Evolução geomorfológica e tectônica da porção norte da Bacia do Amazonas: região do Rio Apuaú (AM)
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Data
2016-11-08
Autores
Nascimento, Mayara Aline Santos Ribeiro do [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A paisagem na Amazônia tem mostrado um quadro geomorfológico evolutivo associado a condicionamentos tectônicos no controle da rede de drenagem, com importantes mudanças nos cursos dos rios associadas a sistemas de falhas no âmbito da Neotectônica. Esta pesquisa compreende o estudo da bacia hidrográfica do rio Apuaú, afluente da margem esquerda do rio Negro na sua porção média, a norte de Manaus, no Estado do Amazonas. Foi subsidiada por estudos estruturais e geomorfológicos apoiados em dados de campo, de sensores remotos e de datação dos depósitos aluvionares. Foram reconhecidos blocos desnivelados do relevo, com rupturas de declive (knickpoints) associadas e controladas por falhas. A rede de drenagem apresenta padrões anômalos dos cursos d’água, capturas, meandros e canais encurvados, alinhamento de canais retilíneos, marcando zonas de juntasou zonas de falhas. Os blocos controlam também a distribuição de terraços, paleoterraços e canais abandonados, e suas datações por LOE apontam para depósitos mais antigos na faixa de 53.000 a 62.200 anos, intermediários na faixa de 20.330 a 23.100 anos, e depósitos atuais. O quadro geológico-estrutural aponta para compartimentos morfotectônicos, controlados por falhas normais e falhas transcorrentes destrais associadas. As falhas normais condicionam blocos rotacionados, a rede de drenagem e a distribuição dos depósitos aluvionares, enquanto as falhas transcorrentes parecem balizar e controlar os blocos na porção norte e leste da bacia hidrográfica. Reconhecidas em campo, as falhas normais formam dois grandes conjuntos, orientados NE-SW a EW e NW-SE, enquanto as falhas transcorrentes destrais predominam com orientação próxima a EW e transcorrentes sinistrais NE-SW. O tratamento das populações de falhas para obtenção de eixos de paleotensões indica um evento distensivo NNW-SSE a NW-SE, interpretado como mais antigo, um evento distensivo NE-SW a EW, ao qual pode ser atribuído o ajuste dos blocos rotacionados, controlados por falhas NW-SE, e um arranjo compressivo NNW-SSE a NW-SE, responsável pelas falhas transcorrentes, ambos mais jovens. A associação entre as falhas transcorrentes destrais EW balizando os blocos abatidos e rotacionados controlados por falhas normais NW-SE promove o rearranjo da rede de drenagem e o ajuste da distribuição das coberturas superficiais, indicando atuação do regime neotectônico, decorrente da interação da Placa Sulamericana com a Placa do Caribe.
The landscape in the Amazon has shown a geomorphological evolution associated to tectonic constraints in controlling the drainage network, with important changes in the stream courses associated with fault systems within the scope of the neotectonic regime. This research comprises the study of the catchment of the Apuaú river, a tributary of the left bank of the Negro river in its middle portion, North of Manaus, in the state of Amazonas. Structural and geomorphological studies supported by field data, remote sensing and dating of alluvial deposits were carried out. Uneven relief blocks were recognized with associated slope ruptures (knickpoints) and controlled by faults. The drainage network has anomalous patterns of water courses, captures, meanders and curved channels, rectilinear alignment of channels, indicating fracture or fault zones. The blocks also control the distribution of terraces, paleoterraces and abandoned channels, and their LOE datings point to older deposits in the range 53,000 to 62,200 years, intermediate ones in the interval of 20,330 to 23,100 years and current deposits. The geological and structural framework points to morphotectonic compartments controlled by normal faults and associated dextral strike-slip faults. Normal fault constrain rotated blocks, drainage network and the distribution of alluvial deposits, while the strike-slip faults seem to delimit and control the blocks in the northern and eastern parts of the hydrographic basin. Recognized in the field, normal faults adjust into two large sets, oriented NE-SW to EW and NW-SE, while strike-slip faults predominate striking close to EW dextral and NE-SW sinistral ones. Fault population analysis to obtain paleostress axis indicates a NNW-SSE to NW-SE extensional event, interpreted as the oldest, followed by one NE-SW to EW distensive event, which can be attributed to the adjustment of rotated blocks, controlled by NW-SE faults, and a compressive arrangement NNW-SSE to NW-SE, responsible for the slip faults.The association between the EW dextral transcurrent faults controlling uneven and rotated blocks affected by NW-SE normal faults promotes the rearrangement of the drainage system and adjusting the distribution of surface covers, indicating actions of the neotectonic regime, due to the interaction of the South American Plate with the Caribbean Plate.
The landscape in the Amazon has shown a geomorphological evolution associated to tectonic constraints in controlling the drainage network, with important changes in the stream courses associated with fault systems within the scope of the neotectonic regime. This research comprises the study of the catchment of the Apuaú river, a tributary of the left bank of the Negro river in its middle portion, North of Manaus, in the state of Amazonas. Structural and geomorphological studies supported by field data, remote sensing and dating of alluvial deposits were carried out. Uneven relief blocks were recognized with associated slope ruptures (knickpoints) and controlled by faults. The drainage network has anomalous patterns of water courses, captures, meanders and curved channels, rectilinear alignment of channels, indicating fracture or fault zones. The blocks also control the distribution of terraces, paleoterraces and abandoned channels, and their LOE datings point to older deposits in the range 53,000 to 62,200 years, intermediate ones in the interval of 20,330 to 23,100 years and current deposits. The geological and structural framework points to morphotectonic compartments controlled by normal faults and associated dextral strike-slip faults. Normal fault constrain rotated blocks, drainage network and the distribution of alluvial deposits, while the strike-slip faults seem to delimit and control the blocks in the northern and eastern parts of the hydrographic basin. Recognized in the field, normal faults adjust into two large sets, oriented NE-SW to EW and NW-SE, while strike-slip faults predominate striking close to EW dextral and NE-SW sinistral ones. Fault population analysis to obtain paleostress axis indicates a NNW-SSE to NW-SE extensional event, interpreted as the oldest, followed by one NE-SW to EW distensive event, which can be attributed to the adjustment of rotated blocks, controlled by NW-SE faults, and a compressive arrangement NNW-SSE to NW-SE, responsible for the slip faults.The association between the EW dextral transcurrent faults controlling uneven and rotated blocks affected by NW-SE normal faults promotes the rearrangement of the drainage system and adjusting the distribution of surface covers, indicating actions of the neotectonic regime, due to the interaction of the South American Plate with the Caribbean Plate.
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Palavras-chave
Morfotectônica, Bacia Amazônica, Datação LOE, Depósitos aluvionares, Análise de população de falhas, Neotectônica, Morphotectonic, Amazonian Basin, LOE dating, Alluvial deposits, Fault population analysis, Neotectonics