Afar Triple Junction (Ethiopia)Review & Open Questions

Resumen

The Afar depression constitutes one of the best exposed triple junctions on Earth where to address the specific details of conti- nental breakup and associated processes (extensional tectonics, volcanism, hydrothermalism, early stage mineral systems, etc). The general view of this specific geodynamic scenario is that it accommodates the movement of three continental plates that diverge on a sphere. A large number of processes take place in such scenario and in the Afar depression they can be addressed in order to asses a number of unresolved issues. There is a lack of knowledge on: i) how and where the strain accumulates before breakup; ii) the architecture of the crust and its transition from thick continental crust to extended crust and, to fully oceanic crust; iii) the extension and significance of the rhyolite outcrops; iv) the interactions of salt and underlying magmas and, v) how is the contrasting topography supported. Surface outcrops, geologic structures, hydrothermal systems, and geomorphology sug- gest a strong involvement of subsurface intrusions at different crustal levels in this active, extensional setting. This suggests that the breakup is mostly based on dike intrusion and magma supply. A number of processes generated by a mantle plume. Never- theless there is very limited knowledge on the geometry of intrusions and their extension how they interact with the overlying ~2000 meters of salt. A relatively rapid evolution of the active volcanic centers has been documented which seems to suggest a decrease on the level of activity of the extensional tectonics. Triple junction environments involve extensional tectonic systems, emplacement of magmas and development of hydrothermal systems all fundamental ingredients in the generation of mineral deposits. In short, the Afar depression is the only place where hydrothermal processes that take place in oceanic ridges can be studied in a subaereal environment in this case in the form of steam. And also the role that the interaction of magmatic fluids with evaporitic environments play in the salinity increase and in the transport of metals to form “brine pools”