Stability of carbonated magmas at the base of the Earth's upper mantle

We measured the density of carbonated basaltic melt containing 5.0 wt.% CO2 at 2573 K and in the pressure range from 16.0 to 20.0 GPa by using the sink/float method with single crystal diamond as a density marker. We observed sinking of diamond at 19.0 GPa and flotation of diamond at 20.0 GPa and 2573 K. Using the third order Birch-Murnaghan equation of state, the calculated isothermal bulk modulus ( K-T) of the carbonated basaltic melt ( 5.0 wt.% CO2) and its pressure derivative ( K') are 16.0 +/- 1.0 GPa and 5.2 +/- 0.2, respectively. Our result implies that magmas can contain up to 3.0 - 4.0 wt.% CO2 to be denser than the surrounding mantle at the top of the 410 km discontinuity.