Degassing-induced chemical heterogeneity at the 2011-2012 Cordón Caulle eruption

Rebecca Paisley,Jack Whattam,Hugh Tuffen,C Ian Schipper,Kim Berlo

doi:10.30909/vol.02.02.211237

Abstract

Low H2O concentrations preserved in the erupted products from the 2011-2012 eruption at Cordón Caulle, Chile, have limited its use as a recorder of the shallow degassing processes responsible for the observed hybrid activity. However, volatile trace element heterogeneity (e.g. Li, Pb, Tl) is observed in different textural domains (e.g. breccias, tuffisites), which each represent the competing processes of fracturing, gas fluxing and melt relaxation occurring at different locations within the upper conduit. Elemental depletions in tuffisite veins record scavenging of metals by the fluxing gas phase. Preserved concentration gradients indicate deep-conduit degassing events are short-lived (~minutes), whilst late-stage activity involves hours of gas venting from a single location. Later-erupted material is more degassed than earlier-erupted bombs indicating a progressive loss of volatiles with eruption duration. Combining in situ textural and volatile trace element analyses can constrain evolving degassing processes in systems that are depleted in H2O and CO2.

Highlights

Prior to the 2008–2009 eruption of Chaitén in Chile, no explosive rhyolitic eruptions had been visually observed by scientists [Castro et al 2014]
To accurately assess degassing processes during the 2011–2012 Cordón Caulle eruption samples must represent degassing events both through time and space. This allows for an understanding of how volatiles degas as magma ascends from depth, and how degassing processes changed in an eruption that was initially explosive transitioned into prolonged hybrid behaviour
The low H2O contents in the 2011–2012 Cordón Caulle erupted products have previously limited our understanding of its degassing systematics [Castro et al 2014]

Summary

Introduction

Prior to the 2008–2009 eruption of Chaitén in Chile, no explosive rhyolitic eruptions had been visually observed by scientists [Castro et al 2014]. The Chaitén eruption was closely followed by another Chilean rhyolitic eruption at Cordón Caulle from 2011 to 2012. During both eruptions simultaneous explosive and effusive activity from the same vent was observed, known as “hybrid” activity [Pallister et al 2013; Schipper et Degassing-induced chemical heterogeneity at Cordón Caulle. The erupted products from Cordón Caulle are H2O-poor (

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Conclusion