Resolving Recharge: quantifying the efficacy of mafic recharge as an eruption initiation mechanism

Abstract:

One of the biggest challenges in volcano science today is better understanding the ultimate driving forces for eruptions, as well as their precursory signals. One mechanism thought to initiate the ascent of magma and subsequent eruption is magma recharge, i.e., an injection of new molten material into a shallow crustal magma storage region. There is an abundance of magmatic systems with petrologic evidence of magma recharge, including reversely zoned crystals with associated abrupt changes in temperature, pressure, and composition. However, the rate and efficacy of magma recharge in instigating eruptions is poorly constrained. To quantify the frequency and efficacy of magma recharge in particular magmatic systems, we are developing an image processing code that automates the identification of individual recharge events recorded as reverse zones in phenocrysts using compositional-related crystal imagery such as BSE images. By analyzing hundreds of crystals from a given eruption, this method aims to analyze a statistically significant number of crystals to determine the number of recharge events recorded per crystal as well as the overall distribution of recharge events in the crystal record of a particular eruption. As a test case we apply the code to the crystal cargo from a sample of the Mount St. Heens (WA, USA) 1980 cryptodome. Preliminary analysis of 44 zoned plagioclase grains suggests the system experienced up to 17 recharge events prior to its mobilization and subsequent eruption. The longer-term goal of the project is to examine the frequency of recharge events over the history of the crystal cargo to quantify the efficacy of recharge in producing eruptions in particular types of magmatic systems. Further, we aim to determine the potential evolution of recharge efficacy throughout the lifespan of magmatic systems.