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Durham University

Department of Earth Sciences

Profile

Publication details for Dr Richard James Brown

Chamberlain, Katy, Barclay, Jenni, Preece, Katie, Brown, Richard, McIntosh, Iona & EIMF, (2020). Deep and disturbed: conditions for formation and eruption of a mingled rhyolite at Ascension Island, south Atlantic. Volcanica 3(1): 139-153.

Author(s) from Durham

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.