Structure et évolution thermique de la croûte supérieure des chaînes de subduction : approches thermologique et modélisation numérique, dans les North Cascades (U.S.A) et de la zone de faille Motagua (Guatemala)

Cette thèse cible l'étude de la structure thermique de la croûte supérieure (<10km) dans les arcs magmatiques continentaux, et son influence sur l'enregistrement thermochronologique de leur exhumation et de leur évolution topographique. Nous portons notre regard sur deux chaînes de montagne appartenant aux Cordillères Américaines : Les Cascades Nord (USA) et la zone de faille Motagua (Guatemala). L'approche utilisée est axée sur la thermochronologie (U-Th-Sm)/He sur apatite et zircon, couplée avec la modélisation numérique de la structure thermique de la croûte. Nous mettons en évidence la variabilité à la fois spatiale et temporelle du gradient géothermique, et attirons l'attention du lecteur sur l'importance de prendre en compte la multitude des processus géologiques perturbant la structure thermique dans les chaînes de type cordillère, c'est à dire formées lors de la subduction océanique sous un continent.Une nouvelle approche est ainsi développée pour étudier et contraindre la perturbation thermique autour des chambres magmatiques. Deux profiles âge-elevation (U-Th-Sm)/He sur apatite et zircon, ont été collectées 7 km au sud du batholithe de Chilliwack, Cascades Nord. Les résultats montrent une variabilité spatiale et temporelle du gradient géothermique lors de l'emplacement magmatique qui peut être contrainte et séparé de l'exhumation. Durant l'emplacement de l'intrusion, la perturbation thermique y atteint un état d'équilibre (-80-100 °C/km) qui est fonction du flux de magma et de ia distance à la source du magma, puis rejoint 40 °C/km à la fin du processus d'emplacement magmatique.Quelques nouvelles données (U-Th)/He, replacées dans une compilation des données existantes dans les Cascades Nord, indiquent une vitesse d'exhumation constante (-100 m/Ma) dans le temps et l'espace entre 35 Ma et 2 Ma, associée à un soulèvement uniforme de la chaîne contrôlé par l'emplacement de magma dans la croûte durant toute l'activité de l'arc. Par contre, après ~2 Ma, le versant humide de la chaîne est affecté par une accélération des taux d'exhumation, jusqu'à 3 km de croûte y sont érodés. Les glaciations ont un triple effet sur l'érosion de cette chaîne: (1) augmentation des vitesses d'érosion, d'exhumation et de soulèvement la où les précipitations sont suffisantes, (2) limitation de l'altitude contrôlé par la position de Γ Ε LA, (3) élargissement du versant humide et contraction du versant aride de la chaîne.Les modifications des réseaux de drainage sont des processus de surface souvent sous-estimés au profil d'événements climatiques ou tectoniques. Nous proposons une nouvelle approche couplant une analyse géomorphologique, des données thermochronologiques de basse température ((U-Th-Sm)/He sur apatite et zircon), et l'utilisation de modélisation numérique thermo-cinématique pour les mettre en évidence et les dater; nous testons cette approche sur la gorge de la Skagit river dans les North Cascades.De nouvelles données (U-Th)/He sur zircons, complétant les données existantes, montrent que le déplacement horizontal le long de la faille transformante continentale Motagua, la limite des plaques Caraïbe/Amérique du Nord, a juxtaposé un bloc froid, le bloc Maya (s.s.), contre un bloque chaud, le bloc Chortis (s.s.) originellement en position d'arc. En plus de donner des gammes d'âges thermochronologiques très différents des deux côtés de la faille, le déplacement horizontal rapide (~2 cm/a) a produit un fort échange thermique latéral, résultant en un réchauffement du côté froid et un refroidissement du côté chaud de la zone de faille de Motagua.Enfin des données (U-Th-Sm)/He sur apatite témoignent d'un refroidissement Oligocène enregistré uniquement dans la croûte supérieure de la bordure nord de la zone de faille Motagua. Nous tenterons ultérieurement de reproduire ce découplage vertical de la structure thermique par la modélisation de la formation d'un bassin transtensif et de circulation de fluides le long de la faille de Motagua. - This thesis focuses on the influence of the dynamic thermal structure of the upper crust (<10km) on the thermochronologic record of the exhumational and topographic history of magmatic continental arcs. Two mountain belts from the American Cordillera are studied: the North Cascades (USA) and the Motagua fault zone (Guatemala). I use a combined approach coupling apatite and zircon (U-Th-Sm}/He thermochronology and thermo- kinematic numerical modelling. This study highlights the temporal and spatial variability of the geothermal gradient and the importance to take into account the different geological processes that perturb the thermal structure of Cordilleran-type mountain belts (i.e. mountain belts related to oceanic subduction underneath a continent}.We integrate apatite and zircon (U-Th)/He data with numerical thermo-kinematic models to study the relative effects of magmatic and surface processes on the thermal evolution of the crust and cooling patterns in the Cenozoic North Cascades arc (Washington State, USA). Two age-elevation profiles that are located 7 km south of the well-studied Chiliiwack intrusions shows that spatial and temporal variability in geothermal gradients linked to magma emplacement can be contrained and separated from exhumation processes. During Chiliiwack batholith emplacement at -35-20 Ma, the geothermal gradient of the country rocks increased to a very high steady-state value (80-100°C/km), which is likely a function of magma flux and the distance from the magma source area. Including temporally varying geothermal gradients in the analysis allows quantifying the thermal perturbation around magmatic intrusions and retrieving a relatively simple denudation history from the data.The synthesis of new and previously published (U-Th)/He data reveals that denudation of the Northern Cascades is spatially and temporally constant at -100 m/Ma between ~32 and ~2 Ma, which likely reflects uplift due to magmatic crustal thickening since the initiation of the Cenozoic stage of the continental magmatic arc. In contrast, the humid flank of the North Cascades is affected by a ten-fold acceleration in exhumation rate at ~2 Ma, which we interpret as forced by the initiation of glaciations; around 3 km of crust have been eroded since that time. Glaciations have three distinct effects on the dynamics of this mountain range: (1) they increase erosion, exhumation and uplift rates where precipitation rates are sufficient to drive efficient glacial erosion; (2) they efficiently limit the elevation of the range; (3) they lead to widening of the humid flank and contraction of the arid flank of the belt.Drainage reorganizations constitute an important agent of landscape evolution that is often underestimated to the benefit of tectonic or climatic events. We propose a new method that integrates geomorphology, low-temperature thermochronometry (apatite and zircon {U-Th-Sm)/He), and 3D numerical thermal-kinematic modelling to detect and date drainage instability producing recent gorge incision, and apply this approach to the Skagit River Gorge, North Cascades.Two zircon (U-Th)/He age-elevation profiles sampled on both sides of the Motagua Fault Zone (MFZ), the boundary between the North American and the Caribbean plates, combined with published thermochronological data show that strike-slip displacement has juxtaposed the cold Maya block (s.s.) against the hot, arc derived, Chortis block (s.s ), producing different age patterns on both sides of the fault and short-wavelength lateral thermal exchange, resulting in recent heating of the cool side and cooling of the hot side of the MFZ.Finally, an apatite (U-Th-Sm)/He age-elevation profile records rapid cooling at -35 Ma localized only in the upper crust along the northern side of the Motagua fault zone. We will try to reproduce these data by modeling the thermal perturbation resulting from the formation of a transtensional basin and of fluid flow activity along a crustal- scale strike-slip fault.

