Deep and disturbed: conditions for formation and eruption of a mingled rhyolite at Ascension Island, south Atlantic

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Katy Jane Chamberlain
Jenni Barclay
Katie Preece
Richard Brown
Iona McIntosh
EIMF

Abstract

The generation of felsic melts (through open or closed system processes) within ocean island volcanoes has been a key area of study since their identification. At Ascension Island in the south Atlantic, explosively erupted felsic melts have, to date, demonstrated a marked absence of signs of magma mixing and crustal assimilation. Here we present the first observations of a fall deposit from Ascension Island recording both macro- and micro-scale evidence for magma mingling. Geochemical analyses of mineral and glass phases, coupled with volatile concentrations of melt inclusions highlight the role of lower-crustal partial melting to produce rhyolitic magmas. Glass textures and the lack of zoning in major mineral phases indicate that mingling with a mafic melt occurred shortly prior to eruption. These inferences of a deep rhyolite production zone, coupled with rapid ascent rates highlight the challenges in forecasting a similar style of eruption at Ascension Island in the future.

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How to Cite
Chamberlain, K. J., Barclay, J., Preece, K., Brown, R., McIntosh, I. and EIMF (2020) “Deep and disturbed: conditions for formation and eruption of a mingled rhyolite at Ascension Island, south Atlantic”, Volcanica, 3(1), pp. 139-153. doi: 10.30909/vol.03.01.139153.
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