oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Paleoproterozoic (~1.88Ga) felsic volcanism of the Iricoumé Group in the Pitinga Mining District area, Amazonian Craton, Brazil: insights in ancient volcanic processes from field and petrologic data
Pierosan, Ronaldo;Lima, Evandro F.;Nardi, Lauro V.S.;Campos, Cristina P. de;Bastos Neto, Artur C.;Ferron, José M.T.M.;Prado, Maurício;
Anais da Academia Brasileira de Ciências , 2011, DOI: 10.1590/S0001-37652011000300012
Abstract: the iricoumé group correspond to the most expressive paleoproterozoic volcanism in the guyana shield, amazonian craton. the volcanics are coeval with mapuera granitoids, and belong to the uatum? magmatism. they have u-pb ages around 1880 ma, and geochemical signatures of α-type magmas. iricoumé volcanics consist of porphyritic trachyte to rhyolite, associated to crystal-rich ignimbrites and co-ignimbritic fall tuffs and surges. the amount and morphology of phenocrysts can be useful to distinguish lava (flow and dome) from hypabyssal units. the morphology of ignimbrite crystals allows the distinction between effusive units and ignimbrite, when pyroclasts are obliterated. co-ignimbritic tuffs are massive, and some show stratifications that suggest deposition by current traction flow. zircon and apatite saturation temperatures vary from 799°c to 980°c, are in agreement with most temperatures of α-type melts and can be interpreted as minimum liquidus temperature. the viscosities estimation for rhyolitic and trachytic compositions yield values close to experimentally determined melts, and show a typical exponential decay with water addition. the emplacement of iricoumé volcanics and part of mapuera granitoids was controlled by ring-faults in an intracratonic environment. a genesis related to the caldera complex setting can be assumed for the iricoumé-mapuera volcano-plutonic association in the pitinga mining district.
The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution
Ruiz, Amarildo S.;Geraldes, Mauro C.;Matos, Jo?o B.;Teixeira, Wilson;Van Schumus, William R.;Schmitt, Renata S.;
Anais da Academia Brasileira de Ciências , 2004, DOI: 10.1590/S0001-37652004000400013
Abstract: isotopic and chemical data of rocks from the cachoeirinha suite provide new insights on the proterozoic evolution of the rio negro/juruena province in sw amazonian craton. six u-pb and sm-nd analyses in granitoid rocks of the cachoeirinha suite yielded ages of 1587-1522 ma and tdm model ages of 1.88-1.75 ga (epsilonnd values of -0.8 to +1.0). in addition, three post-tectonic plutonic rocks yielded u-pb ages from 1485-1389 ma (tdm of 1.77-1.74 ga and epsilonnd values from -1.3 to +1.7). variations in major and trace elements of the cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. these results suggest the following interpretations: (1) the interval of 1590-1520 ma represents an important magmatic activity in sw amazonian craton. (2) tdm and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 ga) continental margin. (3) the 1590-1520 ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of baltica, corroborating the hypothesis of tectonic relationship at that time.
The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution  [cached]
Ruiz Amarildo S.,Geraldes Mauro C.,Matos Jo?o B.,Teixeira Wilson
Anais da Academia Brasileira de Ciências , 2004,
Abstract: Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0). In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7). Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1) The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2) T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga) continental margin. (3) The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.
An overview of the Amazonian Aerosol Characterization Experiment 2008 (AMAZE-08)
S. T. Martin, M. O. Andreae, D. Althausen, P. Artaxo, H. Baars, S. Borrmann, Q. Chen, D. K. Farmer, A. Guenther, S. S. Gunthe, J. L. Jimenez, T. Karl, K. Longo, A. Manzi, T. Müller, T. Pauliquevis, M. D. Petters, A. J. Prenni, U. P schl, L. V. Rizzo, J. Schneider, J. N. Smith, E. Swietlicki, J. Tota, J. Wang, A. Wiedensohler,S. R. Zorn
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010,
Abstract: The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine- and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 μm that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate.
Rb-Sr Geochronology and Geochemical Characteristics of Mafic Dikes in the Nova Lacerda and Conquista D′Oeste Region, Mato Grosso, SW Amazonian Craton
Paulo César Corrêa da Costa,Vicente Antonio Vitório Girardi,Jo?o Batista de Matos,Amarildo Salina Ruiz
Geologia USP : Série Científica , 2009,
Abstract: In the Nova Lacerda and Conquista D’Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafi c dikestrending NNW intrude the Nova Lacerda Granite (1462 ± 12 Ma), within the Jauru Domain, in the Rondonia-San IgnacioProvince (1.55 - 1.3 Ga). The mafi c swarm comprises diabases, metadiabases and amphibolites. Metadiabases originatedfrom uralitization of diabases. These rocks have tholeiitic affi nity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 ± 32 Ma and 1330 ± 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tholeiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source.
