AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
An Entirely New 3-D View of the Crustal and Mantle Structure of a South Atlantic Passive Margin – Santos, Campos and Espírito Santo Basins, Brazil
(1) E&P-EXP, Petrobras, Rio de Janeiro, Brazil.
(2) Cenpes, Petrobras, Rio de Janeiro, Brazil.
The interpretation of 12,000 km of very deep (PSTM to 16 sec., PSDM to 25 km) 2D seismic sections, coupled with gravimetric and magnetometric modeling line-by-line, and the integration of the results with the regional data bank of Petrobras, all together viewed in terms of the recent tectonic models developed for the rupturing and separation of mega-plates, led to a regional (500,000 km2), first-time ever, 3D-view of the deep structure underlying the prolific sedimentary basins of Santos, Campos and Espírito Santo in southeastern Brazil. The three basins are situated onto a continental margin that narrows gradually, from south to north, from a very wide (Santos), through an intermediate (Campos), and then to a narrow (Espírito Santo) passive margin. The crustal structure of the Santos Basin shows a zonation from west to east of alternating bands of NE-SW-trending thin (plastic basement terrains) and thick (resistant basement terrains) stretched continental crust. In vertical section this zonation is displayed as a series of necking zones, leading to a highly irregular, low to moderate crustal taper. Such zonation is less developed in Campos Basin, where the crustal taper is moderate and regular , and practically non-existent in the Espírito Santo Basin, where the crustal taper is high. The gradual narrowing of the alternating bands towards the north in the Santos Basin creates sub-basins similar to V-shaped basins described in the North Atlantic margins of Ireland and Canada. Continental crust perforated by mantle can be seen at the tips of such sub-basins. Exhumation of the mantle marks the continental-oceanic crustal transition and can be mapped continuously from Santos to Espírito Santo; sometimes attaining significant widths. Serpentinization of the exhumed mantle can be deduced from the gravimetric modeling to occur down to several kilometers (6-8) deep. The surface geometry of the mantle subcrop is influenced by major continental and oceanic structures. Oceanic crust is a thin slab of circa 7 to 9 km thick and gradually thins to the east.