14 resultados para Zone melting.
em Biblioteca Digital da Produção Intelectual da Universidade de São Paulo
Resumo:
The Dom Feliciano Belt, situated in southernmost Brazil and Uruguay, contains a large mass of granite-gneissic rocks (also known as Florianopolis/Pelotas Batholith) formed during the pre-, syn- and post-orogenic phases of the Brasiliano/Pan-African cycle. In the NE extreme of this granitic mass, pre-, syn- and post-tectonic granites associated with the Major Gercino Shear Zone (MGSZ) are exposed. The granitic manifestation along the MGSZ can be divided into pre-kinematic tonalitic gneisses, peraluminous high-K calcalkaline early kinematic shoshonitic, and metaluminous post-kinematic granites. U-Pb zircon data suggest an age of 649 +/- 10 Ma for the pre-tectonic gneisses, and a time span from 623 +/- 6 Ma to 588 +/- 3 Ma for the early to post-tectonic magmatism. Negative epsilon Hf (t) values ranging from -4.6 to -14.6 and Hf model ages ranging from 1.64 to 2.39 Ga for magmatic zircons coupled with whole rock Nd model ages ranging from 1.24 to 2.05 Ga and epsilon Nd (t) values ranging from -3.84 to -7.50, point to a crustal derivation for the granitic magmatism. The geochemical and isotope data support a continental magmatic arc generated from melting of dominant Paleoproterozoic crust, and a similar evolution for the granitic batholiths of the eastern Dom Feliciano Belt and western Kaoko Belt. (C) 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
Resumo:
Sao Paulo state (Brazil) has one of the most overpopulated coastal zones in South America, where previous studies have already detected sediment and water contamination. However, biological-based monitoring considering signals of xenobiotic exposure and effects are scarce. The present study employed a battery of biomarkers under field conditions to assess the environmental quality of this coastal zone. For this purpose, the activity of CYP 450, antioxidant enzymes, DNA damage, lipid peroxidation and lysosomal membrane were analysed in caged mussels and integrated using Factorial Analysis. A representation of estimated factor scores was performed in order to confirm the factor descriptions characterizing the studied areas. Biomarker responses indicated signals of mussels` impaired health during the monitoring, which pointed to the impact of different sources of contaminants in the water quality and identified critical areas. This integrated approach produced a rapid, sensitive and cost-effective assessment, which could be incorporated as a descriptor of environmental status in future coastal zones biomonitoring. (C) 2011 Elsevier Inc. All rights reserved.
Resumo:
The physical aspects of the Subtropical Shelf Front (STSF) for the Southwest Atlantic Continental Shelf were previously described. However, only scarce data on the biology of the front is available in the literature. The main goal of this paper is to describe the physical, chemical and biological properties of the STSF found in winter 2003 and summer 2004. A cross-section was established at the historically determined location of the STSF. Nine stations were sampled in winter and seven in summer. Each section included a series of conductivity-temperature-depth (CTD) stations where water samples from selected depths were filtered for nutrient determination. Surface samples were taken for chlorophyll a (Chl-a) determination and plankton net tows carried out above and below the pycnocline. Results revealed that winter was marked by an inner-shelf salinity front and that the STSF was located on the mid-shelf The low salinity waters in the inner-shelf indicated a strong influence of freshwater, with high silicate (72 mu M), suspended matter (45 mg l(-1)), phosphate (2.70 mu M) and low nitrate (1.0 mu M) levels. Total dissolved nitrogen was relatively high (22.98 mu M), probably due to the elevated levels of organic compound contribution close to the continental margin. Surface Chl-a concentration decreased from coastal well-mixed waters, where values up to 8.0 mg m(-3) were registered, to offshore waters. Towards the open ocean, high subsurface nutrients values were observed, probably associated to South Atlantic Central Waters (SACW). Zooplankton and ichthyoplankton abundance followed the same trend; three different groups associated to the inner-, mid- and outer-shelf region were identified. During summer, diluted waters extended over the shelf to join the STSF in the upper layer; the concentration of inorganic nutrients decreased in shallow waters; however, high values were observed between 40 and 60 m and in deep offshore waters. Surface Chl-a ranged 0.07-1.5 mg m(-3); winter levels were higher. Three groups of zoo and ichthyoplankton, separated by the STSF, were also identified. Results of the study performed suggest that the influence of freshwater was stronger during winter and that abundance distribution of Chl-a, copepods and ichthyoplankton was related to the Plata Plume Waters (PPW), rather than to the presence of the STSF. During summer, when the presence of freshwater decreases, plankton interactions seem to take place in the STSF. (C) 2008 Elsevier Ltd. All rights reserved.
