La marge d’Équateur est caractérisée par un bassin avant-arc formé par un socle crétacé et une couverture de sédiments marins d’âge Crétacé à Quaternaire. Le relief de cette zone comprend d’une part la cordillère Côtière proprement dite et la plaine Côtière, située entre la cordillère Côtière et les Andes. Ce travail porte sur l’évolution et le soulèvement de la cordillère Côtière durant le Néogène. Dans un premier temps, nous avons réalisé une étude géologique régionale de la cordillère côtière. À partir de l’analyse stratigraphique et structurale des formations géologiques, nous avons réalisé une carte géologique de la cordillère côtière au 1/500 000 qui nous a permis d’effectuer pour la première fois des corrélations stratigraphique et un schéma structural à l’échelle complète de la cordillère. Dans un deuxième temps nous avons réalisé une étude géomorphologique de la zone. À partir de l’analyse de MNT, d’images satellites et aériennes nous avons défini les principales caractéristiques morphologiques de la zone d’étude. En particulier, le travail a porté principalement sur l’analyse de la géométrie du réseau hydrographique, la mesure de la géométrie des vallées et du profil en long des rivières à l’échelle de la cordillère Côtière. En complément nous avons mesuré le profil longitudinal des terrasses alluviales le long du rio Jama et analysé la morphologie des cônes alluviaux qui se déposent au pied des Andes sur la plaine Côtière. Les résultats ont permis de proposer une évolution du soulèvement de la cordillère Côtière. Les mesures des incisions relatives des rivières suggèrent que le soulèvement de la cordillère Côtière n’est pas homogène et que la cordillère est segmentée en plusieurs blocs dont les taux de soulèvement relatif sont variables: les blocs du Nord présentant les incisions les plus importantes. L’analyse des profils longitudinaux des terrasses alluviales du rio Jama montre une activité néotectonique le long des failles du système de Jama. Le taux de soulèvement estimé à partir de cette analyse est de 0.9 à 1.2 mm/ an pour le segment central de la cordillère Côtière. L’analyse du cône de Santo Domingo, situé aux pieds des Andes, révèle une importante interaction entre le soulèvement de la cordillère Côtière et le remplissage sédimentaire de la plaine côtière dont le résultat est la réorganisation du réseau hydrographique en deux grands bassins hydrographiques: Guayas au Sud et Esmeraldas au Nord. A plus long termes, la géologie et la stratigraphie montrent que la partie du Sud a subis une plus forte érosion (soulèvement ?) qu'au Nord. La mise en évidence de plusieurs discordances à l’échelle régionale montre que la cordillère Côtière s’est soulevée de façon hétérogène depuis le Plio-Pléistocène formant un grand antiforme segmenté et contrôlé par des failles régionales qui présentent une direction proche de la direction du mouvement vers le NE-NNE du bloc Nord-Andin. / The Ecuadorian margin is characterized by a forearc basin composed of a Cretaceous basement covered by marine sediments of the Cretaceous to Quaternary age. The topography of this area displays two main morphological domains: the Coastal cordillera in the west and the Coastal plain in the east at the foothills of Andes cordillera. This work focuses on the genesis of the Coastal cordillera during the Neogene. Firstly, we carried out a geological fieldwork throughout the Coastal cordillera. From stratigraphy and structural studies, we produced a regional geological map of the Coastal cordillera at 1:500000 scale, which have allowed for the first time to realize a regional stratigraphy correlation and determine the structural pattern across the Coastal cordillera. In a second step, we carried out a geomorphologic study of the area. From DEM analysis and satellite and aerial imagery processing, we characterized the main landforms features of the study area. In particular, we focused on the geometry of the drainage network and on the river profiles crossing the Coastal cordillera. In addition, we measured the longitudinal profile of the alluvial terrace treads along the Jama River and analyzed the morphology of alluvial fans that are deposited on the Coastal Plain at the foothills of the Andes cordillera. From the different results obtained, we proposed an evolution scheme of the uplift of the coastal cordillera. The measurements of incisions along river valleys suggest that the uplift of the Costal cordillera is heterogeneous: the cordillera is segmented into several blocks with own uplift rates. The incisions of the northern blocks are the highest. The analysis of the longitudinal profiles along the alluvial terrace treads of the Jama River indicates a recent activity along the faults of the system Jama. The uplift rates estimated from this analysis ranges from 0.9 to 1.2 mm/yr for the central segment of the Coastal cordillera. The analysis of Santo Domingo alluvial fan situated at the foothills of the Andes cordillera reveals a large interaction between the sedimentary filling of the Coastal plain and the contemporaneous uplift of the Andes and the Coastal cordilleras. This interaction results into the reorganization of two major drainage basins: Guayas in the south and Esmeraldas in the north. At long timescales, the geology and stratigraphy of the Neogene formations shows that domains in the southern Coastal cordillera were subject to intense erosion (rising?) with respect to the northern domains. The analysis of the several unconformities evidences that the Coastal cordillera was raised in a heterogeneous way since the Plio-Pleistocene as a large and elongated antiform segmented and controlled by regional faults which have a trend between NE and NNE, which is close to that of the movement to the North Andean block.

