do Gondwana, com a definição de eventos de denudação em torno de: (i) 150-140 Ma, atribuído aos eventos pré-rifte a rifte; (ii) 90-80 Ma, associado ao magmatismo alcalino do Cretáceo Superior; (iii) eventos de 70-60 Ma e 45-35 Ma associados a rearranjos isostático da placa Sul-Americana na região estudada. Evento mais jovem com idades entre 20-10 Ma é reconhecido na margem continental do leste do RS e Uruguai, diretamente conectado à formação do Cone do Rio Grande. / Apatite fission track (FT) thermochronological analyses are used to establish the main events of denudation, erosion and subsidence of the emerse continental margin of South Brazil and Uruguay. The obtained data provide apparent ages ranging from 383.4 ± 40.9 Ma to 9.7 ± 1.2 Ma, between Upper Devonian and Miocene, and mean track length from 14.02 μm to 8.87 μm. Thermal history reconstruction based on apatite fission track thermochronology suggest the occurrence of long term and continuous cooling as well rapid uplift in investigated regions, recorded from Neopaleozoic to the Miocene. The oldest denudation event is well recorded in the Uruguay and Rio Grande do Sul as result of orogenic processes at margin of SW Gondwana, the so-called Gondwanides or San Rafael cycle. In the northern portion of Rio Grande do Sul, Santa Catarina and Paraná was possible to document the escarpment retreat across the rifted continental margin connected to the Mesocenozoic fragmentation and dispersion of Gondwana, defined by the main denudation event as follow: (i) 150-140 Ma, developed during the pre-rift and rift stages; (ii) 90-80 Ma, associated to Upper Cretaceous alkaline ; (iii) 70-60 Ma and 45-35 Ma events due to isostatic rearrangement of South American plate in the study area. The youngest denudation event, aged at 20-10 Ma, is very well defined in the emerse continental margin of east Rio Grande do Sul and Uruguay, and coeval to the Rio Grande Cone formation, a large sedimentary package of 4000 m thick.

A região de estudo localiza-se na porção da Bacia do Camaquã, sendo classicamente conhecida com “Janela Bom Jardim”. Esta área já foi intensamente estudada, principalmente em decorrência dos depósitos minerais amplamente distribuídos. Apesar disso ainda não existe um consenso com relação à evolução tectônica da região, desde processos formadores da bacia até eventos pósdeposicionais, como também com relação ao seu posicionamento estratigráfico dentro da sequência deposicional da Bacia do Camaquã. Dessa forma, este trabalho vem contribuir e acrescentar aos modelos anteriores com dados geocronológicos e termocronológicos, aplicados diretamente às rochas sedimentares da região, bem como, novos dados de estrutural. Para tanto, submetemos seis amostras de rochas sedimentares da região de Minas do Camaquã à análise pelo método U-Pb com LA-ICP-MS e SHRIMP, aplicado a zircões detríticos, no intuito de mapear possíveis áreas fonte dos sedimentos como também, propor uma idade máxima de deposição para a sequência. Estas mesmas amostras foram utilizadas para separação de apatitas para análise termocronológicas (traços de fissão em apatitas), com o objetivo de caracterizar eventos de soerguimento e denudação relacionados à tectônica que afetou a área. O estudo de proveniência possibilitou identificar uma grande contribuição de zircões de idade Brasiliana, principalmente do final do Neoproterozóico e secundariamente populações de zircões de idade Paleoproterozóica, principalmente relacionadas ao Ciclo Transamazônico. A população principal foi correlacionada às intrusões graníticas do Terreno Taquarembó, e possivelmente contribuições do Batólito Pelotas, como também, das sequências vulcano-sedimentares mais antigas da própria Bacia do Camaquã. As idades Paleoproterozóicas foram atribuídas á rochas do Complexo Granulítico Santa Maria Chico e Complexo Encantadas, como também, zircões retrabalhados das rochas metassedimentares do Complexo Metamórfico Porongos. Ainda foi possível estimarmos a idade máxima de deposição da sequência em 554 Ma a partir do grão de zircão mais jovem datado posicionando estas rochas dentro do intervalo deposicional do Grupo Santa Bárbara. A análise por traços de fissão em apatitas permitiu identificar quatro populações de idades principais. Estas populações foram atribuídas à influência de dois eventos orogênicos na margem sul – ocidental do Gondwana: Famatiniana e Gondwanides. O primeiro evento é bem documentado pelas populações de 407-362 Ma e o segundo pelas populações de 302 Ma e 242-211 Ma. A quarta população (133 Ma) foi registrada em uma única amostra indicando um evento térmico ocasionado por intrusões vulcânicas associadas ao vulcanismo Paraná-Etendeka (Cretáceo inferior). Por fim, dados estruturais permitiram identificar uma evolução tectônica complexa, marcada por processos relacionados formação da bacia até reativações pósdeposicionais. Os eventos D1 e D2 foram associados a esforços gerados durante os estágios finais do Ciclo Brasiliano, com campos de tensão S10E-N10W e SE-NW, respectivamente. Um evento D3 com campo de tensão W-L registra reativações causadas pela Orogenia Famatiniana. O evento D4 marcado por uma compressão NNE-SSW e uma extensão NE-SW são relacionados aos processos tectônicos Triássicos (Orogenia Gondwanides). Um último evento D5 extensional (L-W) foi correlacionado aos processos de separação do Gondwana. / The study area is located in the southern portion of the Camaquã Basin, being classically known as "Bom Jardim