Resumo:
High-grade metasedimentary rocks can preserve geochemical signatures of their sedimentary protolith if significant melt extraction did not occur. Retrograde reaction textures provide the main evidence for trapped melt in the rock fabrics. Carvalhos Klippe rocks in Southern Brasilia Orogen, Brazil, present a typical high-pressure granulite assemblage with evidence of mica breakdown partial melting (Ky + Grt + Kfs +/- Bt +/- Rt). The metamorphic peak temperatures obtained by Zr-in-Rt and ternary feldspar geothermometers are between 850 degrees C and 900 degrees C. The GASP bane peak pressure obtained using grossular rich garnet core is 16 kbar. Retrograde reaction textures in which the garnet crystals are partially to totally replaced by Bt + Qtz +/- Fsp intergrowths are very common in the Carvalhos Klippe rocks. These reactions are interpreted as a result of interactions between residual phases and trapped melt during the retrograde path. In the present study the geochemical signatures of three groups of Carvalhos Klippe metasedimentary rocks are analysed. Despite the high metamorphic grade these three groups show well-defined geochemical features and their REE patterns are similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). The high-pressure granulite facies Grt-Bt-Pl gneisses with immature arenite (wacke, arkose or lithic-arenite) geochemical signatures present in the Carvalhos Klippe are compared to similar rocks in amphibolite facies from the same tectonic framework (Andrelandia Nappe System). The similar geochemical signatures between Grt-Bt-Pl gneisses metamorphosed in high-pressure granulite facies and Grt-Bt-Pl-Qtz schists from the Andrelandia and Liberdade Nappes, with minimal to absent melting conditions, are suggestive of low rates of melt extraction in these high-grade rocks. The rocks with pelitic compositions most likely had higher melt extraction and even under such circumstances nevertheless tend to show REE patterns similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). (C) 2012 Elsevier Ltd. All rights reserved.
Resumo:
The north-western sector of the Gharyan volcanic field (northern Libya) consists of trachytic-phonolitic domes emplaced between similar to 41 and 38 Ma, and small-volume mafic alkaline volcanic centres (basanites, tephrites. alkali basalts. hawaiites and rare benmoreites) of Middle Miocene-Pliocene age (similar to 12-2 Ma). Two types of trachytes and phonolites have been recognized on the basis of petrography, mineralogy and geochemistry. Type-1 trachytes and phonolites display a smooth spoon-shaped REE pattern without negative Europium anomalies. Type-2 trachytes and phonolites show a remarkable Eu negative anomaly, higher concentration in HFSE (Nb-Ta-Zr-Hf), REE and Ti than Type-1 rocks. The origin of Type-1 trachytes and phonolites is compatible with removal of clinopyroxene, plagioclase, alkali feldspar, amphibole. magnetite and titanite starting from benmoreitic magmas. found in the same outcrops. Type-2 trachytes and phonolites could be the result of extensive fractional crystallization starting from mafic alkaline magma, without removal of titanite. In primitive mantle-normalized diagrams, the mafic rocks (Mg#= 62-68, Cr up to 514 ppm, Ni up to 425 ppm) show peaks at Nb and Ta and troughs at K. These characteristics, coupled with low Sr-87/Sr-86(i) (0.7033-0.7038) and positive epsilon(Nd) (from +4.2 to + 5.3) features typical of the mafic anorogenic magmas of the northern African plate and of HIMU-OIB-like magma in general. The origin of the mafic rocks is compatible from a derivation from low degree partial melting (3-9%) shallow mantle sources in the spinel/gamet facies. placed just below the rigid plate in the uppermost low-velocity zone. The origin of the igneous activity is considered linked to passive lithospheric thinning related to the development of continental rifts like those of Sicily Channel (e.g.. Pantelleria and Linosa) and Sardinia (e.g., Campidano Graben) in the Central-Western Mediterranean Sea. (C) 2012 Elsevier B.V. All rights reserved.
