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831.
Carolina?P.?N.?MoretoEmail author Lena?V.?S.?Monteiro Roberto?P.?Xavier Robert?A.?Creaser S.?Andrew?DuFrane Gustavo?H.?C.?Melo Marco?A.?Delinardo da Silva Colombo?C.?G.?Tassinari Kei?Sato 《Mineralium Deposita》2015,50(5):517-546
The Southern Copper Belt, Carajás Province, Brazil, hosts several iron oxide–copper–gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U–Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW–ESE shear zones. They encompass Mesoarchean (3.08–2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite–scapolite, biotite–scapolite–tourmaline–magnetite alteration, and proximal potassium feldspar, chlorite–epidote and chalcopyrite formation. U–Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re–Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72–2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90–1.88-Ga ore formation in the Sossego–Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajás Basin formation, the main episode of IOCG genesis (2.72–2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarapé Bahia–Alemão deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajás Province with a single extensive hydrothermal system is precluded. 相似文献
832.
833.
Roberto Patuelli Aura Reggiani Peter Nijkamp Norbert Schanne 《Journal of Geographical Systems》2011,13(1):67-85
In this paper, we present a review of various computational experiments concerning neural network (NN) models developed for regional employment forecasting. NNs are nowadays widely used in several fields because of their flexible specification structure. A series of NN experiments is presented in the paper, using two data sets on German NUTS-3 districts. Individual forecasts are computed by our models for each district in order to answer the following question: How relevant are NN parameters in comparison to NN structure? Comprehensive testing of these parameters is limited in the literature. Building on different specifications of NN models—in terms of explanatory variables and NN structures—we propose a systematic choice of NN learning parameters and internal functions by means of a sensitivity analysis. Our results show that different combinations of NN parameters provide significantly varying statistical performance and forecasting power. Finally, we note that the sets of parameters chosen for a given model specification cannot be light-heartedly applied to different or more complex models. 相似文献
834.
Dino Bindi Lucia Luzi Francesca Pacor Roberto Paolucci 《Bulletin of Earthquake Engineering》2011,9(6):1921-1939
In this work, we analyze the records of the Italian strong motion database (ITACA,
) with the aim of identifying stations affected by site effects that are not captured by standard seismic classification schemes.
In particular, we consider four different site classifications, two of them based on geological/geophysical characteristics
and two driven by data. For each classification we develop a ground motion prediction equation using a random effect approach
to isolate the between-station and within-station distribution of errors. The site coefficients obtained for the different
classes confirm that site amplification effects are significant for both the horizontal and vertical components. The between-station
error normalized to the standard deviation of the between-station error distribution is then used to identify stations characterized
by large errors, attributable to site effects not accounted for by the classification schemes. The results show that large
errors can affect the predictions when the site effects are not uniquely related to the reduction of the seismic impedance
in the uppermost layers. For example, amplifications of ground motion over the long period range are observed for stations
installed within alluvial closed-shape basins, as consequence of locally generated surface waves. For these stations, classifications
based on the horizontal to vertical response spectra ratio are not reliable, since amplifications are also affecting the vertical
component. Another interesting feature which emerges from the analysis is the significant de-amplification of short period
spectral ordinates that seems to be related to stations typically set in at the foundation level of massive structures. To
increase the usefulness of the data set, the most important distinctive features of the strong motion stations are documented
in the ITACA database reports containing the instrument information and the available geological-geotechnical data. 相似文献
835.
