Conduit convection, magma mixing, and melt inclusion trends at persistently degassing volcanoes

Magmas progressively exsolve volatiles as they ascend towards the Earth's surface, such that their volatile content is a function of pressure. Water and carbon dioxide concentrations measured in melt inclusions from degassing volcanoes rarely coincide with modelled degassing trends. I show that observed melt inclusion trends can be reproduced through mixing of magmas, either during convection within the volcanic conduit, or within a subterranean magma reservoir. No fluxing gas phase or post-entrapment loss of water need be invoked. A permeable network allowing gas transport is still required to avoid fragmentation of magma at shallow depths.

Research Highlights► Observed melt inclusion trends are explained by the convection of magmas. ► Mixing can occur in the conduit or in a subterranean reservoir.► Exogenous supplies of CO2 need not be invoked. ► Permeable flow of gas through magma explains the predominance of effusive activity.