Reactivation of a transcrustal plumbing system during a rifting event (Asal Rift, Djibouti)

Abstract

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 inclusion 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. 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 rifting and provide key constraints on the magmatic architecture of incipient oceanic spreading centers.