Bioclimatic constraints to Andean cat distribution: a modelling application for rare species

AimTo identify the bioclimatic niche of the endangered Andean cat (Leopardus jacobita), one of the rarest and least known felids in the world, by developing a species distribution model.LocationSouth America, High Andes and Patagonian steppe. Peru, Bolivia, Chile, Argentina.MethodsWe used 108 Andean cat records to build the models, and 27 to test them, applying the Maxent algorithm to sets of uncorrelated bioclimatic variables from global databases, including elevation. We based our biogeographical interpretations on the examination of the predicted geographic range, the modelled response curves and latitudinal variations in climatic variables associated with the locality data.ResultsSimple bioclimatic models for Andean cats were highly predictive with only 3-4 explanatory variables. The climatic niche of the species was defined by extreme diurnal variations in temperature, cold minimum and moderate maximum temperatures, and aridity, characteristic not only of the Andean highlands but also of the Patagonian steppe. Argentina had the highest representation of suitable climates, and Chile the lowest. The most favourable conditions were centrally located and spanned across international boundaries. Discontinuities in suitable climatic conditions coincided with three biogeographical barriers associated with climatic or topographic transitions.Main conclusionsSimple bioclimatic models can produce useful predictions of suitable climatic conditions for rare species, including major biogeographical constraints. In our study case, these constraints are also known to affect the distribution of other Andean species and the genetic structure of Andean cat populations. We recommend surveys of areas with suitable climates and no Andean cat records, including the corridor connecting two core populations. The inclusion of landscape variables at finer scales, crucially the distribution of Andean cat prey, would contribute to refine our predictions for conservation applications.

