Abstract:The Zitouna rhyolite is the easternmost representative of the Neogene magmatism in the Northeast of Algeria. It is composed of two intrusive rhyolitic apexes: the first outcrop is poorly known and not dated; the second one is greater, and not previously described. It is a well-differentiated rock that does not exceed 12 Ma (Post-Serravallian). Geochemical data show that it belongs to S-type granites with a high peraluminous character corroborating a crustal protolith. The Zitouna rhyolite is considered as the continuation of other neighbouring magmatic episodes and can be related to the late Neogene tectono-magmatic evolution of northeast Africa.Keywords: rhyolite, post-Serravallian, S-type granites, peraluminous, Zitouna, Algeria.Resumen: La riolita de Zitouna es la representación más oriental del magmatismo neógeno en el noreste de Argelia. Está formada por dos cuerpos intrusivos riolíticos: el primer afloramiento es vagamente conocido y no ha sido datado; el segundo es de mayores dimensiones y no ha sido descrito previamente. Se trata de una roca bien diferenciada que no excede de los 12 Ma (Post-Serravaliense). Los datos geoquímicos muestran que corresponde a un granito de tipo S con alto carácter peralumínico, lo que corrobora un protolito cortical. La riolita de Zitouna es considerada como la continuación de otros episodios magmáticos vecinos y puede ser relacionada con la evolución tectono-magmática del noreste africano durante el Neógeno superior.
The paper presents the first study of heavy-mineral sand beaches from the Mediterranean coast of Annaba/Algeria. The studied beaches run along the basement outcrops of the Edough massif, which are mainly composed by micaschists, tourmaline-rich quartzo-feldspathic veins, gneisses, skarns and marbles. Sand samples were taken from three localities (Ain Achir, Plage-Militaire and El Nasr). The heavy-mineral fraction comprises between 74 and 91 vol%. The garnets of the beaches are almandine rich and tourmalines vary with respect to their location from schorl to dravite. Tourmaline at Ain Achir and the Plage-Militaire is schorlits, while at El Nasr beach dravite is ubiquitous. The World Shale Average normalised REE of the sands and the basement outcrops reveal: (i) Ain Achir beach: REE pattern of sand and the coastal rocks from the studied beaches reflects a multiple sources; (ii) Plage-Militaire: the sand and the coastal outcrops show similar LREE and a strong enrichment in HREE, suggesting the presence HREE-rich phases found as inclusions in staurolite; (iii) El Nasr: two types of sand patterns are found: one with flat REE pattern similar to the proximal rocks and other one enriched in HREE suggesting a mixed source.
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