Volcanism in a compressional Andean setting: A structural and geochronological study of Tromen volcano (Neuquèn province, Argentina)

Abstract : We document evidence for growth of an active volcano in a compressional Andean setting. Our data are surface structures and 39Ar-40Ar ages of volcanic products on Tromen volcano. Tromen is an active back-arc volcano in the Andean foothills of Neuquèn province, Argentina. Its volcanic products are unconformable upon Mesozoic strata of the Neuquèn basin. The volcano straddles a N-S trending pop-up, which formed during E-W shortening. The main underlying structures are eastward verging thrusts. Their traces curve around the eastern foot of the volcano. Minor folds and faults also occur in the volcanic cover of Tromen, as a result of E-W shortening. New 39Ar-40Ar ages for these volcanic rocks are younger than 2.27 ± 0.10 Ma and show that Tromen has been active almost continuously from the late Pliocene to the Holocene. We conclude that volcanism and thrusting have been coeval and that magma must have reached the surface in a tectonic setting of horizontal compression. Our results have wider implications for magmatic processes in such settings.