Tectônica transcorrente pós-mesozoica na região de Laguna, litoral de Santa Catarina
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Data
2017-03-21
Autores
Aquaroli, Luis Henrique Souza [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Estudos estruturais realizados na região de Laguna, no litoral sul de Santa Catarina, levaram ao reconhecimento de importantes episódios de deformação rúptil tardios a posteriores ao quadro mesozoico de evolução regional. Na região afloram rochas do domínio geológico do Escudo Catarinense, granitos com ocorrência de grande quantidade de diques básicos derivados do magmatismo Serra Geral que afetou a Bacia do Paraná no Juro-Cretáceo, precursores da quebra do supercontinente Gondwana. Os diques são associados a um dos ramos de uma junção tríplice, de direção NNE-SSW, intrusivos em rochas graníticas pré-cambrianas do Batólito Florianópolis e marcados na paisagem por cristas alinhadas nesta direção e paralelos à linha de costa local. Com o auxílio de imagens de SRTM e Landsat 7 ETM+, foram reconhecidos os principais lineamentos estruturais e quatro direções principais de fraturamento NNE-SSW, NW-NE, NE-NW e E-W. Estes lineamentos formam feixes alinhados ou constituem limites de compartimentos geomorfológicos marcados no relevo e na drenagem. Foram caracterizados, através de informações de campo, sistemas de falhas transcorrentes sinistrais e destrais, secundariamente falhas normais com alto ângulo de mergulho, além de algumas falhas inversas localizadas. Apresentam direções principais NNE, NW, NE e E-W, e cortam todo o conjunto rochoso, deformando tanto granitos e quanto diques de diabásio. Pela análise estrutural dos conjuntos de falhas e pela reconstrução de eixos de paleotensões, foram identificados quatro eventos deformacionais rúpteis distintos. O primeiro estágio, interpretado como desenvolvido entre o Neocretáceo e o Paleoceno, originou falhas transcorrentes sinistrais E-W com σ1 na direção NE-SW. Em sequência, foi estabelecido um evento distensivo com σ3 NE/SW, interpretado como associado ao evento distensivo das bacias cenozoicas do Sudeste do Brasil, entre o Paleoceno e o Oligoceno/Mioceno. O terceiro evento formou estruturas transcorrentes sinistrais N-S e Destrais E-W com σ1 posicionado NW-SE, entre o Neógeno e o Quaternário e, por último um evento transpressivo com σ1 na direção próxima a E-W até ENE/WNW, desenvolvido no Quaternário. Esses eventos estão relacionados às fases deformacionais que afetaram toda a borda leste do Brasil no Cenozoico, sendo os dois primeiros eventos relacionados ao desenvolvimento do Sistema de Riftes do Sudeste do Brasil, com distensão NW-SE bem caracterizada entre o Paraná e o Rio de Janeiro, e os últimos eventos relacionados com a deriva e rotação da Placa Sul-Americana e o ajuste desta em relação à Placa de Nazca, apontando para um quadro associado ao regime neotectônico. Feição de destaque local é a grande importância dos sistemas transcorrentes em relação às falhas normais, principalmente considerando que na região o processo de abertura do Oceano Atlântico e de formação da Bacia de Santos foi condicionado por falhas normais distensivas orientadas NNE-SSW.
