Partial melt compositions of natural carbonated peridotite (KLB-1+2.5 wt % CO2) have been determined at 3 GPa using the diamond aggregate method. Melt obtained at 1350 ¿C is carbonatitic, and with increasing temperature melt composition becomes silicate-rich. These melts are lower in SiO2 and Al2O3 and higher in MgO and CaO compared to dry partial melts of KLB-1 generated at the same pressure. The 1400 and 1450 ¿C liquids have melilititic compositions, which are in good agreement with those of natural alkali-basalts from continental regions. At higher temperatures, partial melts are richer in SiO2, and the compositions of liquids at 1475 and 1525 ¿C approximate nephelinite and basanite respectively. However, they deviate from natural alkaline rocks in that the CaO/(CaO+MgO) ratios are smaller, suggesting that the natural nephelinite and basanite magmas were formed at lower pressures. The compositional trend of natural alkaline rocks, melilitites-nephelinites-basanites, may reflect the effect of decreasing pressure. ¿ 1997 American Geophysical Union