Oblique rifting along transfer zones: The structural evolution model revealed by physical modeling

Abstract

Oblique rifting is a common process that acts during the rupture of continental masses and can evolve to the passive margin stage. The inter-rift (or intra-rift) interaction can occur by transfer zones (TZs). These zones can be formed at the most diverse scales and, on a large scale, can result in the development of oblique rifts. To understand how TZs nucleate and evolve at the plate scale, we simulated, through physical modeling, the development of oblique transfer zones that connect two parallel rifts (with no lateral overlap) developed orthogonally to the extensional direction. Our results showed that obliquity and rheology could play an important role in the structural architecture of rifts that originated in such a structural environment. When the obliquity ranges from low to intermediate (i.e., 20°≤ α ≤ 45°), these rifts can be compartmentalized into two main structural domains - extremity, and central regions - with diachronic evolution and distinct kinematics. Extremity regions are characterized by oblique-slip deformation with intense rotation/tilting of the substrate. The central region is dominated by transcurrent (and oblique-slip) deformation with the presence of marginal plateaus, pull-apart, and oblique basins. Small variations in the obliquity (around 5°) are enough to affect parameters like faults' dip and geometry, and depocenters’ width and depth, thereby promoting changes in the morphology, geometry, architecture, and configuration of TZs. In a more mature stage, and on a continental scale, the TZs evolve into oblique rifts whose margins are composed of oblique and transcurrent fault segments (transfer/transcurrent) that together define a typical zig-zag geometry. The sizes and numbers of these segments depend on the obliquity and the rheology. Transcurrent fault segments are more common when the obliquity is 20° and 25°, in the model with quartz sand only. The modeling data presented here can be compared with the equatorial Atlantic margin of South America, assuming that it may represent an important plate-scale oblique transfer zone (20°) developed between the South and Central Atlantic.