Structural Styles in the IcaraI Basin, Brazilian Equatorial Margin

Abstract

The Icarai Basin, one of the compartments of the larger Ceara Basin located on the Brazilian equatorial margin, presents two distinct structural styles, clearly identifiable in seismic data. On the western side of the basin structures are characterized by intense folding associated with low to high angle thrust faults, whereas on the eastern side of the basin structures are represented by normal faults and tilted half graben. The change from one style to another is gradual, as both decrease in intensity towards the center of the basin, where they coexist. The distribution and relationship of structures along the basin suggests that the Icarai Basin was a transition zone between two distinct stress regimes, one predominantly transtensive and the other predominantly transpressive, which were simultaneously active in adjacent areas during the Lower Cretaceous. The existence of such distinct stress regimes is probably related to the initial geometry of development of the South American equatorial margin.