Unravelling the tectono-metamorphic evolution of the Western Tell basement, North Algeria

The western Mediterranean basin opened progressively from the Oligocene onwards, resulting in the partial inversion, subduction, and incorporation of the Tethyan margins into the Alpine Tell and Rif orogenic belts in North Morocco and Algeria.

While proximal segments of these margins are accessible, the distal portions and the nature of the North African rifted margin crust remain largely unknown. Exceptions exist in the Tell, where various outcrops of basement and ophiolitic sequences were reported, but their origins and paleogeographic significance remain poorly constrained. In this underexplored region, we focus on two geological features sampling potential basement rocks.

Firstly, in the “external metamorphic massifs”, rocks are affected by subduction-related metamorphism of presumed Oligocene or older age. These continental-derived rocks outcropping close to the Oran region are associated with ultramafic rocks, potentially representing fragments of oceanic crust.

Secondly, we can find in the Oran region, basement rocks outcropping within Triassic salt diapirs, including high-grade metamorphic and mantle rocks. These have been interpreted as remnants of the North African rifted margin, brought to the surface by the diapirs.

This study is part of an ongoing Ph.D. aiming to constrain: (1) The tectonic and metamorphic analysis of the “external metamorphic massifs” through PT-t paths, (2) The characterisation of the basement rocks found in the Triassic salt diapirs with petrology, geochemistry and geochronology and (3) A reconstruction of the Tethyan margin geometry and composition.

Results from the Tell will be integrated with those of adjacent Rif belt where remnants of the distal domains have been identified. These complementary features offer a rare opportunity to investigate the evolution of the North African Mesozoic rifted margin from its formation to its eventual deformation during the Mediterranean opening.