Petrography, geochemistry and geochronology of Aghirer Plutonic Granitoid Complex, Eastern Hoggar, Algeria

Abstract

The Assodé-Issalane terrane, situated in the southern region of Algeria, east of the Hoggar, is predominantly composed of Paleoproterozoic metamorphic rocks which were subjected to high-grade amphibolite to granulite facies metamorphism during the Pan-African orogeny, accompanied by large migmatization and granite emplacement. The easternmost region of the Raghane-8°30 shear zone exhibits evidence of the Eburnean orogeny (2.2–2.0 Ga) and multiple granitoid events, indicative of three major orogenic episodes: 800–820 Ma, extensional event (790, 730 Ma), a collision with the West African craton (660 Ma and 630-580 Ma), and a subsequent collision with the Murzuq craton (575-545 Ma), culminating in the regional metamorphism and stabilization of the eastern Hoggar. The present study focuses on the Aghirer Granitic Pluton (AGP), a late, circular granite intrusion that intrudes the 730 Ma Arirer granitic batholith and the Eberjegui basement of the Tadoumet region. A comprehensive suite of analytical techniques was employed, encompassing petrographic examination, geochemical assessment on ten samples obtained from the AGP, and Rb/Sr isotopic geochronological analysis on seven samples. Petrographic and geochemical analyses reveal a potassic calc-alkaline granite and granodiorite composition, suggesting a syn-collisional to late orogenic tectonic setting. Geochemical data indicate its affinity with the lower continental crust with minimal crustal contamination. Rb-Sr geochronology yielded an isochron age of 553 ± 20 Ma, recording the late Pan-African orogeny. The low initial ⁸⁷Sr/⁸⁶Sr ratio further supports the limited role of upper crustal contamination in the magma genesis. These findings provide crucial insights into the magmatic evolution and tectonic history of the Hoggar during the late Pan-African orogeny.