International Geologiical Congress - Oslo 2008


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GTN-01 General contributions to new methods and technologies - Part 1


High-pressure high-temperature neutron diffraction of hydrous minerals


Hongwu Xu, Los Alamos National Laboratory (United States)
Yusheng Zhao, Los Alamos National Laboratory (United States)
Jianzhong Zhang, Los Alamos National Laboratory (United States)
Donald Hickmott, Los Alamos National Laboratory (United States)
Luke Daemen, Los Alamos National Laboratory (United States)
Sven Vogel, Los Alamos National Laboratory (United States)


Significant amounts of water are carried into the mantle at subduction zones in hydrous minerals formed in oceanic crust. Thus studying the stability of hydrous minerals at high pressure and high temperature conditions is important in determining the state/fate of water in the Earth's interior and its effects on mantle rheology and melting. Because neutron scattering is much more sensitive to hydrogen and other light elements than X-rays scattering, in situ high-P/T neutron diffraction is a powerful technique for such studies. Using the high-P/T toroidal anvil apparatus coupled with time-of-flight neutron diffraction at LANSCE, we have investigated the structural and dehydroxylation behavior of several hydrous minerals, including portlandite, brucite, nickel hydroxide and jarosite. Rietveld analysis of the data allowed determination of not only unit-cell parameters but also atomic positions and atomic displacement parameters at various P/T conditions. The bulk moduli and dehydroxylation P/T conditions of these compounds have also been determined. These studies thus provide important insights into the mechanisms of water storage and transport in the deep Earth.


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