Honeycomb Hills, Utah, is a volcanic dome which is the product of a single eruptive cycle froma a fluorine-rich silicic magma. The system is particularly amenable to study because it formed during a single eruptive cycle within which there were developed significant systematic variations in volatile content, phenocryst content, and mineral and whole rock chemical comppsition. Furthermore, the system has not been modified by subsequent volcanic activity. The objective of this study is to establish the physical and chemical processes operating prior to and during the eruption of this compositionally zoned, silicic magma body. The study will focus on the following problems: 1) How did the energetics of the eruption vary, and is it correlated with changes in volatile content or composition, or other physical/chemical heterogeneities? 2) How are the different volatile components distributed in the preeruptive magma body? 3) What is the role of injection of mafic magma in to the system, particularly as a source of heat and a potential eruption trigger? 4) How did the systematic compositional zonation develop? This includes evaluation of evidence for volatile transfer of selected elements, evidence of limited magma mixing during eruption, and the role of fractionation of phenocryst phases. 5) What is the origin of high fluorine rhyolites and how are they related to rare element pegmatites?
