Geochemical modelling of the tonalitic and trondhjemitic granulites from the Itabuna-Salvador-Curaçá Block,Bahia, Brazil     

Ivana Conceição de Araújo Pinho  Johildo Salomão Figueiredo Barbosa  Angela Beatriz de Menezes Leal  Hervé Martin  Jean-Jacques Peucat 《Journal of South American Earth Sciences》2011,31(2-3):312-323

The studied tonalitic and trondhjemitic granulites are located in the SSE granulitic domain of the São Francisco craton, Bahia, Brazil, where they represent most of the southern part of the Archean and Paleoproterozoic Itabuna-Salvador-Curaçá Block (ISCB). Chemically, the tonalitic and trondhjemitic granulites belong to a low-K calc-alkaline suite; their REE patterns are steep with strong LREE/HREE fractionation and no significant Eu anomaly. Garnet-bearing mafic granulites that occur as enclaves in the tonalitic and trondhjemitic granulites were derived from basalts and/or gabbros of tholeiitic affinity. Geochemical modelling showed that the tonalitic and trondhjemitic granulites were produced by moderate fractional crystallization of an assemblage of hornblende and plagioclase, with subordinate amounts of magnetite, apatite, allanite and zircon. The garnet-bearing mafic granulites would be the source of the magmas that generated these rocks. Partial melting left a residue made up of plagioclase, garnet, orthopyroxene and hornblende.  相似文献   

Links between topography,moisture fluxes pathways and precipitation over South America     

Ramiro Ignacio Saurral  Inés Angela Camilloni  Tércio Ambrizzi 《Climate Dynamics》2015,45(3-4):777-789

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A Paleoecological History of the Late Precolonial and Postcolonial Mesohaline Chesapeake Bay Food Web     

Angela A. Sowers  Grace S. Brush 《Estuaries and Coasts》2014,37(6):1506-1515

Geochemical (total nitrogen, total organic carbon, total phosphorus, total sulfur, and carbon and nitrogen stable isotopes) and selected biotic (diatom, foraminifera, polychaete) indicators preserved in two estuarine sediment cores from the mesohaline Chesapeake Bay provide a history of alterations in the food web associated with land-use change. One core from the mouth of the Chester River (CR) (collected in 2000) represents a 1,000-year record. The second core (collected in 1999), from the Chesapeake Bay’s main stem opposite the Choptank River (MD), represents a 500-year record. As European settlers converted a primarily forested landscape to agriculture, sedimentation rates increased, water clarity decreased, salinity decreased in some areas, and the estuarine food web changed into a predominantly planktonic system. Representatives of the benthic macrofaunal community (foraminifera and the polychaetes Nereis spp.) were affected by local changes before there were widespread landscape alterations. Nitrogen stable isotope records indicated that land-use changes affected nitrogen cycling beginning in the early 1700s. Extreme changes were evident in the mid-nineteenth century following widespread deforestation and since the mid-twentieth century reflecting heightened eutrophication as development increased in the Chesapeake Bay watershed. Results also demonstrate how paleoecological records vary due to the degree of terrestrial inputs of freshwater runoff and nutrients at core locations within the Chesapeake Bay.  相似文献   

The volcanic and geothermally active Campi Flegrei caldera: an integrated multidisciplinary image of its buried structure     

M. Piochi  C. R. J. Kilburn  M. A. Di Vito  A. Mormone  A. Tramelli  C. Troise  G. De Natale 《International Journal of Earth Sciences》2014,103(2):401-421