Neste trabalho são caracterizados corpos sub-vulcânicos expostos no nordeste da Cordilheira Ocidental da Colômbia através de estudos petrográficos, análises geoquímicas em rocha-total e datação U-Pb por SHRIMP IIe em zircão. A área de estudo, em um contexto regional, representa um orógeno de acreção no sistema andino, constituído por rochas ígneas de afinidade oceânica amalgamadas contra a margem ocidental de América do Sul e associadas ao desenvolvimento da Grande Província Ígnea do Caribe (Caribbean Large igneous Province-CLIP). As análises em geoquímica elementar evidenciam para os corpos subvulcânicos um ambiente de subducção intra-oceânico de arco primitivo a mais evoluído, com significante contribuição de sedimentos subductados e assinaturas similares às registradas para as rochas vulcânicas e plutônicas presentes na área (Formação Barroso e Tonalito de Santa Fe e Buriticá). Dados isotópicos de Sr e Nd (razão inicial 87Sr/86Sr entre 0.70334 a 0.70543 e ?Nd entre +6.25 a +7.42) indicam uma área fonte de cunha mantélica, típica de rochas de arco, com níveis subordinados de material crustal. Idades U-Pb por SHRIMP IIe em zircão mostram cinco populações de idades correspondentes a: idades Neoarquenas ao redor de 2700 Ma, Paleoproterozoicas em torno de 2100, 2000 e 1800 Ma, Neoproterozoicas ao redor de 600 Ma, Ordovicianas/Devonianas de 460 e 360 Ma, e Cretáceas ao redor de 90 Ma. A população de idades mais novas é interpretada como a idade de cristalização dos corpos estudados, indicando uma relação espacial e temporal com as rochas ígneas da área associadas ao desenvolvimento da CLIP. As quatro populações de idades mais antigas são atribuídas a xenocristais, interpretados como provenientes de sedimentos terrígenos que foram arrastados ao canal de subducção, refletindo processos de reciclagem crustal através do manto em zonas de subducção intra-oceânicas. Foram identificadas duas possíveis áreas fontes para os xenocristais de zircão: o Complexo Marañon e o Maciço de Arequipa, que constituem inliers expostos na margem ocidental de América do Sul e apresentam uma boa correlação entre os eventos magmáticos/metamórficos que registram e às idades dos xenocristais encontrados. A partir destas interpretações, foi restringido o local de formação dos corpos estudados em relação à paleomargem continental, considerando além dados paleomagnéticos e modelos paleogeográficos publicados na zona de estudo. O trabalho fornece um aporte significativo para a compreensão da evolução tectono-magmática da região durante o Cretáceo superior, associada à história geológica da CLIP. / In this study sub-volcanic bodies exposed in the northeast of the Western Cordillera of Colombia are characterized through petrographic descriptions, geochemical analysis in bulk rocks and geochronology U-Pb SHRIMP in zircon. The area, in a regional context, represents an accretion orogen in the Andean system, it is composed of igneous rocks of oceanic affinity accreted to the western margin of South America, and they are associated to the development of the Caribbean Large igneous Province (CLIP). Based on geochemical characterization, the sub-volcanic bodies display patterns of an intra-oceanic subduction environment of primitive to evolved island arc, with significant contribution of subducted sediments, and similar signatures to those reported for the volcanic and plutonic rocks present in the area. (Barroso Formation and Santa Fe and Buriticá Tonalite). The Sr and Nd isotopic data (initial ratios 87Sr/86Sr between 0.70334 a 0.70543 and ?Nd between +6.25 a +7.42) suggest a wed mantle source, typical of arc rocks, with subordinates levels of crustal material. SHRIMP U-Pb data show five age populations that include: Neoarchean age around 2700 Ma, Paleoproterozoic age about of 2100, 2000 and 1800 Ma, Neoproterozoic age of 600 Ma, Ordovician-Devonian age of 460 and 360 Ma, and Cretaceous age around 90 Ma. The younger age population is interpreted as the crystallization age of the studied bodies; it indicated a special and temporal relation with the igneous rocks of the area which are associated with the development of the CLIP. The other four age populations are attributed to xenocrystals, they are interpreted as coming from terrigenous sediments dragged for the subduction area, reflecting process of crustal recycling through the mantle in intra-oceanic subduction zones. We restricted two possible source areas for the xenocrystals zircon: The Marañon Complex and The Arequipa Massif. They are constitute inliers exposed of the western margin of South America and present a good correlation between the magmatic/metamorphic events and the ages of the finding in our xenocristals. Based on these interpretations, we constraint the local of formation of the studied bodies closer to the continental paleomargin, considering also paleomagnetic data and paleogeographic models published in the area. The present study provides a significant contribution for the understanding tectono-magmatic evolution of the region during of Cretaceous, associated with the geological history of the CLIP.

Accelerated tropical glacial melt on the order of 15-18 meters per year since the 1980's in Peru's Cordillera Blanca region is alarming rural communities and urban authorities, causing them to seek technical support for risk management and adaptation actions. Melting glaciers coupled with changing seasonal rainfall patterns has left many rural communities in the upper Rio Santa basin lacking sufficient fresh water supply to support livestock, irrigation and human consumption. In response to these concerns, a Water Evaluation And Planning (WEAP) model was created by the Stockholm Environmental Institute for simulating glacial melt and flow in the Santa River. Through input parameters of climate, glacial runoff, water use, crop acreage, soil type and groundwater interactions, WEAP has the flexibility to model scenarios for different operation schemes. These schemes allow users to determine the most effective ways to regulate their resources and explore adaptation actions (e.g. altering farming practices and building reservoirs) for future planning. This project improved the existing model by including observed water demand data for irrigation, and evaluating the Climate Forecast System Reanalysis (CFSR) dataset to serve as a potential source for filling gaps in the historic climate record. These improvements added robustness to the model and correlated well with historic stream flow at La Balsa (R² = 0.78 , Nash = 0.68). Two scenarios were explored where (1) a 50% reduction in potato crop was replaced with maize for each sub-basin, and (2) a 10% reduction in precipitation was applied over the upper basin. Results show that the WEAP model is sensitive to changes in crop type and rainfall at the sub-basin scale, an encouraging finding for future exploration. This investigation enables communities to base future decisions on technical evidence and provides a basis for educating citizens on the importance of evaluating their available resources under climate change projections / text

Structural analysis of surface and subsurface data from the Middle Magdalena Valley basin and Eastern Cordillera fold-thrust belt to construct a kinematic model for its Cenozoic structural and stratigraphic evolution. The La Salina west-vergent thrust system marks the boundary between the Paleogene foreland basin of the Middle Magdalena basin and the Eastern Cordillera fold-thrust belt. New low-temperature thermochonological and sandstone petrographic analyses provide constraints on ages of thrust deformation and sediment dispersal. Apatite fission track (AFT) and U-Th/He thermochronological results show the timing of three structural events along the La Salina fault system: (1) late Eocene-early Oligocene (~43–35 Ma) initial hanging wall exhumation; (2) continued middle Miocene (~15 Ma) exhumation; and (3) continued but more rapid late Miocene (~12–3 Ma) hanging wall exhumation. Vitrinite reflectance results provide estimates of maximum burial depths for the hanging wall of the La Salina fault ranging from 4 to 6 km., this depth of burial estimates constrain the basin geometry during its late Eocene to late Miocene evolution. The eastern hanging wall of the La Salina fault displays a broad anticline-syncline pair affecting Cretaceous to Eocene strata with no significant faulting, whereas the western footwall contains a complex series of tight, thrust-related folds in Eocene-Quaternary strata. For foreland basin province, a proposed triangle zone accommodates a small amount of east-west shortening (< 1000 m) along the frontal thrust system by east-vergent backthrusting within a broader passive-roof duplex. East-west shortening in the Cenozoic stratigraphic section was also accommodated