The conductivity of the Perm electrical conductivity anomaly (PEC) is indicated by the orange zones, with the thick red line denoting the average conductivity. The thick grey line denotes the global average conductivity model 27 , which can be experimentally explained by wadsleyite and ringwoodite containing 0.45 and 0.35 wt.% water, respectively, in the mantle transition zone (MTZ) under normal geothermal conditions (ΔT = 0 K). The PEC in the upper and lower MTZ suggests excess temperatures of 300 and 250 K, respectively 30 , while the PEC in the lower mantle can be interpreted to possess an excess temperature of 350 K 22 . Dashed and solid blue lines are the melting fractions of wadsleyite (Wd) and ringwoodite (Rt), respectively, based on the two-phase Hashin–Shtrikman upper–bound mixing model 64 and estimated from the MTZ bulk conductivity. The conductivity values of dry wadsleyite and ringwoodite 30 , and hydrous silicate melts 50 are provided on the plot.
