Mobilizing aluminum in crustal and mantle fluids

Aluminum is a major rock-forming element, but its low solubility in H2O at upper crustal conditions has led to the assumption that it is effectively immobile during fluid-rock interaction in the deep crust and upper mantle. However, new experimental results on Al solubility in H2O-SiO2-NaCl fluids at high pressure and temperature challenge this view. The combined effects of temperature, pressure, dissolved SiO2 and NaCl yield increases in corundum (Al2O3) solubility at 800 degrees C, 1 GPa of > 10(3) or 10(4) relative to that at <0.3 GPa in pure H2O. Enhancement of Al solubility is best explained by formation of polynuclear Na-Al-Si-O clusters and/or polymers. Aluminum should not be assumed to be immobile during fluid-rock interaction in deep environments. (C) 2006 Elsevier B.V. All rights reserved.