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The Brown Leucitic Tuff (BLT) is a poorly to strongly lithified compositionally zoned pyroclastic-flow deposit with a minimum volume of 3 to 5 km3. It erupted from Roccamonfina Volcano about 385000 years ago, after formation of the summit caldera. Individual flow units are grouped into three facies (white, brown, and orange) which primarily differ in pumice color, lithic content, and matrix cementation. Pumices from the BLT range from phonolitic leucite-tephrites to leucite-trachytes (7.0 to 2.2 wt% CaO), covering over half of the total spectrum of High-K Series magmas known from Roman Region volcanoes. White-facies units dominate in lower stratigraphic levels and their pumices have the lowest CaO contents, indicating a general trend toward more basic compositions as the eruption evolved. At higher stratigraphic levels, however, orange- and brown-facies units are interbedded with other whitefacies units, indicating reversals in the dominant compositional progression.BLT pumices have crystal contents of 9.9 to 0.6 vol%, with green salite>plagioclase>sanidine>biotite>titanomagnetite>analcime (after leucite)>apatite>pyrrhotite. In most samples, plagioclase (An85–95) and sanidine (Or75–90) have much lower Na2O contents than usually found in coexisting feldspars, yet these are interpreted as equilibrium pairs. Primary leucite has been almost completely replaced by analcime. All samples also contain xenocrysts of colorless diopside and forsteritic olivine (Fo83–92). Recurrent alternations from colorless diopside to green salite are present in single clinopyroxene crystals and appear to reflect a complex history of magma mixing.Whole-rock BLT pumice compositions conform closely to High-K Series lavas from Roccamonfina for all elements except Na2O and K2O. The former is relatively enriched and the latter relatively depleted in mafic BLT pumices with >5.6% CaO; these differences reflect strong analcimization of abundant groundmass leucite crystals in these pumices. Otherwise, major and trace element data support fractionation of observed minerals in generating the compositional diversity among BLT pumices. Mineral assemblages and compositions of cumulate monzonite and syenite nodules carried to the surface during the BLT eruption correspond closely to the fractionated phases predicted by least-squares modeling. 相似文献
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The San Clemente cold seep lies within 100–200 km of other reducing habitats in the NE Pacific, offering an opportunity to compare diversity and species overlap among reducing habitats (i.e. whale‐, kelp‐, and wood‐falls) at similar depths within a single region. Video observations from the research submersible Alvin at the San Clemente seep (1800 m depth) indicated clumps (‘thickets’) of vestimentiferans distributed as meter‐scale patches interspersed with vesicomyid clam beds and black sediments. Sediment‐core samples were collected at distances of 0 to 80–200 m along randomly oriented transects radiating outward from vestimentiferan thickets to evaluate changes in macrofaunal community structure from thickets into the background community. Macrofaunal abundance was elevated at distances of 0–1 m compared to 80–200 m (i.e. the ‘background’ community). The tube‐building frenulate worms Siboglinum spp., along with peracarid crustaceans, dominated sediments within 1 m of vestimentiferan thickets. Species diversity was depressed within 1 m of thickets but with high rates of species accumulation, suggesting that seep sites greatly increase sediment heterogeneity and facilitate colonization by non‐background macrofaunal species. Stable isotope data indicate chemosynthetic nutrition for some dominant macrofaunal species within 1 m of tubeworm thickets. The macrofaunal community near vestimentiferan thickets in San Clemente seep contains intermediate levels of species richness and diversity compared to other deep‐sea seep areas in the northeast Pacific. There was low species overlap between the San Clemente seep macrofauna and communities in reducing habitats near wood‐, whale‐, and kelp‐falls at similar depths within the region, suggesting that seeps harbor a distinct infaunal community. 相似文献
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Fernando?Henrique?Bucco?TallaricoEmail author Neal?Jesse?McNaughton David?Ian?Groves Ian?R.?Fletcher Bernardino?Ribeiro?Figueiredo Jéssica?Beatriz?Carvalho José?Luzimar?Rego Alfredo?Rossetto?Nunes 《Mineralium Deposita》2004,39(1):68-86
