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111.
Marianne Negrini Holger Stunitz Alfons Berger Luiz F. G. Morales 《Contributions to Mineralogy and Petrology》2014,167(3):1-22
We performed high strain (up to 47 %) axial compression experiments on natural quartz single crystals with added rutile powder (TiO2) and ~0.2 wt% H2O to investigate the effects of deformation on the titanium-in-quartz (TitaniQ) geothermobarometer. One of the objectives was to study the relationships between different deformation mechanisms and incorporation of Ti into recrystallized quartz grains. Experiments were performed in a Griggs-type solid-medium deformation apparatus at confining pressures of 1.0–1.5 GPa and temperatures of 800–1,000 °C, at constant strain rates of 1 × 10?6 or 1 × 10?7 s?1. Mobility of Ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains. Microstructural analysis by light and scanning electron microscopy (the latter including electron backscatter diffraction mapping of grain misorientations) shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation (SGR) and grain boundary migration recrystallization (GBMR). In addition, substantial grain growth occurred in annealing experiments after deformation. The GBMR and grain growth are evidence of moving grain boundaries, a microstructure favored by high temperatures. Electron microprobe analysis shows no significant increase in Ti content in recrystallized quartz grains formed by SGR or by GBMR, nor in grains grown by annealing. This result indicates that neither SGR nor moving grain boundaries during GBMR and grain growth are adequate processes to facilitate re-equilibration of the Ti content in experimentally deformed quartz crystals at the investigated conditions. More generally, our results suggest that exchange of Ti in quartz at low H2O contents (which may be realistic for natural deformation conditions) is still not fully understood. Thus, the application of the TitaniQ geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research. 相似文献
112.
Luiz Carlos Cotovicz Junior Eunice da Costa Machado Nilva Brandini Rafaela Cristine Zem Bastiaan Adriaan Knoppers 《Environmental Earth Sciences》2014,72(2):373-386
This study addresses the distribution of total phosphorus (TP) and its inorganic (IP) and organic (OP) fractions, grain-size and organic matter of surface and recent sediments, coupled to the behavior of total and dissolved inorganic phosphorus (TP and DIP) of the water column, of the semi-pristine Guaratuba Bay estuary, SE Brazil. Surface sediment samples were taken at 43 sites spread along the estuarine gradient and recent sediments from 3 short (35 cm long) cores from the upper, central and lower portions of the estuary, respectively. Highest TP and IP concentrations of surface sediments were detected within the upper sector and the transition zone between the upper and central sectors, all characterized by fine sediments, low salinities and water depths. In contrast, the lower sector and its narrow and deep tidal channel, subject to more intense tidal forcing, exhibited a higher fraction of sandy sediments with lower TP, IP and OP contents. In spite of the spatial variability in sediment grain size, IP corresponded to the major fraction of TP in all estuarine sectors and both TP and IP correlated significantly with the fine sedimentary (silt + clay) grain-size fraction. The fine surface sediments acted as a trap for IP at the fresh water–low salinity interface, which also corresponded to the region of a DIP sink in surface waters. In general, the short sediment cores showed that TP and IP contents increased from 15 cm depths to the top layer. Published sedimentation rates from additional cores taken at the sites of the short cores of this study, implied that depositional alterations of TP and IP increased during the early 1970s, which corresponded to the onset of anthropogenic disturbances from crop plantations in the lowland plains of the river end-member and urbanization at the estuary’s mouth and along the adjacent coast. 相似文献
113.
Luiz Augusto Manfré Alexandre Marco da Silva Rodrigo Custódio Urban John Rodgers 《Environmental Earth Sciences》2013,69(3):947-957
Environmental fragility models are important decision tools for policy makers as they help quantify environmental sensitivity and understand the relationship between human activities and environmental quality. The objective of this study was to evaluate three different environmental fragility models within the Brazilian rainforest region and to use the results to develop environmental zone classes. Two rural river basins located in Ibiuna, Sao Paulo state, Brazil, were studied. Input variables, including slope class, relief dissection rate, soil class, lithology, land cover, and climate data, were used to compute environmental fragility classes using three standard models. The model outputs were evaluated on their ability to accurately predict the most sensitive and least sensitive areas. The best models for each region were used to derive environmental zoning maps, including restoration priorities, best regions for agriculture, and areas with high needs for soil management. These maps will help support land use strategies for environmental restoration. This study provides insight into territorial ordering and management of environmental services with a regional perspective. 相似文献
114.
115.
We consider astronomical and geophysical bounds in order to test Kaluza-Klein like models and some particular models of Bekenstein's
theory. Bounds on the free parameteres of the theories are obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
116.
Adi Nusser Luiz N. da Costa Enzo Branchini Mariangela Bernardi M.V. Alonso Gary Wegner C. N. A. Willmer P. S. Pellegrini 《Monthly notices of the Royal Astronomical Society》2001,320(3):L21-L24
We present a comparison between the peculiar velocity field measured from the ENEAR all-sky D n – σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSC z ). The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500 km s−1 at 3000 km s−1 . The general flow patterns in the filtered ENEAR and PSC z velocity fields agree well within 6000 km s−1 , assuming a linear biasing relation between the mass and the PSC z galaxies. The comparison allows us to determine the parameter where Ω is the cosmological density parameter and b is the linear biasing factor. A likelihood analysis of the ENEAR and PSC z modes yields in good agreement with values obtained from Tully–Fisher surveys. 相似文献
117.
