Efficient release of bromine by super-eruptions

Pierre Burckel,John Stix,Clara M Waelkens,Brian Monteleone

doi:10.1130/g49114.1

Abstract

AbstractBromine is a key halogen element in the quantification of volcanic volatiles, but analytical difficulties in measuring its very low abundances have prevented progress in understanding its behavior and its role in volcanic emissions. We present a new data set of bromine, chlorine, and fluorine concentrations in melt inclusions and matrix glasses for two rhyolitic super-eruptions from the Toledo and Valles calderas, New Mexico, USA. We show that before eruption, Br and Cl were efficiently partitioned from the gas-saturated magma into a separate fluid phase, and we calculate the mass of halogens in the fluid phase. We further demonstrate that syn-eruptive magma degassing was negligible during the super-eruptions, so that the main source of halogen emissions must have been the fluid phase. If the fluid phase were erupted, the large mass of Br and Cl could have severely impacted the atmospheric chemistry upon eruption.

Highlights

Halogens are an essential component of magmatic volatile systems and play a crucial role in magma degassing (Aiuppa et al, 2009), atmospheric ozone destruction (Aiuppa et al, 2009; von Glasow et al, 2009), and metal transport (Williams-Jones and Heinrich, 2005)
In the lowerBandelier Tuff (LBT) sequence, F measured in melt inclusions shows a steady decrease upsection, deeper into the magma chamber (Fig. 1)
Upper Bandelier Tuff Trends in the upper Bandelier Tuff (UBT) are similar to those in the LBT, with several key differences: (1) the ranges in concentrations are substantially larger in the UBT; (2) the halogen concentrations themselves are higher; (3) there is a slight increase in Cl and F from the base to top of

Summary

Introduction

Halogens are an essential component of magmatic volatile systems and play a crucial role in magma degassing (Aiuppa et al, 2009), atmospheric ozone destruction (Aiuppa et al, 2009; von Glasow et al, 2009), and metal transport (Williams-Jones and Heinrich, 2005). The second super-eruption, similar in both composition and volume, deposited the upper Bandelier Tuff (UBT) at 1.26 Ma (Phillips et al, 2007) Both eruptions experienced an initial Plinian phase followed by ignimbrites. The Deer Canyon Member of the Valles Rhyolite (Deer Canyon Rhyolite ) erupted immediately after the UBT as resurgence was taking place in Valles caldera (Phillips et al, 2007). This unit is geochemically related to the UBT and represents the final pulse from the UBT magma chamber before fresh magma replenished the system anew (Spell et al, 1993; Wilcock et al, 2013)

Results

Discussion

Conclusion