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31.
Patrick Mercier-Langevin Vicky McNicoll Rodney L. Allen James H. S. Blight Benoît Dubé 《Mineralium Deposita》2013,48(4):485-504
The Boliden deposit (8.3 Mt at 15.9 g/t Au) is interpreted to have been formed between ca. 1894 and 1891 Ma, based on two new U–Pb ID-TIMS ages: a maximum age of 1893.9?+?2.0/?1.9 Ma obtained from an altered quartz and feldspar porphyritic rhyolite in the deposit footwall in the volcanic Skellefte group and a minimum age of 1890.8?±?1 Ma obtained from a felsic mass-flow deposit in the lowermost part of the volcano-sedimentary Vargfors group, which forms the stratigraphic hanging wall to the deposit. These ages are in agreement with the alteration and mineralization being formed at or near the sea floor in the volcanogenic massive sulfide environment. These two ages and the geologic relationships imply that: (1) volcanism and hydrothermal activity in the Skellefte group were initiated earlier than 1.89 Ga which was previously considered to be the onset of volcanism in the Skellefte group; (2) the volcano-sedimentary succession of the Vargfors group is perhaps as old as 1892 Ma in the eastern part of the Skellefte district; and (3) an early (synvolcanic) deformation event in the Skellefte group is evidenced by the unconformity between the ≤1893.9?+?2.0/?1.9 Ma Skellefte group upper volcanic rocks and the ≤1890.8?±?1 Ma Vargfors sedimentary and volcanic rocks in the Boliden domain. Differential block tilting, uplift, and subsidence controlled by synvolcanic faults in an extensional environment is likely, perhaps explaining some hybrid VMS-epithermal characteristics shown by the VMS deposits of the district. 相似文献
32.
Benoît Carry Pierre Vernazza Christophe Dumas William J. Merline Olivier Mousis Philippe Rousselot Emmanuël Jehin Jean Manfroid Marcello Fulchignoni Jean-Marc Zucconi 《Icarus》2012,217(1):20-26
Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron spectroscopy. While Ceres’ visible and near-infrared disk-integrated spectra have been well characterized, little has been done about quantifying spectral variations over the surface. Any spectral variation would give us insights on the geographical variation of the composition and/or the surface age. The only work so far was that of Rivkin and Volquardsen ([2010], Icarus 206, 327) who reported rotationally-resolved spectroscopic (disk-integrated) observations in the 2.2–4.0 μm range; their observations showed evidence for a relatively uniform surface.Here, we report disk-resolved observations of Ceres with SINFONI (ESO VLT) in the 1.17–1.32 μm and 1.45–2.35 μm wavelength ranges. The observations were made under excellent seeing conditions (0.6″), allowing us to reach a spatial resolution of ～75 km on Ceres’ surface. We do not find any spectral variation above a 3% level, suggesting a homogeneous surface at our spatial resolution. Slight variations (about 2%) of the spectral slope are detected, geographically correlated with the albedo markings reported from the analysis of the HST and Keck disk-resolved images of Ceres (Li et al. [2006], Icarus 182, 143; Carry et al. [2008], Astron. Astrophys. 478, 235). Given the lack of constraints on the surface composition of Ceres, however, we cannot assert the causes of these variations. 相似文献
33.
Experimental observations clearly show that the relative humidity (hr) conditions influence significantly the creep behavior of cement‐based materials, indicating that the water present within these materials plays a crucial role. This work presents a creep model for hardened cement pastes (HCP), based on a multiscale homogenization approach. It takes into account both free and adsorbed water contained in the porosity and investigates their effects on the HCP macroscopic creep behavior. The calcium silicate hydrate phase is assumed to be linear viscoelastic, and the Mori–Tanaka scheme is applied in the Laplace–Carson space to the composite formed of porosity, calcium silicate hydrate, and the other main hydrated compounds (which behavior is linearly elastic) by making use of the correspondence principle. With this model, estimations of the evolution of the macroscopic creep behavior of HCP submitted to constant external loading are examined under different hr and compared with available experimental data. Finally, a method for implementing the model in a finite element code is proposed, and simulations of standard creep tests are performed to assess its validity. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
34.
