Major types and time–space distribution of Mesozoic ore deposits in South China and their geodynamic settings     

Mao Jingwen  Cheng Yanbo  Chen Maohong  Franco Pirajno 《Mineralium Deposita》2013,48(3):267-294

The ore deposits of the Mesozoic age in South China can be divided into three groups, each with different metal associations and spatial distributions and each related to major magmatic events. The first event occurred in the Late Triassic (230–210 Ma), the second in the Mid–Late Jurassic (170–150 Ma), and the third in the Early–Mid Cretaceous (120–80 Ma). The Late Triassic magmatic event and associated mineralization is characterized by peraluminous granite-related W–Sn–Nb–Ta mineral deposits. The Triassic ore deposits are considerably disturbed or overprinted by the later Jurassic and Cretaceous tectono-thermal episodes. The Mid–Late Jurassic magmatic and mineralization events consist of 170–160 Ma porphyry–skarn Cu and Pb–Zn–Ag vein deposits associated with I-type granites and 160–150 Ma metaluminous granite-related polymetallic W–Sn deposits. The Late Jurassic metaluminous granite-related W–Sn deposits occur in a NE-trending cluster in the interior of South China, such as in the Nanling area. In the Early–Mid Cretaceous, from about 120 to 80 Ma, but peaking at 100–90 Ma, subvolcanic-related Fe deposits developed and I-type calc-alkaline granitic intrusions formed porphyry Cu–Mo and porphyry-epithermal Cu–Au–Ag mineral systems, whereas S-type peraluminous and/or metaluminous granitic intrusions formed polymetallic Sn deposits. These Cretaceous mineral deposits cluster in distinct areas and are controlled by pull-apart basins along the South China continental margin. Based on mineral assemblage, age, and space–time distribution of these mineral systems, integrated with regional geological data and field observations, we suggest that the three magmatic–mineralization episodes are the result of distinct geodynamic regimes. The Triassic peraluminous granites and associated W–Sn–Nb–Ta mineralization formed during post-collisional processes involving the South China Block, the North China Craton, and the Indo-China Block, mostly along the Dabie-Sulu and Songma sutures. Jurassic events were initially related to the shallow oblique subduction of the Izanagi plate beneath the Eurasian continent at about 175 Ma, but I-type granitoids with porphyry Cu and vein-type Pb–Zn–Ag deposits only began to form as a result of the breakup of the subducted plate at 170–160 Ma, along the NNE-trending Qinzhou-Hangzhou belt (also referred to as Qin-Hang or Shi-Hang belt), which is the Neoproterozoic suture that amalgamates the Yangtze Craton and Cathaysia Block. A large subduction slab window is assumed to have formed in the Nanling and adjacent areas in the interior of South China, triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic W–Sn mineralization. A relatively tectonically quiet period followed between 150 and 135 Ma in South China. From 135 Ma onward, the angle of convergence of the Izanagi plate changed from oblique to parallel to the coastline, resulting in continental extensional tectonics and reactivation of regional-scale NE-trending faults, such as the Tan-Lu fault. This widespread extension also promoted the development of NE-trending pull-apart basins and metamorphic core complexes, accompanied by volcanism and the formation of epithermal Cu–Au deposits, granite-related polymetallic Sn–(W) deposits and hydrothermal U deposits between 120 and 80 Ma (with a peak activity at 100–90 Ma).  相似文献   

Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)     

Jacopo Cabassi  Franco Tassi  Orlando Vaselli  Jens Fiebig  Matteo Nocentini  Francesco Capecchiacci  Dmitri Rouwet  Gabriele Bicocchi 《Bulletin of Volcanology》2013,75(1):1-19

