HIGH-PRESSURE BEHAVIOR OF LAYERED HYDROUS MINERALS

Hydrous mineral phases play a vital role in transporting water into the deep Earth. The efficient transport of water is reliant both on the P-T path of the subducting slab and the concomitant presence of overlapping thermodynamic stabilities of low-pressure hydrous phases. Along warm geothermal gradients there are often gaps between the P-T stability of low-pressure and high-pressure hydrous phases, leading to a thermodynamic “choke point”. Hydrous minerals in hydrated peridotite and hydrated sediments could be better understood in simplified MgO-SiO₂-H₂O (MSH) and Al₂O₃-SiO₂-H₂O (ASH) ternary systems respectively. Intermediate pressure minerals in the MSH ternary system, such as the 10 Å phase are often stable at depths relevant to the “choke point” and allow for efficient transport of water. Similar to the 10 Å phase in the MSH system, the ASH system also exhibits pressure-induced hydration of kaolinite to super-hydrated kaolinite. Layered hydrous minerals are extremely anisotropic, with their interlayer region being the most compressible. Thus, pressure should lead to the contraction of the interlayer region. How, then, is hydration and associated swelling of the interlayer region caused at high pressure? We will present pressure-induced changes in the crystal structure of talc and kaolinite and examine the atomistic scale changes that prompt the crystal structure ready for interlayer hydration.

Acknowledgement: MM acknowledges funding from NSF EAR 1753125.