HR: 1330h
AN: V12C-0604    [PDF]
TI: The Effect of Carbonate Composition and Concentration on the Solidus of Carbonated Eclogite: An Experimental Study at 3 GPa
AU: Dellas, N
EM: ndellas@andrew.cmu.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455 United States
AU: Dellas, N
EM: ndellas@andrew.cmu.edu
AF: Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave, Pittsburgh, PA 15213 United States
AU: * Dasgupta, R
EM: dasg0007@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455 United States
AU: Hirschmann, M M
EM: hirsc022@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455 United States
AB: Subduction of carbonated oceanic crust transfers a substantial amount of carbon into the mantle. Some or all of this carbon is released to surrounding mantle by partial melting of carbonated eclogite, which thus has a key influence on the distribution of carbon in the mantle. Previous experiments have determined melting relations for a particular bulk composition (e.g., 60$%$ eclogite + 40$%$ calcite). However, solidus temperature depends on near solidus melt composition, which may vary in the mantle. Importantly, it may also depend on the composition and quantity of carbonate added to experimental charges. To investigate this effect, we performed partial melting experiments with different starting materials at a single pressure of 3 GPa. Salt Lake crater eclogite (SLE) from Oahu, Hawaii was used as the base silicate composition. This starting material, which is a close approximation of subducted ocean crust after extraction of small degree partial melts/siliceous hydrous fluids, was modified by varying the composition and amount of added carbonates. Near solidus carbonate melt compositions are Na-Fe dolomitic for all starting compositions, whereas the stable carbonate mineral at the solidus varies as a function of added carbonate compositions: SLE+calcite runs produced calcite$_{ss}$ (Ca/(Ca+Mg) = 0.83) whereas Fe-dolomite$_{ss}$ (Ca/(Ca+Mg) = 0.5) is stable when CO$_{2}$ was added as a mixture of Fe-Mg-Ca carbonates. Garnet, cpx, and ilmenite were present at the solidus for all the compositions investigated. The solidus of carbonated eclogite decreases from ${\it ca.}$ 1200 $\deg$C to ${\it ca.}$ 1050 $\deg$C as the molar Ca/(Ca+Mg) and Na$_{2}$O of the bulk starting material was changed from 0.52 to 0.42 and 1.4 to 1.75 wt.$%$ respectively (molar Ca/Na decreased from $\sim$13 to $\sim$9). Also, the solidus of SLE+5 wt.$%$ calcite is near 1125 $\deg$C, but with 10 wt.$%$ calcite it is $\sim$1200 $\deg$C. Larger amounts of added calcite produce near-solidus melts with higher Ca/(Ca+Mg) and Ca/Na, and consequently a higher solidus. Thus, experiments with large amounts of added CO$_{2}$ may not be easily applied to natural carbonated eclogite, which has a small proportion of CO$_{2}$, unless the experimentally-added carbonate produces liquids similar to those expected near the solidus of natural bulk compositions.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 4806 Carbon cycling
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting