Extended Data Fig. 9: Schematic.
From: Deep, hot, ancient melting recorded by ultralow oxygen fugacity in peridotites
Schematic representation of the development of fO2 heterogeneities owing to ancient melting events. a,b, Ancient hot mantle, in which melting initiates in the garnet field. a, Ancient fertile mantle ascends along a hot adiabat, producing large degrees of melting in the garnet stability field and a refractory peridotite residue. b, During garnet-field melting, fO2 is reduced relative to an equivalent, melt-suppressed assemblage. c–f, Modern cool mantle, consisting primarily of fertile material with rafts of previously melted mantle. c, Rafts of refractory material produced by ancient melting (as shown in panel a) may re-ascend along a cool adiabat but will not experience notable further melting owing to their refractory nature. d, Along a cool adiabat, fertile ambient mantle material melts in the spinel stability field. The extent of melting is primarily a function of spreading rate, which determines the pressure at which melting stops. e,f, Modern, fertile mantle will not substantially change in fO2 during melting, although spinel Cr# will increase as melting continues25. Rafts of ancient, refractory material will retain their high spinel Cr# and low fO2 signature produced during ancient melting events.
