Juvenile contribution of the Neoproterozoic Rio Negro Magmatic Arc (Ribeira Belt,Brazil): Implications for Western Gondwana amalgamation     

Miguel Tupinambá  Monica Heilbron  Claudio Valeriano  Rubem Porto Júnior  Fátima Blanco de Dios  Nuno Machado  Luiz Guilherme do Eirado Silva  Júlio Cesar Horta de Almeida 《Gondwana Research》2012,21(2-3):422-438

The ca. 790–600 Ma Rio Negro Complex (RNC) of the Ribeira belt (Brazil) consists of a plutonic portion of a magmatic arc built by the E-vergent subduction of the ESE border of the São Francisco paleoplate during the amalgamation of Western Gondwana.The plutonic series comprises low- to medium-K granitoids (ca. 790–620 Ma) and high-K granitoids and shoshonite rocks (ca. 610–605). The age span of 185 m.y. is suggestive of a long history of arc-related magmatism, continuously or not in time. The Nd isotopic signatures of the RNC consist of εNd(t) ratios from ? 3 to + 5 for the medium-K series shoshonite series and from ? 14 to ? 3 for the younger high-K group. This time-dependent trend of Nd isotopes is indicative of progressive maturity of the arc over time. The same evolution is indicated by Sr data, as the medium-K rocks have ⁸⁷Sr/⁸⁶Sr initial ratios < 0.705 while the high-K rocks yield values between 0.705 and 0.710. The predominance of intermediate rocks over mafic ones suggests an initial intra-oceanic to transitional stage, possibly developed in a distal portion of a passive margin, such as the Japanese arc, evolving to a more developed, differentiated felsic rock associations.The role of transform fault zones, such as the Luanda shear zone, is emphasized in order to explain the consumption of a wide oceanic plate in the inner portion of Western Gondwana.  相似文献   

Influence of the properties of tropical soils in the toxicity and bioavailability of heavy metals in sewage sludge-amended lands     

Ricardo Cesar  Marianna Silva  Juan Colonese  Edison Bidone  Silvia Egler  Zuleica Castilhos  Helena Polivanov 《Environmental Earth Sciences》2012,66(8):2281-2292

The toxicity and potential bioavailability of heavy metals were studied in sewage sludge-amended ferralsols and chernosols, using bioassays with earthworms (Eisenia andrei). Acute toxicity tests and avoidance assays were performed according to standard protocols. Potentially bioavailable concentrations of heavy metals were estimated by quantifying their concentrations in tissues of survival earthworms. The results revealed that soil properties played an important role in the toxicity and bioavailability of heavy metals. In this respect, higher levels of toxicity were detected for the ferralsol. The abundance of 2:1 clay minerals, high fertility and more basic values of pH seem to be very important in the reduction of toxicity levels for earthworms. Organisms exposed to the chernosols were able to uptake higher amount of metals. In that case, higher contents of nutrients in chernosols may have influenced such bioavailability processes. Avoidance responses were the most sensible indicator of toxicity. In the near future, such data can subsidize the establishment of toxic reference concentrations able to reflect the characteristics of important tropical pedological occurrences, supporting the definition of sustainable indicators for using sewage sludge in the tropical agriculture.  相似文献   

A unified assessment of marine Mediterranean assemblages: a lesson from benthic hydroids          下载免费PDF全文

Manuel M. González‐Duarte  Cesar Megina  Doris De Vito  Cristina Goia Di Camillo  Stefania Puce  Stefano Piraino 《Marine Ecology》2016,37(1):155-163

Hydroids are important components of the communities of rocky bottom shallow coastal areas. The hydrozoan fauna of the Mediterranean Sea is probably one of most investigated in the world, with lots of faunistic and biogeographical studies. However, quantitative studies using the same sampling methodology and controlled sampling effort have been restricted to areas in the Western and Central Mediterranean. We compared hydroid assemblages in four areas of the Mediterranean Sea, from the Gulf of Cádiz to the South Adriatic Sea, following the same sampling and quantification methodology. Our analysis showed the dominant Atlantic character of the assemblages of the Gulf of Cádiz and the South Alboran Sea because of the influence of the inflowing Atlantic waters. Conversely, the hydroid assemblages of the North Alboran Sea were more similar to the assemblages in the Ligurian and in the South Adriatic, and with a number of species ranking between the observed in these two Mediterranean zones. Fourteen species were identified as making the most significant contributions to characterizing the Mediterranean hydroid species pool from a quantitative point of view. These taxa include species previously named as typical components of the Mediterranean hydroid fauna as well as those only recently recorded in the region (Eudendrium moulouyensis) and invaders such as Clytia hummelincki.  相似文献   

Layered intrusions and volcanic sequences in Central Brazil: Geological and geochronological constraints for Mesoproterozoic (1.25 Ga) and Neoproterozoic (0.79 Ga) igneous associations     

Cesar Fonseca Ferreira Filho  Márcio Martins Pimentel  Sylvia Maria de Araujo  Jorge Henrique Laux 《Precambrian Research》2010

A 350-km long belt of layered complexes and associated volcano-sedimentary sequences forms a continental-scale feature exposed along the internal portion of the Neoproterozoic Brasília Belt in central Brazil. This study provides new geochronological results and a critical review of the available data of these igneous associations of central Brazil. Precise age dating combined with geological and petrological studies indicate that this belt consists of two distinct igneous rock associations. The 1.25 and 0.79 Ga igneous episodes are constrained by reliable U–Pb zircon ages (SHRIMP and ID-TIMS) obtained in different regions and lithotypes of this belt. Both igneous associations were affected by high-grade metamorphism and tectonism at ca. 0.76 Ga, which partially disrupted the original igneous stratigraphy of the layered complexes and volcano-sedimentary sequences. The present configuration of this belt results from later events, probably caused by final ocean closure and continental collision between the São Francisco and Amazonian continents at ca. 0.63 Ga.  相似文献   

Groundwater system response at sites with different agricultural land uses: case of the Guarani Aquifer outcrop area,Brotas/SP-Brazil     

Rodrigo Lilla Manzione  Bruna Camargo Soldera  Edson Cesar Wendland 《水文科学杂志》2017,62(1):28-35

A system identification approach can be incorporated in groundwater time series analysis, revealing information concerning the local hydrogeological situation. The aim of this work was to analyse water table fluctuations in an outcrop area of the Guarani Aquifer System (GAS) in Brotas/SP, Brazil, using data from a groundwater monitoring network. The water table dynamic was modelled using continuous time series models that reference the hydrogeological system upon which they operate. The model’s climatological inputs of precipitation and evapotranspiration generate impulse response (IR) functions with parameters that can be related to the physical conditions concerning the hydrological processes involved. The interpretation of the model parameters from two sets of monitoring wells selected at different land-use sites is presented, exemplifying the effect of different water table depths and the distance to the nearest drainage location. Systematic trends of water table depths were also identified from model parameters at specific periods and related to plant development, crop harvest and land-use changes.