Central vs. lateral growth and evolution of the < 100 ka Peinado composite volcano, southern Central Volcanic Zone of the Andes

Abstract

Composite volcanoes often display shifts in activity between central and lateral vents that are related to the local stress field and the underlying magmatic plumbing system. The Quaternary Peinado composite volcano in the southern Central Volcanic Zone (CVZ) of the Andes exhibits a striking symmetrical configuration of lateral vents around a main central cone and vent. In this contribution, we carry out detailed mapping, morphometric analysis and unspiked K-Ar dating, together with petrographic and whole-rock major oxides, trace element and Sr-Nd-Pb isotopic analyses, to constrain the growth history of the volcano and the interplay between central and lateral activity. Ten new unspiked K-Ar ages ranging between 36.8 ± 3.8 and 72.6 ± 8.0 ka highlight that Peinado is a young potentially active volcano. A main central cone-building stage ≥70–60 ka of mostly andesitic composition formed the bulk of the edifice. During this stage, vents around the cone base erupted basaltic andesite lava flows that are among the most mafic compositions of CVZ composite volcanoes, possibly related to the location of Peinado on an alignment of mafic monogenetic centers. At ~50–40 ka, the locus of activity shifted to mid-flank vents emplaced around the central vent, with eruption of andesite > basaltic andesite lava flows of similar composition to the central cone. Minor coeval-to-younger activity from the central vent was progressively more felsic, with eruption of dacitic lavas and block and ash flows, and possibly minor fallout. The shift of the bulk of activity from the central to the lateral mid-flank vents was likely related to the effects of the edifice load and magma compositions, with more mafic and dense magmas erupting preferentially through the flank vents and more differentiated magmas from the central vent. Although activity has been dominantly mafic and effusive, an evolution towards more felsic products from the central vent suggests that future activity may be somewhat explosive. The particular configuration of the lateral vents and structures around the central cone, together with other features, point towards a possible future collapse of the edifice, either a sector collapse or a caldera collapse.