Experimental measurements of volatility in igneous systems

点击翻译按钮获取中文摘要

Element volatilities, and their dependence upon temperature and the chemical composition of the gas phase, are of fundamental importance to understanding volcanic emissions, the composition of the Earth and a host of industrial processes. The chemical controls on volatility from high temperature silicate melts are, however, poorly understood and crude approximations are generally made. For instance, direct measurements of volcanic gas compositions must remove an estimated non-volatile, dust component, while the compositions of pre-planetary materials are estimated by assuming that gases condense and evaporate directly to/from solids (which are well understood) rather than to poorly-understood, but physically more realistic, silicate liquids.Unfortunately, to explore the latter requires data that we currently do not posses - such as how volatile an element may be above a silicate (magmatic) melt and what the chemical controls upon volatility are. This basic chemical data is required to refine our understanding of key moments in Earth history, such as the impact that led to the formation of the Moon. These planetary scale events are modelled using complex numerical simulations, but to improve the fit between the observed chemistry of the Moon and that suggested by such models requires a deeper understanding of elemental volatility. The compositions of pre-planetary materials - the 'building blocks' of the terrestrial planets - are estimated by assuming that gases condense and evaporate directly to or from solids - a process which is, relatively, well understood compared to the condensation and evaporation from silicate liquids. This project will directly address this gap in our knowledge.Volcanologists will also benefit by having improved models by which to understand the trace element compositions of volcanic gases. Knowledge of the factors that influence volcanic gas chemistry is key to interpreting the outgassing behaviour of terrestrial volcanic systems. The current method, of removing an estimated non-volatile, dust component, may be obscuring important information concerning magma evolution, and, potentially, volcanic hazards. Given the toxicity of many of the volatile elements, this project is important to both volcanologists and risk/hazard assessors.In this project, I take a novel approach to measuring elemental volatility by firstly measuring the properties of trace components in silicate melts then predicting and testing their expected volatilities under controlled conditions. The immediate aim is to provide a data set of minor and trace element volatilities directly relevant to planetary evolution, volcanic and environmental hazards.