Abstract
The Late Triassic-Liassic evaporites of the Tunisian Central Atlas commonly contain fault blocks of layered or brecciated metabasalts and tuffs. The metabasalts show the effects of two alteration episodes: (1) a greenschist-facies, spilitic assemblage composed of albite, chlorite, actinolite, epidote, calcite, quartz and leucoxene; and (2) a later, potassic alteration assemblage composed of potassium-feldspar, sericite, calcite, chlorite, and hematite. The primary assemblage of plagioclase + titanomagnetite + ophitic pyroxene ± olivine can be identified from crystal pseudomorphs and rare, relict crystals. Based on the abundances and interrelations of immobile elements (Ti, P, Y, Zr, Nb, Ni and Cr), the metabasalts are shown to be tholeiitic basalts with slight alkaline tendencies. Based upon these features, their field relations, and the extensive occurrence of Triassic-Liassic tholeiites across the northwest African margin, the Tunisian metabasalts are considered to be remnants of a widespread basalt province associated with the breakup of Pangaea in the Early Jurassic.
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