Experimental Investigation of Chemical Zoning in Olivine: Applications to Hawaiian Basalt

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Basaltic eruptions are the dominant type of volcanism on Earth by volume. At Kilauea Volcano (Island of Hawai'i, USA), eruptions involving basalt magma have caused societal harm over the last three centuries, including significant human loss and damage to infrastructure. It was recently discovered that far from the tame reputation that Kilauea gained through decades of effusive, lava-flow dominated activity, the volcano actually undergoes cycles of explosive and effusive activity lasting several centuries each. The state of magma reservoirs underneath the volcano, their size, and the frequency at which they receive recharge from the crust and mantle, are main factors in determining whether explosive or effusive activity dominates in any period of time. At Kilauea and in other volcanoes that erupt basalt, olivine is the most commonly occurring mineral phase. Its potential as proxies for unraveling the subterraneous history of magmas cannot be overstated: olivine is a major information capsule that petrologists examine to recover the timing of magmatic processes occurring prior to an eruption. This project focuses on the mineral olivine as a forensics tool to characterize magmatic systems and the tempo of magma recharge under volcanoes like Kīlauea. Laboratory experiments and detailed studies of olivine chemistry within the products from select 20th century Kilauea eruptions will provide critical constraints for identifying transitions in eruptive cycles. The history of magma recharge, mixing and ascent is preserved in olivine in the form of 'chemical zoning', non-random spatial variations in the crystal-forming elements. However, reading and interpreting chemical zoning in olivine can be complicated because different processes may overprint each other. Primary chemical zoning in olivine can be acquired during initial growth in a melt, but this zoning tends to smooth out through time by element diffusion within the crystal lattice. The extent of this diffusion smearing is increasingly used to backtrack the timing of magma mixing and ascent before an eruption occurs. These modern petrological applications have yet to be subject to thorough experimental verification. Using a suite of carefully planned laboratory experiments, this project therefore focuses on deciphering the mechanisms by which olivine acquires chemical zoning for a whole suite of elements during its birth and growth in a basalt melt, and how fast this zoning is modified. A basalt melt will be cooled to different temperatures and left for various durations at the final conditions to induce crystallization and track diffusive re-equilibration through time. To exploit and apply the experimental results to natural systems, olivine from the products of several 20th century eruptions from Kīlauea Volcano (Hawaii) will be investigated for their chemical zoning patterns. The reasons for choosing Kīlauea as a laboratory for olivine studies are manifold. There have been no less than 50 eruptions in the last century (one that is ongoing since 1983), and existing work suggest that the volcano has been undergoing a surge in magma supply since the 1950s. Examining the zoning patterns of olivine in those eruption products and extracting critical timescale information pertaining to pre-eruptive magma injection and recharge will be essential to establish informed projections about future behavior.