The Campi Flegrei caldera in southern Italy is one of the greatest geohazard areas on Earth. Evidence of an active magmatic and geothermal system is provided by ongoing ground uplift, with volcano-tectonic and long-period (LP) seismicity, the persistent degassing of ~1500 tonnes of CO₂ per day, the presence of hot fumaroles at temperatures of 90–150 °C, brine-rich aquifers (with total dissolved solids up to 33 g l^?1) and high thermal gradients in the crust (with temperatures reaching 420 °C at 3,050 m b.s.l.). Since the 1940s, more than 100 exploratory boreholes have been drilled in the area to depths of 80–3,100 m by the Azienda Geologica Italiana Petroli (AGIP) and the Società Anonima Forze Endogene Napoletane (SAFEN). To date, however, no systematic reanalysis of the drilling data has been carried out, and the buried volcanic structure has not been updated using the most recent scientific results and previous findings. By integrating unpublished data from the AGIP and SAFEN reports with published information from geological, volcanological, petrological, petrophysical and geophysical studies, this paper presents an improved picture of the Campi Flegrei caldera that will be useful for volcanic hazard assessment and mitigation in the Naples area and for future research planning. The results suggest that intra-caldera activity has been influenced by how the magmatic system at depths greater than about 4 km has determined the transfer of magma, volatiles, and heat to the overlying geothermal system and, ultimately, to the surface. In particular, intriguing is that the most volcanically active central-eastern sector of the caldera, which is subject to intense bradyseismic ground movement and gas emission, coincides with a structurally delimited subsurface rock volume characterized by an uprising of the 100 °C isotherm, a deep water supply to the shallower aquifer, the early disappearance of secondary calcite, LP seismicity and high seismic S-wave attenuation. In this area, we also document evidence of repeated injection at depths of c. 1.5–3.0 km of isolated and small-volume batches of magma, where occurred their crystallization and degassing. Shallow intrusions and degassing of magma are thus identified as two of the key processes that drive unrest in Campi Flegrei.  相似文献   

Re-thinking colonialism to prepare for the impacts of rapid environmental change   总被引：1，自引：1，他引：0  

Nicholas James Reo  Angela K. Parker 《Climatic change》2013,120(3):671-682

This essay demonstrates how key concepts from ecology can be applied within historical analyses in order to gain insights regarding contemporary environmental change. We employ a coupled human and natural systems conceptual framework in a nascent historical analysis of rapid societal and environmental change in colonial New England, where European colonization led to stark and rapid transformations. Introduced diseases reduced indigenous communities to a fraction of their pre-contact levels. European agriculture and associated pest species, deforestation and overharvest of ecologically influential species were among key aspects of the rapid changes in colonial New England. Cross-continental biotic introductions initiated reinforcing feedback loops that accelerated the transition of human and natural systems into novel states. Integrating colonial history and ecology can help identify important interactions between human and natural systems useful for contemporary societies adjusting to environmental change.  相似文献   

Adaptation of the antioxidant defence system in hydrothermal-vent mussels (Bathymodiolus azoricus) transplanted between two Mid-Atlantic Ridge sites     

Rui Company  Angela Serafim  Richard Cosson  Aline Fiala-Médioni  David R. Dixon  & Maria João Bebianno 《Marine Ecology》2007,28(1):93-99

The vent mussel Bathymodiolus azoricus is the dominant member of the Northern Mid‐Atlantic Ridge (MAR) hydrothermal megafauna, and lives in an environment characterized by temporal and spatial variations in the levels of heavy metals, methane and hydrogen sulphide, substances which are known to increase reactive oxygen species levels in the tissues of exposed organisms. To evaluate the effects of two contrasting hydrothermal environments on the antioxidant defence system of this vent mussel species, a 2‐week transplant experiment was carried out involving mussels collected from the relatively deep (2300 m), and chemical rich, Rainbow vent field. These were transplanted to the shallower (1700 m), and relatively less toxic, Lucky Strike vent field. To achieve this objective, levels of superoxide dismutase, catalase (CAT), total glutathione peroxidase (GPx), selenium‐dependent glutathione peroxidase and lipid peroxidation (LPO) were measured in the gills and mantle tissues of resident and transplant mussels before and after the transplant experiment. With the exception of CAT, the gills of the transplanted mussels had significantly higher antioxidant enzyme activity compared with the basal levels in the donor (Rainbow) and recipient (Lucky Strike) populations; whereas the antioxidant enzyme levels in the mantle tissues of the transplants reflected the baseline levels of activity in the native Lucky Strike mussels after 2 weeks. In contrast, LPO levels were significantly higher in both tissue types in the transplants than in either the source or the recipient populations, which suggested a response to hydrostatic pressure change (note, the transplant animals were brought to the surface for transportation between the two vent fields). The fact that the Rainbow mussels survived the transplant experience indicates that B. azoricus has a very robust constitution, which enables it to cope behaviourally, physiologically and genetically with the extreme conditions found in its naturally contaminated deep‐sea environment.  相似文献   

9C: a survey of radio sources at 15 GHz with the Ryle Telescope   总被引：1，自引：0，他引：1  

Elizabeth M. Waldram  Guy G. Pooley  Keith J. B. Grainge  Michael E. Jones  Richard D. E. Saunders  Paul F. Scott  Angela C. Taylor 《Monthly notices of the Royal Astronomical Society》2003,342(3):915-925

