REE, Zr, Nb concentrations and Sr, Nd isotope compositions have been measured in Copley basalts and andesites, Balaklala rhyolites, and Mule Mountain trondhjemites (northern California) which represent the deep layers of a well preserved intra-oceanic island arc of Siluro-Devonian age.87Sr/86Sr is shifted towards high values (up to 0.707) whereas Ce is preferentially removed from rhyolites. A large proportion of the analyzed samples including some acidic rocks shows a pronounced depletion in light REE. The εNd(T) values of most Copley, Balaklala, and Mule Mountain rocks fall in the range +6 to +8 which suggests that they originated from a normal MORB-type source (εNd(T) ≈ +9) contaminated with either sediments or an OIB-type component.In modern island arcs, only the shallow levels are accessible: comparison with the Copley-Balaklala-Mule Mountain Series suggests that, at depth, an immature island arc is likely to comprise thick layers of LILE-depleted tholeiites and rhyolites intensely altered by pervasive circulation of seawater. Least-square solutions of trace element models suggest that rhyolites and trondhjemites represent remelting of mafic volcanics from the arc basement rather than residual melts of basalt-andesite differentiation. 相似文献
The Raspas Metamorphic Complex of southwestern Ecuador is regarded as the southernmost remnant of oceanic and continental terranes accreted in the latest Jurassic–Early Cretaceous. It consists of variably metamorphosed rock types. (1) Mafic and ultramafic rocks metamorphosed under high-pressure (HP) conditions (eclogite facies) show oceanic plateau affinities with flat REE chondrite-normalized patterns, Nd150 Ma ranging from +4.6 to 9.8 and initial Pb isotopic ratios intermediate between MORB and OIB. (2) Sedimentary rocks metamorphosed under eclogitic conditions exhibit LREE enriched patterns, strong negative Eu anomalies, Rb, Nb, U, Th, Pb enrichments, low Nd150 Ma values (from −6.4 to −9.5), and high initial 87Sr/86Sr and 206,207,208Pb/204Pb isotopic ratios suggesting they were originally sediments derived from the erosion of an old continental crust. (3) Epidote-bearing amphibolites show N-MORB affinities with LREE depleted patterns, LILE, Zr, Hf and Th depletion, high Nd150 Ma (>+10) and low initial Pb isotopic ratios.The present-day well defined internal structure of the Raspas Metamorphic Complex seems to be inconsistent with the formerly proposed interpretation of a “tectonic mélange”. The association of oceanic plateau rocks and continent-derived sediments both metamorphosed in HP conditions suggests that the thin edge of the oceanic plateau first entered the subduction zone and dragged sediments downward of the accretionary wedge along the Wadatti–Benioff zone. Subsequently, when its thickest part arrived into the subduction zone, the oceanic plateau jammed the subduction processes, due to its high buoyancy.In Ecuador and Colombia, the latest Jurassic–Early Cretaceous suture involves HP oceanic plateau rocks and N-MORB rocks metamorphosed under lower grades, suggesting a composite or polyphase nature for the latest Jurassic–Early Cretaceous accretionary event. 相似文献
Field investigations were carried out to determine the occurrence of tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL), the source zone architecture and the aquitard integrity at a 30‐ to 50‐year old DNAPL release site. The DNAPL source zone is located in the clay till unit overlying a limestone aquifer. The DNAPL source zone architecture was investigated through a multiple‐lines‐of‐evidence approach using various characterization tools; the most favorable combination of tools for the DNAPL characterization was geophysical investigations, membrane interface probe, core subsampling with quantification of chlorinated solvents, hydrophobic dye test with Sudan IV, and Flexible Liner Underground Technologies (FLUTe) NAPL liners with activated carbon felt (FACT). While the occurrence of DNAPL was best determined by quantification of chlorinated solvents in soil samples supported by the hydrophobic dye tests (Sudan IV and NAPL FLUTe), the conceptual understanding of source zone architecture was greatly assisted by the indirect continuous characterization tools. Although mobile or high residual DNAPL (St > 1%) only occurred in 11% of the source zone samples (intact cores), they comprised 86% of the total PCE mass. The dataset, and associated data analysis, supported vertical migration of DNAPL through fractures in the upper part of the clay till, horizontal migration along high permeability features around the redox boundary in the clay till, and to some extent vertical migration through the fractures in the reduced part of the clay till aquitard to the underlying limestone aquifer. The aquitard integrity to DNAPL migration was found to be compromised at a thickness of reduced clay till of less than 2 m. 相似文献
The impact of dietary and water exposure on the accumulation and distribution of cadmium (Cd) in subcellular components of the polychaete Capitella sp. I was investigated. Worms were exposed to either dissolved Cd alone ('Water-Only' treatments; WO) or diet-bound Cd alone ('Algae-bound Only' treatments; AO). Thus, WO worms were starved and AO worms were fed. Differential centrifugation was used to fractionate worm homogenates into debris- (DE), mitochondrial- (MI), microsomal- (MC) and cytosolic- (CY) fractions, and the concentration of Cd in these fractions was quantified by radiometric analysis using the specific activity of the (109)Cd radioisotope. Neither exposure route nor Cd exposure affected the total protein content in the worms. However, fed, but not starved worms relocated proteins from the mitochondria to the cytosol in response to Cd exposure. In systems without Cd addition, starvation likewise influenced the distribution of protein between mitochondria and cytosol. Cutaneous uptake and accumulation of Cd from the water was related to surface area while dietary uptake was influenced by the amount of sediment passing through the gut. Irrespective of exposure route, Cd was accumulated primarily in the debris fraction although comparisons between the treatments indicated that relatively less Cd was located in DE and more in MI, MC and CY fractions in worms in AO compared to worms in WO. Cd per unit protein in DE and MI fractions was twice as high as in MC and CY fractions in WO, whereas MC contained the highest Cd content followed by MI, DE and CY fractions in AO worms. Our results stress the importance of exposure route for the internal distribution and toxicity of Cd to deposit feeders such as Capitella sp. I. 相似文献
RésuménUne analyse tectonique du couloir faillé d’Arakapas est menée à partir de la mesure de plus de 3 000 plans striés relevés dans les formations ophiolitiques du Troodos et du Kellaki. Des mesures ont également été effectuées dans les formations du Crétacé terminal — Paléogène et du Néogène, afin de préciser l’âge des différents stades de la déformation. Elles ont été traitées par les méthodes des dièdres droits et du calcul du tenseur des contraintes. Il est montré que le couloir d’Arakapas a été le siège de plusieurs déformations successives. Au Néogène règne un régime en extension qui succède à un jeu décrochant dextre contemporain des compressions d’âge Crétacé terminal à Miocène. Un jeu décrochant antérieur peut-être mis en évidence. Il serait compatible avec le fonctionnement en faille transformante océanique proposé par divers auteurs. 相似文献
Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics. 相似文献
Volcanic flows of Late Paleozoic age in the Pelagonian zone belonging to the internal Hellenic zones, have been studied, for the first time, from petrographical and geochemical viewpoints.
