Ballmer, MD; Ito, G; Cheng, C; (2015) Asymmetric Dynamical Behavior of Thermochemical Plumes and Implications for Hawaiian Lava Composition. In: Carey, R and Cayol, V and Poland, M and Weis, D, (eds.) Hawaiian Volcanoes: From Source to Surface, Geophysical Monograph 208. (pp. 35-57). John Wiley & Sons, Inc

Text Ballmer et al_AGUMon2015.pdf - Published Version Access restricted to UCL open access staff Download (5MB)

Abstract

The Hawaiian Kea and Loa volcano trends have commonly been interpreted as directly reflecting a compositional zonation within the Hawaiian plume stem, inherited from the lowermost mantle. As this zonation is often associated with variations in mafic material and as such materials, especially intrinsically dense eclogites, impact mantle flow, this study aims to characterize the ascent and melting of bilaterally zoned thermochemical plumes. Our geodynamic models predict that plumes bearing ≳12% eclogite tend to stagnate as a deep eclogitic pool (DEP) in the mid-upper mantle where phase changes lead to a maximum in eclogite excess density. This behavior can explain recent seismic-tomography results and predicts thermal asymmetry of material rising out of the DEP to feed the hotspot. Thermal asymmetry is caused by the effects of ambient mantle flow or plume stem zonation on DEP dynamics and ultimately boosts peridotite melting on the melting zone's hotter side. This hotter side is hence less dominated by melting of mafic materials, despite being fed by equally or more such materials than the cooler side. These results suggest that the Kea side of the Hawaiian plume is equally or more eclogitic than the Loa side, opposite to previous interpretations. Care should thus be taken in mapping geographical variations in lava chemistry into the deep mantle.

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