The Breves deposit in the Carajás Copper-Gold Belt, Brazil, a member of the Cu-Au-(W-Bi-Sn) group of deposits, contains about 50 Mt of 1.22% Cu, 0.75 g/t Au, 2.4 g/t Ag, 1,200 g/t W, 70 g/t Sn, 175 g/t Mo and 75 g/t Bi. It is hosted by sandstones and siltstones of the Águas Claras Formation (minimum age of 2,681±5 Ma) in the roof zone of a complex, highly altered granite intrusion. The mineralisation is disseminated in a greisenized zone, resulting from alteration of probable monzogranites and syenogranites. The ore-bearing greisen contains abundant xenomorphic quartz in association with Fe-chlorite and muscovite. The gangue assemblage also includes fluorite, tourmaline, and minor amounts of monazite, xenotime, chlorapatite, thorite, zircon, calcite, siderite and bastnäesite. Copper mineralisation is dominated by chalcopyrite associated with pyrite, arsenopyrite, pyrrhotite and molybdenite. Gold particles, in equilibrium with native bismuth, are common as inclusions in chalcopyrite. The greisen contains sub-economic concentrations of tungsten and niobium that are related to the presence of ferberite, qitianlingite and Nb-rutile. SHRIMP II zircon dating of the host granites gives 207Pb/206Pb ages of 1,878±8 and 1,880±9 Ma for two phases, and a combined age of 1,879±6 Ma. SHRIMP II dating of monazite and xenotime grains in late- to post-mineralisation veins gives a combined 207Pb/206Pb age of 1,872±7 Ma, indistinguishable from the ages of the granites. This provides a genetic connection between the Breves deposit and the ca. 1.88 Ga A-type granite magmatism that typifies the Carajás Belt as part of a much larger, intracratonic magmatic province that extends over much of the Amazonian Craton. The recognition of this association has exploration implications, not only for the geophysical signature of the granite roof zones, but also for likely geochemical dispersion around the deposits of this type.Editorial handling: G. Beaudoin 相似文献
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E.?Di?Bernardino F.?Palacios-RodríguezEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(10):2675-2689
The classic univariate risk measure in environmental sciences is the Return Period (RP). The RP is traditionally defined as “the average time elapsing between two successive realizations of a prescribed event”. The notion of design quantile related with RP is also of great importance. The design quantile represents the “value of the variable(s) characterizing the event associated with a given RP”. Since an individual risk may strongly be affected by the degree of dependence amongst all risks, the need for the provision of multivariate design quantiles has gained ground. In contrast to the univariate case, the design quantile definition in the multivariate setting presents certain difficulties. In particular, Salvadori, G., De Michele, C. and Durante F. define in the paper called “On the return period and design in a multivariate framework” (Hydrol Earth Syst Sci 15:3293–3305, 2011) the design realization as the vector that maximizes a weight function given that the risk vector belongs to a given critical layer of its joint multivariate distribution function. In this paper, we provide the explicit expression of the aforementioned multivariate risk measure in the Archimedean copula setting. Furthermore, this measure is estimated by using Extreme Value Theory techniques and the asymptotic normality of the proposed estimator is studied. The performance of our estimator is evaluated on simulated data. We conclude with an application on a real hydrological data-set. 相似文献
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Within a large collection of lavas from the Roccamonfina volcano are rocks which represent the most mafic samples yet recorded from Roccamonfina and which are amongst the least differentiated lavas found in the Roman co-magmatic region as a whole. These rocks extend both high-K and low-K series to more primitive values. However, petrographic and geochemical considerations rule out a primary origin, and even these mafic samples appear to record the effects of repeated episodes of fractional crystallization and hybridization. Relatively potassic samples from the low-K series are apparently transitional between low-K and high-K series, as previously delineated. However, these intermediate-K samples are not transitional in their Sr isotopic composition, suggesting that there is no continuum between low-K and high-K magma source regions. Rather, the compositional range within the low-K series appears predominantly to reflect variation in the degree of melting of a common mantle source. Analysis of the low-K series data, using an inverse method suggests a source containing amphibole and garnet, and indicates that these phases were consumed during the melting processes responsible for the low-K series magmas. The role of amphibole is further indicated by the association of low K2O with elevated Rb concentration and, for example, higher Ce/Yb. Such variations are taken to reflect the consumption of high K/Rb amphibole during the initial phase of partial melting. 相似文献
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Di Bernardino Annalisa Iannarelli Anna Maria Diémoz Henri Casadio Stefano Cacciani Marco Siani Anna Maria 《Theoretical and Applied Climatology》2022,147(1-2):291-305
Theoretical and Applied Climatology - The extreme temperature events are a concern in recent years due to climate variability particularly in India as there is an increase in the temperature... 相似文献