Atoll lagoons display a high diversity of trophic states due mainly to their specific geomorphology, and probably to their level and mode of human exploitation. We investigated the functioning of the Ahe atoll lagoon, utilized for pearl oyster farming, through estimations of photosynthetic parameters (pulse amplitude modulation fluorometry) and primary production ((13)C incorporation) measurements of the size structured phytoplankton biomass (<2μm and >2μm). Spatial and temporal scales of variability were surveyed during four seasons, over 16months, at four sites within the lagoon. While primary production (P) was dominated by the picophytoplankton, its biomass specific primary productivity (P(B)) was lower than in other atoll lagoons. The variables size fraction of the phytoplankton, water temperature, season, the interaction term station*fraction and site, explained significantly the variance of the data set using redundancy analysis. No significant trends over depth were observed in the range of 0-20m. A clear spatial pattern was found which was persistent over the seasons: south and north sites were different from the two central stations for most of the measured variables. This pattern could possibly be explained by the existence of water cells showing different water residence time within the lagoon. Photoacclimation strategies of the two size fractions differed through their light saturation coefficient (higher for picophytoplankton), but not through their maximum photosynthetic capacity (ETR(max)). Positive linear relationships between photosynthetic parameters indicated that their dynamic was independent of light availability in this ecosystem, but most probably dependent on nutrient availability and/or rapid changes in the community structure. Spatial and temporal patterns of the measured processes are then further discussed in the context of nutrient availability and the possible role of cultured oysters in nutrient recycling. 相似文献
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36.
Léon Dejonghe Benoît Darras Guillermo Hughes Philippe Muchez James S. Scoates Dominique Weis 《Mineralium Deposita》2002,37(2):158-172
The lead isotope compositions of galena and the fluid-inclusion systematics of nine barite-bearing polymetallic (Au, Ag, Pb, Zn) deposits of the central Argentinian Patagonia (Chubut and Rio Negro provinces) have been investigated to constrain the compositions and sources of the mineralizing fluids. Most of the deposits occur as veins, with less common wall-rock disseminations and/or stockworks, and are low-sulfidation epithermal deposits hosted in Jurassic volcanic rocks. Fluid-inclusion homogenization temperatures (Th) from quartz and sphalerite from the deposits fall within the range of 100-300 °C, with the highest measured average temperatures for the most eastern deposits (Mina Angela - 298 °C; Cañadón Bagual - 343 °C). The salinities of the hydrothermal fluids at all deposits were low to moderate (⢪.4 equiv. wt% NaCl). Three groups of ore deposits can be defined on the basis of 206Pb/204Pb ratios for galena and these show a general decrease from west to east (from 18.506 to 18.000). The central Argentinian Patagonia deposits have distinctly less radiogenic lead isotope compositions than similar deposits from Peru and Chile, except for the porphyry copper deposits of central and southern Peru. Galena from the Mina Angela deposit is characterized by very low radiogenic lead isotope compositions (18.000<206Pb/204Pb<18.037 and 38.03<208Pb/204Pb<38.09) and reflects interaction with Precambrian basement. The geographic trend in lead isotope compositions of both galena and whole rocks indicates a crustal contribution which increases eastwards, also reflected in the strontium-neodymium isotope systematics of the host lavas. Finally, due to the lack of precise age determinations for the central Patagonian polymetallic deposits, a potential link with Andean porphyry copper systems remains an open question. 相似文献
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38.
