HR: 15:25h
AN: T43E-08    [Abstracts]
TI: Phase transformation of water under the mantle conditions
AU: * Gregoryanz, E
EM: e.gregoryanz@gl.ciw.edu
AF: Geophysical Laboratory, 5215 Broad Branch Rd., NW, Washington, DC 20015 United States
AU: Lin, J
EM: j.lin@gl.ciw.edu
AF: Geophysical Laboratory, 5215 Broad Branch Rd., NW, Washington, DC 20015 United States
AU: Somayazulu, M
AF: HPCAT Carnegie Institution of Washington, 9700 South Cass Avenue, Argon, IL 60439 United States
AU: Hemley, R
EM: r.hemley@gl.ciw.edu
AF: Geophysical Laboratory, 5215 Broad Branch Rd., NW, Washington, DC 20015 United States
AU: Mao, D
AF: Geophysical Laboratory, 5215 Broad Branch Rd., NW, Washington, DC 20015 United States
AB: Water plays very important role in the physics and chemistry of the planetary interiors. The H$_2$O incorporated in the mantle minerals may change their physical properties such as electrical conductivity, viscosity, and transformation kinetics. Despite numerous theoretical studies, its behavior at high pressures and temperatures (e.g., corresponding to deep planetary interiors) is still poorly understood. Recent studies have led to growing information about the polymorphism of H$_2$O at high pressures and at modest temperatures (300 K and below up to 100 GPa). The hydrogen bonding in the system gives rise to myriad phases (some 15) including stable and metastable crystalline and amorphous and possibly liquid) phases. We have conducted several experiments at high pressures and temperatures using {\it in situ} Raman spectroscopy and synchrotron diffraction techniques. Using both laser heating and external heating techniques we have observed a new transformation in both H$_2$O and D$_2$O at the mantle conditions. The transformation occurs at comparable pressures but lower temperatures to the predicted transition of ice VII to a superionic phase. It is also reversible; upon decompression normal ice VII is recovered at ~20 GPa and 300 K. This unexpected behavior along the melting curve overlaps the conditions present in the interiors of the Neptune and Uranus. As such, the transformation in water should be considered in understanding the magnetic fields, internal structure, and chemistry occurring at depth within the icy planets. More importantly, the existence of a new {\it P-T} phase may have the implications in understanding the solubility of H$_2$O in the mantle minerals, affecting the interpretation of the amount of water in the lower mantle and the physical properties of the hydrous minerals in the interior of the Earth.
DE: 6020 Ice
DE: 6045 Physics and chemistry of materials
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 1025 Composition of the mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting