We construct several modular compactifications of the Hurwitz space \(H^d_{g/h}\) of genus g curves expressed as d-sheeted, simply branched covers of genus h curves. They are obtained by allowing the branch points of the cover to collide to a variable extent, generalizing the spaces of twisted admissible covers of Abramovich, Corti, and Vistoli. The resulting spaces are very well-behaved if d is small or if relatively few collisions are allowed. In particular, for d = 2 and 3, they are always well-behaved. For d = 2, we recover the spaces of hyperelliptic curves of Fedorchuk. For d = 3, we obtain new birational models of the space of triple covers. We describe in detail the birational geometry of the spaces of triple covers of \(P^1\) with a marked fiber. In this case, we obtain a sequence of birational models that begins with the space of marked (twisted) admissible covers and proceeds through the following transformations: (1) sequential contractions of the boundary divisors, (2) contraction of the hyperelliptic divisor, (3) sequential flips of the higher Maroni loci, (4) contraction of the Maroni divisor (for even g). The sequence culminates in a Fano variety in the case of even g, which we describe explicitly, and a variety fibered over \(P^1\) with Fano fibers in the case of odd g. / Mathematics

Concept à la mode depuis quelques décennies, l’écotourisme s’est érigé comme le produit phare des parcs nationaux en régions forestières. Avec la création en 2007 du «Parc Amazonien de Guyane », les Wayana, comme les autres communautés traditionnelles autochtones, n’ont pas échappé au discours lié au développement durable de leur territoire ainsi qu’à la question de l’écotourisme. Mais quelle est la réalité d’un tel concept dans le contexte du tiers sud guyanais, enclavé, dominé par des identités culturelles fortes et marqué par une activité aurifère clandestine et criminelle ? Cette étude s’intéresse particulièrement à la dynamique culturelle et aux tentatives de maintien d’une identité culturelle, dans une société en pleine transition. Afin d’étudier le changement social et culturel, j’ai observé le mode de vie des indiens de l’intérieur de la Guyane tel qu’il se présente aujourd’hui en référence à ce qu’il était hier. Il ressort de notre étude que bien qu’attirés par la modernité, les indiens dépendent toujours des ressources de la nature et se préoccupent de maintenirleur identité. Les moyens de prélever les ressources ont certes évolué, mais ils demeurent au fond non agressifs àl’environnement et à la biodiversité parce que, ces sociétés ont opéré elles-mêmes des choix qui leur permettent de minimiser leur impact négatif sur l’environnement. Il y a donc dans ces sociétés une préoccupation de gestion durable des ressources. On le perçoit aisément dans l’agriculture itinérante, dans la pêche à la nivrée où, après exploitation et prélèvement de la ressource, la zone exploitée est laissée à l’abandon pour sa régénération. La recherche d’un compromis endogène entre un mode de vie traditionnel et un mode de vie moderne est significative à l’observation et à l’analyse de l’évolution de la structure de l’habitat amérindien. Optant aujourd’hui de plus en plus pour un habitat avec parois, cloisonné et recouvert non plus d’une simple toiture végétale mais de tôles ondulées, les Wayana ne renoncent pas pour autant au carbet-hamac, ni à la prohibition des déjections en terre ferme, c’est-à-dire le lieu où vivent les hommes. Les Indiens, dans leur tradition, utilisent les cours d’eau comme des lieux d’aisance. Notre étude montre que cette coutume est répandue chez tous les indiens de l’intérieur de la Guyane parce qu’elle va au-delà d’une simple préoccupation hygiénique et physiologique. Dans ce système culturel, cette coutume n’est pas déterminée systématiquement par l’environnement naturel. Elle obéit avant tout à une logique écologique propre à ces microsociétés, puis à une nécessite de distinguer nettement deux univers : l’univers des animaux et l’univers des hommes. Ainsi, dans lalogique interne des Wayana, ce sont des animaux sauvages qui font leurs déjections à même le sol, tandis que l’homme pour se distinguer a choisi de faire des cours d’eau ses lieux d’aisance privilégiés. Mais, face au changement imposé par le monde extérieur (sédentarisation, croissance démographique, prestations sociales..), la cohérence interne du modèle social et culturel des Wayana est plus que menacé. Dès lors, la mise en oeuvre de l’écotourisme s’apparente à une confrontation de logiques ; un ensemble de logiques exogènes, véhiculé par ses développeurs et ses promoteurs, et unensemble de logiques endogènes véhiculé par les populations autochtones traditionnelles en cohérence