Tectonic constraints on a magmatic plumbing system: The Quetrupillán Volcanic Complex (39°30′ S, 71°43′ W), Southern Andes, Chile

Abstract

The Quetrupillán Volcanic Complex is a composite system, active since the Pleistocene. We combine petrological and geochemical data from its erupted products with structural and geometrical constraints applied to the overall system and region. We conclude that a basaltic source melt is hindered on its ascent through the crust due to a compressional tectonic regime, influenced further by the structural control imposed by the Liquiñe-Ofqui Fault Zone. The stalled melt evolves by fractional crystallisation within the crust and undergoes a degree of crustal contamination, resulting in a network of trachytic melt pockets within a transcrustal magmatic system. Eruptions sourced from these pockets have generated numerous lava flows with trachytic compositions, which have occurred from the summit and flanks of Quetrupillán during the Holocene. Occasionally, some of the basaltic source melt has reached shallow levels within the plumbing system with minor interaction with the trachytic melt, resulting in the eruption of lavas with basalt, basaltic andesite and trachyandesite compositions. We propose a conceptual model for the magmatic system of Quetrupillán, in which the Liquiñe-Ofqui Fault Zone plays an important role in exerting a structural control on the crust on which Quetrupillán resides, influencing magma residence times and pathways to the surface.