by detachment folding, which produced localized areas of steep dips. In the proposed kinematic restoration, the most recent phase of deformation represents out-of-sequence reactivation of the La Salina fault that is consistent with irregular crosscutting relationships of some footwall structures. Earliest exhumation by ~45–30 Ma in the Eastern Cordillera fold-thrust belt province matches (1) an increased proportion of sedimentary lithic fragments; and (2) a high degree of compositional maturity (Q88F4Lf8). Exhumation since ~15 Ma in the foreland province coincides with (1) the highest accumulation rates observed for the upper Miocene Real Group; and (2) a decrease in compositional maturity (Q55F8Lf36). / text

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

Basée sur une étude ethnographique de trois villages quechuaphones de la haute Cordillère sud du Pérou, notre recherche a pour objectif de montrer les différents rôles endossés par les missionnaires qui effectuent des visites ou s’installent sur place, et les impacts causés par leur présence et leurs œuvres. Dans la vie de ces hameaux, certains éléments culturels et sociaux sont dits traditionnels, c’est-à-dire non liés à la culture moderne, comme l’animisme, le catholicisme, le syncrétisme, le travail manuel, l’élevage, l’agriculture. Par le moyen de comparaisons entre les villages sans missionnaires, ceux qui reçoivent la visite de groupe religieux et ceux au sein desquels s’implantent des Églises, nous repérons les pratiques traditionnelles et constatons les évolutions cultuelles et sociales dues aux missions. L’enclavement géographique et linguistique des communautés étudiées, leurs caractéristiques sociales, culturelles et religieuses ainsi que leur environnement hostile font d’elles des terrains missionnaires peu habituels. De ce fait, les individus et les groupes religieux qui les évangélisent jonglent avec beaucoup de contraintes et peu de ressources. Cependant, avec le développement des réseaux routiers, ces villages se désenclavent l’un après l’autre. Par conséquent, le paysage religieux des hameaux d’altitude se modifie, accueillant de plus en plus d’Églises. Ainsi, la mondialisation gagne peu à peu les hautes Andes et le développement de l’activité missionnaire n’est pas seul responsable des mutations socioculturelles observables dans les communautés. Le tourisme et les interventions des O.N.G. et de l’État engendrent elles aussi des changements que chaque Église accompagne et/ou subit aux côtés des populations, réadaptant régulièrement ses méthodes d’évangélisation. La présence des différentes entités religieuses ouvre un nouveau mode de relation avec le monde extérieur. / Based on an ethnographic study of three Quechua speaking villages in the Southern part of the Peruvian highlands, our research seeks to show the diverse roles the missionaries who visit or live in the field assume, and the different impacts caused by their presence and their activities. In the life of these communities, some cultural and social elements are said to be traditional, i.e. not linked to modern culture, like animism, Catholicism, syncretism, manual work, animal breeding, agriculture. By making comparisons between villages that do not have missionary presence, others who do receive missionary visits and those with permanent missions, we identify the religious and social changes that are produced by missionary works. The communities’ geographical and linguistic isolation, their social, cultural and religious characteristics, as well as their inhospitable physical environment make them an uncommon missionary destination. Consequently, religious individuals and groups who evangelize must face many difficulties with few resources. However, with the growing spread of road networks, those villages open up more and more to the cities. Hence the highland communities’ religious landscape changes by welcoming more and more different Churches. Globalization then reaches the high Andes little by little and the development of missionary work is not the only cause to the sociocultural evolutions one can observe in the villages. Tourism and N.G.O. intervention leads to changes, and each Church accompanies and/or deals with them along with the people, readjusting their methods of evangelization on a regular basis. The presence of the diverse religious entities opens a new way of relating to the outside world.

