Late cenozoic basins and kinematics from the southernmost andes in the context of the opening of the drake passage

Abstract

Mesozoic-Cenozoic interaction between South America and Antarctic plates has been a major driverof kinematics in the Southernmost Andes. Late Jurassic - Early Cretaceous opening of the Rocas Verdesoceanic basin was the product of separation, followed by Late Cretaceous basin closure and transpressionalong the Beagle channel due to left-lateral relative displacement. Orogen building continued during thePaleogene, together with progression of sedimentation in the associated Magallanes-Austral marine forelandbasin system. The Eocene early opening of the Drake passage due to Antarctica separation, involved thecombination of strike-slip and extensional tectonics, superposed to the previously consolidated orogen.Since the Oligocene inception of oceanic spreading in the West Scotia Sea, strike-slip deformation has domi-nated, concentrated along the Magallanes-Fagnano fault zone. As a result, Eocene and Miocene continentalpull-apart basins are registered in a hinterland position. Coeval retroarc Miocene sedimentation includes animportant continental volcaniclastic component and an important distributary system funneling sedimentsto deep marine basins. The position of the isolated Miocene basin along the Magallanes strait and on top ofthe fold-thrust belt, when compared to the retroarc sequences, open questions regarding the overall tec-tonic subsidence setting. For example, tectonic loading, dynamic subsidence, and transtension/pull-apartextension seems to be superposed; alternatively, they may be partitioned processes and geographicallydistributed. Furthermore, new detrital zircons provenance data from the retroarc, points out a Miocenereactivation of orogenic sources, coetaneous with pull-apart basins and widespread volcanism.