Resumo:
Categorical data cannot be interpolated directly because they are outcomes of discrete random variables. Thus, types of categorical variables are transformed into indicator functions that can be handled by interpolation methods. Interpolated indicator values are then backtransformed to the original types of categorical variables. However, aspects such as variability and uncertainty of interpolated values of categorical data have never been considered. In this paper we show that the interpolation variance can be used to map an uncertainty zone around boundaries between types of categorical variables. Moreover, it is shown that the interpolation variance is a component of the total variance of the categorical variables, as measured by the coefficient of unalikeability. (C) 2011 Elsevier Ltd. All rights reserved.
Resumo:
The objective of this study was to evaluate the genetic differences among three matrix groups of Cedrela fissilis based on quantitative juvenile variables on a progeny test to define seed collecting zones and use of seeds of this species in the study region as well as to evaluate genetic variability of the sampled material. A progeny test was established in a nursery with seeds from 48 seed trees collected in the municipalities of Rio Negrinho, Mafra and Sao Bento do Sul, state of Santa Catarina, and in the municipalities of Lapa, Rio Negro, Campo do Tenente and Antonio Olinto, state of Parana. Of the collected seed trees, 33 sampled trees were distributed in three sites and 15 trees were dispersed in the studied region. It was used a complete random block design, with 8 replicates and 20 plants per plot. Evaluated data included: emergency rate; seedling base diameter and height (61, 102 and 145 days after the seeds were sowed); seedling survival; number of leaves per seedling; aerial section dry mass and root dry mass; and the foliar area of the third fully expanded leaf measured from the apical meristem. The Maximum Restricted Likelihood Method (REML) was used, using the software SELEGEN for analysis. It was found that the juvenile characters are strongly genetically controlled and they can be used to estimate genetic variability of population samples of Cedrela fissilis. The three groups of trees spatially limited did not significantly differ among each other, allowing to conclude that the three areas are part of the same tree seed transfer zone.
Flux-Line-Lattice Melting and Upper Critical Field of Bi1.65Pb0.35Sr2Ca2Cu3O10+delta Ceramic Samples
Resumo:
We have conducted magnetoresistance measurements rho(T,H) in applied magnetic fields up to 18 T in Bi1.65Pb0.35Sr2Ca2Cu3O10+delta ceramic samples which were subjected to different uniaxial compacting pressures. The anisotropic upper critical fields H (c2)(T) were extracted from the rho(T,H) data, yielding and the out-of-plane superconducting coherence length xi (c) (0)similar to 3 . We have also estimated and xi (ab) (0) similar to 90 . In addition to this, a flux-line-lattice (FLL) melting temperature T (m) has been identified as a second peak in the derivative of the magnetoresistance d rho/dT data close to the superconducting transition temperature. An H (m) vs. T phase diagram was constructed and the FLL boundary lines were found to obey a temperature dependence H (m) ae(T (c) /T-1) (alpha) , where alpha similar to 2 for the sample subjected to the higher compacting pressure. A reasonable value of the Lindemann parameter c (L) similar to 0.29 has been found for all samples studied.
Resumo:
LA-MC-ICP-MS U-Pb zircon dating was performed on syntectonic, early post-collisional granitic and associated mafic rocks that are intrusive in the Brusque Metamorphic Complex and in the Florianopolis Batholith, major tectonic domains separated by the Neoproterozoic Major Gercino Shear Zone (MGSZ) in south Brazil. The inferred ages of magmatic crystallization are consistent with field relationships, and show that the syntectonic granites from both domains are similar, with ages around 630-620 Ma for high-K calc-alkaline metaluminous granites and ca. 610 Ma for slightly peraluminous granites. Although ca. 650 Ma inherited zircon components are identified in granites from both domains, important contrasts on the crustal architecture in each domain are revealed by the patterns of zircon inheritance, indicating different crustal sources for the granites in each domain. The granites from the southern domain (Floriandpolis Batholith) have essentially Neoproterozoic (650-700 Ma and 900-950 Ma) inheritance; with a single 2.0-2.2 Ga inherited age obtained in the peraluminous Mariscal Granite. In the northern Brusque Metamorphic Complex, the metaluminous Rio Pequeno Granite and associated mafic rocks have scarce inherited cores with ages around 1.65 Ga, whereas the slightly peraluminous Serra dos Macacos Granite has abundant Paleoproterozoic (1.8-2.2 Ga) and Archean (2.9-3.4 Ga) inherited zircons. Our results are consistent with the hypothesis that the MGSZ separates domains with distinct geologic evolution; however, the contemporaneity of 630-610 Ma granitic magmatism with similar structural and geochemical patterns on both sides of this major shear zone indicates that these domains were already part of a single continental mass at 630 Ma, reinforcing the post-collisional character of these granites. (C) 2012 Elsevier B.V. All rights reserved.