L’histoire et les mécanismes de soulèvement des Andes centrales ont fait l'objet de débats animés depuis les années 1970. Notre étude se concentre sur l’analyse de la déformation Cénozoïque et de l'exhumation des Andes Centrales dans la région du Sud Pérou : à Cuzco, et dans la région de Nazca entre les cordillères Occidentale et Côtière. En effet, plusieurs auteurs soulignent le rôle du raccourcissement tectonique dans l'épaississement de la croûte, dans l’avant-arc Chilien ou à l’Est dans la région Subandine. Dans les modèles de déformation tectonique active issus du GPS, aucun raccourcissement ni transpression n’est pris en compte sur la bordure Occidentale des Andes au Cénozoïque ou dans les modèles de déformation crustale issus du GPS. La nouvelle cartographie des systèmes de failles actives dans la région sud du Pérou donnent un aperçu de la déformation active à l’échelle crustale pour la marge Pacifique des Andes Centrales. La géomorphologie et les paysages de l'avant-arc andin ont classiquement été présentés comme fossiles depuis le Miocène, sans évidence de structures actives accommodant la déformation cénozoïque. Cependant, les surfaces géomorphologiques bien préservées développées dans l'avant-arc du sud du Pérou fournissent d'excellents marqueurs et des évidences de déformation très nettes depuis le Cénozoïque jusqu’au Quaternaire récent. Ces marqueurs montrent tous un soulèvement des Andes le long de la marge ouest depuis les derniers Millions d’années. Bien que l’initiation et l’évolution de l'exhumation et du soulèvement cénozoïque aient été étudié dans les canyons de Colca et de Cotahuasi, il demeure peu contraint dans le segment nord de l'avant – arc, i.e., dans la région de Nazca. Dans cette étude, nous avons choisi d’apporter de nouvelles données (U-Th)/He et traces de fission sur apatite (AHe) et (AFT) respectivement dans cette région. L’échantillonnage a porté sur la Cordillère Occidentale entre Cañete et Nazca le long de deux nouvelles coupes transversales à la topographie. Le profil Age/Distance à la côte indique une mise en place de relief dans la région Andine au début du Miocène et une évolution découplée des deux systèmes de cordillères Cotière et Occidentale en terme d’exhumation dans le temps. A l’échelle Quaternaire, nous avons cartographié les failles actives pour déterminer leur géométrie, cinématique et les âges maximaux de l’activation de ces failles. Ceci afin de discuter du rôle de cette activité tectonique, précédemment supposée Miocène, dans le soulèvement et l’exhumation de l’avant-arc Andin. Nous avons utilisé la production et l’accumulation du 10Be cosmogénique dans les roches pour déterminer les âges d'exposition d’un escarpement tectonique marquant les derniers épisodes co-sismiques de la faille de Purgatorio. Nos nouveaux résultats, contrastent avec des conclusions précédentes qui concluaient à de l’extension et des vitesses lentes le long de l’avant arc Andin (<0.1mm/an). Les âges très récents indiquent une morphologie « historique » (free face) et deux tremblements de terre Mw6-7 sur ce système de failles transpressives qui se connectent au système principal d’Incapuquio. Les données suggèrent non seulement une déformation active significative de l’avant-arc, mais soulignent aussi l’existence d’un aléa sismique qui n’est toujours pas pris en compte pour les failles crustales dans les Andes. Tandis que l’hypothèse acceptée est que la déformation active est localisée dans le bassin d’avant pays subandin, ou à l’est de la cordillère orientale, nos données suggèrent qu’une partie de la déformation active se localise aussi sur la marge Occidentale ainsi que le long de la faille d'Incapuquio. De plus, les failles observées en néotectonique accommoderaient le partitionnement de la déformation le long de la subduction oblique et ceci n’a jamais été discuté précédemment. Ce mouvement, rigide, en bloc serait du à la présence du craton accrété sur le flanc Ouest et à sa rigidité. / ABSTRACTTiming and mechanisms of uplift in the Central Andes have been a matter of debate since at least the 1970’s. Our study focuses on Cenozoic deformation and exhumation of the Central Andean forearc in Peru, in Cuzco region, and