Antonio Olita Roberto Sorgente Alberto Ribotti Leopoldo Fazioli Angelo Perilli 《Ocean Dynamics》2011,61(7):1005-1016
In this work, we make use of satellite estimates of chlorophyll a, photosynthetically active radiation and sea surface temperatures, to compute regional estimates of primary production integrated throughout the euphotic layer for the Algero-Provençal Basin, by means of a modified version of the vertically generalized production model. The seasonal and interannual variability of the primary production has been analysed over the decade 1997–2007. Empirical orthogonal functions analysis has been applied to decompose the variability of the primary production dataset in orthogonal modes of variability. The seasonal signal is distributed between the two first modes of variability, temporally shifted each other and respectively related to the northern (early spring) and the southern (winter) part of the basin. We found a minimum of the annual production in 2003, when a summer heatwave strongly enhanced the stratification of surface waters, further limiting the injection of nutrients into the surface layers. Maxima in the annual series are found in 1999 and 2005, due to two particularly intense and extended (in space) spring-blooms in the northern part of the basin. These two maxima, clearly identified in space and time by EOF analysis (EOF1 and EOF3), are related to strong mistral-wind interannual events occurring during winters of 1999 and 2005, preceding the blooms by some few months. We found that these production maxima are due both to a more intense production in the usual blooming area (shown by EOF1–PC1) as well as to an exceptional local production in the eastern side of the basin, off the Corsica western coasts (EOF3–PC3). Previous observations of exceptional deep-water formation events in 1999 and 2005, with easterly spots close to the primary production-observed anomalies, and the meridional character of the mistral 1999 and 2005 peaks both support the idea that such eastern PP interannual maxima would be actually due to exceptional production more than to an easterly advection of biomass from the usual bloom area. Finally, the potential link of the observed features with large-scale atmospheric forcing is discussed, and a potential relation of such interannual events with the East Atlantic pattern is drawn. 相似文献
836.
Pedro Filipe de Oliveira Cordeiro José Affonso Brod Matheus Palmieri Claudinei Gouveia de Oliveira Elisa Soares Rocha Barbosa Roberto Ventura Santos José Carlos Gaspar Luis Carlos Assis 《Ore Geology Reviews》2011,41(1):112-121
The Catalão I alkaline–carbonatite–phoscorite complex contains both fresh rock and residual (weathering-related) niobium mineralization. The fresh rock niobium deposit consists of two plug-shaped orebodies named Mine II and East Area, respectively emplaced in carbonatite and phlogopitite. Together, these orebodies contain 29 Mt at 1.22 wt.% Nb2O5 (measured and indicated). In closer detail, the orebodies consist of dike swarms of pyrochlore-bearing, olivine-free phoscorite-series rocks (nelsonite) that can be either apatite-rich (P2 unit) or magnetite-rich (P3 unit). Dolomite carbonatite (DC) is intimately related with nelsonite. Natropyrochlore and calciopyrochlore are the most abundant niobium phases in the fresh rock deposit. Pyrochlore supergroup chemistry shows a compositional trend from Ca–Na dominant pyrochlores toward Ba-enriched kenopyrochlore in fresh rock and the dominance of Ba-rich kenopyrochlore in the residual deposit. Carbonates associated with Ba-, Sr-enriched pyrochlore show higher δ18OSMOW than expected for carbonates crystallizing from mantle-derived magmas. We interpret both the δ18OSMOW and pyrochlore chemistry variations from the original composition as evidence of interaction with low-temperature fluids which, albeit not responsible for the mineralization, modified its magmatic isotopic features. The origin of the Catalão I niobium deposit is related to carbonatite magmatism but the process that generated such niobium-rich rocks is still undetermined and might be related to crystal accumulation and/or emplacement of a phosphate–iron-oxide magma. 相似文献
837.
Roberto Sommariva Tim S. Bates Daniel Bon Daniel M. Brookes Joost A. de Gouw Jessica B. Gilman Scott C. Herndon William C. Kuster Brian M. Lerner Paul S. Monks Hans D. Osthoff Alex E. Parker James M. Roberts Sara C. Tucker Carsten Warneke Eric J. Williams Mark S. Zahniser Steven S. Brown 《Journal of Atmospheric Chemistry》2011,68(4):331-362
Measurements of total peroxy radicals (HO2?+?RO2) and nitrate radical (NO3) were made on the NOAA research vessel R/V?Brown along the U.S. Gulf Coast during the TexAQS 2006 field campaign. The measurements were modelled using a constrained box-model based upon the Master Chemical Mechanism (MCM). The agreement between modelled and measured HO2?+?RO2 was typically within ??40% and, in the unpolluted regions, within 30%. The analysis of the model results suggests that the MCM might underestimate the concentrations of some acyl peroxy radicals and other small peroxy radicals. The model underestimated the measurements of NO3 by 60?C70%, possibly because of rapid heterogeneous uptake of N2O5. The MCM model results were used to estimate the composition of the peroxy radical pool and to quantify the role of DMS, isoprene and alkenes in the formation of RO2 in the different regions. The measurements of HO2?+?RO2 and NO3 were also used to calculate the gas-phase budget of NO3 and quantify the importance of organic peroxy radicals as NO3 sinks. RO2 accounted, on average, for 12?C28% of the total gas-phase NO3 losses in the unpolluted regions and for 1?C2% of the total gas-phase NO3 losses in the polluted regions. 相似文献
838.
