Intrusive origin of the Sudbury Igneous Complex: Structural and sedimentological evidence

In recent years, many geoscientists have come to believe that the Sudbury event was exogenic rather than endogenic. Critical to a recent exogenic hypothesis is the impact melt origin of the Sudbury Igneous Complex (SIC). Such origin implies that the SIC was emplaced before deposition of the Whitewater Group, in contrast to origins in which the SIC postdates the lithification of the Onaping Formation. Structural and sedimentological evidence is summarized herein that supports an intrusion of the SIC after lithification of all Whitewater Group strata, and conflicts with the hypothesis advanced by other researchers

Parametric generation of second sound in superfluid helium: linear stability and nonlinear dynamics

We report the experimental studies of a parametric excitation of a second sound (SS) by a first sound (FS) in a superfluid helium in a resonance cavity. The results on several topics in this system are presented: (i) The linear properties of the instability, namely, the threshold, its temperature and geometrical dependencies, and the spectra of SS just above the onset were measured. They were found to be in a good quantitative agreement with the theory. (ii) It was shown that the mechanism of SS amplitude saturation is due to the nonlinear attenuation of SS via three wave interactions between the SS waves. Strong low frequency amplitude fluctuations of SS above the threshold were observed. The spectra of these fluctuations had a universal shape with exponentially decaying tails. Furthermore, the spectral width grew continuously with the FS amplitude. The role of three and four wave interactions are discussed with respect to the nonlinear SS behavior. The first evidence of Gaussian statistics of the wave amplitudes for the parametrically generated wave ensemble was obtained. (iii) The experiments on simultaneous pumping of the FS and independent SS waves revealed new effects. Below the instability threshold, the SS phase conjugation as a result of three-wave interactions between the FS and SS waves was observed. Above the threshold two new effects were found: a giant amplification of the SS wave intensity and strong resonance oscillations of the SS wave amplitude as a function of the FS amplitude. Qualitative explanations of these effects are suggested.Comment: 73 pages, 23 figures. to appear in Phys. Rev. B, July 1 st (2001

Pastoral Herding Strategies and Governmental Management Objectives: Predation Compensation as a Risk Buffering Strategy in the Saami Reindeer Husbandry

Previously it has been found that an important risk buffering strategy in the Saami reindeer husbandry in Norway is the accumulation of large herds of reindeer as this increases long-term household viability. Nevertheless, few studies have investigated how official policies, such as economic compensation for livestock losses, can influence pastoral strategies. This study investigated the effect of received predation compensation on individual husbandry units’ future herd size. The main finding in this study is that predation compensation had a positive effect on husbandry units’ future herd size. The effect of predation compensation, however, was nonlinear in some years, indicating that predation compensation had a positive effect on future herd size only up to a certain threshold whereby adding additional predation compensation had little effect on future herd size. More importantly, the effect of predation compensation was positive after controlling for reindeer density, indicating that for a given reindeer density husbandry units receiving more predation compensation performed better (measured as the size of future herds) compared to husbandry units receiving less compensation

Tectonic and metamorphic events in the westernmost Grenville Province, central Ontario: new results from high-precision U–Pb zircon geochronology