between the Western Cordillera and the Coastal Cordillera in Nazca region. Our new mapping of active faults provides new insights into the Cenozoic to present-day crustal deformation of the Central Andean Western margin. Until now, apart from some local studies, the geomorphology of the Andean forearc has classically been presented as a remnant Miocene landscape with no significant active structures accommodating the Cenozoic deformation. Thanks to new high-resolution optical imagery, the well-preserved geomorphic surfaces developed within the forearc of southern Peru provide excellent regional markers to map patterns of deformation. Pertaining to the Cenozoic history, while the timing of uplift-related exhumation and Cenozoic exhumation has been studied in Colca and Cotahuasi canyons, it remain poorly constrained in the northern segment of the Central Andean forearc. I report new apatite (U–Th)/He (AHe) and fission track (AFT) ages from the western Cordillera between Cañete and Nazca along two new cross sections. The ages in Nazca region reflect relatively recent (since ~10Ma) relief creation along the western margin of the Altiplano, similar to what is described south in Colca region.The Quaternary tectonic history is revealed by the newly mapped fault segments affecting the Miocene deposits within forearc. Through field and remote mapping, I determined fault geometries and maximum ages for the activity of the faults systems based on stratigraphic relationships in order to assess the role of this tectonic activity in the Western Cordillera uplift and exhumation.To understand the Holocene tectonic history, we use in situ produced 10Be to determine the exposure ages of the free face and tectonic scarp of the Purgatorio Fault in order to map the temporal evolution of its seismotectonic activity. Our new results display evidence of transpression and the formation of meter-high coseismic scarps as well as very recent exposure ages indicating a youthful fault morphology and Mw6-7 earthquakes occurring along the Purgatorio fault segments. These new data are in contrast with some previous conclusions for this region which suggest extension and/or slow rates of deformation for this region and time period. Further, these new data not only suggest significant active deformation within the forearc, but also highlight a potential seismic hazard for the region that not take into account crustal forearc faults.While the general assumption is that active deformation is localized in the Subandean fold and thrust belt, or east of the Western Cordillera in the Altiplano, our data support a model where active deformation is occurring in the western margin as well, along the Incapuquio Fault and other neotectonic faults that accommodates the partitioning of the subduction oblique convergence.These crustal active faults and more precisely the “not migrating to the trench” Incapuquio fault zone reveal the rigid motion of the forearc. Our new model is nevertheless compatible with the recently published GPS data that measure a southeastward movement at 4–5 mm/yr relative to a stable South America reference frame. This rigid motion is in part due to the presence of the rigid Greenvillian accreted craton, that behave as a sliver, and rather tilt than deform through time.

Neste trabalho são caracterizados corpos sub-vulcânicos expostos no nordeste da Cordilheira Ocidental da Colômbia através de estudos petrográficos, análises geoquímicas em rocha-total e datação U-Pb por SHRIMP IIe em zircão. A área de estudo, em um contexto regional, representa um orógeno de acreção no sistema andino, constituído por rochas ígneas de afinidade oceânica amalgamadas contra a margem ocidental de América do Sul e associadas ao desenvolvimento da Grande Província Ígnea do Caribe (Caribbean Large igneous Province-CLIP). As análises em geoquímica elementar evidenciam para os corpos subvulcânicos um ambiente de subducção intra-oceânico de arco primitivo a mais evoluído, com significante contribuição de sedimentos subductados e assinaturas similares às registradas para as rochas vulcânicas e plutônicas presentes na área (Formação Barroso e Tonalito de Santa Fe e Buriticá). Dados isotópicos