General petrological overview of volcanic rocks from Asal-Ghoubet area (Djibouti)

The entire Asal-Ghoubet rift is covered by hyaloclastites and lacustrine limestones being overload by recent-aged basalts. The volcanic units in this region are characterized by the pahoehoe and aa type lavas. These lavas show porphyric and aphyric textures and the phenocrysts are composed of plagioclase, olivine and clinopyroxene. There are also the same minerals in the matrix. Opaque minerals are composed of magnetite and ilmenite and they are also present in the matrix. Magnetites are found in the matrix as relicts and ilmenites are also found as fine- grained crystals. All the volcanic rocks enrichment in large ion lithophile elements (LILE) and in heavy rare earth elements (HFSE) according to MORB in normalized N-MORB patterns. REE values of volcanic rocks normalized to chondrite show a transitional trend between N- MORB and E-MORB values. These samples display an enrichment in LREE and slight depletion in HREE. These rocks have MORB or transitional MORB properties; they may have been derived from the magma formed by partial melting of the mantle which is enriched by LILE.