Geologia do sudoeste do Estado de Goiás : Integração de dados geológicos e aerogeofísicos de alta densidade

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The airborne magnetic and gamma ray spectrometry data related to the Airborne Geophysic Survey Project of the State of Goiás (Block 1) executed between 2004 and 2006 and considered of high density by the acquisition and treatment configuration, were integrated in GIS environment with the existing geologic information, in the SW Goiás region located from the Bom Jardim de Goiás region, eastward to the Córrego do Ouro area. To the treatment, analysis and interpretation of the data were applied traditional techniques like qualitative analysis of individually processed images, binary and ternary compositions and radioelement ratios. The interpretations for acquisition of the geophysical domains maps were driven by existing knowledge, considering all geologic information and field observations, resulting in a product equivalent to a lithogeophysic map in 1:100.000 scale. The geologic-geophysical integration allowed the characterization of sixteen units enclosing ninety-one subunits, which had been grouped in accordance with its chronology and tectonic setting. These geologic units display Archean to Neocretaceous ages. The Cenozoic coverage was eliminated in the final map. The main results are bellow summarized. Identification of new regions with similar gamaespectrometric and field features, typical of the paleoproterozoic units. Delimitation of a north-south trend with orthognaissic sequences and older paleoproterozoic supracrustal rocks and/or neoproterozoic units evolved from these protolites, extending of south of Moiporá until north of the Jussara Town. Optimization of the geologic contacts of the vulcano-sedimentary units that compose the Magmatic Arc of Goiás, as well as the recognition of new areas of these units in other sectors of the investigated region. Identification in the field of acid metavulcanic rocks, composed by metatuffs intercalated with metagraywacks bellowing to the Cuiabá Group, displaying metamorphic-deformational patterns similar to those imprinted in the Bom Jardim de Goiás Group. This facts, retaken the discussion about the Cuibá Group (outcropping at Bom Jardim City neighborhoods) geotectonic positioning in relation to the vulcano-sedimentary sequences of the Magmatic Arc of Goiás. The Ortogneiss of the West of Goiás as previously referred in literature was individualized in several lithotypes and renamed as Neoproterozoic Island Arc Granitites. In the same way the several granite batholites belonging the sin-, late- and post-orogenic granites could be delimited. The late-, sin-, and post-orogenic granites are distinguish from the Neoproterozoic Island Arc Granitites by the highest K, Th and U, and between them, of oldest (sin-orogenic granite) for newest A-Type post-orogenic granites, by the increasing of the radioelements in special of the Th and U. Possible presence of extensional tectonic environment to north of the occurrence area of the Piranhas Formation. In this unit, there were found, thin intercalations of volcanoclastic rocks (riolite-riodycitic tuffs and crystal tuffs which must represent the volcanic equivalents of the granofiric dikes and stocks that crosscut these sediments, attesting the occurrence of acid magmatic activity throughout the evolution of the Piranhas Graben. Individualization of different sub-units that comprise the paleozoic formations of the Paraná Basin, with emphasis to the Ponta Grossa Formation in function of its prospective interest. Delimitation of mafic, ultramafic, carbonatitic and sienitic bodies as well as the associated fenite zones, relatade to the Goiás Alkaline Province (GOAP). These rocks are distinguished not only from the higher gamma spectrometric magmatic pattern but also by the higher magnetic amplitude and continuity in subsurface disclosed for magnetic products of ascending continuation. Among the alkaline bodies that compose the GOAP, three bodies are distinguished by the distinctive behavior of U, K and Th, being characterized for high magnetic amplitude and as excessively impoverishment in K, however showing strong enrichment in U and Th. These features indicate that these bodies are carbonatitic intrusions. Two of these carbonatitic bodies present circular morphology and are known in literature under the assignment of Morro Preto and Caiapó. The third body is elongates according the ENE xiv direction, located about 10 km westward of the previous ones. Equivalent feature is observed in a small sector of the Córrego dos Bois Complex. The region can be segmented, due to the structural framework, in three great domains called blocks, separated by NS structures: - West or Bom Jardim Block structuralized NNE; - Central or Iporá Block structuralized NNW and - East or Córrego do Ouro Block structuralized NE. Internally the blocks present an orthogonal lineaments pattern where the NE and NW directions predominate over the NS and EW trends. The great faults are marked by magnetic structures, or by gamaespectrometric structures and/or of relief features. Some of these fault systems separate great crustais segments and the main systems are called: Araguaia, Serra Negra, Piranhas, Montes Claros de Goiás, Moiporá-Novo Brasil and Serra Dourada. The Araguaia Fault System, with NE-SW trend, of low to moderate angle separates the northwest lands with magnetic signature that suggests the presence in that sector of Archean and/or paleoproterozóicas rocks. The Montes Claros de Goiás Fault System, with NS trend, of high dip angle, wit extensional nature seems to restrict the west granites with sin-orogenic characteristics. The Moiporá-Novo-Brazil Fault System, with NS trend, of moderate to high angle, with directional-extensional kinematics put together lands of different ages from archean and paleoproterozóicas with neoproterozoic isotopic signature units or derivate from these protolith. This system also includes neoprotozoic units, with predominant youthful isotopic signature, westward. The structural setting of the area shows a long history, with successive reactivations. The oldest phase is marked by sub-horizontal foliation with low dipping for the south quadrants, indicated thrust kinematics for north and for old rigid nuclei represented in the south by the Paraná Craton, hidden under the sediments of the Paraná Basin and in the south by the Goiás Massive. Late reactivations of compressional character are registered by the sincinematic anorogenic granite positioning these occurrence of about 500 - 550 My, induced probably for the final inversion of the Paraguay Belt, marking the end of the Brasiliano Cycle in the region. In the Phanerozoic the region was submitted to extensional tectonic, related to the installation of the and Paraná Basin and to the opening of the Atlantic Ocean. Among these events there are distinguished the Arc of the Paranaíba, Flexura de Goiânia and Bom Jardim and the extensional event, with possible evolvement of mantelic plume in the Upper Cretaceous when the GOAP was formed. The integration of the high density aerogeofísic data of southwestern of Goiás with the geologic, geocronologic and geochemistry data, digital land model and other geophysical products allowed a considerable advance in the geologic knowledge of the region, resulting in the optimization of geologic unit mapping, subdivision of differentunits and the regional structural setting, beyond identifying and delimiting units of geologic/geotectonic uncertain positioning.

ASSUNTO(S)

geologia geografia física - goiás

ACESSO AO ARTIGO

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