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ABSTRACT. This paper presents the results of satellite-derived gravimetry for Abrolhos Continental Shelf and the adjacent areas, States of Esp´irito 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 tocontinental 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 upto 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-typewith 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 continentalrise, 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 Esp´irito Santo basin, has coherent free-air and Bougueranomalies 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 strengthwithout isostatic compensation. The normal faults of basin border are limited within upper crust. The CRS-type, as Pedro Can´ario basin, has low local residual Bougueranomaly 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 todeep normal fault between continental slope and continental rise. The oceanic side border is sustained by mechanical strength of the basement. The CRF-type, BesnardPassage, is a continental rift basin originated from mantle pull-apart tectonism. The rift bottom is under complete isostatic compensation. The normal faults of the grabenborder 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 satelite para a Plataforma Continental de Abrolhos e as areas adjacentes, ES-BA, e discute as geneses tectonicas das bacias sedimentares. As anomalias ar-livre e Bouguer na plataforma continental mostram um aumento gradativo a partir da costa ate a quebra da plataforma continental. A diferenca total de 135mGal indica afinamento da crosta continental de 4,5 km. A anomalia Bouguer se apresenta alem da quebra da plataformae continua ate o assoalho abissal. A diferenca total de 260 mGal sugere afinamento crustal de 9,0 km. Na area estudada, observam-se dois tipos de margem continental passiva: 1) Tipo ES com talude continental alto, elevacao continental baixa e curta e anomalias ar-livre e Bouguer altos; 2) Tipo SP com talude continental baixo, elevacao continental alta e extensa e anomalias gravimetricas baixas. Existem tres tipos de bacias sedimentares com estrutura geologica e genesis tectonicas diferentes: 1) Bacias na plataforma continental, Tipo CSH; 2) Bacias na elevacao continental, Tipo CRS; 3) Bacia de rifte continental, Tipo CRF. O Tipo CSH, como a bacia do Espirito Santo, possui anomalias ar-livre e Bouguer coerentes 40 a 50 mGal mais baixas do que as areas adjacentes. Os depositos sedimentares sao de 2,0 a 2,5 km de espessura. A depressao do embasamento e sustentada pela rigidez mecânica sem compensacao isostatica. As falhas normais das bordas de bacias sao limitadas dentro da crosta superior. O Tipo CRS, como a bacia Pedro Canario, tem baixa anomalia Bouguer local com diferenca de 40 mGal. Os depositos sedimentares tem mais de 2,7 km de espessura. A borda da bacia do lado continental esta sob compensacao isostatica devido a falha normal profunda entre talude continental e elevacao continental. Aborda do lado oceânico e sustentada pela rigidez mecânica do embasamento. O Tipo CRF, Passagem Besnard, e uma bacia do rifte continental originada do tectonis mode distensao do manto. O fundo da bacia esta sob compensacao isostatica completa. As falhas normais da borda do graben continuam ate o manto. A profundidade da Moho ao longo do rifte e pelo menos 6,5 km mais rasa do que as areas adjacentes. Palavras-chave: gravimetria por satelite, Plataforma Continental de Abrolhos, bacia sedimentar, afinamento crustal, compensacao isostatica.

revista brasileira de geofísica

SATELLITE-DERIVED GRAVIMETRY FOR ABROLHOS CONTINENTAL SHELF, STATES OF ESPÍRITO SANTO AND BAHIA, BRAZIL, AND ITS RELATION TO TECTONIC GENESIS OF SEDIMENTARY BASINS