Al-Haruj basalts that represent the largest volcanic province in Libya consist of four lava flow phases of varying thicknesses, extensions, and dating. Their eruption is generally controlled by the larger Afro-Arabian rift system. The flow phases range from olivine rich and/or olivine dolerites to olivine and/or normal basalts that consist mainly of variable olivine, clinopyroxene, plagioclase, and glass. Olivine, plagioclase, and clinopyroxene form abundant porphyritic crystals. In olivine-rich basalt and olivine basalt, these minerals occur as glomerophyric or seriate clusters of an individual mineral or group of minerals. Groundmass textures are variably intergranular, intersertal, vitrophyric, and flow. The pyroclastic, clastogenic flows and/or ejecta of the volcanic cones show porphyritic, vitrophric, pilotaxitic, and vesicular textures. They are classified into tholeiite, alkaline, and olivine basalts. Three main groups are recorded. Basalts of phase 1 are generated from tholeiitic to alkaline magma, while those of phases 3 and 4 are derived from alkaline magma. It is proposed that the tholeiitic basalts represent prerift stage magma generated by higher degree of partial melting (2.0–3.5%) of garnet-peridotite asthenospheric mantle source, at shallow depth, whereas the dominant alkaline basalts may represent the rift stage magma formed by low degree of partial melting (0.7–1.5%) and high fractionation of the same source, at greater depth in an intra-continental plate with OIB affinity. The melt generation could be also attributed to lithosphere extension associated with passive rise of variable enriched mantle. 1. Introduction The volcanic rocks territory of Libya ranging in age from the Eocene to present day occur. The age of these predominantly basaltic rocks decreases from north to south. The Central Al-Haruj Al-Abyad (CHA) basalt flows cover the southern part of the Al-Haruj total volcanic province between 26°N and 26° 30′N latitudes and 16° 45′E and 18°E longitudes in the central Libya. It is featured by close structural and genetic relationship with the Al-Haruj al-Abyad total volcanic system, so the present authors adopt a similar classification of the volcanic pile as it had been elaborated in the previous works [1–3] distinguishing 4 major eruption phases and 11 subphases or flow units. The origin of the volcanism is still not clear. The Al-Haruj flood basalt field (45,000？km2) is the largest of four Tertiary to Recent volcanic provinces in central Libya [1] (Figure 1). The CHA falls within the Al-Haruj basalt field; it is located
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