Geological and SHRIMP II U-Pb constraints on the age and origin of the Breves Cu-Au-(W-Bi-Sn) deposit,Carajás,Brazil

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     

Spatial distribution and ecotoxicity of petroleum hydrocarbons in sediments from the Galicia continental shelf (NW Spain) after the Prestige oil spill

The distribution of aliphatic and aromatic hydrocarbons was determined in surface sediments collected at 36 stations along the Galicia continental shelf (NW Spain), following the Prestige oil spill. Sampling was performed in December 2002, just after the accident, and in February and September 2003. Concentrations of PAHs (summation operator 13 parent components) were in the range of 0.9-422 microg/kgdw, the highest values being close to coastal urban areas (e.g. Pontevedra and A Coru?a), whereas in the stations of the area most heavily impacted by the spill (off Costa da Morte) concentrations were in the range of 14.8-89.6 microg/kgdw, with a certain predominance of alkylated compounds, which may suggest a mixture of petrogenic and pyrolytic sources. The detailed study of petrogenic molecular markers (e.g. steranes and triterpanes) showed the occurrence of an old (weathered) petrogenic chronic pollution in the shelf sediments but not of the Prestige oil, with the possible exception of few stations in the area of Costa da Morte. This was attributed to the heavy nature of the spilled oil that was barely dispersed in the water column and mainly stranded on the coast or sedimented in the form of oil patches. The addition of increasing amounts of fuel oil to a representative sediment sample showed that the molecular indices were indicative of the presence of the Prestige oil when the amount was above 1g/kg of sediment. The toxicity of selected samples (showing the higher PAH concentrations) was tested using the bivalve embryogenesis bioassay. Embryogenesis success reached high values in all cases (80-88%, with 86% in the control), indicating a lack of toxicity in the sediments and supporting the conclusion that the patchiness of the fuel eventually reaching the seafloor reduced its impact on the benthic communities of the Galician shelf.     

Starbursts at space ultraviolet wavelengths

Starbursts are systems with very high star formation rate per unit area. They are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. The similarities between the physical properties of local starbursts and high-z star-forming galaxies, highlight the cosmological relevance of starbursts. On the other hand, nearby starbursts are laboratories where to study violent star formation processes and their interaction with the interstellar and intergalactic media, in detail and deeply. Starbursts are bright at ultraviolet (UV) wavelengths, as they are in the far-infrared, due to the ‘picket-fence’ interstellar dust distribution. After the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues:

The determination of the initial mass function (IMF) in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments: A Salpeter IMF with high-mass stars constrains well the UV properties.

The modes of star formation: Starburst clusters are an important mode of star formation. Super-stellar clusters have properties similar to globular clusters.

The role of starbursts in AGN: Nuclear starbursts can dominate the UV light in Seyfert 2 galaxies, having bolometric luminosities similar to the estimated bolometric luminosities of the obscured AGN.

The interaction between massive stars and the interstellar and intergalactic media: Outflows in cold, warm and coronal phases leave their imprints on the UV interstellar lines. Outflows of a few hundred km s^?1 are ubiquitous phenomena in starbursts. These metal-rich outflows and the ionizing radiation can travel to the halo of galaxies and reach the intergalactic medium.

The contribution of starbursts to the reionization of the universe: In the local universe, the fraction of ionizing photons that escape from galaxies and reach the intergalactic medium is of a few percent. However, in high-z star-forming galaxies, the results are more controversial.

Despite the very significant progress over the past two decades in our understanding of the starburst phenomenon through the study of the physical processes revealed at satellite UV wavelengths, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. High-spatial resolution spectra are also needed to isolate the light from the center to the disk in UV luminous galaxies at z = 0.1–0.3 found by GALEX. Thus, a new UV mission furnished with an intermediate spectral resolution long-slit spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.     

