Molecular modeling of the 10-Å phase at subduction zone conditions

Details Molecular modeling of the 10-Å phase at subduction zone conditions Molecular modeling of the 10-Å phase at subduction zone conditions

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004e%26psl.222..517w&link_type=abstract

Earth and Planetary Science Letters, Volume 222, Issue 2, p. 517-527.

Computer Science

5

10-Å Phase, Talc, Water, Molecular Dynamics, Hydrogen Bonding, Water In The Mantle, Dhms

Scientific paper

Molecular dynamics (MD) modeling of the 10-Å phase, Mg3Si4O10(OH)2.xH2O, with x=2/3, 1.0 and 2.0 shows complex structural changes with pressure, temperature and water content and provides new insight into the structures and stabilization of these phases under subduction zone conditions. The structure(s) of this phase and its role as a reservoir of water in the mantle have been controversial, and these calculations provide specific predictions that can be tested by in situ diffraction studies. At ambient conditions, the computed structures of talc (x=0) and the 10-Å phases with x=2/3 and 1.0 are stable over the 350-ps period of the MD simulations. Under these conditions, the 10-Å phases show phlogopite-like layer stacking in good agreement with previously published structures based on powder X-ray diffraction data for samples quenched from high-pressure and high-temperature experiments. The calculations show that the 10-Å phase with x=2.0 is unstable at ambient conditions. The computed structures at P=5.5 GPa and T=750 K, well within the known stability field of the 10-Å phase, change significantly with water content, reflecting changing H-bonding configurations. For x=2/3, the layer stacking is talc-like, and for x=1.0, it is phlogopite-like. The calculations show that transformation between these two stackings occurs readily, and that the talc-like stacking for the x=2/3 composition is unlikely to be quenchable to ambient conditions. For x=2.0, the layer stacking at P=5.5 GPa and T=750 K is different than any previously proposed structure for a 10-Å phase. In this structure, the neighboring basal oxygens of adjacent magnesium silicate layers are displaced by b/3 (about 3 Å) resulting in the Si atoms of one siloxane sheet being located above the center of the six-member ring across the interlayer. The water molecules are located 1.2 Å above the center of all six-member rings and accept H-bonds from the OH groups located below the rings. The b/3-displaced structure does not readily transform to either the talc-like or phlogopite-like structure, because neither of these stackings can accommodate two water molecules per formula unit. There is likely to be a compositional discontinuity and phase transition between the b/3-displaced phase and the phase with phlogopite-like stacking. The simulations reported here are the first to use the recently developed CLAYFF force field to calculate mineral structures at elevated pressures and temperatures.
Tel.: +1-217-333-7414; fax: +1-217-244-4996.

Affiliated with

Also associated with

No associations

Rating

Molecular modeling of the 10-Å phase at subduction zone conditions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Molecular modeling of the 10-Å phase at subduction zone conditions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Molecular modeling of the 10-Å phase at subduction zone conditions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1057692