Audit report on the Great River Regional Waste Authority for the years ended June 30, 2005 and 2006

Audit report on the Great River Regional Waste Authority for the years ended June 30, 2005 and 2006.

The Fox River Needs Your Help, 2007

The Fox River is on Iowa’s impaired waters list. By working to reduce pollution in the watershed, we can make the Fox River healthy again.

Modelling the effect of minor orthopaedic day surgery on patient mood at the early post-operative period: a prospective population-based cohort study.

OBJECTIVE: The effect of minor orthopaedic day surgery (MiODS) on patient's mood. METHODS: A prospective population-based cohort study of 148 consecutive patients with age above 18 and less than 65, an American Society of Anaesthesiology (ASA) score of 1, and the requirement of general anaesthesia (GA) were included. The Medical Outcomes Study - Short Form 36 (SF-36), Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) were used pre- and post-operatively. RESULTS: The mean physical component score of SF-36 before surgery was 45.3 (SD=+/-10.1) and 8 weeks following surgery was 44.9 (SD=+/-11.04) [n=148, p=0.51, 95% CI=(-1.03 to 1.52)]. For the measurement of the changes in mood using BDI, BAI and SF-36, latent construct modelling was employed to increase validity. The covariance between mood pre- and post-operatively (cov=69.44) corresponded to a correlation coefficient, r=0.88 indicating that patients suffering a greater number of mood symptoms before surgery continue to have a greater number of symptoms following surgery. When the latent mood constructs were permitted to have different means the model fitted well with chi(2) (df=1)=0.86 for which p=0.77, thus the null hypothesis that MiODS has no effect on patient mood was rejected. CONCLUSIONS: MiODS affects patient mood which deteriorates at 8 weeks post-operatively regardless of the pre-operative patient mood state. More importantly patients suffering a greater number of mood symptoms before MiODS continue to have a greater number of symptoms following surgery.

River and Stream Health in Iowa, 2001

A report by the Iowa Department of Natural Resources on how the health of Iowa's River and Stream are today.

Project AWARE 2006 Iowa River, 2007

This monthly report from the Iowa Department of Transportation is about the water quality management of Iowa's rivers, streams and lakes.

Toward a Statistically Robust Assessment of Social and Solidarity Economy Actors. Conceptual Development and Empirical Validation

Many definitions and debates exist about the core characteristics of social and solidarity economy (SSE) and its actors. Among others, legal forms, profit, geographical scope, and size as criteria for identifying SSE actors often reveal dissents among SSE scholars. Instead of using a dichotomous, either-in-or-out definition of SSE actors, this paper presents an assessment tool that takes into account multiple dimensions to offer a more comprehensive and nuanced view of the field. We first define the core dimensions of the assessment tool by synthesizing the multiple indicators found in the literature. We then empirically test these dimensions and their interrelatedness and seek to identify potential clusters of actors. Finally we discuss the practical implications of our model.

Splitting rivers at their seams: bifurcations and avulsion

River bifurcations are critical but poorly understood elements of many geomorphological systems. They are integral elements of alluvial fans, braided rivers, fluvial lowland plains, and deltas and control the partitioning of water and sediment through these systems. Bifurcations are commonly unstable but their lifespan varies greatly. In braided rivers bars and channels migrate, split and merge at annual or shorter timescales, thereby creating and abandoning bifurcations. This behaviour has been studied mainly by geomorphologists and fluid dynamicists. Bifurcations also exist during avulsion, the process of a river changing course on a floodplain or in a delta, which may take 102103 years and has been studied mainly by sedimentologists. This review synthesizes our current understanding of bifurcations and brings together insights from different research communities and different environmental settings. We consider the causes and initiation of bifurcations and avulsion, the physical mechanisms controlling bifurcation and avulsion evolution, mathematical and numerical modelling of these processes, and the possibility of stable bifurcations. We end the review with some open questions. Copyright (c) 2012 John Wiley & Sons, Ltd.