Relevant petrographical data and the geochemical analysis lead us to consider that:
1. (a) the basic lavas can be linked to tholeitic basalts.
2. (b) the acid lavas are associated to metarhyolites.
3. (c) the two magmatic flows do not originate from the same parental magma.
The geochemical results obtained, compared to those from other deposits of nearly the same age outcropping around the Mediterranean, indicate that the latest Hercynian volcanism has been affected by intra-plate distension phenomena preceding the great Lower Mesozoic break-up which caused the formation of the Tethys Ocean.
It is remarkable that in the Mesogean Basin the sedimentary environment is nearly similar to that described in this paper. The volcanic flows end up in a sialic sedimentary basin containing coarse detritic formations that resulted from erosion of the Variscan chain along the southern margin of the European continent.
Abstract
Dans la zone pélagonienne appartenant aux zones internes helléniques, des coulées volcaniques d'âge paléozoïque supérieur sont étudiées, pour la première fois, pétrographiquement et géochimiquement. Les différents agencements pétrographiques et les analyses géochimiques nous apprennent que:
1. (a) les laves basiques peuvent être rattachées á la famille des basaltes tholéitiques.
2. (b) les laves acides s'apparentent aux métarhyolites.
La quantification des différents éléments analyses nous amène á considérer que les deux lignées magmatiques ne sont pas issues d'un même magma parental.
La comparaison des résultats géochimiques avec d'autres gisements, sensiblement contemporains affleurant autour de la Méditerranée actuelle, nous indique que le volcanisme fini-hercynien est assujetti á des phénomènes de distension intraplaques, préparatoires á la grande fracturation mésozoïque inférieure ayant donné naissance á l'océan téthysien.
Ce qui est remarquable dans le bassin mésogéen, c'est que l'environnement sédimentaire est toujours, á peu près, comparable á celui que nous décrivons ici. En effet, les coulées volcaniques s'épanchent dans un bassin sédimentaire á fond sialique au sein de formations détritiques grossières nées de la destruction de la chaîne varisque sur la bordure méridionale du continent europeen. 相似文献
The eastern part of the Western Cordillera of Ecuador includes fragments of an Early Cretaceous (≈123 Ma) oceanic plateau accreted around 85–80 Ma (San Juan–unit). West of this unit and in fault contact with it, another oceanic plateau sequence (Guaranda unit) is marked by the occurrence of picrites, ankaramites, basalts, dolerites and shallow level gabbros. A comparable unit is also exposed in northwestern coastal Ecuador (Pedernales unit).
Picrites have LREE-depleted patterns, high Ndi and very low Pb isotopic ratios, suggesting that they were derived from an extremely depleted source. In contrast, the ankaramites and Mg-rich basalts are LREE-enriched and have radiogenic Pb isotopic compositions similar to the Galápagos HIMU component; their Ndi are slightly lower than those of the picrites. Basalts, dolerites and gabbros differ from the picrites and ankaramites by flat rare earth element (REE) patterns and lower Nd; their Pb isotopic compositions are intermediate between those of the picrites and ankaramites. The ankaramites, Mg-rich basalts, and picrites differ from the lavas from the San Juan–Multitud Unit by higher Pb ratios and lower Ndi.
The Ecuadorian and Gorgona 88–86 Ma picrites are geochemically similar. The Ecuadorian ankaramites and Mg-rich basalts share with the 92–86 Ma Mg-rich basalts of the Caribbean–Colombian Oceanic Plateau (CCOP) similar trace element and Nd and Pb isotopic chemistry. This suggests that the Pedernales and Guaranda units belong to the Late Cretaceous CCOP. The geochemical diversity of the Guaranda and Pedernales rocks illustrates the heterogeneity of the CCOP plume source and suggests a multi-stage model for the emplacement of these rocks. Stratigraphic and geological relations strongly suggest that the Guaranda unit was accreted in the late Maastrichtian (≈68–65 Ma). 相似文献
下载免费PDF全文