Caracterizacao litoquimica e aspectos petrologicos de rochas vulcanicas da Formacao Serra Geral: regiao centro-sul do Estado do Parana

This work defines the main volcanic types of Central-Southern Parana State (Serra Geral Formation), their stratigraphic relations, and which petrological process are able to explain the observed volcanic associations. -from English summary

Geochemical Study of the Itabirite Iron Ores of the Alegria Mine - Quadrilátero Ferrífero, Minas Gerais, Brazil

The iron ores of Alegria mine are composed of itabirites enclosing minor bodies of high-grade ores. The itabirites are classified according to mineralogical composition in five types: martite-rich, goethite-rich, specularite-rich, magnetite-rich and anphibolite-rich ores. The hematites are martite-rich, magnetite-rich, specularite-rich and more rarely, amphibolite-rich. Other classification criteria of the ores are based on the physical properties and the degree of compaction. As such, the itabirites and hematites can be classified as hard, friable and soft types. The mineralogical/textural evolution of the ores is linked to the pressure and temperature conditions that accompanied the tectonic processes in anphibolite facies and the different degrees of subsequent surficial weathering processes. Petrographic and microstructural studies indicate that the magnetite and amphibole bearing itabirites represent the parent rocks that created the other itabirites and that the specularite itabirites and the hard martite types are related to silica dissolution and redeposition in zones of high and low strain. Most of itabirites ores correspond to chert oxide facies banded iron formation, except the goethite and amphibole bearing itabirite that resemble a silicate or oxide-silicate facies with minor carbonate impurities. The great mass and pods of soft martite itabirites are probably shaley oxide facies BIFs with little volcanic contribution. Trace element contents of the Alegria's itabirites show strong dissimilarities with BIFs associated with volcanism (Algoma type), but closely ressemble to the Lake Superior type, with high content in Cr, Co and low V, Ni, Cu and Zn. Although the absolute contents of REE present in the Alegria's itabirites are, in general very low, the pattern when normalised by NASC is similar to the great majority of the Archean and Paleoproterozoic BIFs elsewhere in the world, and characterised by positive Eu anomaly.

As rochas intrusivas da Formação Serra Geral na Porção leste da Bacia do Paraná no Estado de São Paulo: Aspectos petrográficos e geoquímicos - Resultados preliminares

The purpose of this paper is to present preliminary aspects of the petrography and chemistry of intrusive rocks (sills and dykes) from the eastern portion of the Parana Basin in the State of Säo Paulo. Data from 80 samples of the region show a subaphyric and subophitic nature and have plagioclase (25-50%), augite (3-39%), pigeonite (0-10%) and magnetite (4-20%) as an essential minerals. Apatite and quartz are present as accessory minerals. The geochemical data of intrusive rocks show a basic to intermediate composition (48% < SiO 2 < 56%) and a high Ti nature (TiO 2 > 2%). Based on the minor and trace composition of the intrusive rocks, two different magma types were recognized, named Paranapanema and Pitanga. The spatial distribution of these magma types is not alleatory in the studied region. The intrusive rocks of Pitanga magma type are displayed in the Campinas-Paulinia region, while the Paranapanema magma type cover a large region above that one, between Rio Claro and Cajuru. Furthermore, the chemical composition of the lava flows of the Serra Geral Formation, sampled in this work, reveals a magma of Urubici type. So, the intrusive rocks of the eastern portion of the of State Säo Paulo are not the extension of the lava flows, or they aren't a portions which don't reach the surface.

Litogeoquímica E aspectos Petrogenéticos dos basaltos da Província Magmática do Paraná na porção centro-norte do Estado de São Paulo

The petrographic and geochemical characterization of flood basalts of Serra Geral Formation are here presented. The investigated areas are situated in four different regions of São Paulo state: Jaú, Ribeirão Preto, Franca and Fernandópolis. They represent almost the total area of outcrops of basalts in the São Paulo State. The petrographical data reveals that these rocks are constituted mainly by plagioclase (30-40%), pyroxenes, augite and pigeonita (20-30%) and magnetite (5-15%), and show a intergranular texture and its varieties intersertal, hialophitic and pilotaxitic. The geochemical data show a basic and tholeiitic affinity of the studied basalts, with high-Ti content (TiO2 > 1.8%), typical of the northern region of Paraná Basin. Three different magma-types were recognized: Paranapanema, Urubici and Pitanga. The first magma-type is concentrated in the Fernandópolis region, the second in the Franca region, and the Pitanga occurs in the Ribeirão Preto and Jaú regions. The distribution patterns of these magma-types and the detailed study of geochemical data showed that they are, probably, generated by a melting of a continental lithospheric mantle.