Guoxiang Chi Benoît Dubé Kenneth Williamson Anthony E. Williams-Jones 《Mineralium Deposita》2006,40(6-7):726-741
The Campbell-Red Lake gold deposit in the Red Lake greenstone belt, with a total of approximately 840 t of gold (past production + reserves) and an average grade of 21 g/t Au, is one of the largest and richest Archean gold deposits in Canada. Gold mineralization is mainly associated with silicification and arsenopyrite that replace carbonate veins, breccias and wallrock selvages. The carbonate veins and breccias, which are composed of ankerite ± quartz and characterized by crustiform–cockade textures, were formed before and/or in the early stage of penetrative ductile deformation, whereas silicification, arsenopyrite replacement and gold mineralization were coeval with deformation. Microthermometry and laser Raman spectroscopy indicate that fluid inclusions in ankerite and associated quartz (Q1) and main ore-stage quartz (Q2) are predominantly carbonic, composed mainly of CO2, with minor CH4 and N2. Aqueous and aqueous–carbonic inclusions are extremely rare in both ankerite and quartz. H2O was not detected by laser Raman spectroscopic analyses of individual carbonic inclusions and by gas chromatographic analyses of bulk samples of ankerite and main ore-stage quartz (Q2). Fluid inclusions in post-mineralization quartz (Q3) are also mainly carbonic, but proportions of aqueous and aqueous–carbonic inclusions are present. Trace amounts of H2S were detected by laser Raman spectroscopy in some carbonic inclusions in Q2 and Q3, and by gas chromatographic analyses of bulk samples of ankerite and Q2. 3He/4He ratios of bulk fluid inclusions range from 0.008 to 0.016 Ra in samples of arsenopyrite and gold. Homogenization temperatures (T
h–CO2) of carbonic inclusions are highly variable (from −4.1 to +30.4°C; mostly to liquid, some to vapor), but the spreads within individual fluid inclusion assemblages (FIAs) are relatively small (within 0.5 to 10.3°C). Carbonic inclusions occur both in FIAs with narrow T
h–CO2 ranges and in those with relatively large T
h–CO2 variations. The predominance of carbonic fluid inclusions has been previously reported in a few other gold deposits, and its significance for gold metallogeny has been debated. Some authors have proposed that formation of the carbonic fluid inclusions and their predominance is due to post-trapping leakage of water from aqueous–carbonic inclusions (H2O leakage model), whereas others have proposed that they reflect preferential trapping of the CO2-dominated vapor in an immiscible aqueous–carbonic mixture (fluid unmixing model), or represent an unusually H2O-poor, CO2-dominated fluid (single carbonic fluid model). Based on the FIA analysis reported in this study, we argue that although post-trapping modifications and host mineral deformation may have altered the fluid inclusions in varying degrees, these processes were not solely responsible for the formation of the carbonic inclusions. The single carbonic fluid model best explains the extreme rarity of aqueous inclusions but lacks the support of experimental data that might indicate the viability of significant transport of silica and gold in a carbonic fluid. In contrast, the weakness of the unmixing model is that it lacks unequivocal petrographic evidence of phase separation. If the unmixing model were to be applied, the fluid prior to unmixing would have to be much more enriched in carbonic species and poorer in water than in most orogenic gold deposits in order to explain the predominance of carbonic inclusions. The H2O-poor, CO2-dominated fluid may have been the product of high-grade metamorphism or early degassing of magmatic intrusions, or could have resulted from the accumulation of vapor produced by phase separation external to the site of mineralization.Geological Survey of Canada contribution 2004383. 相似文献
39.
