Kinematic evolution of the Patagonian retroarc fold-and-thrust belt and Magallanes foreland basin, Chile and Argentina, 51°30′S
The kinematic evolution of the Patagonian fold-and-thrust belt and cogenetic Magallanes retroarc foreland basin is reconstructed using new geologic mapping, two-dimensional (2-D) seismic-reflection data, and zircon U/Pb geochronology. Results span an ~160-km-wide transect of the thrust belt and Magallanes Basin near 51°30′S and highlight the influence of inherited extensional structures on basin paleogeography, syntectonic sedimentation, and Late Cretaceous–Neogene foreland shortening. South of 50°S, the Patagonian fold-and-thrust belt developed on oceanic and attenuated crust of the predecessor Late Jurassic Rocas Verdes rift basin, resulting in a collisional nature to early fold-and-thrust belt development and foreland sedimentation atop rifted South American crust. We identify six principal stages of development between Late Cretaceous and Neogene time. A palinspastic restoration indicates ~32–40 km (~19%–23%) of retroarc shortening following closure of the Rocas Verdes Basin and incipient growth of the thrust belt. More than half of the estimated crustal shortening occurred synchronously with the deep-water phase of Late Cretaceous foreland basin sedimentation. Subsequent deformation migrated into the foreland, accounting for ~12 km of shortening across the Cretaceous–early Miocene basin fill. Thick-skinned thrust faulting along multiple detachment levels in Paleozoic metamorphic basement resulted in –5 km of foreland uplift and exposure of preforeland basin deposits. The final phase of early Miocene deformation ca. 21–18 Ma may reflect enhanced coupling between the continental and oceanic lithospheres, causing foreland basement uplifts as the Chile Ridge spreading ridge approached the trench. We speculate that Neogene foreland shortening was accommodated by reactivation of Mesozoic normal faults zones and accounts for broad uplift of the Patagonian fold-and-thrust belt.