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Millennial storage of near-Moho magma

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Science  19 Jul 2019:
Vol. 365, Issue 6450, pp. 260-264
DOI: 10.1126/science.aax4092

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Millennial magma reserves

Lava erupts after being stored as magma deeper underground. Silica-rich magmas characteristic of volcanoes like Pinatubo are stored for thousands to hundreds of thousands of years. However, we have little understanding of the time scales for deeper basaltic magma like that supplying Icelandic volcanoes. Mutch et al. used diffusion of chromium and aluminum atoms to show that these magmas are stored for hundreds to thousands of years at the crust-mantle boundary. This discovery elucidates the time scale for understanding how magma is created and stored and how it erupts.

Science, this issue p. 260

Abstract

The lower crust plays a critical role in the processing of mantle melts and the triggering of volcanic eruptions by supply of magma from greater depth. Our understanding of the deeper parts of magmatic systems is obscured by overprinting of deep signals by shallow processes. We provide a direct estimate of magma residence time in basaltic systems of the deep crust by studying ultramafic nodules from the Borgarhraun eruption in Iceland. Modeling of chromium–aluminum interdiffusion in spinel crystals provides a record of long-term magmatic storage on the order of 1000 years. This places firm constraints on the total crustal residence time of mantle-derived magmas and has important implications for modeling the growth and evolution of transcrustal magmatic systems.

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