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

Abstract

The Chile Triple Junction (CTJ) episodically migrated northward during the past 14 Ma from 54° S to its present-day position at 46°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°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°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 ∼0.1-0.2% 500 km east of the trench. Tilt measured in the southeastern part of the central Patagonian basin (∼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.