Preservation of H2O heterogeneity in the Icelandic mantle

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• Simon Matthews (University of Cambridge)
• Tuesday 09 May 2023, 12:00-13:00
• Department of Earth Sciences, Tilley Lecture Theatre.

If you have a question about this talk, please contact Oscar Branson.

It is well established that the mantle is chemically heterogeneous on length scales of 10s of kilometres or less; a product of recycling melting residues and subducted lithosphere, followed by stirring and mixing during vigorous convective cycling. We might also expect these mantle components to have distinct H2O concentrations, determined by their history of hydrous alteration near Earth’s surface, devolatilization during subduction, or H2O extraction during melting. However, the rapid diffusion of H+ in mantle minerals acts to dampen or remove this H2O heterogeneity during transport from the lower mantle. The persistence of H2O heterogeneity can place a lower bound on the length scales of mantle heterogeneity.

Since subaerially erupted lavas lose most of their volatile element budget prior to or during eruption, volatile studies are limited to glasses quenched at high pressures, their eruption having occurred on the sea floor or at the base of glaciers. I will present new H2O , trace element, and radiogenic isotope analyses, alongside compiled data, for glasses erupted on the submarine ridges adjacent to Iceland, subglacial glasses on Iceland, and olivine-hosted melt inclusions from 8 primitive Icelandic eruptions. To estimate pre-eruptive volatile concentrations, we develop methods for filtering melt inclusion datasets for the effects of H2O degassing and H+ diffusion.

Together, the datasets demonstrate pervasive small-scale H2O heterogeneity is present throughout the mantle beneath Iceland and the surrounding spreading ridges, implying small-scale mantle heterogeneities are large enough that H+ diffusion has not eroded their presence.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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• Department of Earth Sciences Seminars (downtown)
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