Variscan to late-Variscan record in Lesser Kabylia (Northeastern Algeria)

AlKaPeCa terranes—comprising the Alboran, Kabylia, Peloritani, and Calabria domains—represent Mesozoic terranes involving Paleozoic metamorphic basement that was dispersed to form the allochthonous internal zones of peri-Mediterranean orogens (Betics and Maghrebides). Our study focuses on the Lesser Kabylia Massif (Algerian Tell), where a granitoid-gneiss-schist high-grade basement divides structurally into the Texenna-Skikda Upper Nappe (TS-UN) overthrust onto the Beni-Ferguen Lower Nappe, both with Alpine overprint on Variscan basement.

To update the petro-geochronological framework, we combined petrological analysis, thermodynamic modelling, in-situ LA-ICP-MS U-Th-Pb dating of zircon and monazite, and LA-SS-ICP-MS U-Pb monazite      dating in key lithologies. The high-grade rocks in TS-UN comprise felsic migmatites (Grt–Pl–Kfs–Qtz–Bt ± Sill/F ± Sp) cross-cut by Permian Grt–Trm-bearing Beni Khettab granitoid and enclosing mafic-to-ultramafic granulite lenses, including Opx–Cpx–Amp–Pl–Qtz–Ilm mafic granulites. Pseudosection modelling of Sill–Grt-bearing felsic migmatite constrains peak conditions to ~7.5–6 kbar and ~790–770 °Cand mafic granulite records comparable high-grade conditions of ~7–6.4 kbar) and ~830–780 °C. Monazite U–Pb dates form a ca. 30 Myr spread from ca. 290 to 260 Ma. The monazite textures and compositional maps show embayment into high Y monazite core and porosity, textures typical of coupled dissolution–precipitation (CDP) replacement. The age spread is therefore interpreted as a result of monazite growth at ca. 300–290 Ma and its replacement at ca. 280–270 Ma rather than continuous monazite growth over ca. 30 Myr. This age continuum coincides with those first order one obtained from zircons  .

We note that no significant Alpine metamorphic imprint occurs in the migmatites of TS-UN, except one xenotime grain (ca. 17 Ma). In contrast, the underlying kinzigities of the TS-UN and Beni-Ferguen Lower Nappe record HP Alpine reworking at ~28 Ma and retrogression at ~25 Ma. This bimodality matches Rif observations (Bakili et al., 2024).

Our results will be integrated into a compilation at the scale of the AlKaPeCa blocks. Together with a comparison to the rest of the Variscan orogen, this will help decipher the Variscan versus Alpine imprint and improve our understanding of the role of these blocks in the final closure of the Paleotethys Ocean and the amalgamation of Pangea