de Sr e Nd (razão inicial 87Sr/86Sr entre 0.70334 a 0.70543 e ?Nd entre +6.25 a +7.42) indicam uma área fonte de cunha mantélica, típica de rochas de arco, com níveis subordinados de material crustal. Idades U-Pb por SHRIMP IIe em zircão mostram cinco populações de idades correspondentes a: idades Neoarquenas ao redor de 2700 Ma, Paleoproterozoicas em torno de 2100, 2000 e 1800 Ma, Neoproterozoicas ao redor de 600 Ma, Ordovicianas/Devonianas de 460 e 360 Ma, e Cretáceas ao redor de 90 Ma. A população de idades mais novas é interpretada como a idade de cristalização dos corpos estudados, indicando uma relação espacial e temporal com as rochas ígneas da área associadas ao desenvolvimento da CLIP. As quatro populações de idades mais antigas são atribuídas a xenocristais, interpretados como provenientes de sedimentos terrígenos que foram arrastados ao canal de subducção, refletindo processos de reciclagem crustal através do manto em zonas de subducção intra-oceânicas. Foram identificadas duas possíveis áreas fontes para os xenocristais de zircão: o Complexo Marañon e o Maciço de Arequipa, que constituem inliers expostos na margem ocidental de América do Sul e apresentam uma boa correlação entre os eventos magmáticos/metamórficos que registram e às idades dos xenocristais encontrados. A partir destas interpretações, foi restringido o local de formação dos corpos estudados em relação à paleomargem continental, considerando além dados paleomagnéticos e modelos paleogeográficos publicados na zona de estudo. O trabalho fornece um aporte significativo para a compreensão da evolução tectono-magmática da região durante o Cretáceo superior, associada à história geológica da CLIP. / In this study sub-volcanic bodies exposed in the northeast of the Western Cordillera of Colombia are characterized through petrographic descriptions, geochemical analysis in bulk rocks and geochronology U-Pb SHRIMP in zircon. The area, in a regional context, represents an accretion orogen in the Andean system, it is composed of igneous rocks of oceanic affinity accreted to the western margin of South America, and they are associated to the development of the Caribbean Large igneous Province (CLIP). Based on geochemical characterization, the sub-volcanic bodies display patterns of an intra-oceanic subduction environment of primitive to evolved island arc, with significant contribution of subducted sediments, and similar signatures to those reported for the volcanic and plutonic rocks present in the area. (Barroso Formation and Santa Fe and Buriticá Tonalite). The Sr and Nd isotopic data (initial ratios 87Sr/86Sr between 0.70334 a 0.70543 and ?Nd between +6.25 a +7.42) suggest a wed mantle source, typical of arc rocks, with subordinates levels of crustal material. SHRIMP U-Pb data show five age populations that include: Neoarchean age around 2700 Ma, Paleoproterozoic age about of 2100, 2000 and 1800 Ma, Neoproterozoic age of 600 Ma, Ordovician-Devonian age of 460 and 360 Ma, and Cretaceous age around 90 Ma. The younger age population is interpreted as the crystallization age of the studied bodies; it indicated a special and temporal relation with the igneous rocks of the area which are associated with the development of the CLIP. The other four age populations are attributed to xenocrystals, they are interpreted as coming from terrigenous sediments dragged for the subduction area, reflecting process of crustal recycling through the mantle in intra-oceanic subduction zones. We restricted two possible source areas for the xenocrystals zircon: The Marañon Complex and The Arequipa Massif. They are constitute inliers exposed of the western margin of South America and present a good correlation between the magmatic/metamorphic events and the ages of the finding in our xenocristals. Based on these interpretations, we constraint the local of formation of the studied bodies closer to the continental paleomargin, considering also paleomagnetic data and paleogeographic models published in the area. The present study provides a significant contribution for the understanding tectono-magmatic evolution of the region during of Cretaceous, associated with the geological history of the CLIP.

