Fig. 9: Comparison of MORB-source normalised36 incompatible trace and volatile element patterns in orthopyroxene-rich garnet peridotites from the Kaapvaal craton (this work and ref. 9) with potential sources of excess silica.
From: The role of C-O-H-F-Cl fluids in the making of Earth’s continental roots
The compositions of the orthopyroxene-rich garnet harzburgites are compared with: a mean composition of Al-depleted and Al-enriched komatiites61,62,104; b subduction-related supercritical fluids generated in high-pressure experiments66; and c fluids with a similar composition to those found in diamond inclusions. The calculated concentrations of a 50%:50% mix of depleted melt residue and Al-depleted komatiite are shown as a green dashed line on (a). (b) and (c) also show the calculated composition of a metasomatic agent in equilibrium with garnet79 in orthopyroxene-rich garnet harzburgite BD2125. This assumes that 30% of the incompatible trace element content of BD2125 garnets is derived from the metasomatic agent, consistent with mass balance calculations of the amount of excess silica (see text for discussion). Elements increase in incompatibility during mantle melting from right to left. Data are from ref. 10 unless stated otherwise in the legend.
