Modern and past volcanic degassing of iodine
Résumé
We have monitored iodine degassing from a melt to a water vapor during decompression (i.e. magma ascent). Experiments
have been performed by combining diamond anvil cells experiments with synchrotron X-rays fluorescence analysis. Partition
coefficients DI
fluid/melt measured for a pressure and temperature range of 0.1–1.8 GPa and 500–900 C, range from 41 to 1.92,
values for room conditions DI
fluid/glass (quenched samples) are equal to or higher than 350. We show that iodine degassing with
water is earlier and much more efficient than for lighter halogen elements, Cl and Br. Iodine is totally degassed from the silicate
melt at room conditions. By applying these results to modern volcanology, we calculate an annual iodine flux for subduction
related volcanism of 0.16–2.4 kt yr1. We suggest that the natural iodine degassing may be underestimated, having
possible consequences on the Earth’s ozone destruction cycle. By applying this results to the Early Earth, we propose a process
that may explain the contrasted signature of I, Br and Cl, strongly depleted in the bulk silicate Earth, the most depleted
being iodine, whereas fluorine is almost enriched. The Earth may have lost heavy halogen elements during an early water
degassing process from the magma ocean.