avec leur vision holistique du monde, aboutissant soit à des formes de compromis, soit à des formes d’antagonismes objectant toute forme de négociation. / A fashionable concept for some decades, « ecotourism » has been selected as the leading product for National Parks and large forests areas. With the opening, in 2007, of the “Amazonian park of Guyana “, the “Wayana”, like other local traditional communities, have not escaped from theories related to sustainable development as well as the “ecotourism”. But what reality stands behind such a concept in the southern part of Guyana, geographically isolated, and under the influence of strong cultural identities and a clandestine and criminal gold extraction activity. The current study tries to understand the cultural movement and their ambition to maintain a cultural identity, in a society in complete transition. In order to study the social and cultural changes, the author has observed the Indians way of life in the heart of Guyana today, as opposed as to how it was yesterday. Our study points out that, although very interested by the modern world, Indians still depend on natural resources and are concerned with the preservation of their identity. Their ways of using resources have certainly evolved, but they remain basically respectful of the environment and biodiversity because these societies function in order to minimize any negative impacts on their environment. These societies are therefore concerned with the management of their resources in a durable way. It’s easily perceivable in the itinerant agriculture, also in the fishing “à la nivrée”, where the area is left unexploited for regeneration after resources have been used. The search for an endogen compromise between a traditional way of life and a modern one is quite significant when one observes and analyzes the evolution of the Amerindian habitat. Opting more and more for buildings with partitions and separations, not just covered with basic vegetable roofs but with metallic material, the “Wayana” have not abandoned the use of “carbet-hamoc”, nor of open air toilets where the population live. Indians, traditionally, use streams as toilets. Our study shows that this custom is the same for all Indians living in the interior territories of Guyana, because it goes beyond a simple hygienic and physiological concern. In their cultural system, this rule is not systematically imposed by the natural environment. It’s governed above all by an ecological logic, pertinent to these micro societies, followed by the necessity to clearly identify two different worlds: the animal world and the human world. According to internal “Wayana” logic, it is only wild animals that use the ground for their excretions, whilst human beings, in order to distinguish themselves, use streams. But, facing changes brought about by the external world (sedentary life, demographic expansion, social care…), the internal coherence of the social and cultural model of the “Wayana” is in jeopardy. Installing a culture of “ecotourism” therefore seems to confront logics: one set of exogenous logics brought on by its promoters and another set of endogenous logics maintained by the autochthon traditional populations fitting with their holistic vision of the universe, leading either to some form of compromise or to antagonist attitudes opposed to any type of negotiation.

Submitted by Edisangela Bastos (edisangela@ufpa.br) on 2017-05-02T20:07:43Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_GeocronologiaZircaoMonazita.pdf: 6498084 bytes, checksum: 1d6867735e98e0abb4607eb52f655f68 (MD5) / Approved for entry into archive by Edisangela Bastos (edisangela@ufpa.br) on 2017-05-02T22:02:58Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_GeocronologiaZircaoMonazita.pdf: 6498084 bytes, checksum: 1d6867735e98e0abb4607eb52f655f68 (MD5) / Made available in DSpace on 2017-05-02T22:02:58Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_GeocronologiaZircaoMonazita.pdf: 6498084 bytes, checksum: 1d6867735e98e0abb4607eb52f655f68 (MD5) Previous issue date: 2006-11-16 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / CPRM - Companhia de Pesquisa de Recursos Minerais / Serviço Geológico do Brasil / FINEP - Financiadora de Estudos e Projetos / O Domínio Bacajá está localizado na porção sudeste do Cráton Amazônico e representa o segmento meridional da Província Maroni-Itacaiúnas que é constituída de orógenos paleoproterozóicos e blocos arqueanos retrabalhados durante o Ciclo Transamazônico (2,2-1,95 Ga). Este domínio é composto de granitóides, rochas charnoquíticas e supracrustais, ortognaisses, migmatitos e granulitos para e ortoderivados. Dados geocronológicos prévios das rochas desse domínio