Petrographic and geochemical study of magmatic rocks in the Souk El Thenine region

Purpose. This study aims to clarify the age, petrographic nature, and geochemical affinity of the magmatic rock outcrops of the Souk El Thenine region, previously described only as “ophites”, by characterizing their mineralogy, major- and trace-element chemistry, as well as tectonomagmatic setting. Methodology. Seven samples (ST1, ST2, ST3, ST4, E2, E3, and E5) were collected from two outcrops hosted in Triassic strata. Petrographic study was carried out by polarizing microscopy on thin sections, mineralogical phases were identified by X-ray diffraction (XRD), and major- and trace-element contents were determined by X-ray fluorescence and ICP-MS. Chemical data were plotted on TAS, AFM, K2O-SiO2, TiO2-MnO-P2O5, Ti-Zr-Y, and F1-F2 discriminant diagrams, and a 40Ar/39Ar age determination was performed on amphibole from sample E5. Findings. Two chemically and texturally distinct groups were identified. Samples ST1-ST3 are basalts (SiO2 = 44.66‒45.50 wt.%), whereas samples ST4, E2, E3, and E5 are basaltic diorites with higher SiO2 (52.00‒56.21 wt.%) and lower MgO. Nearly all discriminant diagrams indicate a tholeiitic affinity for both groups, with an intraplate to mid-ocean-ridge signature. The 40Ar/39Ar spectrum on amphibole from sample E5 yields a partial plateau age of 210  10 Ma, attributed to the Upper Triassic opening of the Tethys. Originality. This work provides the first integrated petrographic, geochemical, and geochronological characterization of the Souk El Thenine magmatic bodies, resolving their long-standing informal classification as undifferentiated “ophites” into two genetically related rock types of Triassic age. Practical value. The results refine the lithological and chronological framework of Mesozoic magmatism in the Babors region of Petite Kabylie and northeastern Algeria, providing reference geochemical data for future regional correlation and mineral-exploration studies.