Le "cadre géologique" dans l'article de géologie en français et en anglais: crédibilité et retenue sur le terrain

While the features of the scientific research article have been widely investigated in numerous disciplines over the past 15 years, relatively scant attention has been paid to the important discipline of geology. Moreover, within the sub-discipline of petrology, we find a sub-section as yet unrecognized in the extensive literature on the research article. The " Geological Setting ", an introductory part-genre occurring before the onset of petrological analysis, is a multi-functional description which frames researchers' results within their geological context. It is argued that this part-genre is not only a complex of the topography, geological history and characteristics of the research site, but also serves to establish the authors' credentials and authority as experts, while allowing them to maneuver through conventional modesty in presenting terrain results. Similarities at the macro-level and general discourse structure are found in both the French and English texts, with important stylistic differences on a local level.Tandis que les caractéristiques de l'article scientifique ont été beaucoup étudiées pour de nombreuses disciplines depuis une quinzaine d'années, celles de la géologie restent relativement ignorées. Pourtant, dans la sous-discipline de la pétrologie on trouve une sous-section jusqu'ici méconnue: le cadre géologique, un " sous-genre " introductif précedant la présentation de l'analyse des échantillons. On verra que ce sous-genre se compose des caractéristiques pétrologiques du terrain étudié, sa topographie et son histoire géologique. Il établit également l'expertise et la crédibilité des auteurs, tout en conservant la modestie et le silence. On trouve des similarités entre les textes français et anglais dans leurs macro-structures, mais des différences de style existent au niveau local de la communauté de discours

Détermination de la sensibilité potentielle des roches cristallophylliennes à l'altération chimique à partir de leur composition chimique

9 pages, 2 tableauxNational audienceLa sensibilité potentielle des roches cristallines à l'hydrolyse dépend très fortement de leur composition minéralogique. Un indice d'altérabilité (Ia) calculé à partir de la composition chimique globale des matériaux non altérés permet de prendre indirectement en compte le facteur minéralogique. Cet indice est particulièrement utile dans le cas des roches cristallophylliennes, pour lesquelles l'observation des lames minces renseigne mal sur la composition modale. Un indice de sensibilité à la décohésion chimique (Id), au caractère plus empirique, intègre l'influence de l'agencement des minéraux

Estrutura e geoquí­mica das fases magmática e tardimagmática em zircões do maciço graní­tico de Peneda-Gerês (NW Pení­nsula Ibérica)

Efectuou-se um estudo da estrutura interna e composição química dos zircões de granitos do maciço de Peneda-Gerês (granitos de Gerês, Paufito, Illa e Carris) com recurso a microscópio electrónico de varrimento (MEV) e microssonda electrónica. Este estudo permitiu caracterizar as fases magmática e tardimagmática e, ainda, constatar a existência de domínios de alteração nas zonas dos cristais mais ricas em elementos vestigiais (U, Th). Esta alteração é claramente mais expressiva nos zircões mais tardios (subtipos S5, G1) do granito de Carris e traduz-se em estruturas com forma botrioidal e de cor escura em imagem de electrões retrodifundidos (MEV). A grande expressividade destes domínios de alteração nos zircões do granito de Carris, em constraste com a sua limitada expressividade em zircões dos restantes granitos do maciço de Peneda-Gerês, permite supor que este fenómeno de alteração esteja relacionado com a maior abundância de fluidos hidrotermais que afectaram domínios mais susceptíveis dos cristais de zircão. Refira-se que, espacialmente associados ao granito de Carris, ocorrem filões e filonetes quartzosos e quartzo-feldspáticos com mineralizações em volframite, molibdenite, pirite, etc, correspondendo às zonas mais mineralizadas do maciço de Peneda-Gerês.A study of the internal structure and chemical composition of zircon from the main granitic units of the Peneda-Gerês granitic massif (Gerês, Paufito, Illa and Carris granites) was undertaken. This study permitted to characterize the zircons’ magmatic and late magmatic phases and, additionally, revealed the existence of alteration domains in the zones of the zircons which are richer in trace elements (U, Th). This alteration is notoriously more expressible in the late crystallizing zircons (subtypes S5, G1) of theCarris granite and appears as botrioidal structures of dark colour in back scattered electron imagery (SEM). The important expression of this alteration in the Carris granite, in contrast to the limited expression in zircons of the other granites, permits to envisage that this alteration is associated with a greater abundance of hydrothermal fluids that affected the more susceptible domains of the zircon crystals. It should be referred that spatially associated with the Carris granite occur quartz and quartz-feldspar veins with mineralizations of wolframite, molybdenite, pyrite, etc, corresponding to the most mineralized zone of the Peneda-Gerês massif.Fundação para a Ciência e a Tecnologia (FCT) - Programa de Financiamento Plurianua