A conceptual hydrogeological model of ophiolite hard-rock aquifers in Oman based on a multiscale and a multidisciplinary approach 总被引：2，自引：1，他引：1
Benoît Dewandel Patrick Lachassagne Françoise Boudier Saïd Al-Hattali Bernard Ladouche Jean-Louis Pinault Zaher Al-Suleimani 《Hydrogeology Journal》2005,13(5-6):708-726
Ophiolites are found all over the world: from the Alps to the Himalayas, in Cuba, Papua-New Guinea, New Caledonia, Newfoundland, etc. They are composed of hard rocks—basalt, dolerite, gabbro and peridotite, which are formed at the mid-oceanic ridges, with specific ridge-related tectonic fracturing and intense hydrothermal alteration. Their geological and thus their hydrogeological properties differ from those of both granite or classical gabbro and classical basaltic lava. A conceptual hydrogeological model of these hard-rock aquifers was developed based on the convergent results of a multidisciplinary approach at several spatial scales, from rock-sample (centimetre) to catchment (kilometre), on well-preserved ophiolite rocks in Oman. In ophiolite rocks, groundwater circulation takes place mostly in the fissured near-surface horizon (50 m thick), and, to a lesser degree, in the tectonic fractures. Hydrograph analysis (Water Resour Res 34:233–240, 1977), interpretation of numerous pumping tests using both classical Theis and dual porosity models [Water Resour Res 32:2733–2745, 1996; Comput Geosci J (in press)], and mercury porosity and hydraulic conductivity lab-measurements support the aquifer parameter estimates. The hydraulic conductivity K of the fissured horizon is estimated at 10–5 to 10–6 m/s for gabbro and dolerite, and 10–7 m/s for peridotite. The storage coefficient S of the peridotite aquifer is estimated at 10–3 and appears to be controlled mainly by microcracks (20 to 100 m wide). Tectonic fractures in the ophiolite have similar hydrodynamic properties regardless of lithology (10–1<T<10–4 m2/s and 10–1<S<10–3) though the probability of obtaining productive wells is two to three times greater in gabbro and dolerite than in peridotite. Some of the tectonic fractures produce small hydrothermal, hyperalkaline springs in the peridotite. The water budget and hydrochemistry of the Oman ophiolite are characterized and support the conceptual hydrogeological model. Despite low annual rainfall, a relatively low hydraulic conductivity and a significant storage coefficient explain why most of the streams in peridotite are perennial.
Résumé Les ophiolites se trouvent partout dans le monde : des Alpes à lHymalaya, à Cuba, Papouasie Nouvelle-Guinée, Nouvelle Calédonie, etc. Les ophiolites sont composées de roches dures basaltiques, de dolérites, gabbros et péridotites, qui sont formées aux rides mi-océaniques, avec, en relation avec les rides, une fracturation tectonique et une altération hydrothermale intense. Leurs propriétés géologiques et hydrogéologiques diffèrent de celles des granites ou des gabbros classiques ou des laves basaltiques classiques. Un modèle hydrogéologique conceptuel des aquifères de hard-rock a été développé sur les résultats convergents dune approche multidisciplinaire à différentes échelles spatiales, de léchantillon de roche de quelques centimètres à la taille du bassin versant en kilomètres, des ophiolites bien conservées dOman. Dans les roches ophiolitiques, la circulation des eaux souterraines est surtout localisée dans les fissures dun horizon de surface de plus dune cinquantaine de mètres et à un degré moindre dans les fractures tectoniques. Lanalyse des hydrographes (Water Resour Res 34:233–240, 1977), linterprétation des nombreux essais de pompage utilisant des modèles classiques de Theis et des modèles à double porosité (Water Resour Res 32:2733–2745, 1996; Comput Geosci J (Soumis), la porosité au mercure et la conductivité hydraulique calculée en laboratoire supportent lestimation des paramètres de laquifère. La conductivité hydraulique K de lhorizon fissuré est estimée entre 10–5 et 10–6 m/s pour les gabbros et les dolérites, et 10–7 m/s pour les péridotites. Le coefficient demmagasinement S de laquifère de péridotite est estimé à 10–3 et semble être contrôlé par les micro-fractures (20 à 100 m de largeur). Les fractures tectoniques dans les ophiolites possèdent des propriétés hydrodynamiques en regard de la lithologie (10-1<T<10-4 m2/s et 10-1/S/10-3) bien que la probabilité dobtenir des puits productifs est trois plus grand dans le grabbro et la dolérite que la péridétite. Quelques unes des fractures tectoniques produisent de petites sources hydrothermales hyperalcalines dans la péridotite. Le bilan hydrologique et hydrochimique de lophiolite dOman caractérise le modèle hydrogéologique conceptuel. Malgré des faibles précipitations annuelles, une relativement basse conductivité hydraulique et un coefficient demmagasinement significatif expliquent pourquoi la plus part des cours deau sur les péridotites ne sont jamais taris.
