Late Cenozoic tectonics of the Southern Chile Trench

Marine geophysical data from off-shore of southern Chile are used to define the interaction between the Chile Ridge and Chile Trench during late Cenozoic time. We identify three distinct ridge-trench collision events. Between 14 and 10 Ma a 700-km-long, nearly continuous section of the Chile Ridge was sub-ducted between 55°S and 48°S. Shorter sections of the ridge, offset by large transform faults, were subducted at 6 and 3 Ma between 48°S and 47°S. At the present-day triple junction, the subduction of the ridge has a strong influence on the Chile Trench. In this region the landward trench slope has undergone a recent episode of subduction-driven tectonic erosion: the trench slope is narrower and steeper than along other sectors of the margin and the trench axis has migrated shoreward. Evidence exists for late Neogene and Quaternary uplift and plutonism on the adjacent continental margin. South of 48°S, where collision took place between 10 and 14 Ma, the effects of collision are much less pronounced. In particular, the landward trench slope does not appear to have been subjected to extensive tectonic erosion. We conclude that the configuration of the spreading centers and transform faults on the Chile Rise is the chief factor controlling ridge-trench tectonic interaction. Tectonic erosion of the landward trench slope and tectonic activity in the adjacent continental margin are much greater when short sections of ridge, offset by large transform faults, are subducted. A major sub-marine channel leads along the trench axis south-ward from the triple junction. This channel cuts across the outer trench rise and carries sediment westward to the Mornington Abyssal Plain. The Paleogene tectonic history of the southern Chile Trench includes a southward migrating, ridge-trench collision involving the Farallon-Aluk spreading center in Eocene time.