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31.
Chiara Lesti Massimiliano Porreca Guido Giordano Massimo Mattei Raymond A. F. Cas Heather M. N. Wright Chris B. Folkes Josè Viramonte 《Bulletin of Volcanology》2011,73(10):1535-1565
Estimates of pyroclastic flow emplacement temperatures in the Cerro Galán ignimbrite and Toconquis Group ignimbrites were
determined using thermal remanent magnetization of lithic clasts embedded within the deposits. These ignimbrites belong to
the Cerro Galán volcanic system, one of the largest calderas in the world, in the Puna plateau, NW Argentina. Temperature
estimates for the 2.08-Ma Cerro Galán ignimbrite are retrieved from 40 sites in 14 localities (176 measured clasts), distributed
at different distances from the caldera and different stratigraphic heights. Additionally, temperature estimates were obtained
from 27 sample sites (125 measured clasts) from seven ignimbrite units forming the older Toconquis Group (5.60–4.51 Ma), mainly
outcropping along a type section at Rio Las Pitas, Vega Real Grande. The paleomagnetic data obtained by progressive thermal
demagnetization show that the clasts of the Cerro Galán ignimbrite have one single magnetic component, oriented close to the
expected geomagnetic field at the time of emplacement. Results show therefore that most of the clasts acquired a new magnetization
oriented parallel to the magnetic field at the moment of the ignimbrite deposition, suggesting that the clasts were heated
up to or above the highest blocking temperature (T
b) of the magnetic minerals (T
b = 580°C for magnetite; T
b = 600–630°C for hematite). We obtained similar emplacement temperature estimations for six out of the seven volcanic units
belonging to the Toconquis Group, with the exception of one unit (Lower Merihuaca), where we found two distinct magnetic components.
The estimation of emplacement temperatures in this latter case is constrained at 580–610°C, which are lower than the other
ignimbrites. These estimations are also in agreement with the lowest pre-eruptive magma temperatures calculated for the same
unit (i.e., 790°C; hornblende–plagioclase thermometer; Folkes et al. 2011b). We conclude that the Cerro Galán ignimbrite and Toconquis Group ignimbrites were emplaced at temperatures equal to or higher
than 620°C, except for Lower Merihuaca unit emplaced at lower temperatures. The homogeneity of high temperatures from proximal
to distal facies in the Cerro Galán ignimbrite provides constraints for the emplacement model, marked by a relatively low
eruption column, low levels of turbulence, air entrainment, surface–water interaction, and a high level of topographic confinement,
all ensuring minimal heat loss. 相似文献
32.
33.
34.
Counting only the hits? The risk of underestimating the costs of stringent climate policy 总被引:2,自引:2,他引:0
This paper warns against the risk of underestimating the costs—and the uncertainty about the costs—of achieving stringent stabilization targets. We argue that a straightforward review of integrated assessment models results produces biased estimates for the more ambitious climate objectives such as those compatible with the 2°C of the European Union and the G8. The magnitude and range of estimates are significantly reduced because only the most optimistic results are reported for such targets. We suggest a procedure that addresses this partiality. The results show highly variable costs for the most ambitious scenarios. 相似文献
35.
Thermohaline Anomalies in the Spring and Early Summer of 2000 in the Gulf of Trieste 总被引:1,自引:0,他引:1
Abstract. In the framework of the Interreg II Project (July 1998 - June 2001), hydro-logical, chemical and biological data were collected in the Gulf of Trieste.
During spring and summer 2000, some particular thermohaline anomalies were observed in the Gulf of Trieste. Especially in May and June the water body showed: a very strong thermohaline stratification, an increase of advective salt water coming from the south and the presence of sharp pycnoclines. In July the temperature was higher than usual in the whole water column. Moreover, in late May and in June, massive mucilaginous aggregates were observed along the water column and at the surface.
In order to highlight these particular thermohaline features the hydrological data of 16 stations were analysed (Fig. 1). Two stations, in particular, were considered: one offshore (St. AA1, average depth 20 m) and one close to the coast (St. C1, average depth 17 m). For these two stations a best-fit analysis, computed over 11 and 7 years, respectively, was performed on temperature, salinity and density excess data.
Moreover, the hydrological features were compared with the rainfall, air temperature, wind speed data (Istituto Sperimentale Talassografico di Trieste - ISTT) and the Isonzo River's flow rate (Direzione Regionale dell'Ambiente - Regione F. V. G.) collected from January 1998 to December 2000. 相似文献
During spring and summer 2000, some particular thermohaline anomalies were observed in the Gulf of Trieste. Especially in May and June the water body showed: a very strong thermohaline stratification, an increase of advective salt water coming from the south and the presence of sharp pycnoclines. In July the temperature was higher than usual in the whole water column. Moreover, in late May and in June, massive mucilaginous aggregates were observed along the water column and at the surface.
In order to highlight these particular thermohaline features the hydrological data of 16 stations were analysed (Fig. 1). Two stations, in particular, were considered: one offshore (St. AA1, average depth 20 m) and one close to the coast (St. C1, average depth 17 m). For these two stations a best-fit analysis, computed over 11 and 7 years, respectively, was performed on temperature, salinity and density excess data.
