Investigation of volcanic silicate-melt inclusions

Volcanic eruptions are driven by the escape of volatile elements and compounds such as water, carbon dioxide, chlorine, sulfur, and fluorine from magmas. These volatiles are also important in the formation of mineral deposits within the Earth's crust. However, since many of these constituents are highly mobile, it is extremely difficult to measure the abundances of volatiles in magmas and magmatic rocks. Fortunately, some crystals growing in magmas may enclose and trap small quantities of silicate melt; as the magma crystallizes and cools, the trapped melt is quenched to form volcanic glass, i.e. a silicate-melt inclusion. Our studies of silicate-melt inclusions from Mt. Vesuvius, Italy, and from other volcanoes in Africa, Mexico, and the western United States are useful in understanding the processes of volcanic eruption and the formation of mineral deposits.

References

• Webster, J.D., Thomas, R., Rhede, D., Forster, H.-J., and Seltmann, R. (1997) Melt inclusions in quartz from an evolved peraluminous pegmatite: geochemical evidence for strong tin enrichment in fluorine-rich and phosphorus-rich residual liquids. Geochimica et Cosmochimica Acta, 61, 2589-2604.

• Taylor, R.P., Jackson, S.E., Longerich, H.P., and Webster, J.D. (1997) In situ trace-element analysis of individual silicate melt inclusions by laser ablation microprobe-inductively coupled plasma-mass spectrometry. Geochimica et Cosmochimica Acta, 61, 2559-2567.

• Webster, J.D., Burt, D.M., and Aguillon, R.A. (1996) Volatile and lithophile trace- element geochemistry of heterogeneous Mexican tin rhyolite magmas deduced from compositions of melt inclusions, Geochimica et Cosmochimica Acta, 60, 3267-3283.

• Webster, J.D., Congdon, R.D., and Lyons, P.C. (1995) Determining pre-eruptive compositions of late Paleozoic magma from kaolinized volcanic ashes: Analysis of glass inclusions in quartz microphenocrysts from tonsteins. Geochimica et Cosmochimica Acta, 59, 711-720.

• Webster, J.D., and Duffield, W.A. (1994) Extreme halogen abundances in tin-rich magma of the Taylor Creek rhyolite, New Mexico. Economic Geology, 89, 840-850.

• Webster, J.D., Taylor, R.P., and Bean, C. (1993) Pre-eruptive melt composition and constraints on degassing of a water-rich pantellerite magma, Fantale Volcano, Ethiopia. Contributions to Mineralogy and Petrology, 114, 53-62.

• Webster, J.D. and Duffield, W.A. (1991) Volatiles and lithophile elements in Taylor Creek Rhyolite: Constraints from glass inclusion analysis. American Mineralogist, 76, 1628-1645.

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