Phase relations in hydrous MORB at 18-28GPa: implications for heterogeneity of the lower mantle

Details Phase relations in hydrous MORB at 18-28GPa: implications for heterogeneity of the lower mantle Phase relations in hydrous MORB at 18-28GPa: implications for heterogeneity of the lower mantle

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005pepi..150..239l&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 150, Issue 4, p. 239-263.

Physics

21

Scientific paper

The phase relations in hydrous and anhydrous mid-ocean ridge basalt were determined at pressures of 18 28 GPa. Liquidus phase relations in hydrous and anhydrous MORB are different. Garnet is the liquidus phase at pressures below 21 GPa, Ca Al (CAS) phase and stishovite are the liquidus phases at pressures of 22 27 GPa, and stishovite and Ca-perovskite are the liquidus phases above 27 GPa, whereas Ca-perovskite is a liquidus phase of anhydrous MORB at pressures above 23 GPa. Under subsolidus conditions, we have found that in the hydrous MORB system the stability fields of Al-bearing perovskite and Na Al (NAL) phase might shift to lower pressure by about 1.5 GPa compared to the dry MORB system. This shift could be explained by oxidation of a garnet-bearing assemblage by hydrous fluid and formation of Fe3+-bearing aluminous perovskite at lower pressures relative to the anhydrous system and/or differences in water solubility of the phases existing in perovskite-bearing assemblages. Our data indicate that hydrous basaltic crust remains denser than peridotite along the geotherm of a subducting slab, i.e. there is no density crossover between peridotite and basalt. Therefore, in slabs going through the 660 km discontinuity, basalt would gravitationally sink into the lower mantle under relatively hydrous conditions. The delamination of former basaltic crust near the 660 km discontinuity might be possible under relatively dry conditions of subduction. There are no stable highly hydrous phases in MORB above 10 GPa even at lower temperatures corresponding to subducting slabs. Therefore, MORB cannot be an important carrier of water to the deep Earth interior. However, it can be constantly supplied by water-bearing fluid from the underlying peridotite part of the descending slab. Thus, it is plausible that water can control subduction of the oceanic crust into the lower mantle.

Affiliated with

Also associated with

No associations

Rating

Phase relations in hydrous MORB at 18-28GPa: implications for heterogeneity of the lower mantle 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 relations in hydrous MORB at 18-28GPa: implications for heterogeneity of the lower mantle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Phase relations in hydrous MORB at 18-28GPa: implications for heterogeneity of the lower mantle will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1165670