Experimental Constraints on Pelite Melting in Subduction Zones: a New Approach Using HP Metapelites
Abstract
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 Gåsetjorn unit in the Norwegian Caledonides. Here, 400-410 million years ago, ocean sediments were subducted beyond 50 km and heated to 600° 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 Gåsetjorn 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 Gåsetjorn unit and we found a 20 kb fluid-saturated solidus between 625° C and 650° C. This is the lowest pelite solidus yet obtained at these depths.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.T24A..07L
- Keywords:
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- 3630 Experimental mineralogy and petrology;
- 1030 Geochemical cycles (0330)