Orogenic shortening and the origin of the Patagonian orocline (56° S.Lat)

A maximum shortening of 600 km and a minimum of 300 km was calculated for the southernmost extreme of the Patagonian Andes orocline. A regional balanced cross-section was restored in four stages that represent the main events of compressive deformation. The mid-Cretaceous event produced a maximum shortening of 430 km associated with high grade regional metamorphism in Cordillera Darwin and a period of fast subsidence in the Magallanes foreland basin during the Late Cretaceous. The Late Cretaceous–Cenozoic events produced a maximum shortening of 170 km, of which 40 km correspond to Late Cretaceous, 50 km to Paleogene, and 80 km to Neogene events. A set of evolutive profiles at lithospheric scale from Jurassic to Present time shows that, assuming a maximum shortening of 600 km, the mass balance is attained only if the back arc oceanic lithosphere created during the early rifting stage is partially consumed by a short episode of reverse subduction during the mid-Cretaceous compressive event. A set of six maps showing the palinspastic restoration of the Patagonian Andes orocline indicates that a maximum shortening of 600 km at the southern extreme is compatible with the available geologic data and geometrically compatible with paleomagnetic arc rotations of nearly 90°.