Subsurface magmatic structure beneath the nested Awasa-Corbetti caldera complex, Main Ethiopian Rift, as determined from gravity data

Abstract

The nested Awasa–Corbetti caldera complex (ACC) in the central Main Ethiopian Rift (MER) encompasses the Corbetti caldera complex, which is presently one of the volcanoes undergoing the most rapid uplift in the region and with notable seismic activity. Previous studies provided limited insight into the subsurface crustal structure and the magma plumbing systems beneath this active volcano. To address this gap, we used terrestrial gravity data combined with geological mapping, seismic, and magnetotelluric models to image the crustal structure. We analyzed the gravity data using wavelength filtering, upward continuation, and 2D forward modeling. Gravity anomaly maps show magmatic intrusions beneath the Corbetti and Shalla caldera complexes and the eastern rift margin (Wondo Genet volcanic zone). 2D density models indicated that these intrusions lie at depths of approximately 10–20 km beneath Corbetti, 7–12 km beneath Shalla, and 5–7 km beneath the Wondo Genet volcanic zone. Upward continuation and band pass filtering suggest that the individual caldera complexes have discrete intrusions within the upper crust, with a larger magmatic intrusion that is continuous beneath all of the caldera complexes in the mid to lower crustal depths. The upward continuation and band-pass gravity anomaly maps also reveal volcanic zones along the rift borders (Wagebeta and Chike), indicating that dike injection has added magma along the rift margins. On a regional scale, the gravity maxima align with WNW-ESE-trending intra-rift structures that crosscut the MER. These anomalies show spatial correspondence with the Goba-Bonga volcano-tectonic lineament, suggesting that this inherited structural discontinuity may facilitate magma transport both in the rift margin and in the nested ACC. By integrating 2D gravity, geological, geodetic, seismic, and magnetotelluric models, we created a 3D conceptual model. This model reveals that a network of deep mafic intrusions and shallow mafic intrusions supplies the upper crust beneath the Corbetti and Shalla caldera complex, correspondingly. Our results show that rift evolution in the middle and latter stages occurs from dike intrusion but may also include magmatic processes that occur just outside the rift.

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