Extended Data Fig. 2: Y and Yb partitioning in major mantle minerals.

a−c, Y and Yb partition coefficients between minerals (clinopyroxene, orthopyroxene and olivine) and silicate melt as a function of pressure. Error bars are 1 SD and are smaller than symbol size where absent. Experimental data are presented as mean values ± 1 SD. Partitioning data for clinopyroxene (cpx): 6 GPa and 1410 °C⁷⁶; 3 GPa and 1380 °C⁷⁷; 1.5 GPa and temperature of 1255–1315 °C^78,79,80; 1 atm and 1080−1100 °C⁸¹. Partitioning data for orthopyroxene and olivine at 1.5 GPa and 1275–1315 °C are from refs. ^79,80. d, Y and Yb partition coefficients between (peridotitic versus pyroxenitic) garnet and silicate melt as a function of pressure or temperature. Experimental data from ref. ²². The solidus of nominally dry peridotite as a function of pressure (0 to 8 GPa) was taken from Hirschmann²⁵. Note that Y and Yb are highly incompatible in olivine (D < 0.05), and so olivine would play a very limited effect on melt Y/Yb ratios during peridotite mantle melting. We also note that Y and Yb partition coefficients in (peridotitic versus pyroxenitic) garnet are temperature- and pressure-dependent and decrease with increasing pressure and temperature. Considering that the solidus increases with pressure²⁵, it is reasonably to suggest that D_{Y, Yb}^garnet/melt are highly pressure-dependent. e, Calculated D_Y/Yb between garnet/cpx and silicate melt as a function of pressure. The green model line was calculated by exponentially weighted moving average (the same data as D_Yb and D_Y in b²²). f, Calculated Y/Yb ratios of silicate melt (assumed to be equilibrated with mantle with varying cpx-garnet modal proportions) as a function of pressure.