Les âges isotopiques U–Pb sur les zircons métamorphiques extraits des dykes de métadiabase déformés et amphibolitisés, et des pegmatites anatectiques non comprimées, ont été déterminés pour encadrer chronologiquement les événements de déformation plastique associés à leur recristallisation et déformation postérieures. Les échantillons prélevés dans la Ceinture des gneiss centraux de la province de Grenville, dans la région méridionale de la baie Georgienne, autorisent l'établissement d'un lien entre les régions qui ont été formées durant les mêmes épisodes de déformation plastique. Trois fractions de zircon extraites d'un dyke atténué, localisé dans le domaine de Moon River ont donné des âges concordants équivalents de 1062, 1065 et 1064 ± 2 Ma, tandis que les fractions d'un autre dyke ont procuré des âges concordants équivalents de 1052, 1051 et 1050 ± 2 Ma qui datent l'épisode de métamorphisme. Les zircons d'un dyke plissé du domaine de Go Home ont fourni des âges concordants équivalents de 1049, 1047 et 1046 ± 2 Ma, tandis qu'un éclat d'excroissance livré par la pegmatite anatectique non comprimée, dans la charnière du pli, a procuré un âge concordant de 1047 ± 2 Ma, suggérant que le même processus aurait présidé la croissance du zircon métamorphique dans le pli ainsi que l'intrusion de la pegmatite postérieure à la déformation. Une pegmatite anatectique, localisée dans la zone d'étranglement d'un dyke de métadiabase boudiné, dans le domaine d'Ahmic, a livré deux fractions de zircon avec les âges concordants équivalents de 1079 et 1080 ± 2 Ma, coïncidant avec l'âge de 1078 ± 2 Ma d'un de grain d'excroissance typique extrait de la migmatite hôte. Les zircons extraits de la métadiabase présentent des âges similaires, mais leur détermination est moins précise à cause du faible niveau de l'uranium et une concentration réduite. Les résultats des analyses U–Pb fournis par le granite de Love Lake, situé à la frontière des domaines de Parry Sound–Ahmic sont ambigus, cependant ils reflètent peut-être une déformation de cette structure postérieure à 1068 Ma, soit l'âge de la titanite contenue dans ces roches. L'une et l'autre des limites supérieur ou inférieur de la discordia du zircon, autour de 1050 et 1372 Ma, pourraient correspondre à l'âge de la mise en place du granite. Les zircons d'un dyke post-datant la migmatisation au faciès des granulites dans le domaine de Parry Sound ont enregistré une altération métamorphique vieille de 1114 ± 2 Ma, mais des grains hérités d'âges plus anciens ont été trouvés dans d'autres fractions. La déformation plastique dans les domaines de Go Home et de Moon River est apparue entre 1047 et 1064 Ma, ce dernier domaine fut probablement mis en place durant cet intervalle, tandis que la déformation plastique dans le domaine d'Ahmic, d'âge plus précoce (1080 Ma), est probablement associée au chevauchement du domaine de Parry Sound. Les âge des dykes métamorphiques du domaine de Parry Sound impliquent l'absence d'une phase de migmatisation postérieure à 1114 Ma, mais une phase de migmatisation antérieure à la formation des dykes, compatible avec la dé rivation plus exotique de ce domaine. L'âge de  Ma, obtenu pour les dykes de pegmatite transectants et postérieurs à la migmatite, définit l'âge limite supérieur attribuable à l'événement de déformation tardive dans le domaine d'Ahmic

Envisioning 2050 : Climate Change, Aquaculture and Fisheries in West Africa, Dakar, Senegal, 14-16th April 2010

French version available in IDRC Digital Library: Vision 2050 : Changement climatique, pêche et aquaculture en Afrique de l’Ouest, du 14 au 16 avril 2010, Dakar, SénégalThis report presents the activities and results of the workshop Envisioning 2050: Climate Change, Aquaculture and Fisheries in West Africa. The objectives of the workshop were to discuss critical issues and uncertainties faced by the fisheries and aquaculture sector in Ghana, Senegal and Mauritania, build sectoral scenarios for 2050 and discuss the implication of these scenarios in the context of climate change for the countries and the region. During the workshop participants were introduced to scenariobuilding methodologies, identified drivers of change and ranked them according to their importance and levels of uncertainty. Participants then constructed four consistent scenarios for 2050 for each country. The scenarios raised several questions including: Can aquaculture address both national food security and macroeconomic growth? Should regional trade be promoted or access to global markets prioritised? How will climate change affect fishery resources, especially small pelagic fish like sardines, which are an important export commodity for Senegal and Mauritania? Participants also assessed the implications of the different scenarios in terms of climate change and research and development in the fisheries and aquaculture sector. It was agreed that a regional or sub-regional effort is needed to better integrate scientific knowledge and to put into place coherent fisheries policies. Additionally, a better understanding of the impacts of climate change on the sector is needed, with for instance, the development of coupled climate-fisheries models for major commercial fisheries in the region. Participants unanimously agreed that strategic planning and foresight studies methodologies should be widely disseminated. Indeed the opportunity for reflective and creative thinking was recognised as an important part of planning - especially adaptation planning - to climate change. Finally, the workshop provided a rare opportunity to include in a foresight study, art projects by youth on the future of the fisheries sector and the coasts as an exhibition and discussion theme (“Visions of the Future: What is African Youth telling us about our Ocean?”). Empowering youth on climate change issues and integrating their needs into adaptation planning is essential as they will be the ones most affected by future developments