Antonella Bertagnini Alessio Di Roberto Massimo Pompilio 《Bulletin of Volcanology》2011,73(9):1229-1243
The persistent normal activity of Stromboli is occasionally interrupted by sudden and highly energetic explosive events called
Strombolian paroxysms. These phenomena together with landslide-generated tsunamis represent the most hazardous manifestations
of present-day volcanic activity at Stromboli. The most recent paroxysms, on 5 April 2003 and 15 March 2007, have drawn attention
to these energetic events because they significantly threatened inhabitants and tourists. Historical accounts and field evidence
indicate, however, that even larger paroxysms, in terms of volume, dispersal of products and intensity of explosive phenomena,
occurred in the recent past. During these paroxysms incipiently welded spatter deposits mantled the north and south rims of
the Sciara del Fuoco down to low elevations, extending much farther than the similar deposits from recent observed events
(5 April 2003 and 15 March 2007). In order to identify, characterize and discriminate among products of these outstanding
spatter-forming eruptions, more than 50 stratigraphic sections were measured and sampled. Stratigraphic, sedimentological
and radiometric (14C) data indicate that only two paroxysms produced spatter that reached very low elevations and inhabited areas: the first
occurred in the 16th century and the last in AD 1930. Analysis of texture and deposit components reveals that the early phases
of the two eruptions were driven by distinctly different eruptive dynamics. Both identified paroxysms are at least one order
of magnitude greater than any similar event observed by monitoring systems at Stromboli. These two large paroxysms were the
most powerful volcanic events at Stromboli in the last eighteen centuries. 相似文献
839.
Roberto E. San Juan-Farfán Lkhamsuren Bayarjargal Björn Winkler Eiken Haussühl Miguel Avalos-Borja Keith Refson Victor Milman 《Physics and Chemistry of Minerals》2011,38(9):693-700
We have measured the pressure-induced change in the lattice dynamics of diaspore, α-AlO(OH), by in situ Raman spectroscopy
up to 25 GPa. The spectra are evaluated by density functional perturbation theory-based atomistic model calculations. The
assignment of calculated to experimentally observed Raman bands is based on the calculation of Raman intensities. We discuss
the accuracy of the approach employed for these calculations and explain the relative magnitudes of mode Grüneisen parameters. 相似文献
840.
This work discusses the synsedimentary structural control affecting the turbidites of the Marnoso-arenacea Formation (MAF) deposited in an elongate, NW-stretched foredeep basin formed in front of the growing Northern Apennines orogenic wedge. The stratigraphic succession of the MAF (about 4000 m thick) records the progressive closure of the Apennine foredeep basin due to the NE propagation of thrust fronts. In this setting, Langhian to Serravallian turbidites are overlain by Tortonian mixed turbidite deposits, i.e. sandstone-rich low-efficiency turbidites. The high-resolution stratigraphic framework of basin-plain turbidites has made it possible to identify five informal stratigraphic units (I, II, III, IV, V) mainly on the basis of the structural control highlighted by: 1) the presence of topographic highs and relative depocentres detected through a progressive flattening approach, and 2) the presence of thrust-related mass-transport complexes and the progressive appearance and disappearance of five bed types (Types 1, 2, 3, 4, 5) considered important to understand the interaction between flow efficiency and basin morphology. By contrast, the upper part of the MAF succession (Tortonian in age) is formed by more sandstone-rich systems characterized by beds whose origin is likely to depend, at least in part, upon flow decelerations related to topographic confinement due to the progressive closure of the foredeep. The vertical and lateral distribution of these types of beds is, therefore, useful for the reconstruction of the morphological evolution of structurally controlled basins; in the MAF example, this is mainly due to the progressive narrowing of the foredeep caused by the propagation of the main thrust fronts toward the foreland. 相似文献