This paper focuses on the chemical and isotopic features of dissolved gases (CH₄ and CO₂) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH₄ and CO₂. The δ¹³C-CH₄ and δD-CH₄ values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH₄ is mainly produced by microbial activity. The δ¹³C-CO₂ values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO₂ contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO₂ source feeding the regional thermal and cold CO₂-rich fluid emissions. In contrast, the relatively low δ¹³C-CO₂ values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO₂. Chemical and isotopic compositions of dissolved CO₂ and CH₄ at different depths are mainly depending on (1) CO₂ inputs from external sources (hydrothermal and/or anthropogenic); (2) CO₂–CH₄ isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO₂ and CH₄ concentrations. In the hypolimnion, where the δ¹³C-CO₂ values progressively increase with depth and the δ¹³C-CH₄ values show an opposite trend, biogenic CO₂ production from CH₄ using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ¹³C-CO₂ values, and measured δ¹³C_TDIC values are not consistent, indicating that CO₂ and the main carbon-bearing ion species (HCO₃ ^?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO₂ and CH₄. This study demonstrates that the vertical patterns of the CO₂/CH₄ ratio and of δ¹³C-CO₂ and δ¹³C-CH₄ are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO₂ input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.  相似文献   

Multilayer simulations for accurate geological interpretations of SHARAD radargrams     

M.G. Spagnuolo  F. Grings  P. Perna  M. Franco  H. Karszenbaum  V.A. Ramos 《Planetary and Space Science》2011,59(11-12):1222-1230

SHARAD (SHAllow RADar) is a nadir-looking Synthetic Aperture Ground Penetrating Radar on board NASA's 2005 Mars Reconnaissance Orbiter. There are three main characteristics that define the performance of this instrument: ground penetration (due to the operational frequency, the observed echoes can be related to reflections from surface or subsurface), spaceborne operation (the first reflection does not necessarily correspond to the nadir reflection), and nadir looking SAR (there will always be left/right ambiguities). All this implies that there will be surface/subsurface range ambiguity and the geological interpretation of the radargrams cannot be straightforward. In order to avoid data misinterpretation, a simulator of SHARAD’s expected response for a given observation geometry and topography is needed. Simulations can take into account all surface/subsurface reflections in order to identify common families of ambiguities and facilitate the interpretation. In this work we present SHARSIM (SHARAD Radargram SIMulator), a software tool designed to simulate SHARAD radargrams taking as inputs Mars surface information and hypothetical subsurface structure. Its performance is analyzed by investigating typical artifacts and by a direct comparison with real radargrams. We show that SHARSIM simulations can help to discern between artifacts and real subsurface features in order to make accurate geological interpretations.  相似文献   

Characterization of the atmosphere above a site for millimeter wave astronomy     

Francesco Tony Nasir  Franco Buffa  Gian Luigi Deiana 《Experimental Astronomy》2011,29(3):207-225

The Sardinia Radio Telescope (SRT) is a challeging scientific project managed by the National Institute for Astrophysics (INAF), it is being developed at 30 km North of the city of Cagliari, Italy. The goal of the SRT project is to build a general purpose, fully steerable, 64 m diameter radio telescope, capable of operating with high efficiency in the centimeter and millimeter frequency range (0.3–100 GHz). In portions of this frequency range, especially towards the high end, astronomical observations can be heavily deteriorated by non-optimal atmospheric conditions, especially by water vapor content. The water molecule permanent electric dipole in fact, leads to pressure broadened rotational transitions around the 22.23 GHz spectral line. Furthermore, water vapor’s continuum absorption and emission may influence higher frequency observations too. To a lower degree, cloud liquid black body radiation can also affect centimeter and millimeter observations. In addition to this, inhomogeneities in water vapor distributions can cause signal phase errors which introduce a great amount of uncertainty to VLBI mode observations. The Astronomical Observatory of Cagliari (OA-CA) has obtained historical timeseries of radiosonde profiles conducted at the airport of Cagliari. Through the radiosonde measurements and an appropriate radiative transfer model, we have performed a statistical analysis of the SRT site’s atmosphere which accounts for atmospheric opacity at different frequencies, integrated water vapor (IWV), integrated liquid water (ILW) and cloud cover distributions during the year. This will help to investigate in which period of the year astronomical observations at different frequencies should be performed preferably. The results show that, at the SRT site, K-band astronomical observations are possible all year round, the median opacity at 22.23 GHz is 0.10 Np in the winter (Dec-Jan-Feb) and 0.16 Np in the summer (Jun-Jul-Aug). Integrated water vapor during winter months ranges, on average, between 7 and 15 mm. Cloud cover is usually not present for more than 36% of the time during the year. The atmospheric opacity study indicates that observations at higher frequencies (50–100 GHz) may be performed usefully: the median opacity at 100 GHz is usually below or equal to 0.2 Np in the period that ranges from January to April.  相似文献   

Chemical Reduction of Hexavalent Chromium Present in Contaminated Soil using a Packed-bed Column Reactor     

Débora V. Franco  Leonardo M. Da Silva  Wilson F. Jardim 《洁净——土壤、空气、水》2009,37(11):858-865

Soil samples extracted from a contaminated landfill with hexavalent chromium, Cr(VI), were treated in a packed-bed column reactor applying different reductant solutions under controlled flow conditions. In all cases, the kinetic study concerning removal of Cr(VI) from packed soil revealed the overall process (leaching and redox reaction) is described by pseudo-first order kinetics. The complexity of the process taking place in non-isotropic medium (packed soil) was evidenced by dependence of the overall pseudo-first order kinetic rate constant, k*, on treatment time, volumetric flow rate, and composition and concentration of the reductant solution. A phenomenological equation was proposed in order to represent k* in non-ideal conditions. The comparative study concerning the use of different reductants revealed application of ferrous sulphate, Fe(II), under flow conditions furnished the best results, since in this case the redox process reached a considerable extent and the reduced chromium, Cr(III), was immobilized in packed soil as an insoluble mixed compound.  相似文献   

Pier scour monitoring system by bed-level image tracking     

Wen-Yi CHANG  Jihn-Sung LAI  Teng-Yi YU  Franco LIN  Lung-Cheng LEE  Whey-Fone TSAI  Chin-Hsiung LOH 《国际泥沙研究》2014,29(2):269-277

A scour monitoring system with a micro camera tracking the bed-level images is proposed in this study.Two image recognition algorithms have been developed to support the bed-level image tracking approach.Through the laboratory experiments of pier scour,this study demonstrates that the proposed system is able to accurately monitor the scour-depth evolution in real time.In addition,five commonly-used temporal scour models are employed to simulate scour-depth evolution and their results are compared with monitoring data.In general,the results indicate that the proposed scour monitoring system has the potential for further applications in the field.  相似文献   

Erratum to: Second California Assessment: integrated climate change impacts assessment of natural and managed systems. Guest editorial     

Guido Franco  Daniel R. Cayan  Susanne Moser  Michael Hanemann  Myoung-Ae Jones 《Climatic change》2012,113(3-4):1099-1100

  相似文献   

Evolution of fluid geochemistry at the Turrialba volcano (Costa Rica) from 1998 to 2008   总被引：3，自引：1，他引：2  

O. Vaselli  Franco Tassi  E. Duarte  E. Fernandez  R. J. Poreda  A. Delgado Huertas 《Bulletin of Volcanology》2010,72(4):397-410

Turrialba (10°02′N, 83°45′W) is a 3,349-m high stratovolcano belonging to the Holocene “Cordillera Central” volcanic belt of Costa Rica. The summit consists of three EW-oriented craters (East, Central, and West). Since its last eruptive phase (1864–1866), the Central and West craters have displayed modest fumarolic activity, with outlet temperatures clustering around 90°C. In 2001, seismic swarms, ground deformation, and increasing fumarolic activity occurred. From 2005 to 2008, new fumarolic vents opened between and within the Central and West craters, and along the western and southwestern outer flanks of the volcanic edifice. These physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages: (1) hydrothermal (from 1998 to autumn 2001), characterized by the presence of H₂O, CO₂, H₂S, and, to a very minor extent, HCl and HF; (2) hydrothermal/magmatic (autumn 2001–2007), with the appearance of SO₂ and a significant increase of HCl and HF; and (3) magmatic-dominated (2007–2008), characterized by increased SO₂ content, SO₂/H₂S > 100, and temperatures up to 282°C. Accordingly, gas equilibrium in the CO₂-CH₄-H₂ system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions. The chemical–physical modifications of Turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems. Nevertheless, the risk of rejuvenation of the volcanic activity cannot be excluded, and an appropriate seismic, ground deformation, and geochemical monitoring program is highly recommended. Turrialba lies at a distance of 35 and 15 km from San José and Cartago, respectively, the two largest cities in Costa Rica.  相似文献   

