Ghat Basement Province is the westernmost of all major basement provinces in Libya. It lies way to the southwest of the city of Ghat. The province is of irregular shape, covers three IRC map sheets, trends about N40o-45oW and attains a maximum width of 90 km at the upper part of its lower half (see black bar, map at right). Like Tibesti Basement Province, GBP is of Pan African age. Because the author of these pages has not carried out any field work in any part of GBP, all the information included herein (other than our discussion, which is marked under such a heading below) is taken from published data that will be cited where applicable.

Ghat Basement Province is dominated by granitic to granodioritic batholiths and minor diorite and gabbro of Upper Proterozoic age (Pt2, IRC, 1985) that pierce through a metamorphic sequence of which only rafts are exposed in the southern part of the province. These rafts consist, in order of decreasing abundance (from east to west), of phyllite and schist, granulite and marble streaked with micaceous bands (Grubic, 1984). According to Saggerson (1978), "the metamorphic assemblage is of amphibolite to granulite facies" and thus it is presumably of a much higher grade than most parts of the Tibestian metamorphic terrain. The igneous suite is intruded by micro granite and micro diorite dikes as well as quartz veins. Radulovic (1984) divided the intrusive rocks of the Ghat Sheet into migmatitic granites, mixed and syn-tectonic granites and intrusive granites. Although it was stated (op. cit.) that the migmatitic granites appears to have transitional nature with the mixed and tectonic granites, the relationships between these different bodies of granite are, nonetheless, very vague and remain poorly understood.

DISCUSSION: The description by Grubic (1984) of the metamorphic assemblage appears to be a reversal of the position of the two major belts of Tibesti Basement Province. Although a certain grade of metamorphism may not extend uniformly for hundreds of kilometers, it would be a great discovery if it can be proven that the Pan African metamorphic belts of Libya ran in a repetitious form due to some sort of isoclinal folding (and possibly repeated thrusting) where synforms and antiforms become virtually indistinguishable.

Saggerson (1978) and Grubic (1984) referred to the occurrence of rocks of granulite facies in the area of GBP. It seems that Saggerson was referring to migmatitic granite whereas Grubic meant a metamorphic grade. Migmatization is a metamorphic process that could lead to igneous rock forming such as the mixed and syn-tectonic granite and migmatic granite (shown at right), and hence, the province has an imprint of high-grade regional metamorphism. The granodiorite could be intrusive and appears to be post-tectonic. The increased grade of metamorphism westward (albeit lacking uniformity) in the GBP is thus noteworthy if it to be found that it led to preponderance of anatectic granite, which are shown on the map at right to occupy the larger part of the province. Dominance of batholithic granite and related rocks in GBP resembles the make up of the western belt of TBP. Relevant to the process of migmatization, one notes that In OBP, it has taken on quartzo-feldspathic  gneiss whereas it involved schist and diorite in the subsurface.

Relevant to ages, if the Upper Proterozoic age reported by IRC the (1985) was for gabbroic dikes as is the case for Al'Oweinat diabase, then one might assume some rock assemblage commonality throughout the basement of Libya regardless of age of the province as an independent entity.

REFERENCES: Grubic, A., 1984. Geological Map of Libya (scale 1:250,000). Adrar In Yahia Sheet (NF32-3) + explanatory booklet, 35 p. Indust. Res. Centr., Tripoli.

IRC, 1985, Geological Map of Libya, First Ed., Scale: 1,1,000,00, Tripoli.

Saggerson, E.P., 1978. Metamorphic Map of Africa (Scale 1:10,000,000) (incl. explanatory text, 56 pp.). UNESCO, Paris.