TAKING THE PULSE OF KILAUEA VOLCANO: USING ZONED OLIVINE TO DECIPHER MAGMATIC TIMESCALES

Kīlauea is one of the world’s most active volcanoes. Understand the timing of its past magmatic events will enhance our ability to predict future eruptions, that might affect thousands of people living in the volcano’s vicinity. Here we use chemical zoning in olivine, an early forming mineral in Hawaiian basalts, to reveal the timescales of magmatic processes for the early episodes (1983-1986) of the Pu‘u ‘Ō‘ō eruption, Kīlauea’s long-lived and most voluminous historical eruption. Reverse zoning of forsterite (Fo;[Mg/(Mg+Fe)]x100) is common in olivine crystals from episode 6, 8, and 9 (1983) lavas, consistent with previous interpretations of magma mixing. Bimodal olivine populations in these lavas support the interpretation of mixing between high-MgO summit magmas in equilibrium with olivines of ~ Fo 84, and stored rift zone magma with ~Fo 81 olivine. Timescales derived from numerical models of Fe and Mg diffusion indicates magma mixing occurred ~1 to 7 months prior to the episode 8 eruption. Olivine from episods 40 and 46 also show normal and reverse Fo zoning, indicating that magma mixing continued at least until 1986, contrary to prior interpretations. Timescales for episode 40 olivines range widely (~2 months to 6 years) and suggest mixing of a higher-MgO summit magma (~Fo 84) with rift magma (~Fo 82.5) 3-6 years before the episode 40 eruption. In addition, some profiles support a later intrusion of evolved rift magma (~Fo 81.5) starting 7 months prior to the episode 40 eruption. Subtle chemical variations within olivine phenocrysts from early Pu‘u ‘Ō‘ō lavas thus yield new insights into the magma storage architecture during one of the best-studied eruptions of Kīlauea’s magmatic history.