Structural studies carried out in the region of Laguna, on the southern coast of Santa Catarina, led to the recognition of important episodes of brittle deformation pointing to late to post-Mesozoic regional evolution. In the region outcrop rocks of the Catarinense Shield geological domain, with a great number of basic dykes derived from the Serra Geral magmatism that affected the Paraná Basin in the Jurassic-Cretaceous times, precursors of the supercontinent Gondwana break-up. The dikes are associated to the NNE-SSW branch of a regional triple junction, they are intrusive in Precambrian granitic rocks of the Florianópolis Batolith and they are marked in the landscape by aligned ridges in this direction and parallel to the local coastline. With the use of SRTM and Landsat images, the principal structural lineaments and four main directions of NNE, NW, NE and E-W fracture were recognized. These lineaments form aligned clusters or constitute limits between geomorphological compartments marked in the relief and drainage patterns. Through field information, sinistral and destral transcurrent fault systems were characterized, secondly accompanied by steep normal faults as well as some localized inverse faults.They present the main directions NNE, NW, NE and E-W and cut the whole rocky set, deforming both granites and diabase dikes. By the structural analysis of the fault sets and by the paleostress reconstructions, four different deformational events were identified. The first stage, interpreted as developed between the Neocretaceous and the Paleocene, originated E-W sinistral transcurrent faults with σ1 in the NE-SW direction. In sequence, a distensive event was established with σ3 NE / SW, interpreted as associated to the distensive event of the Cenozoic basins of Southeastern Brazil, between the Paleocene and the Oligocene / Miocene. The third event formed sinistral N-S and dextral E-W structures with σ1 positioned NW-SE, during Neogene and Quaternary, and finally a transpressive event with σ1 in the direction close to E-W to ENE/WNW developed in the Quaternary. These events are related to the deformational phases that affected the entire eastern border of Brazil in the Cenozoic, being the first two events related to the development of the Riftes System of the Southeast of Brazil, with a well characterized NW-SE distensive event between Paraná and Rio de Janeiro, and the last events are related to the drift and rotation of the South American Plate and the its adjustment in relation to the Nasca Plate, pointing to a brittle framework associated with the neotectonic regime. Local highligth for the great importance of transcurrent systems in relation to normal faults, especially considering that in the region the process of opening of the Atlantic Ocean and formation of the Santos Basin was conditioned by NNE-SSW oriented distensive normal faults.
Structural studies carried out in the region of Laguna, on the southern coast of Santa Catarina, led to the recognition of important episodes of brittle deformation pointing to late to post-Mesozoic regional evolution. In the region outcrop rocks of the Catarinense Shield geological domain, with a great number of basic dykes derived from the Serra Geral magmatism that affected the Paraná Basin in the Jurassic-Cretaceous times, precursors of the supercontinent Gondwana break-up. The dikes are associated to the NNE-SSW branch of a regional triple junction, they are intrusive in Precambrian granitic rocks of the Florianópolis Batolith and they are marked in the landscape by aligned ridges in this direction and parallel to the local coastline. With the use of SRTM and Landsat images, the principal structural lineaments and four main directions of NNE, NW, NE and E-W fracture were recognized. These lineaments form aligned clusters or constitute limits between geomorphological compartments marked in the relief and drainage patterns. Through field information, sinistral and destral transcurrent fault systems were characterized, secondly accompanied by steep normal faults as well as some localized inverse faults.They present the main directions NNE, NW, NE and E-W and cut the whole rocky set, deforming both granites and diabase dikes. By the structural analysis of the fault sets and by the paleostress reconstructions, four different deformational events were identified. The first stage, interpreted as developed between the Neocretaceous and the Paleocene, originated E-W sinistral transcurrent faults with σ1 in the NE-SW direction. In sequence, a distensive event was established with σ3 NE / SW, interpreted as associated to the distensive event of the Cenozoic basins of Southeastern Brazil, between the Paleocene and the Oligocene / Miocene. The third event formed sinistral N-S and dextral E-W structures with σ1 positioned NW-SE, during Neogene and Quaternary, and finally a transpressive event with σ1 in the direction close to E-W to ENE/WNW developed in the Quaternary. These events are related to the deformational phases that affected the entire eastern border of Brazil in the Cenozoic, being the first two events related to the development of the Riftes System of the Southeast of Brazil, with a well characterized NW-SE distensive event between Paraná and Rio de Janeiro, and the last events are related to the drift and rotation of the South American Plate and the its adjustment in relation to the Nasca Plate, pointing to a brittle framework associated with the neotectonic regime. Local highligth for the great importance of transcurrent systems in relation to normal faults, especially considering that in the region the process of opening of the Atlantic Ocean and formation of the Santos Basin was conditioned by NNE-SSW oriented distensive normal faults.
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Palavras-chave
Sistemas transcorrentes, Análise estrutural, Reconstrução de eixos de paleotensão, Evolução tectônica, Neotectônica