Constraining magma storage conditions at a restless volcano in the Main Ethiopian Rift using phase equilibria models

摘要

The Main Ethiopian Rift hosts a number of peralkaline volcanic centres, several of which show signs of recent unrest. Due to the low number of historical eruptions recorded in the region and lack of volcanic monitoring, Conditions of magma storage in the Main Ethiopian Rift remain poorly constrained. Aluto is one of these restless volcanic centres and identifying magma storage conditions is vital for evaluating the significance of recent periods of unrest. Using Aluto as a case study, we explore magma storage conditions using Rhyolite-MELTS thermodynamic modelling software. We performed-150 fractional crystallisation models using a primitive basalt as the starting composition, and for a range of pressures (50-300 MPa), initial H2O contents (0.5-3 wt%) and oxygen fugacities (QFM 2-Q,FM + 1). Predicted liquid lines of descent from these models are compared with published whole rock data and, together with new observations of natural phase assemblages and erupted mineral compositions, provide constraints on magma storage conditions.