Subduction factory - 1. Theoretical mineralogy, densities, seismic wave speeds, and H2O contents

Publication Type  Journal Article
Year of Publication  2003
Authors  Hacker, B. R.; Abers, G. A.; Peacock, S. M.
Journal Title  Journal of Geophysical Research-Solid Earth
Volume  108
Issue  B1
Pages  -
Journal Date  Jan 18
ISBN Number  0148-0227
Accession Number  ISI:000181799800002
Key Words  subduction; seismic velocities; mineral physics; h2o; high-pressure stability; lawsonite-bearing eclogites; system mgo-sio2-h2o msh; elastic properties; phase-a; hydrous phases; oceanic-crust; thermal structure; northwest turkey; tavsanli region

[1] We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for mid-ocean ridge basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (< 1.3 wt % H2O), and the uppermost mantle ranges from unhydrated to &SIM;20% serpentinized (&SIM;2.4 wt % H2O). Anhydrous eclogite cannot be distinguished from harzburgite on the basis of wave speeds, but its &SIM;6% greater density may render it detectable through gravity measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and V-P/V-S ratios indicate that mantle wedges locally reach 60-80% hydration.


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URL  <Go to ISI>://000181799800002
DOI  Doi 10.1029/2001jb001127