HR: 17:40h
AN: T24A-07    [Abstracts]
TI: Experimental Constraints on Pelite Melting in Subduction Zones: a New Approach Using HP Metapelites
AU: * LeVay, B
EM: blevay@geosc.psu.edu
AF: Department of Geosciences Penn State University, Deike Bldg, University Park, PA 16802 United States
AU: Kerrick, D
EM: kerrick@geosc.psu.edu
AF: Department of Geosciences Penn State University, Deike Bldg, University Park, PA 16802 United States
AU: Eggler, D
EM: eggler@geosc.psu.edu
AF: Department of Geosciences Penn State University, Deike Bldg, University Park, PA 16802 United States
AB: During subduction, sea-floor pelites melt and enrich the mantle wedge with many of the elements that give arc magmas their unique chemistry. This melt allows us to constrain subduction thermal models; e.g., the plate must be hotter than the experimentally determined pelite solidus. Previous melting experiments used marine red clays, but we know from high pressure and ultra-high pressure terrains that prograde metamorphism changes the composition of sediments before they reach sub-arc depths. A prime example of this alteration comes from the G†setjorn unit in the Norwegian Caledonides. Here, 400-410 million years ago, ocean sediments were subducted beyond 50 km and heated to 600$\deg$C. These minimally retrograded metapelites have a higher aluminum to silica ratio than any modern sea-floor sediment and they are depleted in potassium, sodium, magnesium, and calcium. Thus, the G†setjorn metapelite is a more appropriate starting material than marine clay for deep melting experiments. We performed high pressure melting experiments on a sample from the G†setjorn unit and we found a 20 kb fluid-saturated solidus between 625$\deg$C and 650$\deg$C. This is the lowest pelite solidus yet obtained at these depths.
DE: 3630 Experimental mineralogy and petrology
DE: 1030 Geochemical cycles (0330)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting