Continental breakup in magmatic provinces: An Ethiopian example

Mechanical processes largely control the along-axis segmentation of contine ntal rifts; however, asthenospheric processes strongly influence the along- axis segmentation of midocean ridges. We examine the distribution of strain and magmatism in the transitional active Main Ethiopian rift. Magmatic con struction, diking, and faulting during the past 1.6 m.y. have created simil ar to 20-km-wide, similar to 60-km-long magmatic segments with or without a xial valleys. Magmatic segments are arranged en echelon within the similar to 100-km-wide rift valley bounded by mid-Miocene border faults, Geodetic d ata show that magmatic segments at:commodate > 80% of the strain across the rift, indicating that border faults are no longer the locus of extension. Comparison with mid-ocean ridges suggests that magmatic segments, rather th an detachment faults, mark the ocean-continent boundary in rifts with a rea dy magma supply. Magmatic margins, therefore, may contain detachments aband oned during continental breakup, The processes of localized dike intrusion with underplating would produce strips of mafic crust transitional to ocean ic crust, but without coherent. seafloor-spreading magnetic anomalies.