Al'Oweinat is one of three major provinces that define the litho-tectonic framework of the basement of Libya. It is the second largest aerially, lies near the southeastern border of the country, with small extension into both Egypt and Sudan. In the area of Jabal Arkeno and Jabal Al'Oweinat, it is overlain by sandstone of Eocambrian to probably Carboniferous age. Al Oweinat Basement Province comprises a rock assemblage that is the oldest in northeast Africa, as it has rocks of Upper Archean to Upper Proterozoic age consisting of high grade metamorphic suites as well as intrusions of dioritic to gabbroic affinity. The largely peneplaned basement, except for an elevated part around Jabal Arkeno, is intruded by four major Tertiary ring complexes showing wide lithological spectrum as their rock constituents range from nepheline syenites and equivalents on one side to granites and related rocks on the other side of the silica continuum.

Based on deformation styles and mode of diabase dike emplacement, the province is divisible into three domains: Northern, Central, and Southern. The metamorphic suites are of granulite to amphibolites facies and include charnockite and diopside-bearing gneiss, hornblende-hypersthene gneiss, amphibolite, quartzo-feldspathic (granitic) to garnetiferous gneiss, specularite-magnetite gneiss, migmatite, marble, cataclasite, and mylonite as well as ultramylonite. Although low to retrograde metamorphism is locally noted, the metamorphic suites appear to have evolved primarily from mafic to intermediate igneous rocks via regional, high-grade metamorphism. The suite has an imprint of multiple folding phases, the earliest of which (F1) survived as relics embedded within the more dominant, younger F2 and F3

folds. The latter characterize much of the Southern domain whereas F2 folding is predominant in the Central and Northern domains.

Although contiguous and sharing common lithologic and structural features, each domain shows a folding pattern that is different from the others. Whereas folding in the northern domain is tight and apparently isoclinal with axial planes trending northeasterly, it is less tight and domal in the Central domain. Folding in the Southern domain is flexural on a megascopic scale, more open, but shows some flow nevertheless. On flanks of the mega folds, mesofolds show axial planes that fan slightly from northeast to northwest. Diabase dikes of both right- and left-lateral types transect the basement in all domains, but they also vary in frequency and trend from north to south. In general, deformation of the basement does not appear to have been influenced in any notable measure by the Tertiary intrusions.

It is of great interest to note progressive variation of deformational style and intensity within the metamorphic suites across the vast basement terrain, and to also document trend variation in diabase dike emplacement from north to south. Whereas the dikes assume a N55-60^oE in the Northern Domain, they became progressively more easterly toward the south (Fig. 2). Crustal shortening is greatest in the Northern and Central domains in comparison to the Southern Domain. Variation in dike orientation from north to south suggests either rotation of a tensile system or rotation of a segment of the crust itself. On a regional scale, it appears that Al’Oweinat Basement Province is an isolated remnant of a previously larger shield. However, subsurface basement rocks of migmatitic affinity bears some similarities to migmatized gneiss south of Jabal Al’Oweinat. Whether the Upper Archean to Upper Proterozoic province has a westward subsurface extension remains a subject of conjecture. Added to distinction of Al'Oweinat Basement Province is the fact that it has obviously escaped the Pan African orogeny that affected the other parts of the basement of Libya.