Geóloga / En la alta cordillera, a la latitud del Valle del Huasco, existe un relleno de alrededor de 1.000 metros de sedimentos continentales, miocenos, asignados a las Gravas de Atacama y, actualmente, designadas como Formación Laguna Grande. Estudios regionales indican que estos depósitos serían producto de la erosión del Relieve Incaico, alzado durante el Eoceno, que habría generado numerosos depósitos clásticos en el norte del país. Sin embargo, no existen estudios previos, sedimentológicos ni estratigráficos, que permitan establecer la proveniencia, ni el origen de este depósito en particular. Con base en lo anterior, se definió el objetivo de este trabajo, que consiste en estudiar la evolución geológica de la Cordillera Frontal, durante el Neógeno, alrededor de los 28°45 S. Las metodologías aplicadas en este trabajo incluyen, en primer lugar, la reconstrucción del paleorelieve y análisis de la arquitectura de la cuenca, mediante la interpolación del contacto mapeado entre gravas y basamento; y el estudio de la historia de incisión y relleno de los sedimentos de Formación Laguna Grande, a partir de estudios sedimentológicos y estratigráficos, y de conteos modales y análisis de proveniencia. La interpolación del contacto entre gravas y basamento indicó que los sedimentos se depositaron sobre una superficie de bajo relieve, que mantea suavemente hacia el sur. También se apreció la existencia de un relieve al Oeste y al Norte de la superficie de bajo relieve. Por otro lado, se estimó el espesor actual del depósito, que varía desde 300 m en la zona norte, hasta más de 900 m en el sur. A partir de la estratigrafía y sedimentología estudiadas en terreno, se definieron seis facies sedimentarias que, a grandes rasgos, indican que las gravas de la Formación Laguna Grande fueron depositadas en un ambiente fluvial - aluvial, que refleja el clima árido dominante de esta zona, desde el Mioceno. Los conteos modales indican una procedencia de un basamento alzado, con signaturas de arco volcánico en la base y el techo de la columna. Variaciones en el redondeamiento de los clastos, la presencia de intraclastos en el lado oriental del depósito, junto con las variaciones en la signatura de la proveniencia de las gravas, indican un posible aporte desde el Este para la porción superior de los sedimentos. Con base en lo planteado anteriormente, este trabajo establece que las gravas de la Formación Laguna Grande derivan de una fuente cercana, asociada al relieve que limitaba la cuenca al Norte y Oeste de la zona de estudio. Estos relieves fueron alzados durante la Orogenia Incaica, y su erosión generó, en gran medida, los sedimentos que, posteriormente, se depositaron sobre una suave superficie erosiva. Sin embargo, existe evidencia no concluyente para inferir la existencia de un relieve de menor magnitud ubicado al Este de la zona de estudio, que habría aportado material sedimentario, en menor medida.

Doctor en Ciencias, Mención Geología / Modificaciones del relieve provocados por procesos geológicos de gran escala como el alzamiento de cordilleras tiene importantes efectos en las condiciones climáticas y generan cambios significativos del paisaje. De esta forma, variaciones en las condiciones de temperatura y precipitación de una región afectan directamente la distribución, diversidad y composición de la vegetación. En la actualidad la dirección de flujo de los ríos en el sur de Sudamérica es principalmente hacia el oriente, sin embargo, aún no es claro cuál fue la dirección de las corrientes y las zonas de proveniencia en el pasado. Cambios en las direcciones de paleocorrientes ocurridos durante el Cenozoico en la Cuenca de Magallanes, junto con cambios de ambientes, pasando de marinos a transicionales y finalmente a ambientes continentales, procesos que fueron identificados en el sector de Sierra Baguales, al norte del Parque Nacional Torres del Paine, podrían vincularse con el levantamiento de los Andes Patagónicos, proceso que a su vez podría asociarse a cambios paleoclimáticos y paleoecológicos que habrían sido provocados por el efecto de sombra de lluvia y apertura del paso Drake durante el Oligoceno, cambios paleogeográficos que a su vez coinciden con modificaciones de las zonas de aporte de sedimentos a la Cuenca de Magallanes y la posición relativa de Península Antártica. El presente estudio evalúa cual fue el efecto de los procesos tectónicos como el levantamiento de los Andes Patagónicos, apertura del Paso Drake y cambios en las zonas de proveniencia. Se discute el vínculo entre la evolución de la Cuenca de Magallanes y la posición de la Península Antártica. Estos procesos fueron evaluados a partir de la evolución espacio-temporal de las paleocorrientes y el establecimiento de las zonas que aportaron detritos a la Cuenca durante el Cenozoico en Sierra Baguales, adicionalmente, junto con la evolución tectónica y sedimentológica del sector, se analiza la respuesta de la vegetación en términos de diversidad y composición, comportamientos analizados bajo un contexto de cambio climático global durante el Cenozoico donde especialmente se discute la respuesta de la vegetación frente a procesos de enfriamiento como el ocurrido durante el Oligoceno.