Parâmetros físicos pré-eruptivos do magmatismo ácido da província magmática do Paraná: Resultados preliminares

A set of 12 samples of acid rock types Palmas (ATP) and Chapecó (ATC) was used to determine the chemical composition of plagioclase and pyroxene by electron microprobe, with the purpose to get information about the pressure and temperature of crystallization of these rocks. The results show that the pyroxene of ATP rocks (3,2 ± 1,2 kbar, max = 5,1 kbar and 1028 ± 38°C) were formed under pressure conditions higher than those ATC (1,8 ± 0,9 kbar, max = 3,4 kbar and 995 ± 26oC). However, the pressures obtained from plagioclase showed higher pressures for ATC (3.2 ± 1 kbar, max = 6,4 kbar and 1033 ± 12°C) than ATP (1,9 ± 1 kbar, max = 4,8 kbar and 1043 ± 5°C), suggesting that the crystallization of rocktype ATP began with the formation of pyroxene and plagioclase almost simultaneously at a depth of around 17 km while the ATC, began with the crystallization of plagioclase at a depth of about 21 km (assuming a gradient of 3,3 kbar/km). The geothermometry of plagioclase allow us to calculate the concentration of water from about 1 ± 0,3% H2O for both acid rock types. Additional calculations allow us to get the depth of water exsolution of magmatic liquid at 30m below the surface. Although the data are still preliminary and insufficient to model the extrusion of these rocks, they point out to an effusion mechanism of a partially fluidized magma by volatile, which would spread to large areas with small friction with the surface that would increased with the increase of viscosity caused by the loss of volatile and decreasing of temperature, developing coherent structures as lava flows.

Evolução tectônica dos altos estruturais de Pitanga, Artemis, Pau D'Alho e Jibóia - Centro do Estado de São Paulo

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Petrologia e caracterização geoquímica das fontes mantélicas da região noroeste da província magmática do Paraná

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evolução termocronológica por traços de fissão em apatita e zircão das Bacias da Transição Proterozóico-Fanerozóico de Camaquã (RS), Castro (PR), Eleutério (SP/MG), Jaibaras e Cococi (CE)

Pós-graduação em Geologia Regional - IGCE

New insights on the occurrence of peperites and sedimentary deposits within the silicic volcanic sequences of the Parana Magmatic Province, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Geologia do depósito de ouro do alvo guarda-mor, na sequência Jaupaci (Israelândia - GO)

The study area of the Guarda-Mor target (Israelândia-GO) contextualizes the terrains of the estaern portion of the Arenópolis Magmatic Arc, more accurately, the Neoproterozoic associations inserted in the field of the Jaupaci volcano-sedimentary sequence. The mapped area is located in the central-western of Goiás state. The presente paper has as main objective to characterize the structural, petrographic and litogeochemistry of the target rocks beyond to compare these factors with the Mina Bacilândia rocks (Fazenda Nova-GO) in order to assess the genetic similarity of volcano-sedimentary units and deposits associated. The Guarda-Mor target is represented by the Jaupaci metavolcanic rocks sequence presenting bimodal volcanism. This sequence consists in metafelsic rocks like sericite/muscovite quartz schist, phyllite and metarriolites and/or metariodacites with calc-alkaline geochemical signature and metamafic rocks with tholeiitic character formed by actinolite - chlorite schist and chlorite - quartz schist. Besides the package of supracrustal rocks also can be observed the occurrence of a local intrusion syn- to late - tectonic named Granito Subvulcânico. In the study area beyond the marked volcanism also seen an event of crustal melting granitogênese evidenced by the presence of 2 granites at the east and the west of the map, Granito Israelândia and Granito Iporá respectively. Structural analysis both at the macro and micro have identified 3 deformation phases. The types of rock on the region record features in the metamorphic facies top and down. These features were subdivided into 3 metamorphic areas: the east and West areas show thermal metamorphism due to intrusion of adjacente granites while the central domain displays features of regional metamorphism. Gold mineralization of the Guarda –Mor deposit target suggests a possible structural control beyond pronounced the hydrothermal alteration. The mineralization may also be...

Quimioestratigrafia do vulcanismo ácido mesozóico da província magmática do Paraná: porção SE do estado de Santa Catarina

The Mesozoic acid volcanism of the Paraná-Etendeka Province can be considered as one of the biggest events of its kind in the Earth's surface, and its study have attracted special interest in characterizing the end of magmatism that preceded the rupture process and the formation of continental Africa and South America Although significant, the acid volcanism featuring Members Chapecó Palmas and Serra Geral Formation represents only 2.5% of the total generated by the magmatic rocks and perhaps therefore the existing literature on these rocks is well less significant than that on the basalts. However, there are still aspects still unclear about the origin and evolution of these rocks in relation to the associated basalts. Thus, two profiles were selected, called RA and TA, which be a systematic collection of samples from the base where the Botucatu Formation sandstones occur at the top, where they observe Palmas acid rock type. These samples should be analyzed for major, minor and trace elements and treated in specific diagrams to define the vertical variation lithochemistry and their possible relationships with the associated basalts

Modelagem gravimétrica no Lineamento Guapiara, sul do Estado de São Paulo

The Guapiara Lineament is an important geological feature of the State of São Paulo, Brazil, associated with Mesozoic volcanism in the Paraná Basin. This paper aims at the interpretation and modeling of gravity data collected at a semi-detailed scale between Capão Bonito and Apiaí to identify the geometry of crustal partitioning along this lineament. Maps of Bouguer anomaly in the area show a remarkable positive gravimetric anomaly oriented NW-SE, which coincides with the orientation of the greater concentration of dikes associated with the Guapiara Lineament. The crustal model developed from anomalies shows a significant thinning of the crust in the area and corroborates previous studies. The crustal thinning was caused by mantle rise, reflecting the epirogenetic activity generated by the propagation of the divergent tectonic forces that occurred at the margin of the South American Plate during the Cretaceous.