Experimental Determination of Boron Isotopic Fractionation Between Fluid and Silicate Melts

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Hervig0106659The isotopes of boron have been shown to fractionate from one another as boron is lost from a silicate melt into coexisting water vapor. Work funded by this proposal will measure the amount of boron isotope fractionation between melts and a variety of fluids for melts of basaltic, andesitic, and granitic composition. Fluids will be water or carbon dioxide, or mixtures thereof. A range of temperatures will be studied to mimic natural conditions. The evolution of silicate melts (magmas) during generation, transport, and cooling (either at the surface of the earth or below) generally involves (at one stage or another) the formation of a fluid phase. The experimental data on boron fractionation proposed here will allow the application of a new stable isotope system to unraveling the history of silicate melts. A specific application is to magmas formed along volcanic arcs. Study of these samples can help constrain the varying contribution of the subducting slab to the source regions of these melts, and can clarify the effects of degassing during the ascent of magmas.