Navegando por Autor "OLIVEIRA, Junny Kyley Mastop de"

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Caracterização estrutural da borda sudeste do sistema transcorrente Carajás com ênfase nas rochas do terreno granítico-gnáissico
(Universidade Federal do Pará, 2002-04-05) OLIVEIRA, Junny Kyley Mastop de; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The Itacaiúnas Belts is placed in the east board of the Amazonian Craton. It is dividid into two main tectonic domains: (1) the Carajás and Cinzento Strike Slip systems that expose Archaean and Proterozoic volcano-sedimentary rocks; and (2) several sets of imbricated thurst fans covering the large basement area. The Carajás Strike Slip System (CSSS) is formed by sets of interrupted, anastomosed lineament, trending around the E-W direction, where both acid and basic volcanic rocks together with ironstones, quartzites (Grão Pará Group); sandstones, mudstones (Águas Claras Formation) and conglomerates (Gorotire Formation) are present inside a kilometer-scale dilational jog. These rocks cover the granitic-gneissic rocks of the Archaean basement. Proterozoic granites are intruded in almost all these rocks forming several plutons. The CSSS is cut by the Carajás Fault representing the most important particular structural feature associated to the Archaean tectonic evolution of the region. The basement of the region, exposed to the south of the CSSS is affected by an early ductile sinistral transpressional event of deformation able to develop a foliation on the rocks. A later ductile-brittle deformational event is overprinting the early mylonitic fabric. This feature has been related to an important hydrothermal episode of alteration including several pulses. On the basis of this general tectonic setting was defined the main aim of this research is which related to the presence of the later planar and linear ductile-brittle fabrics that overprint the early ductile foliation of the basement rocks. The occurrence, age and role of this earlier fabric in the tectonic evolution of the region is not well known. Previous studies have shown the close relation between this deformational feature and the presence of important ore deposits (mainly Au and Cu) distributed along the area. The studied area is located in the SE board of the CSSS, in the basement terrain and is geographically limited by the coordinates 6º 19'56'S; 6º 3508'S and 49º 4913"W; 50º 16'36"W. This study was developed by 1:50.000 scale geological mapping, 3 supported by remote sensing techniques, focusing the geometry and kinematics of the related structures, and also detail scale mapping (1:100) of selected areas and outcrops. The mapping revealed the presence of rocks from the Pium Complex (granolites; about 3.0Ga); Xingu Complex (gneisses, granitoids, amphibolites and migmatites; 2.8Ga); Plaque Suite (biotite — granites; 2.7Ga); Grão Pará Group (basalts, amphilolites, quatzites and ironstones; 2.7 Ga); Proterozoic Granites (2.0-1.8Ga). The Pium and Xingu complexes and Plaque Suite rocks are marked by the presence of an important milonitc foliation trending about the E-W, WNW-ESE and N-S directions always stepling dipping (>70º). The E-W trendding foliation is the most important. This fabric is better represented by a spaced, disjunctive, anastomosing, sometimes smooth foliation closely associated to several milonitic features. This foliation is associated to a partitioned ductile transpressional episode of deformation developed under both sinistral (more important) and destral displacements. A second non-pervasive planar-linear deformational fabric is observed overprinting the early milonitic one. This features are present in both basement and supracrustal rocks (mainly the Grão Pará Group) where this early fabric may be not present. This new foliation is a brittle cleavage that can reach different stages of development from a coarse brechia placed along fault zones to a spaced disjunctive cleavage (from a typical fracture cleavage to a slaty cleavage) along shear bands. This foliation may be accompanied for a structural constructed lineation (slickenlines and slickensides). The general orientation of this set of foliation places around the NW-SE and NE-SW directions, most of them along the first trend. This fabric is associated to a sinistral-dextral transpressional deformational event, able to reativate part of the early milonitic one. Hydrothermal mineral assemblages forming veins fills the shear bands and associated features. This fabric is supposed to be formed by cataclastic flow during high fluid-pressure along tectonic conducts related to the Carajás Fault reactivation during its nucleation about 2.7Ga.