Resumen Las rocas ofiolitas se encuentran en muchas partes del mundo desde los Alpes a los Himilaya, Newfoundland, Nueva Caledonia etc. Son rocas duras compuestas de basalto, dolerita, gabro y peridotita que son formadas por los cordones medio-oceánicos y por fracturación relacionada con los cordones tectónicos específicos y alteración hidrotermal intensa. La geología y los propiedades hidrogeológicas varian entre las de granito y gabro clásico y lava de basalto clásico. Se desarrolló un modelo conceptual de los acuíferos de las rocas duras Basado en los resultados convergentes de un enfoce multidisciplinario a varias escalas a partir de muestras de roca (centímetro) a cuenca kilómetro) enfocado en las rocas ofilíticas bien preservados en Oman. En las rocas ofiolíticas la circulación de agua ocurre principalmente en el horizonte de fisuras cercanas a la superficie (>50 m de espesor) y en un grado menos importante en fracturas tectónicas. Los estimados de los parámetros de estos acuíferos se basan en análisis de hidrógrafos (Water Resour Res 34:233–240, 1977), en la interpretación de pruebas de bombeo usando los modelos clásicos de Theis y de porosidad doble (Hamm y Bidaux 1996; Lods y Gouze, [en prensa]), y porosidad de mecurio y conductividad hidraúlica medida en el laboratorio. La conductividad hidraúlica K del horizonte fisurado se estima en 10E-5 a 10E-6 m-s para gabro y dolerita y 10E-7 para peridotita. El coeficiente de abastecimiento S del acuífero peridotita se estima en 10–3 y parece ser controlado principalmente por microfracturas (20 to 100 m de ancho). Las fracturas tectónicas en la ofiolita tienen propiedades hidrodinámicas similares independientes de la litología (10–1<T<10–4 m2/s and 10–1<S<10–3) pero la probabilidad de obtener pozos productivos es dos o tres veces mayor en gabro que en dolerita o peridotita. Algunas de las fracturas tectónicas producen pequeñas descargas de agua hidrotermal hiperalcalina en la peridotita. El presupuesto e hidroquímica de las ofilitas de Omán se caracteriza y apoya en el modelo conceptual hidrogeológico. La baja lluvia anual, una conductividad hidraúlica relativamente baja y un coeficiente de abastecimiento importante explican porqué la mejoría de los drenajes en peridotita es peremne.相似文献
40.
Laura Airaghi Nicolas Bellahsen Benoît Dubacq David Chew Claudio Rosenberg Emilie Janots Maxime Waldner Valérie Magnin 《Journal of Metamorphic Geology》2020,38(2):183-204
Pre-kinematic greenschist facies metamorphism is often observed in granites and basement units of mountain belts, but rarely dated and accounted for in orogenic cycle reconstructions. Studying pre-kinematic alteration is challenging because of its usual obliteration by subsequent syn-kinematic metamorphism often occurring at conditions typical of the brittle–ductile transition. It is, however, to be expected that pre-kinematic alteration has major implications for the rheology of the upper crust. In the 305 Ma-old Variscan basement of the Bielsa massif (located in the Axial Zone of the Pyrenees), successive fluid–rock interaction events are recorded in granites below 350°C. Combined microstructural and petrographic analysis, low-T thermobarometry and in situ U–Th/Pb dating of anatase, titanite and monazite show extensive pre-orogenic (pre-Alpine) and pre-kinematic alteration related to feldspar sericitization and chloritization of biotite and amphibole at temperatures of 270–350°C at 230–300 Ma. This event is followed by a second fluid–rock interaction stage marked by new crystallization of phyllosilicates at 200–280°C and is associated with the formation of mylonitic shear zones and fractures parallel to the shear planes. U–Pb anatase and monazite ages as well as the microtextural relationships of accessory minerals suggest an age for this event at 40–70 Ma, consistent with independent regional geology constraints. The Variscan basement was therefore softened at late to post-Variscan time, at least 150–200 Ma before the main Alpine shortening while Alpine-age compression (c. 35–50 Ma) leads to the formation of a dense net of mylonites. The associated deformation, both distributed at the scale of the Bielsa massif and localized at decametric scale in mylonitic corridors, precedes the strain localization along the major thrusts of the Axial Zone. The Bielsa massif is a good example where inherited, pre-orogenic upper crustal softening controls the deformation patterns in granitic basement units through low-grade metamorphic reactions. 相似文献