Moreover, the hydrological features were compared with the rainfall, air temperature, wind speed data (Istituto Sperimentale Talassografico di Trieste - ISTT) and the Isonzo River's flow rate (Direzione Regionale dell'Ambiente - Regione F. V. G.) collected from January 1998 to December 2000. 相似文献
36.
Massimo Chiaradia Dave Banks Robert Cliff Robert Marschik Antoine de Haller 《Mineralium Deposita》2006,41(6):565-573
The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raúl–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raúl–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raúl–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raúl–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits. 相似文献
37.
38.
Luca Bracchini Antonio Tognazzi Arduino Massimo Dattilo Franco Decembrini Claudio Rossi Steven Arthur Loiselle 《Aquatic Sciences - Research Across Boundaries》2010,72(4):485-498
In the past two decades, optical properties of chromophoric dissolved organic matter (CDOM) in marine environments have been
extensively studied. Many of these studies report CDOM properties for the offshore environment where this complex mixture
of optically active compounds is strongly diluted. Nevertheless, autochthonous and allochthonous sources have been identified
and sinks related to photodegradation and bacterial activity have been demonstrated. The calculation of the spectral slope
of the CDOM absorption curve has been proven to be useful and is often reported. However, a rigorous uncertainty analysis
of the slope calculation is rarely reported. In this paper, we propose a method to evaluate the uncertainty of CDOM spectral
slope calculated between 270 and 400 nm, using both naturally sampled and artificial solutions. We use these results to study
the ultra-oligotrophic waters of the Mediterranean Sea (central eastern basin), where little is known about CDOM spatial distribution.
We show that dilutions of both artificial and natural samples produce a Gaussian distribution of spectral slopes, indicating
that consistent values may be determined, with a typical uncertainty of ±0.0004 nm−1 when absorption at 300 nm was greater then 0.1 m−1 (0.1 m pathlength). Comparing the distribution of spectral slopes from central eastern basin samples to a Gaussian distribution,
we show differences between measurements that were significantly different. These values allow us to distinguish possible
sources (algal derived CDOM), sinks (e.g. photo-bleaching) at different depths. We propose a subdivision of CDOM compounds
into refractory and semilabile/refractory pools and evaluate the CDOM spectral slope of algal derived CDOM released at or
near deep chlorophyll maximum. 相似文献
39.
Maren Kahl Sumit Chakraborty Fidel Costa Massimo Pompilio Marco Liuzzo Marco Viccaro 《Bulletin of Volcanology》2013,75(2):1-14
One of the major objectives of volcanology remains relating variations in surface monitoring signals to the magmatic processes at depth that cause these variations. We present a method that enables compositional and temporal information stored in zoning of minerals (olivine in this case) to be linked to observations of real-time degassing data. The integrated record may reveal details of the dynamics of gradual evolution of a plumbing system during eruption. We illustrate our approach using the 2006 summit eruptive episodes of Mt. Etna. We find that the history tracked by olivine crystals, and hence, most likely the magma pathways within the shallow plumbing system of Mt. Etna, differed considerably between the July and October eruptions. The compositional and temporal record preserved in the olivine zoning patterns reveal two mafic recharge events within months of each other (June and September 2006), and each of these magma supplies may have triggered the initiation of different eruptive cycles (July 14–24 and August 31–December 14). Correlation of these observations with gas monitoring data shows that the systematic rise of the CO2/SO2 gas values is associated with the gradual (pre- and syn-eruptive) supply of batches of gas-rich mafic magma into segments of Etna’s shallow plumbing system, where mixing with pre-existing and more evolved magma occurred. 相似文献
40.
Francesco Di Benedetto Daniele Borrini Andrea Caneschi Gabriele Fornaciai Massimo Innocenti Alessandro Lavacchi Carlo Andrea Massa Giordano Montegrossi Werner Oberhauser Luca A. Pardi Maurizio Romanelli 《Physics and Chemistry of Minerals》2011,38(6):483-490
An extensive characterisation of the magnetic properties of synthetic powders of kuramite, with formal composition Cu3SnS4, was performed. Powders were investigated through superconducting quantum interference device (SQUID) magnetometry, electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM) and microanalysis. SEM and TEM reveal the presence of nanodimensioned particles. XRPD clearly shows that Cu3SnS4 crystallised in a cubic sphalerite-type structural model, in spite of the stannite-type tetragonal structure described for the natural phase. This difference arises from a full random distribution of cations. Synthetic kuramite nanopowders exhibit a marked paramagnetism, originated by the presence of Cu(II), definitely assessed by EPR measurements. Moreover, the overall magnetic behaviour of the sample cannot be simply ascribed to diluted paramagnetism, and this suggests the presence of strong superexchange interactions among Cu(II) ions even at room temperature. The main consequences of these results are the definitive assessment of the chemical formula Cu(I)2Cu(II)SnS4 and of a random distribution of Cu(II), Cu(I) and Sn(IV) ions within the available tetrahedral sites. 相似文献