Biochemical and microbial features of shallow marine sediments along the Terra Nova Bay (Ross Sea,Antarctica)   总被引：1，自引：0，他引：1  

Franco Baldi  Davide Marchetto  Francesco Pini  Renato Fani  Luigi Michaud  Angelina Lo Giudice  Daniela Berto  Michele Giani 《Continental Shelf Research》2010

Shallow marine sediments were collected from seven stations (three of which located at Gerlache Inlet, two at Tethys Bay, one at Adelie Cove and one just beneath the Italian Research Base) along the Terra Nova Bay coast (Ross Sea, Antarctica). Their chemical, biochemical and microbiological properties were studied in order to provide further insights in the knowledge of this Antarctic benthic ecosystem. Overall, the organic carbon (OC) represented the major fraction of total carbon (TC) and displayed concentrations similar to or slightly lower than those previously measured in Antarctic bottom sediments. The biopolymeric carbon within OC ranged from 4.1% to 19.9% and showed a wide trophic range (65–834 μg g⁻¹ d.w.). Proteins (PRT) represented on average the main biochemical class contributing to labile organic carbon, followed by lipids (LIP) and carbohydrates (CHO). The activity of aminopeptidase, β-d-glucosidase, alkaline phosphatase and esterase was checked, giving the highest values at Tethys Bay and at the deepest water sediments. The principal component analysis, which was computed considering physical, chemical (elemental and biochemical sedimentary composition) and microbiological parameters (including bacterial abundance, ectoenzymatic activities, T-RFs richness and diversity indices), allowed to obtain two main clusters (“Tethys Bay” and “other stations”). Based on data obtained, two representative 16S rRNA clone libraries using samples from Tethys Bay and Gerlache Inlet were constructed. The sequences of 171 clones were compared to those available in public databases to determine their approximate phylogenetic affiliations. Both aerobic and anaerobic bacteria were disclosed, with the majority of them affiliated with the Gamma- and Deltaproteobacteria, Bacteroidetes and Acidobacteria. The occurrence of strictly anaerobic bacteria suggests that sediments might also undergo anoxic conditions that, in turn, could favor the accumulation of PRT in respect to CHO, assuming that fermentation of amino acids is slower than that of sugars from decomposing polysaccharides.  相似文献   

Electrochemical Ozone Production as an Environmentally Friendly Technology for Water Treatment     

Débora V. Franco  Wilson F. Jardim  Julien F. C. Boodts  Leonardo M. Da Silva 《洁净——土壤、空气、水》2008,36(1):34-44

Perspectives, advances and environmental aspects concerning electrochemical ozone production applied to water purification are presented and discussed in relation to the conventional corona process (silent electric discharge). Ozone generated using a laboratory‐made electrochemical reactor was applied for the discoloration/degradation of dyes used in the Brazilian textile industry and for degradation of endocrine disruptors. A constant ozone load of 0.35 ± 0.02 g/h was used throughout. The study, concerning color removal from dye solutions, revealed that total discoloration is rapidly achieved. The degradation rate of the textile dyes evaluated by TOC is little affected by the dye composition and considerably influenced by the pH and ozonation time. Analysis of the COD/TOC‐ratio indicates that ozonation increases oxidation feasibility of the organic matter (dye by‐products) when compared to the original compounds. Ozonation of mixed aqueous solutions containing different endocrine disruptors revealed these compounds are totally degraded with a very high removal rate.  相似文献