Abstract The offshore South Caribbean deformed belt (SCDB) is a 100-km-wide (62 mi), late Cenozoic sedimentary accretionary prism formed where the Caribbean plate is obliquely subducted beneath northern South America. Progradation of deltaic deposits of the 1500-km-long (932 mi) Magdalena River over the SCDB and tectonic deformation of the deltaic sedimentary rocks has created one of the youngest (last 10 Ma) and thickest (5–18 km [3–5 mi]) accretionary prisms in the world. We use three types of data (deep-penetration, seismic-reflection profiles, gravity modeling collinear with the seismic lines, and structural restorations) to describe the late Miocene to Recent thrust kinematics of the 10- to 18-km-thick (6.2–11.1 mi) SCDB formed above the subducting Caribbean Oceanic Plateau whose crust varies in thickness from 17 km (10.6 mi) in the southern part of the 180-km-long (111 mi) study area to 8 km (4.9 mi) in the north. In the southern area of thicker subducted plateau crust, the structural style is characterized by Neogene growth strata defining a major thrusted sequence that is backthrust in a landward direction, deformed by reactivation of preexisting faults as out-of-sequence thrust (OOST) faults, common shale diapirism, and active, margin-parallel strike-slip faults that accommodate the oblique-slip component of subduction. In the northern area of thinner oceanic crust (6–8 km [3.7–4.9 mi]), the structural style includes seaward-verging, imbricated thrust fans with less prominent backthrusting and strike-slip faulting, and more prominent shale diapirism. Proposed controls for the observed structural differences between the northern and southern areas include (1) more buoyancy of the subducted plate in the southern area due to its greater crustal thickness, and (2) the presence of more overpressured and ductile deformed shale layers with associated shale diapirs in the north.

Abstract The Cañones fault zone in north-central New Mexico is a boundary between the Colorado Plateau to the west and the Rio Grande rift to the east. It consists of a major fault, the Cañones fault, and a series of synthetic and antithetic normal faults within the Abiquiu embayment in the northwestern Española basin. The Cañones fault is a southeast-dipping high-angle normal fault, striking ~N20°E in the south, N40°E in the middle, and east-west at its northern end. The synthetic and antithetic faults are sub-parallel to the major fault. Detailed fault kinematic studies from the master fault reveal that the trends of slickenlines range S85°E - S70°E, and average approximately S76°E. Slickenlines on antithetic faults trend S20°W – N30°W, clustering at ~ N70°W. The attitude of fault surfaces and slickenlines indicate east-southeast/west-northwest extension within the Cañones Fault Zone. The sense of motion on the major fault is normal dominantly with left-slip. Fault throw is at least 225 m, based on Mesozoic units as hanging wall and footwall cutoffs. Thus, the heave is as ~143 m and the left-lateral displacement is ~60 m, given the averaged fault attitudes. In contrast to sub-horizontal Permian-Triassic units in its footwall, hanging wall strata of the Cañones fault zone dips in two directions: west-dipping Jurassic Entrada, Todilto, and Morrison formations; and south-east-dipping Eocene El Rito, Oligocene Ritito, and Oligocene-Miocene Abiquiu formations. Tilted Jurassic strata suggest that the overall structure is monoclinal, probably resulting from Laramide orogeny shortening. The Eocene-Miocene basin fill sediments, surprisingly, dip 10° – 30° away from the Cañones Fault, instead of dipping northwest towards the fault. This phenomenon, in contrast to the prediction of the rollover structure, suggests a different mechanism on this fault zone. Field observation provides direct evidence that basinward tilting is accommodated by multiple antithetic normal faults that cut through Permian to Miocene units. We propose that extensional fault-propagation folding model is a possible mechanism to result in the regional tilting of the basin fill. During upward propagation of the fault tip, horizontal-axis rotation and antithetic and synthetic faulting occur within a triangle zone above the fault tip. Alternatively, a buried large-scale low-angle normal fault can also generate such basinward tilting. In this scenario, the Cañones fault and other southeast-dipping normal faults are antithetic faults that grow on the detachment. These hypothetical mechanisms take into account the antithetic faulting within a rift-bounding fault zone and can be indicative of the evolution of other rift basins in which basin fills dip to the axis, such as the eastern Española basin and San Luis basin in northern New Mexico and southern Colorado.