Extended Data Figure 6: Frictional melt chemistry.
a, BSE image of the different phases and textures observed in the products of the rotary shear experiments, along with eight numbered locations of geochemical analyses acquired with the EPMA. b, Normalized geochemical composition of major elements for each analysis. Comparison of the chemical analyses with the textures reveals the variable heterogeneity of the rock products by frictional melting. Analyses 1 and 2 present pyroxene crystals in the seemingly undisturbed host rock and as fragments in the melt zone respectively; they do not show any degree of contamination. Similarly, analysis 3 presents a Fe-oxide crystal and analyses 6 and 8 present plagioclase crystals in the host rock which have not been chemically altered by the products of frictional melting. Analysis 4 presents a protomelt consisting of orthopyroxene with high concentration of Fe-oxide. Analysis 5 also presents a protomelt but this time the chemical composition, and in particular the intermediate concentrations of MgO, CaO and FeO, suggests that it is a mixing product of molten plagioclase and orthopyroxene crystals in a ratio nearing 1:1. Analysis 7 presents the geochemistry of the more homogenized central frictional melt zone, resulting from the mixing of the molten crystals described above.
