Dehydration of δ-AIOOH in earth’s deep lower mantle

Abstract

δ-AlOOH has been shown to be stable at the pressure–temperature conditions of the lower mantle. However, its stability remains uncertain at the conditions expected for the lowermost mantle where temperature is expected to rise quickly with increasing depth. Our laser-heated diamonδ-anvil cell experiments show that δ-AlOOH undergoes dehydration at ~2000 K above 90 GPa. This dehydration temperature is lower than geotherm temperatures expected at the bottom ~700 km of the mantle and suggests that δ-AlOOH in warm slabs would dehydrate in this region. Our experiments also show that the released H2O from dehydration of δ-AlOOH can react with metallic iron, forming iron oxide, iron hydroxide, and possibly iron hydride. Our observations suggest that H2O from the dehydration of subducting slabs, if it occurs, could alter the chemical composition of the surrounding mantle and core regions.