Carbonated eclogite at 3.5-5.5 GPa – the effect of the capsule material on solidus temperatures

We experimentally investigated a nominally anhydrous, K-bearing, altered MORB composition GA1 + 10% CaCO 3 (GA1cc), from 1050-1400°C and 3.5-5.5GPa.This composition (see Table in the abstract 10IKC-081) models deep subduction of carbonated oceanic crust, the major process for replenishment of the earth's deep carbon cycle.All experiments were conducted in 1.27 cm diameter end-loaded Boyd-England type piston-cylinder apparatuses in the Research School of Earth Sciences, The Australian National University with two types of capsules: "Pt with inner graphite (Pt-Gr)" and "Au-Pd".A 200 ton press was employed for the experiments at 3.5 and 4.5 GPa, while for 5 and 5.5 GPa experiments an ultrahigh pressure 500 ton pistoncylinder press was used.The observed phase assemblages were used to construct an experimental P-T phase diagram (Fig. 1).The subsolidus phase assemblages for both sets of experiments (Pt-Gr and Au-Pd) consist of clinopyroxene, garnet, carbonate, rutile, K-Feldspar, coesite (at 4.5 and 5.0 GPa) and apatite (observed only in the Pt-Gr subsolidus run).The textures observed in the experiments change dramatically with the degree of melting.Abovesolidus experiments contain quenched partial melts which differ in two sets of runs.In Pt-Gr runs the partial melts can be subdivided into four types.With increasing temperature at any given pressure they are: low-degree siliceous melts,