This book summarises the geological knowledge accumulated on Afar in the last 60 years. It aims to show how Afar is, and will remain, a real "hot spot" for geological and geophysical research, providing an "open book" access to the earth processes along diverging plate boundaries, study of both continental and oceanic lithosphere and underlying asthenosphere, margins and transitions, including magmatic, volcanic, tectonic, sedimentary, hydrothermal and geodynamic processes.
The Afar Triangle is a geological depression that developed where the Gulf of Aden, Red Sea and East African Rift Valley meet. It is also considered as one of the most important mantle plumes of the earth system. In 1967, when the first expedition was organized, little information was available on the geology of the area, and even geographic base maps were lacking. When the first satellite photographs were made available from the Apollo and Gemini space missions, a whole picture of the Red Sea – Gulf of Aden region was made available, providing a new vision of the Afar triangle.
Besides its geological particularities described in Geology of Afar (East Africa), which makes from it the only place in the world where an oceanic plate boundary can be observed at free air with all its successive steps of development, the Afar Triangle is also known as one of the cradles of first extinct hominids. The Middle Awash area contains sites of several fossil discoveries, such as the well known Lucy.
Afar is also a place where hydrothermal processes display conditions suitable for the study of the most primitive forms of life (archaebacterial). It is also one of the places in the world (with Iceland) where the most important quantity of telluric energy is made available at the surface for geothermal development. These processes and others well developed in Afar – like evaporation – also lead to the development of mineral deposits of economic interest. In addition, Afar is also an area where important climate changes occurred in the recent quaternary period, with successions of rather wet periods, characterized by wide lakes extending in the south and western parts of the depression, with arid phases as the one prevailing at present. This may relate with the fact that it is also one of the major sites of the origin of the human mankind. As a whole, it is for nowadays care a place where the climate change issues finds its most pregnant illustration.
Besides the geological knowledge provided in Geology of Afar (East Africa), it also shows that Afar is an area where a singular human population developed with its own language and culture, which adapted to the rugged landscape and extremely dry and hot climate. Besides Geology of Afar (East Africa)'s use for scientists and students the author hopes it will also serve the needs of the Afar nation, presently split in three different countries as a result of the recent history.
Part I Afar: global context
- Global and regional geodynamic context
- Relief climate, people, languages and toponymy, exploration history
- Regional domes (Ethiopian and Kenyan) and mantle plume
- The EAR, Afar, Red Sea and Aden rifts
- Origin of mankind, origin of life
Part II Afar geology
- Afar volcanic chronology
- Afar sedimentary units
- Sub-regional approach and geological field description
- The axial ranges
- The central volcanoes of Afar margins and transverse alignments
Part III Crust, mantle, magmas and geodynamics
- Afar magmatic evolution: partial melting of the mantle and differentiation by crystal fractionation
- The recent/present volcano-tectonic events
- Afar in relation with the EAR (continental rift valley)
- The Gulf of Tadjoura, penetration on land of the oceanic Aden ridge
- The Red Sea Link, and rotation of the Danakil block
- Plate boundaries and microplates within Afar
- The Afar mantle plume, discussion
Part IV Applied geology and socio-economic issues
- Thermal manifestations
- Geothermal potential and development perspective
- Mineral resources
- One Afar nation, 3 countries, a social and political issue
- Conclusion: emerged ocean, origin of mankind and life, sustainable future of the planet