Neogene uplift of central eastern Patagonia: Dynamic response to active spreading ridge subduction?

The Chile Triple Junction (CTJ) episodically migrated northward during the past 14 Ma from 54 degrees S to its present-day position at 46 degrees 30'S, as different almost trench-parallel spreading segments entered in subduction. This migration resulted in the opening of an asthenospheric window below Patagonia, inducing a disturbance in the regional mantle convection. On the overriding plate, the middle Miocene time corresponds to a major change in the central Patagonian basin dynamics, with a transition from subsidence to generalized uplift. The detailed mapping and the morphological study of post-middle Miocene terraces evidence regional-scale trench-parallel tilt histories that differ depending on latitude. South of 46 degrees 30'S, the slopes of the fluvial terraces indicate a change from northward to southward tilt during late Miocene. Terraces younger than the early Pliocene do not show any trench-parallel tilt. North of 46 degrees 30'S, in contrast, only northward tilt, active until the Pleistocene, is recorded. We use a semianalytical model of dynamic topography which suggests that the northward migration of the Chile Triple Junction should be accompanied by a dynamic uplift of the central Patagonian basin. Uplift would cause both north directed and south directed tilt, north and south of the triple junction, respectively, with values of similar to 0.1-0.2% 500 km east of the trench. Tilt measured in the southeastern part of the central Patagonian basin (similar to 0.1%) is comparable to values predicted using the semianalytical model. The dynamic topography associated to the Chile ridge subduction may have exerted a major control on the Neogene dynamics of Patagonia.