Episodic spreading and rift propagation: New paleomagnetic and geochronologic data from the Afar Nascent passive margin

Abstract

A recent model proposes that Afar is one of the few areas in the world where the formation of a passive margin by rift propagation can be observed directly. Forty sites spread over approximately 10,000 km 2 in the Republic of Djibouti, between the Asal and Abhe rifts, have been sampled for paleomagnetic and geochronologic study. Most basalt samples have a single stable magnetic component, often already clear in the natural remanent magnetization. The remanent direction of sites younger than about 1 Ma is consistent with the expected axial dipole direction, whereas sites between 1.35 and 2.25 Ma old form a microblock that was rotated by 14.5°±7.5° clockwise, probably between 1.3 and 1 Ma. The rotation is attributed to rift propagation. This study shows that spreading and rift propagation in Afar are episodic and lead to alternate “effusive” and “tectonic” phases that may be of general significance for accreting plate boundaries.