Satellite-Derived Gravimetry for Abrolhos Continental Shelf, States of Espírito Santo and Bahia, Brazil, and Its Relation to Tectonic Genesis of Sedimentary Basins

Abstract

ABSTRACT. This paper presents the results of satellite-derived gravimetry for Abrolhos Continental Shelf and the adjacent areas, States of Espírito Santo and Bahia, Brazil, and discusses tectonic genesis of the sedimentary basins. The free-air and Bouguer anomalies on the continental shelf show a gradual increase from coast to continental shelf break. The total difference of 135 mGal indicates crust thinning of 4.5 km. The Bouguer anomaly increases beyond the shelf break and continues up to the abyssal plane. The total difference of 260 mGal suggests crustal thinning of 9.0 km. The studied area has two types of passive continental margin: 1) ES-type with high continental slope, low and narrow continental rise, and high free-air and Bouguer anomalies; 2) SP-type with low continental slope, high and wide continental rise, and low gravity anomalies. There are three types of sedimentary basins with different geologic structure and tectonic genesis: 1) Basins on the continental shelf, CSH-type; 2) Basin on the continental rise, CRS-type; 3) Continental rift basin, CRF-type. The CSH-type, as Espírito Santo basin, has coherent free-air and Bouguer anomalies 40 to 50 mGal lower than the adjacent areas. The sedimentary deposits are 2.0 to 2.5 km thick. The basement depression is sustained by mechanical strength without isostatic compensation. The normal faults of basin border are limited within upper crust. The CRS-type, as Pedro Canário basin, has low local residual Bouguer anomaly with difference of 40 mGal. The sedimentary deposits are more than 2.7 km thick. The continental side basin border is under isostatic compensation due to deep normal fault between continental slope and continental rise. The oceanic side border is sustained by mechanical strength of the basement. The CRF-type, Besnard Passage, is a continental rift basin originated from mantle pull-apart tectonism. The rift bottom is under complete isostatic compensation. The normal faults of the graben border continue to the mantle. The Moho depth along the rift is at least 6.5 km shallower than the adjacent areas.Keywords: satellite-derived gravimetry, Abrolhos Continental Shelf, sedimentary basin, crustal thinning, isostatic compensation. RESUMO.Este artigo apresenta os resultados da gravimetria por satélite para a Plataforma Continental de Abrolhos e asáreas adjacentes, ES-BA, e discute as gêneses tectônicas das bacias sedimentares. As anomalias ar-livre e Bouguer na plataforma continental mostram um aumento gradativo a partir da costa até a quebra da plataforma continental. A diferença total de 135 mGal indica afinamento da crosta continental de 4,5 km. A anomalia Bouguer se apresenta além da quebra da plataforma e continua até o assoalho abissal. A diferença total de 260 mGal sugere afinamento crustal de 9,0 km. Naárea estudada, observam-se dois tipos de margem continental passiva: 1) Tipo ES com talude continental alto, elevação continental baixa e curta e anomalias ar-livre e Bouguer altos; 2) Tipo SP com talude continental baixo, elevação continental ...