Amazonian Fruits: An Overview of Nutrients, Calories and Use in Metabolic Disorders  [PDF]
Moacir Couto de Andrade Júnior, Jerusa Souza Andrade
Food and Nutrition Sciences (FNS) , 2014, DOI: 10.4236/fns.2014.517182
Abstract: Amazonian fruits are outstanding in quality. They are consumed as true delicacies of nature by the Brazilian population. Besides their attractive attributes, i.e. appearance, different textures and distinctive flavors, their nutritional value is diversified in the type of calories and the functional food ingredients. In addition to being very palatable, Amazonian fruits provide energy-rich macronutrients (lipids, proteins and carbohydrates), micronutrients (minerals, water-soluble vitamins and fat-soluble vitamins), prebiotics (dietary fibers, especially pectin), bioactive substances (carotenoids and polyphenols), variety in the diet and improvement in the organoleptic properties and digestibility of (mixed) foods. This study first aimed to review concepts applicable to nutritional constituents and caloric contents of Amazonian fruits. It also attempted to clarify the potential use of these fruits in metabolic disorders (i.e. diabetes mellitus and/or obesity). To fulfill these purposes, 12 fruits were chosen for their dietetic significance in the Brazilian Amazonia.
Delamination and destruction of the North China Craton
Shan Gao,JunFeng Zhang,WenLiang Xu,YongSheng Liu
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0395-9
Abstract: This article presents an overview on recent developments in studies of chemical and physical processes of lithospheric delamination with respect to destruction of the North China Craton. It is emphasized that the pyroxenite source resulting from interaction between eclogite-derived melt and peridotite is a direct consequence of delamination. The pyroxenite source thus formed has unique mineralogical and geochemical features, which characterize Mesozoic basalts of the North China Craton. Melt-peridotite interaction played an important role in refertilization of cratonic lithospheric mantle, leading to density increase, weakening and final destabilization of the North China Craton. The nature of the melt is the key to distinguish mechanisms of destructing this craton.
Isotopic constrains on the Proterozoic geological history of the Amazonian Craton
C. C. G. Tassinari,K. Sato
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891597
Abstract:
Destruction geodynamics of the North China craton and its Paleoproterozoic plate tectonics
RiXiang Zhu,TianYu Zheng
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0451-5
Abstract: Much attention has been paid in the last two decades to the physical and chemical processes as well as temporal-spatial variations of the lithospheric mantle beneath the North China craton. In order to provide insights into the geodynamics of this variation, it is necessary to thoroughly study the state and structure of the lithospheric crust and mantle of the North China craton and its adjacent regions as an integrated unit. Based on the velocity structure of the crust and upper mantle constrained from seismological studies, this paper presents various available geophysical results regarding the lithosphere thickness, the nature of crust-mantle boundary, the upper mantle structure and deformation characteristics as well as their tectonic features and evolution systematics. Combined with the obtained data from petrology and geochemistry, a mantle flow model is proposed for the tectonic evolution of the North China craton during the Mesozoic-Cenozoic. We suggest that subduction of the Pacific plate made the mantle underneath the eastern Asian continent unstable and able to flow faster. Such a regional mantle flow system would cause an elevation of melt/fluid content in the upper mantle of the North China craton and the lithospheric softening, which, subsequently resulted in destruction of the North China craton in different ways of delamination and thermal erosion in Yanshan, Taihang Mountains and the Tan-Lu Fault zone. Multiple lines of evidence recorded in the crust of the North China craton, such as the amalgamation of the Archean eastern and western blocks, the subduction of Paleo-oceanic crust and Paleo-continental residue, indicate that the Earth in the Paleoproterozoic had already evolved into the plate tectonic system similar to the present plate tectonics.
Geophysical contribution for the study of the Granitic Batholit Santa Helena, southwest of the Amazonian Craton  [PDF]
Vanessa Biondo Ribeiro,Marta Silvia Maria Mantovani
Geologia USP : Série Científica , 2012,
Abstract: The Santa Helena batholith is subject of many controversies concerning its geographical extension, lithological constitution,geochemical characterization and geotectonic setting. This paper aims to contribute for a better understanding ofthis intrusion using geophysical data (gammaspectrometric and aeromagnetic). These data were obtained through surveyscontracted by the Geological Survey of Brazil (CPRM) flown over the study region. Given the compositional variety of therocks, we analyzed the susceptibility contrast (magnetometry) and distribution of radioelements (K, Th and U, measuredby gammaspectrometry) in the batholith. The resulting geophysical signature is different when comparing the northern andsouthern parts of the body, suggesting the presence of two distinct suites. The boundary between these two suites coincideswith the location of an approximately N75°W oriented fault system that extends through the batholith.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.