Analysis of past and future dam formation and failure in the Santa Cruz River (San Juan province, Argentina)

Around 11.5 * 106 m3 of rock detached from the eastern slope of the Santa Cruz valley (San Juan province, Argentina) in the first fortnight of January 2005. The rockslide?debris avalanche blocked the course, resulting in the development of a lake with maximum length of around 3.5 km. The increase in the inflow rate from 47,000?74,000 m3/d between April and October to 304,000 m3/d between late October and the first fortnight of November, accelerated the growing rate of the lake. On 12 November 2005 the dam failed, releasing 24.6 * 106 m3 of water. The resulting outburst flood caused damages mainly on infrastructure, and affected the facilities of a hydropower dam which was under construction 250 km downstream from the source area. In this work we describe causes and consequences of the natural dam formation and failure, and we dynamically model the 2005 rockslide?debris avalanche with DAN3D. Additionally, as a volume ~ 24 * 106 m3of rocks still remain unstable in the slope, we use the results of the back analysis to forecast the formation of a future natural dam. We analyzed two potential scenarios: a partial slope failure of 6.5 * 106 m3 and a worst case where all the unstable volume remaining in the slope fails. The spreading of those potential events shows that a new blockage of the Santa Cruz River is likely to occur. According to their modeled morphometry and the contributing watershed upstream the blockage area, as the one of 2005, the dams would also be unstable. This study shows the importance of back and forward analysis that can be carried out to obtain critical information for land use planning, hazards mitigation, and emergency management.

Aproximacíon Teórico-Conceptual a la Metáfora y el Símbolo

La metáfora y el símbolo constituyen eje central de esta investigación, la cual en principio no pretende ser un estudio exhaustivo de estos conceptos, tarea que requeriría muchos años de indagación y búsqueda, al ser éste un primer acercamiento a un controvertido, sugerente e interesante problema que se encuentra no sólo en las raíces de nuestro lenguaje, sino también de nuestro pensamiento y por tanto del devenir filosófico. El recurso de la metáfora y el símbolo, no sólo es propio de la literatura sino común a toda obra humana. Tal es el caso de los mitos, las alegorías, la poesía, las obras de teatro, los ensayos —que a menudo los contienen— y los modelos a escalas tanto teóricos como reales con los que trabaja la ciencia para luego, transferir lo peculiar de la ficción heurística a la realidad.

Project AWARE 2007 Raccoon River, 2008

This monthly report from the Iowa Department of Transportation is about the water quality management of Iowa's rivers, streams and lakes.

Resurgence of HIV infection among men who have sex with men in Switzerland: mathematical modelling study.

BACKGROUND: New HIV infections in men who have sex with men (MSM) have increased in Switzerland since 2000 despite combination antiretroviral therapy (cART). The objectives of this mathematical modelling study were: to describe the dynamics of the HIV epidemic in MSM in Switzerland using national data; to explore the effects of hypothetical prevention scenarios; and to conduct a multivariate sensitivity analysis. METHODOLOGY/PRINCIPAL FINDINGS: The model describes HIV transmission, progression and the effects of cART using differential equations. The model was fitted to Swiss HIV and AIDS surveillance data and twelve unknown parameters were estimated. Predicted numbers of diagnosed HIV infections and AIDS cases fitted the observed data well. By the end of 2010, an estimated 13.5% (95% CI 12.5, 14.6%) of all HIV-infected MSM were undiagnosed and accounted for 81.8% (95% CI 81.1, 82.4%) of new HIV infections. The transmission rate was at its lowest from 1995-1999, with a nadir of 46 incident HIV infections in 1999, but increased from 2000. The estimated number of new infections continued to increase to more than 250 in 2010, although the reproduction number was still below the epidemic threshold. Prevention scenarios included temporary reductions in risk behaviour, annual test and treat, and reduction in risk behaviour to levels observed earlier in the epidemic. These led to predicted reductions in new infections from 2 to 26% by 2020. Parameters related to disease progression and relative infectiousness at different HIV stages had the greatest influence on estimates of the net transmission rate. CONCLUSIONS/SIGNIFICANCE: The model outputs suggest that the increase in HIV transmission amongst MSM in Switzerland is the result of continuing risky sexual behaviour, particularly by those unaware of their infection status. Long term reductions in the incidence of HIV infection in MSM in Switzerland will require increased and sustained uptake of effective interventions.