Paula Garcia Carvalho do Amaral Paulo César Fonseca Giannini Florence Sylvestre Luiz Carlos Ruiz Pessenda 《第四纪科学杂志》2012,27(2):181-191
This paper provides a paleoenvironmental reconstruction of a Late Quaternary lagoon system in the Jaguaruna region of Santa Catarina state, southern Brazil. Integrated results of bulk sedimentary organic matter characterization (δ13C, δ15N and C/N), microfossil (pollen and diatom) and grain‐size analysis from three shallow cores (~2.5 m depth) allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca. 5500 cal a BP. The lagoonal system in this area was more extensive during the mid‐Holocene than today, with a gradual and continuous lagoon–sea disconnection until the present. We add to the debate regarding relative sea‐level (RSL) variations for the Brazilian coast during the Holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems. The multi‐proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes, which are not necessarily linked to RSL fluctuations and/or to climatic variations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
118.
Sonia Maria Barros de Oliveira Luiz Carlos Ruiz Pessenda 《Journal of South American Earth Sciences》2012,33(1):1-7
Sediments of the Lagoa Vermelha (Red Lake), situated in the Ribeira Valley, southeastern Brazil, are made of a homogeneous, organic-rich, black clay with no visible sedimentary structures. The inorganic geochemical record (Al, As, Ba, Br, Co,Cs, Cr, Fe, Mn, Ni, Rb, Sc, Sb, V, Zn, Hg and Pb) of the lake sediments was analyzed in a core spanning 2430 years. The largest temporal changes in trace metal contents occurred approximately within the last 180 years. Recent sediments were found to be enriched in Pb, Zn, Hg, Ni, Mn, Br and Sb (more than 2-fold increase with respect to the “natural background level”). The enhanced accumulation of Br, Sb, and Mn was attributed to biogeochemical processes and diagenesis. On the other hand, the anomalous concentrations of Pb, Zn, Hg and Ni were attributed to pollution. As Lagoa Vermelha is located in a relatively pristine area, far removed from direct contamination sources, the increased metal contents of surface sediments most likely resulted from atmospheric fallout. Stable Pb isotopes provided additional evidence for anthropogenic contamination. The shift of 206Pb/207Pb ratios toward decreasing values in the increasingly younger sediments is consistent with an increasing contribution of airborne anthropogenic lead. In the uppermost sediments (0-10 cm), the lowest values of the 206Pb/207Pb ratios may reflect the influence of the less radiogenic Pb from the Ribeira Valley District ores (206Pb/207Pb between 1.04 and 1.10), emitted during the last 50 years. 相似文献
119.
Luiz Carlos Ruiz Pessenda Paulo Eduardo De Oliveira Milene Mofatto Vanda Brito de Medeiros Ricardo Jos Francischetti Garcia Ramon Aravena Jos Albertino Bendassoli Accio Zuniga Leite Antonio Roberto Saad Mario Lincoln Etchebehere 《Quaternary Research》2009,71(3):437-452
The lack of paleoecological records from the montane Atlantic Rainforest of coastal Brazil, a hotspot of biological diversity, has been a major obstacle to our understanding of the vegetational changes since the last glacial cycle. We present carbon isotope and pollen records to assess the impact of the glaciation on the native vegetation of the Serra do Mar rainforest in São Paulo, Brazil. From ca. 28,000 to 22,000 14C yr BP, a subtropical forest with conifer trees is indicative of cool and humid conditions. In agreement carbon isotopic data on soil organic matter suggest the presence of C3 plants and perhaps C4 plants from 28,000 to 19,000 14C yr BP. The significant increase in the sedimentation rate and algal spores from 19,450 to 19,000 14C yr BP indicates increasing humidity, associated to an erosion process between 19,000 and 15,600 14C yr BP. From 15,600 14C yr BP to present there is a substantial increase in arboreal elements and herbs, indicating more humid and warmer climate. From 19,000 to 1000 14C yr BP, δ13C values indicated the predominance of C3 plants. These results are in agreement with studies in speleothems of caves, which suggest humid conditions during the last glacial maximum. 相似文献
120.
Sonia Maria Barros de Oliveira Soraya Elaine Marques Gouveia Saia Luiz Carlos Ruiz Pessenda Deborah Ines Teixeira Favaro 《Chemie der Erde / Geochemistry》2009,69(4):395-405
A 172 cm-long sediment core was collected from a small pristine lake situated within a centripetal drainage basin in a tropical karst environment (Ribeira River valley, southeastern Brazil) in order to investigate the paleoenvironmental record provided by the lacustrine geochemistry. Sediments derived from erosion of the surrounding cambisoils contain quartz, kaolinite, mica, chlorite and goethite. Accelerator mass spectroscopy (AMS) 14C dating provided the geochronological framework. Three major sedimentary units were identified based on the structure and color of the sediments: Unit III from 170 to140 cm (1030±60–730±60 yr BP), Unit II from 140 to 90 cm (730±60–360±60 yr BP) and Unit I from 90 to 0 cm (360±60–0 yr BP). Results of major and trace element concentrations were analysed through multivariate statistical techniques. Factor analysis provided three factors accounting for 72.4% of the total variance. F1 and F2 have high positive loadings from K, Ba, Cs, Rb, Sr, Sc, Th, light rare earth element (LREE), Fe, Cr, Ti, Zr, Hf and Ta, and high negative loadings from Mg, Co, Cu, Zn, Br and loss on ignition (LOI). F3, with positive loadings from V and non-metals As and Sb, accounts for a low percentage (9.7%) of the total variance, being therefore of little interpretative use. The profile distribution of F1 scores reveals negative values in Units I and III, and positive values in Unit II, meaning that K, Ba, Cs, Rb, Sr, Sc, Th, LREE, Fe, Cr, Ti, Zr, Hf and Ta are relatively more concentrated in Unit II, and Mg, Co, Cu, Zn and Br are relatively more abundant in Units I and III. The observed fluctuations in the geochemical composition of the sediments are consistent with slight variations of the erosion intensity in the catchment area as a possible response to variations of climatic conditions during the last millennium. 相似文献