Variations in Hawaiian Plume Flux Controlled by Ancient Mantle Depletion

Abstract

Mantle plumes—upwellings of buoyant rock in Earth's mantle—feed hotspot volcanoes such as Hawai‘i. The size of volcanoes along the Hawai‘i–Emperor chain, and thus the magma flux of the Hawaiian plume, has varied over the past 85 million years. Fifteen and two million years ago, rapid bursts in magmatic production led to the emergence of large islands such as Pūhāhonu, Maui Nui and Hawai‘i, but the underlying mechanisms remain enigmatic. Here, we use new radiogenic Ce–Sr–Nd–Hf isotope data of Hawaiian shield lavas to quantify the composition and proportion of the different constituents of the Hawaiian plume over time. We find that most of the Hawaiian mantle source is peridotite that has experienced variable degrees of melt depletion before being incorporated into the plume. We show that the most isotopically enriched LOA-type compositions arise from the aggregation of melts from more depleted, trace element-starved peridotite, causing the over-visibility of melts from recycled crust in the mixture. Our results also show that upwelling of chemically more depleted, and thus less dense, more buoyant mantle peridotite occurred synchronously to an observed burst of magma production. Buoyancy variations induced by variably depleted peridotite may not only control the temporal patterns of volcanic productivity in Hawai‘i, but also those of other plumes world-wide. The excess buoyancy of depleted peridotite may therefore be an underrated driving force for convective mantle flow, trigger and sustain active upwelling of relatively cool plumes, and control the geometry of mantle upwellings from variable depths.