The fields chosen for the first observations of the cosmic microwave background with the Very Small Array have been surveyed with the Ryle Telescope at 15 GHz. We have covered three regions around RA  00^h 20^m Dec. +30°  , RA  09^h 40^m Dec. +32°  and RA  15^h 40^m Dec. +43° (J2000.0)  , an area of  520 deg²  . There are 465 sources above the current completeness limit of  ≈25 mJy  , although a total of  ≈760  sources have been detected, some as faint as 10 mJy. This paper describes our techniques for observation and data analysis; it also includes source counts and some discussion of spectra and variability. Preliminary source lists are presented.  相似文献   

A Survey for EHB Stars in the Galactic Bulge     

Donald M. Terndrup  Deokkeun An  Angela Hansen  Ruth C. Peterson  Alistair R. Walker  Elaine M. Sadler 《Astrophysics and Space Science》2004,291(3-4):247-252

We present a progress report on an extensive survey to find and characterize all types of horizontal-branch stars in the nuclear bulge of the Galaxy. We have obtained wide, shallow imaging in UBV of ≈12 square degrees in the bulge, with follow-up spectroscopy for radial velocities and metal abundance determinations. We have discovered a number of metal-rich blue HB stars, whose presence in the bulge is expected by the interpretation of the extragalactic ultraviolet excess. Very deep images have been obtained in UBV and SDSS u along the bulge minor axis, which reveal a significant number of EHB candidates fainter than B=19, i.e., with the same absolute magnitudes as EHB stars in several globular clusters.  相似文献   

Gamma-ray and synchrotron emission from neutralino annihilation in the Large Magellanic Cloud     

Argyro Tasitsiomi  Jennifer Gaskins  Angela V. Olinto   《Astroparticle Physics》2004,21(6):637-650

We calculate the expected flux of γ-ray and radio emission from the LMC due to neutralino annihilation. Using rotation curve data to probe the density profile and assuming a minimum disk, we describe the dark matter halo of the LMC using models predicted by N-body simulations. We consider a range of density profiles including the NFW profile, a modified NFW profile proposed by Hayashi et al. (2003) to account for the effects of tidal stripping, and an isothermal sphere with a core. We find that the γ-ray flux expected from these models may be detectable by GLAST for a significant part of the neutralino parameter space. The prospects for existing and upcoming Atmospheric Cherenkov Telescopes (ACTs) are less optimistic, as unrealistically long exposures are required for detection. However, the effects of adiabatic compression due to the baryonic component may improve the chances for detection by ACTs. The maximum flux we predict is well below EGRET's measurements and thus EGRET does not constrain the parameter space. The expected synchrotron emission generally lies below the observed radio emission from the LMC in the frequency range of 19.7–8550 MHz. As long as σv<2×10⁻²⁶ cm³ s⁻¹ for a neutralino mass of 50 GeV, the observed radio emission is not primarily due to neutralinos and is consistent with the assumption that the main source is cosmic rays. We find that the predicted fluxes, obtained by integrating over the entire LMC, are not very strongly dependent on the inner slope of the halo profile, varying by less than an order of magnitude for the range of profiles we considered.  相似文献   

Dodging alligators,rattlesnakes, and backyard docks: a political ecology of sweetgrass basket-making and conservation in the South Carolina Lowcountry,USA     

Patrick T. Hurley  Angela C. Halfacre 《GeoJournal》2011,76(4):383-399

There is growing recognition among political ecologists of the need to examine shifting natural resource regimes and their effects on livelihoods in “First World” places. This emerging literature has variously examined the “Third World within,” the persistence of “subsistence activities” in the “First World,” and the “reterritorialization” of land tenure and access. However, much of this work has tended to focus on traditional extractive industries in the American West, indigenous claims to lands and resources in the U.S. and Canada, and non-timber resources on public lands. In contrast, we use a case study of African-American sweetgrass basket-makers, associated with the Gullah culture, in South Carolina’s lowcountry to examine the ways in which ongoing amenity-driven residential development is fundamentally reshaping resource access on private lands. Historically, basket-makers harvested the materials (primarily sweetgrass or Mulenbergia filipes) needed for their culturally important art form from accessible, rural, and privately held tracts of land in close proximity to their communities, but development pressures and changes in resident interpretation of property rights has decreased access to basket-making resources. The case is particularly illuminating, as it examines the emergence of ‘conservation subdivisions’ in the region and raises important questions about what “rural uses” and users are being conserved through responses to exurban, suburban, and urban development in formerly rural areas.  相似文献