Lithium diffusion in olivine records magmatic priming of explosive basaltic eruptions

Abstract

The short duration (e.g., hours to days) of magmatic processes leading up to volcanic eruptions are challenging to characterize using conventional petrologic and geophysical methods. This is especially true for eruptions that occurred prior to the implementation of seismic and geodetic monitoring (mid-20th century). We present a new application of diffusion chronometry that utilizes lithium zoning in olivine phenocrysts to investigate the timing of late-stage, pre-eruptive magma mixing at Kīlauea Volcano (Hawai‘i). The diffusive re-equilibration of sub-ppm changes in lithium concentration are modeled in rapidly quenched, well-oriented olivine from six eruptions during a dominantly explosive period (1500–1820 CE). Lithium timescales reveal repeated intrusion of primitive composition magma into Kīlauea's shallow (∼2–6 km) reservoir system typically only a few days prior to each eruption. These timescales are shorter than the weeks to years retrieved from modeling Fe–Mg and Ni zoning in the same olivine crystals, which record earlier magma mixing events. The short Li timescales indicate that an intrusion primed the shallow magma reservoir potentially only hours to a few days before an eruption. Late-stage intrusions and mixing events should thus be investigated at other basaltic volcanoes to better understand pre-eruptive processes, so that eruption scenarios can be better constrained.