Carpathian Journal of Earth and Environmental Sciences

In Cambrian aged Hasáwnah Formation from Wāw al Kabir area (Central Sahara, Lybia), among the detritic grains of the sandstone, a few „exotic” grains were identified. We described rock fragments of 0,1–1,4 mm size: biotitic granite or gneiss, quartzose micaschists, sericitic-chloritic schists, graphitic schist, blastopsamitic silt and sandstone, acide volcanic rocks, altered basic glass and chert. Part of the well rounded quartz grains shows truncated owergrowth rims. They represent, in fact, fragments of older sandstone with overgrowth quartz cement.
The microsonde analyse of an acide volcanic rock fragment resulted granodioritic (=dacitic) composition.
Part of rock fragments are originate from granite basement and its mezo-and epimetamorphic mantle, which outcrop in NW part of Dor el Gussa Arch. The anchimetamorfic silt and sandstone fragments come from Infracambrian Mourizidie Formation. It is probable, that in source area of Hasáwnah Formation, quartzose sandstone, older that Cambrian age appear. From the small unmetamorphosed volcanic rock fragments the characteristic products of a subaquatic volcanic sequence were recognized; the so-called Steinemann’s trinity: basalt (basic glass!) – keratofir – chert. Thus, there are a hypothetic ophiolitic belt somewhere about here.

J. KALMAR & S. M. TURKI (2006). Infracambrian rocks as "exotic" clastics in Hasawnah Sandstone Formation, Wãw al Kabir area, Libya