The Itajaí Basin located in the southern border of the Luís Alves Microplate is considered as a peripheral foreland basin related to the Dom Feliciano Belt. It presents an excellent record of the Ediacaran period, and its upper parts display the best Brazilian example of Precambrian turbiditic deposits. The basal succession of Itajaí Group is represented by sandstones and conglomerates (Baú Formation) deposited in alluvial and deltaic-fan systems. The marine upper sequences correspond to the Ribeirão Carvalho (channelized and non-channelized proximal silty-argillaceous rhythmic turbidites), Ribeirão Neisse (arkosic sandstones and siltites), and Ribeirão do Bode (distal silty turbidites) formations. The Apiúna Formation felsic volcanic rocks crosscut the sedimentary succession. The Cambrian Subida leucosyenogranite represents the last felsic magmatic activity to affect the Itajaí Basin. The Brusque Group and the Florianópolis Batholith are proposed as source areas for the sediments of the upper sequence. For the lower continental units the source areas are the Santa Catarina, São Miguel and Camboriú complexes. The lack of any oceanic crust in the Itajaí Basin suggests that the marine units were deposited in a restricted, internal sea. The sedimentation started around 600 Ma and ended before 560 Ma as indicated by the emplacement of rhyolitic domes. The Itajaí Basin is temporally and tectonically correlated with the Camaquã Basin in Rio Grande do Sul and the Arroyo del Soldado/Piriápolis Basin in Uruguay. It also has several tectono-sedimentary characteristics in common with the African-equivalent Nama Basin.
ABSTRACT. This paper presents a 2.5D gravimetric model generated from 315 new gravity stations obtained along a NW-SE 750 km geophysical transect in the northeastern portion of the Borborema Province, NE Brazil. The regional and residual components of the gravity field were modeled separately. Modeling of the regional anomalies revealed a crustal thickness variation from 28 to 32 km, considering the average densities of about 2.8 g/cm 3 for the continental crust and 3.3 g/cm 3 for lithospheric mantle. High frequency residual anomalies were interpreted on the density contrasts between a 10 km thick upper crust and a broad assembly of supracrustal covers and basement units, which show density values between 2.55 to 2.9 g/cm 3 . The current configuration of the Borborema Province lithosphere is clearly the result of the Mesozoic South American -African breakup of West Gondwana, which overprinted the Brasiliano-Pan African orogenic structures.Keywords: gravimetric modeling, lithosphere, Borborema Province.
RESUMO.Este trabalho apresenta um modelo gravimétrico 2,5D gerado a partir de 315 novas estações gravimétricas levantadas ao longo de uma seção transversal NW-SE com 750 km de extensão na porção setentrional da Província Borborema, NE do Brasil. A modelagem gravimétrica foi aplicada separadamente nas componentes regional e residual do campo gravitacional. A modelagem 2,5D das anomalias regionais revelou que a profundidade da interface crosta-manto varia de 28 a 32 km, considerando uma densidade média de 2,8 g/cm 3 para a crosta continental e de 3,3 g/cm 3 para o manto litosférico. As anomalias residuais de alta frequência foram interpretadas a partir do contraste de densidade da crosta superior, com uma espessura não superior a 10 km, e uma ampla associação litológica, com densidades variando de 2,55 a 2,9 g/cm 3 . A configuração geotectônica litosférica atual da Província Borboremaé claramente resultado da ruptura dos continentes Sul-Americano e Africano no Mesozoico, na qual boa parte dos vestígios das estruturas tectônicas de grandes profundidades formadas durante a orogênese Brasiliana/Pan-Africana foi mascarada peloúltimo episódio tectônico responsável pela fragmentação do Gondwana Ocidental.
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