Holocene volcanism and vertical displacements along a major intra-arc transpressional system in the Southern Andes

As for other convergent margins, Quaternary volcanism in the Southern Andes is strongly related ta the kinematics of margin-parallel intra-arc fault systems. Microtectonic analysis shows evidence of post-Pliocene NE dextral transpression over the entire arc, at least from 38° to 46°S where the Liquifie-Ofqui Fault system (LOF) develops. Nevertheless, the Holocene activity along this fault remains poorly known and no clear evidence for strike-slip displacement has been found. Holocene flank cones on stratovolcanoes are mainly oriented NE, compatible with the ongoing dextral transpression if they are interpreted as maximum horizontal stress (chmax) indicators (e.g., Nakamura, 1977) . In addition, some isolated oblique (NE) chains of Holocene monogenetic centres can be assumed as tension cracks (e.g ., Dhont et al., 1995) and therefore support the dextral transpression. Nevertheless, master faults from the LOF system does not show clear strike-slip displacement markers on surface nor when it runs underneath the Holocene volcanic centres or eut long-live river valleys. In contrast , morphological features along these faults suggest recent vertical displacement with westward downgoing blocks. Because several monogenetic cones lie on top of traces of north-south master faults of the LOF system, the nature of the relationship between vertical movements and volcanism is a key topic for understanding the Holocene tectornagrnatic evolution in Southern Andes. ln this contribution we examine an area of the volcanic arc around 39°S, where outstanding morphological features suggest vertical di splacement controlled by rnaster faults of the LOF system and several stratovolcanoes and monogenetic cones were built on top of the fault traces or over different structural blocks bound by them.