Schorl Breakdown at Upper Mantle Conditions: Insights from an Experimental Study at 3.5 GPA

Hydrogen and B input throughout the Earth's mantle is continuously fed through a sequence of dehydration and breakdown reactions of hydrous and B-bearing mineral phases stable at different conditions along the subducting slabs. Therefore, the stability of minerals hosting these elements plays a fundamental role. Tourmaline hosts very large amounts of B (up to 14 wt% of B2O3) along with hydroxyl groups (up to 4 wt% of H2O), thus representing a crucial mineral to investigate the fate of B and H in diverse geological settings. The recent finding of tourmaline minerals in ultra-high pressure metamorphic rocks has raised important questions about the actual tourmaline stability field, paying special attention to the high pressure and temperature stability limits of the various tourmaline species.