利用遥感技术建立墨西哥热带地上生物量模型(英文)

Spatially-explicit estimation of aboveground biomass(AGB) plays an important role to generate action policies focused in climate change mitigation,since carbon(C) retained in the biomass is vital for regulating Earth’s temperature.This work estimates AGB using both chlorophyll(red,near infrared) and moisture(middle infrared) based normalized vegetation indices constructed with MCD43A4 MODerate-resolution Imaging Spectroradiometer(MODIS) and MOD44B vegetation continuous fields(VCF) data.The study area is located in San Luis Potosí,Mexico,a region that comprises a part of the upper limit of the intertropical zone.AGB estimations were made using both individual tree data from the National Forest Inventory of Mexico and allometric equations reported in scientific literature.Linear and nonlinear(expo-nential) models were fitted to find their predictive potential when using satellite spectral data as explanatory variables.Highly-significant correlations(p = 0.01) were found between all the explaining variables tested.NDVI62,linked to chlorophyll content and moisture stress,showed the highest correlation.The best model(nonlinear) showed an index of fit(Pseudo-r2) equal to 0.77 and a root mean square error equal to 26.00 Mg/ha using NDVI62 and VCF as explanatory variables.Validation correlation coefficients were similar for both models:lin-ear(r = 0.87**) and nonlinear(r = 0.86**).     

Microfossils of Polynesian cultigens in lake sediment cores from Rano Kau, Easter Island

Previous wetland vegetation records from Easter Island showing deforestation and Polynesian agriculture are limited to cores that rely on pollen, with a single cultigen pollen type identified: Urticaceae/Moraceae, possibly Broussonetia payrifera (paper mulberry). Here we redress this by also using phytolith and starch analyses on four lake sediment cores on a ~350-m transect along the southwest edge of Rano Kau, focusing on in-washed basal clayey layers. We also use a new method, Fourier transform infrared spectroscopy, to positively identify degraded starch collected from sedimentary deposits. The cores are the first samples recovered from an area in the lake that (a) lies below the relict village of Orongo, (b) is near a section of the crater believed to be most accessible from the Pacific coast, and (c) is far from the northern crater rim and receives high solar radiation, a likely benefit for crops of tropical origin. Pollen and phytoliths are abundant in the clayey layers and sparse in overlying layers of organic lake detritus and living rhizomes. Mixing of core deposits as a result of human activity has disordered the radiocarbon sequence, precluding development of an reliable chronology. Containing microfossils of several introduced cultigens, the clayey layers represent gardened terraces that have slumped into the lake. The data indicate large-scale deforestation and a mixed-crop production system including Broussonetia papyrifera, Colocasia esculenta (taro), Dioscorea alata (greater yam), Ipomoea batatas (sweet potato), Lagenaria siceraria (bottle gourd) and Musa (banana) sp. The data show (a) the potential for using the combined analyses to provide direct evidence of Polynesian horticulture on Easter Island and (b) that the island’s wetlands potentially hold extensive horticultural records. The study highlights the concept of ‘transported landscapes,’ whereby colonising people replace indigenous forests with artificial, imported agricultural landscapes.     

Spatial trends in heavy metals and nitrogen deposition in Navarra (Northern Spain) based on moss analysis

A biomonitoring survey using the moss species Hypnum cupressiforme Hedw. was performed in the North of Navarra (Spain) in 2006. The levels of V, Cr, Mn, Ni, Cu, Zn, As, Zr, Cd, Hg and Pb, and the total nitrogen content were determined in the samples by means of ICP-MS, CV-AA, and the Kjeldahl method. PCA analysis showed a differentiation between lithogenic (V, Cr, Mn, Ni, As and Zr) and anthropogenic elements (Mn, Cu, Zn, Cd, Hg and Pb). Spatial distribution maps were drawn using the kriging method, in order to identify the most affected areas and the main pollution sources. A similar spatial distribution was observed for the elements belonging to each group separated by the PCA, showing an important contribution from metal industries located in the Basque Country, as well as influence of long-range transboundary pollution processes. Background levels were also determined for the study area, along with the contamination factor for the different elements analysed. Mosses seemed to be good biomonitors of N deposition in areas of accumulation.     

