Pan-African eclogite-facies tectonic mélange in the Egéré area, Tuareg Shield (Algeria): Integrated approaches for lithological and structural mapping

The Tuareg Shield is made up of 25 terranes separated by extensive shear zones that are several hundred km-long, which have been attributed to a northward post-collisional tectonic escape during the Pan-African orogeny. The development of these shear zones was accompanied by abundant high-K calc-alkaline batholiths and plutons (~630–580 Ma). In the northern Egéré-Aleksod terrane of Central Hoggar (LATEA metacraton), the Egéré area exhibits minimal Pan-African magmatism, preserving earlier tectonic events such as subduction, collision, and terrane exhumation. The Egéré region consists of a parautochthonous amphibolite-facies unit (Arechchoum Group) and three eclogite-facies nappe units (Lower Egéré, Upper Egéré, and Oneral groups). These were thrust over the Archean Amadror cratonic core after the subduction of the LATEA passive margin superstructure to which they belong. These units have Paleoproterozoic protoliths, predominantly magmatic in the Arechchoum Group, or mixed magmatic and sedimentary in the Egéré Group, while the Oneral Group, which forms the uppermost nappe, comprise Neoproterozoic sediments. Space-borne imagery data are used to map the eclogitic layers, integrated with magnetic and gravity surveys to delineate major shear and thrust zones. In addition, 2D modelling of magnetic and gravity data was used to investigate the upper crust, revealing a Pan-African granitic batholith and a large ultramafic-mafic bod at depth. The results allowed detailed geological mapping of such a complex tectonic mélange belonging to both lower and upper plate segments. Integrated with the published geochronological data, this mélange includes rocks with Rhyacian to Statherian, Calymmian, and Early Cryogenian ages, all of which underwent Late Cryogenian high-pressure metamorphism, followed by Ediacaran high-temperature metamorphism and tectonic escape processes. Our results reveal the complex tectonic evolution of a former passive margin that was subducted to great depths during the Pan-African orogeny. The preservation of early subduction and exhumation events provides key insights into tectonometamorphic processes and deep crustal evolution in this high-pressure metamorphic terrane.