Transform Margin Rift Architecture: An Example from the Brazilian Equatorial Margin

摘要

The Equatorial Atlantic evolved from a transform margin to an oblique-passive margin from the early rifting to early drifting stages. The entire Equatorial region of the South Atlantic behaved as a globalscale accomodation zone linking the evolving Central and Southern Atlantic ocean basins. Lithospheric keels and the roots of thick, stable Proterozoic cratons worked as an anchor, preventing and postponing the continental rupture. The transition, from a continental transform margin to an oblique- passive margin,lasted approximatelly 10 m.y. Once oceanic lithosphere started to be created at the main transtensional segments, large offset transform faults developed. Remarkable differences are observed between adjacent basins. Deformation partitioning ocurred at the equatorial margin due to the coaxiality of the progressive deformation. Diachronous deformation occurred as a function of the degree of obliquity of each basin at a specific time. Individual segments of the margin are associated with individual strike-slip basins at early rifting stages and have different amounts of obliquity with a decrease in obliquity from south to north. Because, basement faults form and develop during rifting their geometry gets locked at the time of first emplacement of oceanic crust. Therefore, the geometry of the basement and basement faults can be used to reconstruct the geometries of the original strike-slip basins prior to oceanic spreading.