Resumo:
The Niquelandia Complex, Brazil, is one of the world's largest mafic-ultramafic plutonic complexes. Like the Mafic Complex of the Ivrea-Verbano Zone, it is affected by a pervasive high-T foliation and shows hypersolidus deformation structures, contains significant inclusions of country-rock paragneiss, and is subdivided into a Lower and an Upper Complex. In this paper, we present new SHRIMP U-Pb zircon ages that provide compelling evidence that the Upper and the Lower Niquelandia Complexes formed during the same igneous event at ca. 790 Ma. Coexistence of syn-magmatic and high-T subsolidus deformation structures indicates that both complexes grew incrementally as large crystal mush bodies which were continuously stretched while fed by pulses of fresh magma. Syn-magmatic recrystallization during this deformation resulted in textures and structures which, although appearing metamorphic, are not ascribable to post-magmatic metamorphic event(s), but are instead characteristic of the growth process in huge and deep mafic intrusions such as both the Niquelandia and Ivrea Complexes. Melting of incorporated country-rock paragneiss continued producing hybrid rocks during the last, vanishing stages of magmatic crystallization. This resulted in the formation of minor, late-stage hybrid rocks, whose presence obscures the record of the main processes of interaction between mantle magmas and crustal components, which may be active at the peak of the igneous events and lead to the generation of eruptible hybrid magmas. (C) 2012 Elsevier B.V. All rights reserved.
Resumo:
Abstract Background Leptospirosis is a zoonosis which is spread through contamined running water. This contaminations is seriously affected by the flooding which occurs in the area surrounding the Aricanduva river. The transmission of the disease results mainly from the contact of water with soil contaminated by the urine of infected animals. We aimed to conduct an epidemiological survey on Leptospirosis cases in Sao Paulo East Zone area. Method The analysis conducted in this study was based on data collected from the health authorities of that region close the Aricanduva river between 2007 and 2008 years, which give the rates of confirmed cases, mortality and death from human Leptospirosis. Other information concerned with the relationships among rainfall index, points of flooding and incidence of Leptospirosis. Results We observed a direct and important water contamination. Records of flooding points and dates of the reported cases in the region showed a direct relationship from which the period of higher rainfall also recorded an increase in cases. The annual record of the city and the region and rainfall regions also presented correlation. Conclusion The association between the indices of flooding and Leptospirosis cases indicates that preventive measures are necessary to avoid exposing the community.
Resumo:
Seismogenic fault reactivation of continental-scale structures has been observed in a few intraplate areas, but its cause is still amatter of debate. The objective of the present study is to analyze two seismic swarms that occurred along the EW-trending Pernambuco ductile shear zone and in a NE-trending branch, in 2007 and 2010 in São Caetano County, Northeastern Brazil.We studied both epicentral areas using a nine- and a seven-station network during 180 and 54 days, respectively. The results indicate that the 2007 swarm correspond to a right-lateral, strike–slip fault with a normal component of slip (strike 74°, dip 60°, and rake−145°) and the 2010 swarmcorresponds to a normal fault (strike 265°, dip 79°, and rake −91°). The former reactivated a NE-trending branch, whereas the latter reactivated the main E-W-trending mylonitic belt of the Pernambuco shear zone. These results are consistent with seismogenic reactivation of this major structure, generated by the present-day EW-trending compression and NS-trending extension, as observed by previous studies. This shear zone was reactivated as rift faults in the Cretaceous during the South America–Africa breakup. However, our study confirms that the basement fabric such as continental-scale ductile shear zones, show evidence of crustal weakness outside areas of previous rifting, and it reveals the potential for large earthquakes along dormant rift segments associated with major basement shear belts.