Continental lithospheric mantle by heat supplied from underlying

Continental flood basalt (CFB) provinces exhibit geochemical characteristics which are different from their oceanic basalts counterparts. These compositional variations have been attributed to difference in their mantle sources and/or to effect of crustal contamination (Piccirillo et al., 1989; Gibson et al., 1995; Simon and Chris, 1995and Miranda et al., 1997). Perhaps most of CFB provinces such as Parana, Etendeka, Karoo, Ferrar and Deccan are thought to be associated to mantle plume (Hawkesworth et al., 1986, 1988; Macdougall, 1988; Piccirillo and Melfi, 1988; Melluso et al., 1995 and Peate, 1997). Many studies reveals that mantle plume has been widely invoked in the genesis of CFB, but the actual role of the mantle plume remains controversial; dose the plume trigger melting of the lithosphere by thermal upwelling? And/or is the mantle plume the main source of the magma?(Richards et al., 1989; White and McKenzie, 1989; Campbell and Griffiths, 1990).

Geochemical variations of basaltic lavas in continental settings is essentially controlled by a number of parameters including mantle temperature, lithospheric thickness and/or degree of partial melting, source composition and certain shallow level processes such as crustal contamination and crystal fractionation (McKenzie and Bickle, 1988). Generally for the geochemical variation of single province three widely advocated hypotheses have been used (i) spatially variable partial melting within upwelling convicting mantle plume (Cambell and Griffiths, 1990;Gibson et al., 1995), followed by variable extent of crustal contamination (Foder, 1987).  (ii) Wet melting of laterally heterogeneous sub-continental lithospheric mantle by heat supplied from underlying mantle plume (Gallagher and Hawkesworth, 1992). (iii) Mixing of picritic oceanic island basalt (OIB) type melt derived from a mantle plume with mafic ultrapotassic melts as they rise through the sub-continental lithospheric mantle (SCLM) (Ellam and Cox, 1991).

Previous petrological studies in Ethiopian plateau focused on the voluminous northwestern plateau (Berhe et al., 1987; Mohe et al., 1988; Hofmann et al., 1997; Ayalew et al., 2002; Davies et al., 2003 and Kiffer et al., 2004). Very little is known for the southeastern Ethiopian plateau basalts (Zanettin et al., 1980). In the southeastern Ethiopian plateau approximately 600m basaltic lava succession of pyroxene and plagioclase-aphyric basalt termed as Reira basalt (Berhe et al., 1987). This study reports major and trace element data for basaltic lavas collected from poorly known southeastern Ethiopian plateau with the aim to characterize their geochemical signatures. The result obtained will be used to constrain their petrological relations with their counterparts in northwestern Ethiopian.