Abstract
The Afar region in East Africa is located
above the Afar Plum, which means that the complicated history of tectonic activity
and volcanism of this region is directly attributable to the interaction between
the plume and the overlying lithospheric mantle. The volcanic rocks of the Afar
are not underlying by continental crust except along the margins of the Afar
region. Therefore, the compositional variation of the volcanic rocks has resulted
from the heterogeneity of the magma source, from the extent of melting during
magma formation, by mixing of magmas derived from different mantle sources,
and by fractional crystallization of magmas at shallow depth below the surface.
For the marginal magmas, assimilation of Precambrian basement rocks of grantic
composition is possible, but for the Afar region, this is not an option.
Relatively little petrological and geochemical research has been done in the
Danakil Depression to confirm or disprove the structural and tectonic models
established for this area. This study employs both petrographic analysis and
chemical analysis, mostly in the form of trace and rare-earth element comparisons;
to classify the likely source magmas and processes involved in rock formation
at various locations within the depression. Overall, petrographic analysis reveals
olivine-rich basalts that are generally vesicular, with varying abundance of
Fe-Ti oxides. Trace and rare-earth element chemical data place the majority
of samples in the transitional to mid-ocean ridge basalts (MORB). Further analysis
provides evidence for fractional crystallization of an uncontaminated, enriched
magma source.
