The goal of this one-year project is to determine the feasibility of using volcanic rocks from the Aleutian islands and Alaska to estimate the water content, as well as the pressure and temperature of crystallization, of arc magmas. Water is central to the origin and evolution of magmas associated with subduction zones, yet there are currently few direct measurements of the water content of arc magmas, and none to date published for Aleutian-Alaska volcanoes. The investigators are collecting mafic tephra from a small number of Aleutian-Alaska volcanoes, then analyzing glassy melt inclusions hosted in olivine, clinopyroxene and plagioclase phenocrysts by ion microprobe, electron microprobe, and laser ablation inductively coupled plasma mass spectrometry, in order to obtain water concentration data, and to apply various thermobarohygrometers. Such data are needed to address fundamental questions regarding the origin of tholeiitic versus calc-alkaline igneous differentiation trends, the melting process beneath arc volcanoes, and volatile cycling at subduction zones. The Aleutian-Alaska arc, because of its great diversity of magma types and systematic variations in geophysical parameters, has long been central to many of these debates, but lacking the water data needed to resolve them.
