Other
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.128..313y&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 128, no. 3-4, p. 313-325
Other
24
Basalt, Carbonates, Earth Mantle, Eclogite, Melts (Crystal Growth), Refractivity, Subduction (Geology), Barometers, Geotemperature, Peridotite, Scanning Electron Microscopy, Surface Temperature
Scientific paper
Calcitic carbonate is a very common low temperature alteration mineral in vugs and veins in oceanic basalts. Transport of altered basaltic crust through high PT conditions during subduction may involve loss of fluids and possible melting reactions but the behaviour of carbonate is quite unknown. In order to constrain this behavior, a series of fO2-buffered piston-cylinder experiments were performed at pressures from 1.5 to 3.5 GPa and temperatures of 700-1000 C. a composition representative of altered oceanic basalt (synthesised with excess H2O at 2.0 GPa and 700 C, producing a quartz + rutile-bearing garnet-amphibolite assemblage) was run with 10 wt% calcite. These experiments demonstrate that carbonate remains as a fefractory phase in rutile eclogite residue, in equilibrium with hydrous dacitic, in andesitic melts to temperatures greater than 900 C over the pressure interval 1.5-3.5 GPa. At low pressures (P = 1.5-2.0 GPa) and high temperatures (T greater than or = 850 C) calcite decarbonates, producing amphibolite or eclogite residue in equilibrium with hydrous siliceous melt and a CO2-rich fluid. Representative slab geotherms traverse the residual carbonate stability field, under both sub- and super-solidus (silicate solidus) conditions. Examination of compositions of co-existing phases in the experiments reveal PT-sensitive garnet-carbonate exchange equilibria which could, with further experimentation, be developed as geothermometers or barometers applicable to carbonate-bearing eclogites.
Green David H.
Yaxley Gregory M.
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