The Edough Massif garnetites: evidences for a metamorphosed paleo-garnet beach-sand placer (Cap de Garde, Annaba, Northeast Algeria)

Abstract

This study shows that the garnetites from the "Cap de Garde", Ain Achir beach, Edough Massif, Algeria, are metamorphosed clastic sediments enriched in garnet fragments like beach-sands or beach-placers. The garnets are embedded in a matrix composed of biotite and isometric grains of staurolite and quartz suggesting a former beach placer deposit. All garnets are zoned and show the same conspicuous angular core, with strong chemical contrast to their mantle.  These cores are interpreted as clasts of metamorphic origin and part of the placer deposit. The distinct chemical composition, morphology and recorded temperature history of the garnet cores relative to rims indicate that the garnets from the garnetites grew during a complex metamorphic history (amphibolite to granulite-facies). The garnetites are the equivalent of the dark portions of the modern light and dark sands at Ain Achir beach.