Magma and Underplating in the Ethiopian Lower Crust From a Re-analysis of EAGLE Active-Source Seismic Profiles

Abstract:

A reanalysis of wide-angle seismic data collected along and perpendicular to the Main Ethiopian Rift reveal previously undetected magmatic addition to the lower crust, reflecting increased magma storage and crustal modification beneath the rift valley and adjacent plateaus. A lower crustal magma chamber imaged at ~24 km depth beneath Boset volcano is one of the deepest melt bodies observed in an extensional environment. Beneath the Ethiopian plateau, where previous studies suggest an extensive and thick underplate, we show that a 6-8 km thick, localized zone of magmatic intrusion into the lower crust better matches all existing data. The magmatic lens beneath the rift and the magmatically intruded lower crust appear to be associated with recent magmatism in the Wonji Fault Belt (WFB) and Silti-Debre Zeyit Fault Zone (SDFZ). Active extension and magmatic intrusion in the lower crust may drive rift propagation into the cratonic block of the Ethiopian plateau from the rift valley rather than following the existing rifted crust.