Structure of the upper crust at the axis segmentation stage of rift evolution as revealed by gravity data: Case study of the Gedemsa magmatic segment, Main Ethiopian Rift

Abstract

The upper crustal structure of the individual tectono-magmatic segments within the Main Ethiopian Rift is poorly understood. The Gedemsa tectono-magmatic segment (GTMS) is considered to be within an intermediate stage of rift development with magma-assisted rifting contributing to overall extension. The interpretation of gravity data from Global Gravity Model plus2013 has provided an insight on the nature and structure of the shallow upper crust beneath the GTMS within the Central Main Ethiopian Rift. A detailed investigation of the structure of the shallow upper crust based on 2D gravity models, 3D geologic interpretation maps, and residual and upward continued gravity anomaly maps indicate the occurrence of dense, mafic intrusions at depths between 10-20 km and 5–10 km beneath the Tullu Moye-Gedemsa and Boku volcanic centers, respectively. The gravity data indicate at deeper depths, the GTMS (25 km wide and 60 km long) is elongated parallel to the Main Ethiopian Rift axis. Our 2D gravity modeling indicates that the Quaternary faults within the Wonji Fault Belt are closely associated with the dense magmatic intrusions as the faults aid in transporting melt from the deeper crustal melt areas to the shallow magma chambers.