Window". This area has been intensely studied, mainly due to the ore deposits widely distributed. Yet there is still no consensus regarding the tectonic evolution of the region, since basin inception processes until postdepositional events, but also regarding its stratigraphic position within the depositional sequence Basin Camaquã. Thus, this work contributes to previous models with geochronological and thermochronological data, applied directly to the sedimentary rocks of the region, as well as new structural data. Therefore, we submitted six samples of sedimentary rocks from the Camaquã Mines region to U-Pb method with LA-ICP-MS e SHRIMP applied to detrital zircons in order to map possible source areas of the sediments, as well as, proposing a maximum depositional age for the sequence. These same samples were used for apatite separation for thermochronological analysis (apatite fission tracks), with the aim of characterizing uplift and denudation events related to tectonics process that affected the area. Provenance study enabled us to identify a large contribution of Brasiliano zircon ages, especially from Late-Neoproterozoic and secondarily, zircons populations of Paleoproterozoic age, mainly related to Trans-Amazonian Cycle. The main population was correlated with granitic intrusions from Taquarembó Terrene and possibly contributions from Pelotas Batholith, as well as, from older volcano-sedimentary sequences of the Camaquã Basin. Paleoproterozoic ages were assigned to rocks of Santa Maria Chico Granulitic Complex and Encantadas Complex, as well as, reworked zircons from metasedimentary rocks of Porongos Metamorphic Complex. Still it was possible to estimate the maximum deposition age of the sequence on 554 Ma from the youngest zircon grain dated. Previous isotopic data allow positioning these rocks within the depositional range of Santa Bárbara Group. Apatite fission track analysis identified four main ages populations. These populations were attributed to the influence of two orogenic events on the Southwestern margin of Gondwana: Famatinian and Gondwanides. The first event is well documented by the 407-362 Ma age populations and the second by the 302 Ma and 242-211 Ma. The fourth population (133 Ma) was recorded in only one sample indicating a thermal event caused by volcanic intrusions associated with volcanism Paraná-Etendeka (Lower Cretaceous). Finally, structural data allowed identifying a complex tectonic evolution, characterized by basin inception processes until post-depositional reactivations. The events D1 and D2 were associated with stresses generated during the final stages of the Brazilian Cycle with stress fields of S10E-SE-NW and SE-NW, respectively. A third event (D3) with W-L stress field records the reactivation Famatinian Orogeny. The D4 event marked by a NNE-SSW compression and a NE-SW extension related to Triassic tectonic processes (Gondwanides Orogeny). One last extensional (W-L) event (D5) was correlated to the processes of separation of Gondwana.

Made available in DSpace on 2014-06-11T19:26:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-10-05Bitstream added on 2014-06-13T20:14:55Z : No. of bitstreams: 1 fracalossi_cp_me_rcla.pdf: 1652239 bytes, checksum: 44f88bcded0aee03b826c091bf22a576 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Neste trabalho foram desenvolvidos estudos termocronológicos e hidroquímicos próximos às cidades de Limeira e Americana, centro do estado de São Paulo. A aplicação da análise dos isótopos de urânio nas águas subterrâneas do aqüífero Itararé permitiu o reconhecimento do aumento de 234U a partir das áreas topograficamente mais elevadas para áreas topograficamente mais baixas, ou seja, a razão de atividade 234U/238U aumentou a partir das áreas de recarga. O uso do método de análises de traços de fissão em apatita registrou através das histórias térmicas, um apagamento total dos traços de fissão com início de retenção dos traços a partir de 118 Ma para a amostra TF-856 e 97 Ma para a amostra TF-858. Estas idades registram o primeiro período de soerguimento da área com início de geração das paleoáreas de recarga. Posteriormente, entre o Cretáceo Superior e o Paleoceno, um período de aquecimento foi evidenciado e mais tarde, a partir do Eoceno até os dias atuais a área passa por uma nova fase de soerguimento. Este trabalho introduz a utilização do método de análise por traços de fissão no reconhecimento de altos estruturais para a caracterização de paleoáreas de recarga. / For this research were done thermochronological and hydrochemical studies close to Limeira and Americana cities, central region of São Paulo State. Using the U-isotopes analysis in groundwater from Itararé aquifer was identified a larger quantity of U234 from higher to lower topographic areas, which means that the 234U/238U activity rate got higher from recharge areas. The application of apatites fission-track analysis registered, through thermal histories, the total resetting of the fission-tracks from 118 Ma for the sample TF-856 and 97 Ma for the sample TF-858. These ages register the first uplift time of this area which caused the origin of the paleo-recharge areas. Between Upper Cretaceous and Paleocene a heating period was registered and afterwards, from Eocene to the present time, is evidenced that the area gets a new uplift phase. This work suggests the use of fission-tracks analysis for the recognition of structural height and its consequence to the paleo-recharge areas.

