Reactivation of a Transcrustal Plumbing System During an Eruptive Rifting Event (Asal Rift, Djibouti): volatiles and chemical compositions of melt inclusions and zoned crystals

The architecture of plumbing systems, and the dynamics of magma-mush mobilisation during eruptions have received a great deal of attention in recent years. Magmatism plays a central role in rift dynamics, yet the structure and evolution of magma plumbing systems during continental break-up remain poorly constrained. The Afar Rift offers a rare opportunity to study active plate divergence and associated magma processes. We investigate the 1978 Ardoukoba fissural eruption in the Asal Rift, a syn-rift volcanism archetypal example and the most recent eruption in this segment of the Afar Rift system. Using a comprehensive dataset of melt inclusions and host mineral compositions, volatile contents (H₂O, CO₂, δD) and thermobarometry, we reconstruct the transcrustal plumbing system and track magma storage, transfer and degassing during the eruption. We show that magmas feeding the system derived from heterogeneous mantle sources, whose signatures are preserved in melt inclusions. Our results reveal polybaric magma recharge events destabilizing the system, triggering progressive tapping of increasingly deeper mush zones. The eruption began with shallow, evolved melts and transitioned to deeper, more primitive melts and crystal cargos. These findings offer a high-resolution view of magma dynamics during rift-related eruptions and provide key constraints on the magmatic architecture of incipient oceanic spreading centres.