The Systematics Of Chlorine, Lithium, And Boron And Delta Cl-37, Delta Li-7, And Delta B-11 In The Hydrothermal System Of The Yellowstone Plateau Volcanic Field

Chlorine, lithium, and boron are trace elements in rhyolite but are enriched in groundwater flowing through rhyolite because they tend to partition into the fluid phase during high-temperature fluid-rock reactions. We present a large data set of major element and delta Cl-37, delta Li-7, and delta B-11 compositions of thermal water and rhyolite from Yellowstone Plateau Volcanic Field (YPVF). The Cl/B, Cl/Li, delta Cl-37 (-0.2 parts per thousand to +0.7 parts per thousand), and delta B-11 (-6.2 parts per thousand to -5.9 parts per thousand) values of alkaline-chloride thermal waters reflect high-temperature leaching of chlorine, lithium, and boron from rhyolite that has delta Cl-37 and delta B-11 values of +0.1 parts per thousand to +0.9 parts per thousand and -6.3 parts per thousand to -6.2 parts per thousand, respectively. Chlorine and boron are not reactive, but lithium incorporation into hydrothermal alteration minerals result s in a large range of Cl/Li, B/Li, and delta Li-7 (-1.2 parts per thousand to +3.8 parts per thousand) values in thermal waters. The relatively large range in delta Li-7 values of thermal waters reflects a large range of values in rhyolite. Large volumes of rhyolite must be leached to account for the chloride, lithium and boron fluxes, implying deep groundwater flow through rhyolite flows and tuffs representing Yellowstone's three eruptive cycles (similar to 2.1 Ma). Lower Cl/B values in acid-sulfate waters result from preferential partitioning of boron into the vapor phase and enrichment in the near-surface water condensate. The Cl/B, Cl/Li, delta Li-7 (-0.3 parts per thousand to +2.1 parts per thousand), and delta B-11 (-8.0 parts per thousand to -8.1 parts per thousand) values of travertine depositing calcium-carbonate thermal waters which discharge in the northern and southern YPVF suggest that chlorine, lithium, and boron are derived from Mesozoic siliciclastic sediments which contain detrital material from the underlying metamorphic basement.