indicam retrabalhamento de crosta arqueana e formação de crosta juvenil durante o Ciclo Transamazônico. O presente estudo foi baseado em levantamentos de campo, petrografia, geoquímica isotópica e geocronologia, tendo como objetivo identificar os eventos ígneos e metamórficos de alto grau que ocorreram na porção oeste Domínio Bacajá a fim de entender sua evolução crustal. Os dados geocronológicos existentes, somados aos novos dados de geocronologia em zircão (U-Pb SHRIMP e Evaporação de Pb) e isótopos de Nd para as rochas das associações litológicas que ocorrem na área de estudo permitiram identificar e datar eventos magmáticos ocorridos do Neoarqueano ao Orosiriano, com auge da formação de crosta durante o Riaciano. Ortognaisses de 2,67-2,44 Ga e remanescentes de rochas metavulcânicas de 2,45 Ga marcam o primeiro evento de formação de crosta na porção oeste Domínio Bacajá, com uma acresção a cerca de 2,7 Ga e contaminação por crosta mesoarqueana (ca. 3,0 Ga). Um segundo evento de acresção há aproximadamente 2,5 Ga e um de retrabalhamento de crosta mesoarqueana foram respectivamente registrados em rochas metavulcânicas de 2,36 Ga e granitóides 2,34 Ga associados. Esses eventos provavelmente estão relacionados à amalgamação de um arco de ilha tardi sideriano a um microcontinente arqueano. Granitóides de 2,21-2,18, Ga, com contribuição crustal neoarqueana (ca. 2,8 Ga), e de 2,16-2,13 Ga, formados por mistura de um componente juvenil de ca. 2,3 Ga com fontes crustais arqueanas, estão relacionados a arcos magmáticos riacianos colididos contra um continente arqueano-sideriano. Esta colisão foi marcada pela formação de granitóides de 2,10 Ga (sincolisionais ?), com prováveis fontes a partir de rochas do arco magmático tardio, e de granitóides e rochas charnoquíticas de 2,09-2,07 Ga (pós-colisional) formados respectivamente por fusão de fontes arqueanas (3,0-2,7 Ga) e mistura com o componente juvenil transamazônico (ca. 2,3 Ga). Por fim, no Domínio Bacajá e adjacências ocorreram eventos magmáticos orosirianos, marcados pela formação local de granitóides de 1,99 Ga, cuja relação com o Ciclo Transamazônico é incerta, e pelo magmatismo de ca. 1,88 Ga de ambiente extensional. Ambos os eventos com contribuição crustal neoarqueana (ca. 2,8 Ga) que sugerem participação da crosta arqueana do Domínio Bacajá.. Eventos metamórficos de alto grau e de anatexia foram identificados nos gnaisses e granulitos para e ortoderivados do oeste do Domínio Bacajá. No entanto, os estudos petrológicos e geocronológicos foram enfocados nas rochas metassedimentares pelíticas de alto grau por serem melhores marcadores desses eventos. Esses eventos foram datados por U-Pb SHRIMP em zircão e monazita, Evaporação de Pb e U-Pb ID-TIMS em zircão e Sm-Nd em granada e rocha total. As rochas metassedimentares de alto grau apresentaram fontes detríticas dominantemente arqueanas (3,1-2,5 Ga) e foram afetadas por eventos tectono-termais riacianos, preliminarmente identificados pelas idades isocrônicas Sm-Nd em granada (2208 e 2025 Ma). Contudo, existem evidências sugestivas de um evento metamórfico de alto grau de cerca de 2,3 Ga que poderia estar relacionado a provável colisão tardi-sideriana. Os eventos de alto grau transamazônicos iniciaram com uma migmatização de 2147-2123 Ma em condições P-T de fácies anfibolito superior registrada nos grãos de zircão e núcleos de cristais de monazita. Este evento foi contemporâneo à formação de granitóides dos arcos magmáticos riacianos, podendo estar relacionado à colisão do arco mais precoce. Um evento anatético há 2109 Ma foi detectado nos sobrecrescimentos em cristais de zircão, sugestivamente relacionado ao principal evento de colisão continental riaciana identificado nos orógenos transamazônicos do Escudo das Guianas. Apesar de ter havido a formação de granitóides e rochas charnoquíticas contemporâneas, nos metapelitos estudados esse evento foi marcado por uma modesta anatexia. Por fim, um metamorfismo de fácies anfibolito superior a granulito, de baixas pressões (4-6 kbar / 700-800ºC), há cerca de 2070 Ma foi registrado nos cristais de monazita e zircão, seguido de um possível evento de perda de Pb na monazita há 2057 Ma. A ocorrência de intrusões quartzo dioríticas e charnoquíticas contemporâneas ao metamorfismo granulítico sugerem processo de underplating de magma máfico e adelgaçamento crustal durante o estágio pós-colisional. Os eventos ígneos e metamórficos do oeste do Domínio Bacajá são análogos aos registrados em outros domínios transamazônicos do Cráton Amazônico e da América do Sul. Em escala global, a colagem riaciana há 2,1 Ga tem sido relacionada à colisão das paleoplacas do leste da América do Sul contra o oeste da África que desencadeou