RETROARC EXTENSION ASSOCIATED WITH REACTIVATION OF BASEMENT STRUCTURES AND RETROARC VOLCANISM (38º30S - 71ºW)

One of the most important concentrations of retroarc volcanic complexes in the entire Southern Andes is present at 38º30'S. This complex was developed during the last 1.6 Ma after an episode of shallow subduction (34º30'-39ºS).

These volcanic complexes comprise calderas and domes that are amalgamated in a volcanic plateau of 50 x 50 kilometers.

Their genesis is associated with dextral movements linked to the young activity of the northern intra-arc Liquiñe-Ofqui fault system (38º-46ºS).

Quaternary faulting is associated with volcanic lavas next to the drainage divide, east of the volcanic arc.

Moreover, volcanic depressions with quadrangular geometries, as well as linear controls in fissural monogenetic basaltic fields, suggest that well-known basement structures located to the east with similar orientations have defined the emplacement of magmas.

Aeromagnetic data contribute to define the basement segmentation formed during ancient phases of crustal attenuation in the zone (Late Triassic-Early Jurassic).

As a case study, we have identified the final geometry and distribution of the Pino Hachado volcanic complex (38º30'S-71ºW). It is formed by 8 calderas, 4 of which were unknown before the present study and all of which are deeply influenced by deep basement structure.