Crystal scavenging from mush piles recorded by melt inclusions

Olivine-hosted melt inclusions are commonly used to determine pre-eruptive storage conditions. However, this approach relies on the assumption that co-erupted olivines have a simple association with their carrier melts. We show that primitive olivine crystal cargoes and their melt inclusions display a high degree of geochemical disequilibrium with their carrier melts at Kīlauea Volcano, Hawai’i. Within a given eruption, melt inclusions trapped in primitive olivine crystals exhibit compositional diversity exceeding that in erupted lava compositions since 1790 CE. This demonstrates that erupting liquids scavenge crystal cargoes from mush piles accumulating diverse melt inclusion populations over timescales of centuries or longer. Entrainment of hot primitive olivines into cooler, evolved carrier melts drives post-entrapment crystallization and sequestration of CO2 into vapour bubbles, producing spurious barometric estimates. While scavenged melt inclusion records may not be suitable for the investigation of eruption-specific processes, they record timescales of crystal storage and remobilization within magmatic mush piles.
The increasingly prevalent view of magmatic systems as mush-dominated challenges the common assumption that melt inclusions record the pre-eruptive storage and processing of the melts they were erupted with. Here, the authors show that melt inclusions from Kīlauea Volcano, Hawai'i exhibit extreme compositional diversity, consistent with the accumulation of inclusion-bearing crystals in magmatic mush zones for >170 years before their eventual eruption in unrelated carrier melts.