Phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere

Details Phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere Phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere

Apr 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986pepi...42..255l&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 42, Issue 4, p. 255-262.

Physics

27

Scientific paper

Serpentine may be regarded as a hydrous form of a 1:1 (molecular) mixture of olivine and pyroxene, or a simplified hydrous `pyrolite' upper mantle composition. The phase behaviour of two natural serpentines, having the approximate compositions of (Mg0.99Fe0.01)3Si2O5(OH)4 and (Mg0.91Fe0.09)3Si2O5(OH)4, was investigated between 60 and 280 kbar (inclusive) at 700 ~ 1000°C in a diamond-anvil pressure cell coupled with laser heating. By incorporating earlier work, the results suggest that at pressures greater than 30 kbar and temperatures in the range 600 - 1000°C serpentine displays the following sequence of phase transformations with increasing pressure:
serpentine 40-60 kb forsterite + talc + water
70-80 kbforsterite + orthoenstatite + water100 kg forsterite + clinoenstatite + water
120 kb clinoenstatite + phase A + water
130 kb stishovite + phase A + brucite
180 kg stishovite + phase B + brucite
220kb ?? None of the high-pressure phases expected in olivine and pyroxene, such as the spinel modification of olivine, the ilmenite and perovskite modifications of pyroxene, was observed in serpentine up to about 280 kbar loading pressure. On the basis of these results, the effect of H2O on phase transformations of olivine and pyroxene at high pressures and high temperatures has been deduced. It has been found that the modified spinel phase of Mg2SiO4 does not occur in the system having a 1:1 mixture of forsterite and enstatite and containing more than about 4 wt.% H2O. The spinel phase of Mg2SiO4 does not appear at its equilibrium transition boundary (modified spinel <--> spinel) in the same system containing more than about 3 wt.% H2O. Thus, if more than about 4 wt.% H2O is present in the middle portion of a subducting lithosphere, the so-called 400-km seismic discontinuity observed in the normal mantle may not take place in the downgoing slabs. Where these transitions do occur at a low H2O content, the associated change in density and, accordingly, the magnitude of discontinuities in the seismic wave velocities, would be reduced by a factor of 2-3 if 2 wt.% H2O is present in the system.

Affiliated with

Also associated with

No associations

Rating

Phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere 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 Phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1103614