a formação de um supercontinente no Paleoproterozóico. / The Bacajá domain is located in the southeastern Amazonian craton and represents the southern part of the Maroni-Itacaiúnas province, which comprises Paleoproterozoic orogens and Archean blocks reworked during the Transamazonian cycle (2.2–1.95 Ga). This domain is composed of granitoids, charnockitic and supracrustal rocks, orthogneisses, migmatites, metaigneous granulites and high-grade metasedimentary rocks. The previous geochronological data denote reworking of Archean crust and formation of juvenile crust during the Transamazonian cycle. The present study was based on field work, petrography, isotope geochemistry and geochronology in order to identify the igneous and high-grade metamorphic events in the western part of the Bacajá domain and to discuss its crustal evolution. The previous geochronological data, plus new data on zircon (U-Pb SHRIMP and Pbevaporation) and Nd isotope data for the igneous and meta-igneous rocks of the lithologic associations from the study area allowed the identification and dating of magmatic events from Neoarchean to Orosirian times, with a climax of crust formation during the Rhyacian. The 2.67- 2.44 Ga orthogneisses and 2.45 Ga metavolcanoclastic rock remnants are related to the first event of crust formation in the western Bacajá domain marked by an accretion at ca. 2.7 Ga and contamination by Mesoarchean crust (ca. 3.0 Ga). A second event of accretion at ca. 2.5 Ga and reworking of Mesoarchean crust were identified in 2.36 Ga metavolcanic rocks and associated 2.34 Ga granitoids, respectively. They are probably related to the amalgamation of a late Siderian island arc to an Archean microcontinent. The 2.21-2.18 Ga granitoids with Neoarchean crustal sources (ca. 2.8 Ga) and 2.16-2.13 Ga granitoids formed by mixture of a 2.3 Ga juvenile component with Archean crustal sources are related to Rhyacian magmatic arcs that collided against an Archean-Siderian continent. This collision was marked by the formation of 2.10 Ga granitoids (syncollisional rocks ?), probably originated from sources related to late magmatic arc rocks, and of charnockitic rocks and granitoids of 2.09-2.07 Ga (post-collisional rocks) formed respectively by mixture of Ryacian crustal sources and the 2.3 Ga juvenile component and by melting of Archean crust (3.0-2.7 Ga). There are Orosirian magmatic events identified in 1.99 Ga granitoids, whose correlation with the Transamazonian cycle is controversial, and by the extensional magmatism of ca. 1.88 Ga. Both events have Neoarchean crustal sources (ca. 2.8 Ga), probably derived from the Bacajá domain. The high-grade metamorphic events and associated anatexis were identified in the metaigneous and metasedimentary rocks from the western Bacajá domain. However, the petrologic and geochronological studies focused only on the high-grade metasedimentary rocks. These rocks have dominantly Archean detrital sources (3.1-2.5 Ga) and were affected by Rhyacian metamorphic events preliminary constrained by Sm-Nd whole rock-garnet isochrones (2208- 2025 Ma), but there is little evidence suggesting the existence of a high-grade metamorphic event at 2.3 Ga, that could be related to the collage of the late Siderian island arc. High-grade Transamazonian metamorphism commenced with a 2147-2123 Ma migmatization event that took place under upper amphibolite facies P-T conditions and was preserved in zircon overgrowths and in the cores of monazite grains. This event could be related to the collision of the early Rhyacian magmatic arc against to a Neoarchean-late Siderian continent. An anatectic event at 2109 Ma was recorded on unzoned rims of zircon crystals, which is probably it related to the continental collision at 2.1 Ga that has been identified in the Transamazonian orogens of the French Guiana shield. Despite the formation of synchronous granitoids and charnockitic rocks during this collision, in the studied metapelites it was a modest anatexis. After that, a low pressure granulite facies metamorphism (4-6 kbar / 700-800 ºC) at ca. 2070 Ma was registered on monazite and zircon grains, followed by a possible Pb-loss event at 2057 Ma. The existence of coeval quartz diorite and charnockitic intrusions suggests underplating of mafic magma and crustal thinning during the post-collisional period. The igneous and metamorphic events of the western Bacajá domain are analogue to those identified in other Transamazonian domains of the Amazonian craton and South America. In global scale, the 2.1 Ga collage has been correlated to the collision of the paleoplates of eastern South America and western Africa that triggered the formation of a Paleoproterozoic supercontinent.

L'eau des fleuves, des rivières, des lacs et des réservoirs ne représente que 0,26 % des 2,5 % (35 millions de km3) d'eau douce disponibles à l’état liquide sur Terre, or sa qualité et quantité ont fortement diminué ces dernières années. Sa dégradation a des conséquences sur l'agriculture, la santé, l'environnement et l'économie des territoires et est aujourd'hui au centre des préoccupations sociétales. Les objectifs de la présente thèse sont pour trois fleuves localisés dans le Bouclier des Guyanes, au nord de l'Amérique du Sud (le Maroni, l'Oyapock, l'Orénoque): (i) d'utiliser et d'adapter des outils novateurs de télédétection pour suivre et quantifier, sur du long terme, leurs charges sédimentaires en suspension, (ii) d'évaluer l'existence de tendances spatio-temporelles, ainsi que de ruptures dans les chroniques de données, (iii) de quantifier la part organique et minérale de ces charges, (iv) d'apprécier le rôle des facteurs naturels (débits et précipitations) et anthropiques (surfaces urbaines, agricoles et minières) sur les tendances observées et enfin, (v) de discuter de seuils de charges pour le suivi de la qualité de l'eau. Les résultats ont montré qu'il est possible de suivre les concentrations de matières en suspension, pour les fleuves Orénoque et Maroni avec une erreur relative de 32 et 25% respectivement. Sur la période 2000-2016, des tendances spatio-temporelles régulières ont été observées pour l'Orénoque, alors qu'elles sont en augmentation pour le Maroni avec une rupture en 2009 et en diminution pour l'Oyapock depuis 2008 (données in situ). Un lien fort avec l'augmentation de la déforestation pour les surfaces minières et les précipitations est observé pour le Maroni alors que pour l'Oyapock les tendances sont liées aux débits.Pour les deux années d'études (2014-2016), les charges minérales ont représenté la plus forte fraction des particules transportées dans les eaux du Maroni au Saut Hermina (en moyenne 93 %) et de l'Oyapock au Saut Maripa (en moyenne 82 %) avec une grande variabilité selon les mois de la teneur en carbone dans les matières transportées et pour les deux fleuves. Enfin, les rapports C/N et C/Chl-a ont dévoilé des matières organiques d'origine principalement endogène avec une forte biomasse chlorophyllienne surtout durant les basses eaux. / The water of rivers, lakes and reservoirs represents only 0.26 % of the 2.5 % (35 million of km3) of fresh water available on the liquid state on Earth, but its quality and quantity strongly decreased these last years. Her degradation has consequences on the farming, the health, the environment and the economy of territories and is now in the center of the societal concerns. The objectives of the present thesis are for three rivers located in the Guiana Shield, in the North of South America (the Maroni, the Oyapock, the Orinoco): i) to use and to adapt innovative tools of remote detection to follow and quantify, on the long term, their sedimentary loads, ii) to estimate the existence of spatiotemporal trends, as well as breaks in the chronicles of data, iii) to quantify the organic and mineral part of these loads, iv) to appreciate the role of the natural (discharge and precipitation) and the anthropological factors (urban, agricultural and mining surfaces) on the observed trends and finally, v) to discuss thresholds of concentrations for the quality monitoring of the river water.The results showed that it is possible to follow the concentrations of suspension materials, for rivers Maroni and Orinoco with a relative error of 25 and 32 % respectively. Over the period 2000-2016, regular spatiotemporal trends were observed for the Orinoco, while they are increasing for Maroni with a break in 2009 and in decrease for the Oyapock since 2008 (in situ data). A strong link with the increase of the deforestation for the mining surfaces and the precipitation is observed for the Maroni catchment while for the Oyapock the trend is explained by the specific water discharge.For two years of studies (2014-2016), the mineral loads represented the strongest fraction of particles transported in the Maroni River at Saut Hermina (on average 93 %) and in the Oyapock River at Saut Maripa (on average 82 %) with a high variability according to the months of the content in carbon in the transported materials and for both rivers. Finally, report C/N and C/Chl-a revealed organic matters of mainly endogenous origin with a strong chlorophyll biomass and especially during the low water period.