Ultrasonic Velocity Measurements on Silicate Liquids

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LangeEAR-0087764The primary goal of this proposal is to measure the zero pressure compressibility of a variety of silicate liquids over a wide temperature range using an ultrasonic acoustic interferometer. Our high-temperature capability will be used to: (1) obtain relaxed sound speeds on liquids that are too viscous for such measurements below 1600 degrees C (e.g., dacite and rhyolite), (2) access melts with exceptionally high liquidus temperatures (e.g., peraluminous melts, komatiite, peridotite), and (3) improve constraints on the temperature dependence of melt compressibility by measuring relaxed sound speeds over temperature intervals that span several hundred degrees. In addition, experiments are planned to examine variations in the compressibility of silicate melts undergoing composition-induced coordination change of cations (Al3+, Fe3+, Ti4+) at one bar. These experiments will provide analogies for understanding the consequences of pressure-induced coordination change of cations on melt density. A final application is to silicate melts containing volatile components (fluorine and phosphorous) and a variety of carbonatite liquids. All of the proposed sound speed measurements at zero pressure (one bar) will provide a critical complement to in-situ methods that allow density and compressibility to be derived at pressure.