A review of the geology, structural controls and tectonic setting of Copahue volcano, Southern Volcanic Zone, Andes, Argentina.

FOLGUERA, ANDRÉS; ROJAS VERA, EMILIO; VÉLEZ, M. LAURA; TOBAL, JONATHAN; ORTS, DARÍO; AGUSTO, MARIANO; CASELLI, ALBERTO TOMÁS; RAMOS, VÍCTOR A.

Copahue Volcano: The smoking mountain between Argentina y Chile

Springer-Verlag Berlin Heidelberg

Año: 2015; p. 3 - 22

The Copahue Volcano lies in the Southern Volcanic Zone, although its geology and local structural controls differ from its neighbor-active volcanic centers. Most of its geology is substantially older than active volcanoes at these latitudes, being the postglacial component relatively minor. Initial stages comprise Early Pliocene basandesitic eruptions associated with extensional (transtensional?) processes that ended with the formation of a series of rhomboedric calderas that emitted important amounts of ignimbrites in the Latest Pliocene-Early Pleistocene. The Copahue Volcano concentrates the Pleistocene activity of one of those calderas, the Agrio Caldera, previously to the emplacement and development of the Present arc front to the west. Volcano morphology reflects this particular evolution looking more degraded than the Antuco, Callaqui and Lonquimay volcanoes located immediately to the west in the arc front. Most of its volume is Early Pleistocene in age showing a thin resurfacing cover in synglacial (>27 Ka) and postglacial times. Synglacial stage occurred mainly to the east of the Copahue Volcano towards the caldera interior in a series of independent, mostly monogenetic centers. Contrastingly, postglacial eruptions occurred as both central and fissural emissions reactivating the old Pleistocene conduits. Its particular geological record and eastern longitudinal position indicate that this center was probably part of the Late Pliocene-Pleistocene arc mostly developed in the axial and eastern Andes. Narrowing and westward retraction of the arc front, proposed in previous works for the last 5 Ma at 38ºS, could have been the result of the eastward migration of the asthenospheric wedge during slab steepening. Reasons for this relatively long-lived eruptional history in the Copahue Volcano would be connected to the particular geometry of the active Liquiñe-Ofqui dextral strike-slip fault system that abandons the arc front at these latitudes in Quaternary times dissecting the retroarc area. This behavior could be due to the collision of the oceanic Mocha plateau at these latitudes, as recently proposed. This jump and related deflection would have produced local transtensional deformation associated with abundant emissions of syn- and postglacial products that could have resurfaced partially this relatively old center.