The most recent volcanic activity of the Manda Hararo rift segment (Central Afar, Ethiopia): new dating and petrological processes associated with the eruption sequences

The Manda Hararo rift segment in the Afar depression (Ethiopia) represents a key location to study the timing, style, and evolution of volcanic activity within an active continental rift close to the Ocean-Continent Transition (OCT) stage. Despite its importance, the southern part of this segment has remained poorly documented. In this study, we provide a detailed mapping based on a combination of medium-resolution spectral imagery and a unique dataset of very-high-resolution Pléiades images. We combine this map with volcanological observations, major and trace element analyses, and cosmogenic 36Cl surface exposure dating to investigate the very last eruptions and volcanic history of two sub-segments (Gumat Mali and Gablaytu). Our results show that the last volcanic activity occurred at Gablaytu between ~3.20 and 1.50 ka and at Gumat Mali between ~1.90 and 0.61 ka. Petrological data indicate that the Gumat Mali sequence was driven by reservoir recharge with new, less differentiated magma that hybridized with a more evolved mush, enhancing magma mobilization. The Gablaytu sequence records progressive magma differentiation and plagioclase assimilation and/or accumulation. For both sub-segments, these processes control magma evolution prior to eruption and indicate a complex transcrustal plumbing system characterized by magma storage, recharge, and interaction within vertically connected reservoirs. The documentation of these historical and recent volcanologic activities also help to draw potential regional hazards for populations settled nearby these volcanic centres, including parts of Semera district, which should consider both effusive episodes from axial fissures and potentially extremely energetic phreatomagmatic phase, that characterize the initiation of the historical sequence at Gumat mali.Our observations support the recognition of two self-consistent sub-segments within the wide Central Afar magmatic system with their own associated plumbing system: the Gumat Mali sub-segment located in the direct prolongation of the Dabbahu segment corridor and the en-échelon lateral Gablaytu sub-segment along the Manda and Unda Hararo Hararo axis. This illustrates the intimate links between tectonic structures, magma storage and upward migration in controlling the expression of first and second order segmentation in such zones of the Afar depression close to the OCT.