Le but de cette thèse est l'utilisation d'une approche multidisciplinaire qui combine des techniques d'analyse pétrologique, de la géochimie et de la thermochronologie afin de reconstituer l'évolution des Alpes occidentales pendant l'Oligocène et le Miocène et d'en déduire les implications géodynamiques. Ces techniques permettent à la fois d'identifier le bassin de drainage des sédiments et les taux d'exhumation dans ce bassin de drainage. L'enregistrement de cette évolution est préservé dans les bassins d'avant pays de chaque côté des Alpes occidentales en France et en Italie. Les techniques d'analyse pétrologique utilisées ici sont l'observation macroscopique, l'observation en lames minces, l'analyse par spectromètre Raman et l'étude de minéraux lourds. De nombreuses études ont été réalisées afin d'analyser les minéraux lourds des bassins alpins. Celles-ci permettent de déterminer la provenance des minéraux. Lors de ce projet, nous avons réalisé des analyses Raman sur des serpentinites permettant de distinguer les différents types de serpentinites. Or les Alpes internes montrent une gradation du métamorphisme croissant vers l'est, qui implique une variation des types de serpentinites vers l'est (association lizardites et antigorites dans les zones de basse température, antigorites exclusivement dans les zones de haute température). L'analyse de l'arrivée des différents types de serpentinites de part et d'autre de la chaîne permet de définir la position des réseaux de drainage dans les Alpes internes et de positionner la ligne de partage des eaux. La géochimie sur les basaltes détritiques permet d'analyser le type de basaltes et donc d'identifier leurs sources. Des basaltes non métamorphiques ont été identifiés en quantité importante dans les bassins d'avant-pays côté français démontrant la répartition importante de matériels océaniques obduits sur les Alpes internes à l'Oligocène. Les âges de thermochronologie détritique comparés à l'âge de dépôt permettent de déterminer le lag-time et donc le taux d'exhumation maximum de la zone érodée. En effet, la modélisation des isothermes permet de déterminer un taux d'exhumation à partir du lag-time. L'analyse des taux d'exhumation le long de la colonne stratigraphique à Barrême montre un pulse d'exhumation à partir d'une période très brève dans le temps : 30±1 Ma à des taux d'exhumation compris entre 1,5 à 2 km/Ma, qui correspond à la mise en place des Alpes internes. Ces taux d'exhumation correspondent à des taux d'exhumation importants mais inférieurs à ce que l'on peut trouver dans l'Himalaya actuellement. Ils sont toutefois comparables à l'activité d'exhumation dans des montagnes jeunes. De récents travaux de modélisation montrent que le retrait de slab peut être consécutif à une rupture de slab profond. Notre équipe propose que dans les Alpes occidentales, la rupture et le retrait de slab a permis la mise en place du corps d'Ivrea comme un poinçon au dessus du slab. / The aim of this dissertation was to use a multidisciplinary approach, combining petrologic, geochemical and geo-thermochronologic analyses, to reconstruct the topographic and exhumational evolution of the Western Alps during Oligocene and Early Miocene times, in relation to regional geodynamic events. Because the sedimentary record of this evolution is preserved in the foreland basins on the both sides of the Western Alps in France and Italy, this approach allows identifying sediment provenance and exhumation rates in the drainage areas. Petrological analyses used here were macroscopic observations in the field (pebbles counts), thin section analyses, and Raman spectrometry on detrital serpentinite pebbles and serpentine sand grains. The different serpentine species (antigorite, lizardite etc.), can be traced back to specific source lithologies because the metamorphic grade of the rocks exposed in the Western Alps increases eastward, with antigorite (HT serpentine) bearing rocks in the eastern piedmont complex and mixed lizardite-antigorite (LT serpentine) in the western piedmont complex. Analysis of serpentine species in the foreland basin deposits on both sides of the Alps allows determining changes in the paleo-Durance and paleo-Dora Riparia drainage areas and the position of the drainage divide, which have not changed since the Early Miocene. Major and trace element analyses of non-metamorphic basalt pebbles from the Barrême basin hint at the Chenaillet (or equivalent) obducted ophiolite in the internal Western Alps as the most likely source. Fission-track (FT) analysis of detrital apatite and zircon were used to determine maximum and average exhumation rates during the Oligocene. A pulse of fast erosional exhumation at about 30±1 Ma had rates on the order of 1.5-2 km/Myr, while average rates were about 0.2-0.3 km/Myr. FT and U/Pb double dating of single zircons show that the signal of fast exhumation is not an artifact caused by volcanic contamination at around 30 Ma. The rapid creation of high relief and associated exhumation rates are related to isostatic surface uplift after slab break-off beneath the Western Alps at 35-30 Ma, followed by slab retreat which allowed emplacement of the Ivrea body vertical indenter that supports the high topography in the internal Western Alps.