Magma-cumulate mixing identified by U-Th disequilibrium dating

Here we present the first U-Th isotopic evidence for mixing between a crystal mush and a magma in an andesite from the island of Santorini, in the Aegean arc. The lava contains crystal populations from two sources of distinct thorium isotope composition: one from a basic cumulate; the other phenocrysts from a dacite magma. The crystal populations have statistically indistinguishable crystallization ages of 79+14sub(-12) kyr and 93+29sub(-22) kyr, and are thought to have physically intermingled just before eruption. The crystals did not re-equilibrate and hence retain the isotopic compositions and ages of the parental materials. (author)