Gas kinematics in the halo of the warm ULIRG PKS1345+12

We use long-slit spectra taken with the William Herschel Telescope on La Palma and high-resolution Hubble Space Telescope imaging to study the gas kinematic in the halo of the ultraluminous infrared/radio galaxy PKS1345+12 (z=0.122). Our long-slit spectra show line splitting at the locations of massive star clusters ( $10^{6}<M_{\mathrm{SSC}}^{\mathrm{YSP}}<10^{7}$ M_⊙), indicating that they are moving at up to 450 km?s^?1 with respect to the local ambient gas. Given their kinematics, it is plausible that these super star clusters have been formed either in fast-moving gas streams or tidal tails that are falling back into the nuclear regions as part of the merger process, or as a consequence of jet-induced star formation linked to the extended, diffuse radio emission detected in the halo of the galaxy.     

Trees, lateral shrinkage and building damage

This article presents the study conducted and the actions taken to stabilise the foundations of 25 low-rise (two/three-storey) buildings in Alcázar de San Juan (Ciudad Real, central Spain). Owing to the immediate attention required, it was decided that the study would focus on procuring a synthetic model that would be able to provide a satisfactory explanation for the tendency of the movements, overlooking the detailed model of each building. This analysis pointed out that the mobilisation was probably due to both the shrinkage caused by the existing trees during the dry-growing seasons, and to the loss of lateral confinement caused by the excavation of a service trench adjacent to the footings of the buildings. In keeping with this mechanism, stabilization was carried out by transplanting the trees growing near the damaged buildings and installing a line of piles to provide lateral support to the footings. The evolution of the damage was therefore stopped.     

Structural features of humic acids from a sedimentary sequence in the Guadiana estuary (Portugal–Spain border)

The structural characteristics of humic acids (HAs) from two different depths of a sedimentary sequence representing the last 13 kyr in the valley of Guadiana river estuary (SW Portugal/Spain border) have been approached using a combination of spectroscopic techniques, wet chemical degradation methods (sequential oxidation with sodium persulfate followed by KMnO₄, and oxidation with RuO₄) and analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in the presence and absence of tetramethylammonium hydroxyde (TMAH). The aim was to obtain complementary information on the sources and alteration of the organic matter (OM) provided by a previous study on the vertical distribution of terrestrial and phytoplankton biogeochemical markers in the sequence. Both the FT-IR (Fourier transformed infrared) and ¹³C NMR (nuclear magnetic resonance) spectra showed a close similarity with the structural characteristics of the HA samples. NMR signals in the alkyl region (0–45 ppm) as well as FT-IR band patterns typical for methoxyl-substituted aromatic rings pointed to the presence of an important aliphatic domain, as well as to lignin-derived compounds. This finding was confirmed using analytical pyrolysis. In addition, the main TMAH thermochemolysis products were typical lignin-derived methoxyphenols with both guaicyl and syringyl nuclei. The detection of methoxyphenol units with three to six carbon atom (C₃–C₆) side chains suggests that lignin and possibly suberin were only partially degraded. Compounds arising from proteins and polysaccharides were also detected, although in lesser and varying amount. The major products from persulfate oxidation were series of n-alkanes (C₁₆–C₃₃ with clear odd/even predominance) and n-fatty acids, both saturated (C₁₀–C₂₆ with strong even/odd predominance) and unsaturated, which may arise from the above aliphatic biomacromolecules. The major products from permanganate oxidation of the persulfate residue were α,ω-diacids (C₆–C₁₁) originating from oxidation of the ether bonds linking the building blocks constituting the core of the HA structure. Aromatic compounds (phenols, methoxy-dimethoxybenzene carboxylic acid and benzene di-, tri-, tetra- and pentacarboxylic acids), most probably derived from the aromatic backbone of the HAs, that may also include lignin moieties as well as other polyphenols (flavonoids and tannins) were also detected. The RuO₄ oxidation also released series of n-alkanes (C₁₆–C₃₃), linear saturated fatty acids (C₁₀–C₂₈) and α,ω-diacids (C₇–C₂₅), as well as traces of benzene polycarboxylic acids. Regarding the usefulness of the various techniques used, they provide complementary information. Indeed, spectroscopic techniques and analytical pyrolysis provide information on the backbone of the HAs, and on their origin, whereas the oxidative degradations provide different information on the structural features of the HA, particularly the nature of the linking between the building blocks. In general, the data support the idea that the HAs still contain information about the signature of aliphatic and aromatic biomacromolecules contributing to the OM deposited. The presence of lignin-derived residues suggests a large input from terrestrial carbon throughout the core.