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The studied region is located in the northern domain of the Marrakech High Atlas (MHA) of the Moroccan Variscan belt. WNW-ESE elongated-shaped granitoid outcrop surrounded by metasedimentary and volcano-sedimentary rocks that are possibly early Cambrian to Ordovician in age. This present work presents detailed field-structural, petrographic, WR-geochemistry, and geochronological data of granitic intrusion and high-grade metamorphism country rocks in perspective to contribute to a better understanding of the relationships between the emplacement of Variscan granitoids and ductile deformation overprinted in the high-grade metamorphic metasediments. Geometrical and kinematical analysis revealed that the emplacement was controlled by three Variscan deformational events (D1, D2, and D3). The first one (D1) is subdivided into two stages: NNE-SSW trending D1a and WNW-ESE conjugate sinistral ductile shear zone (D1b). D2 deformation shows N-S to NNE-SSW trending crenulation cleavage, and D3 event led to the formation of ENE-WSW trending sinistral brittle-ductile shear zones. The D1b sinistral shearing event is shown by shear sense kinematic indicators of shear or transport during a non-coaxial deformation (i.e., S-C fabric/foliation, mica fish, and syn-kinematic rotational porphyroblast, stretching lineation). These fabrics reveal sinistral syn-kinematic shearing during this transpressional stage, leading to intrusion emplacement. Regional metamorphic mineral assemblages in metapelitic rocks range from greenschist to upper amphibolite facies. The 295.8 ± 0.8 Ma U–Pb zircon age obtained by ID-TIMS in zircon fractions from one sample of the Adassil massif provides, therefore, an age for the D1 event in this region, which is in full agreement with the proposed models for the geodynamical evolution of the Moroccan Variscides. The whole-rock geochemistry, U–Pb zircon dating, and Sr–Nd data for the intrusion allow constraint the main Variscan deformation recorded in the surrounded metasedimentary rocks, the peak of regional metamorphism, and the syn-D1 emplacement of Adassil intrusion during the dextral oblique collision between Gondwana and Laurussia.

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Age Constraints of Main Variscan Deformation and Plutonism in the Adassil Region (Marrakech High-Atlas, Moroccan Variscan Belt)

  • 会议论文

  • 发表日期：

    2025年

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  • Mohamed Hadani,
  • Maria do Rosario Azevedo,
  • Rui Dias,
  • Fernando Corfu

摘要

The studied region is located in the northern domain of the Marrakech High Atlas (MHA) of the Moroccan Variscan belt. WNW-ESE elongated-shaped granitoid outcrop surrounded by metasedimentary and volcano-sedimentary rocks that are possibly early Cambrian to Ordovician in age. This present work presents detailed field-structural, petrographic, WR-geochemistry, and geochronological data of granitic intrusion and high-grade metamorphism country rocks in perspective to contribute to a better understanding of the relationships between the emplacement of Variscan granitoids and ductile deformation overprinted in the high-grade metamorphic metasediments. Geometrical and kinematical analysis revealed that the emplacement was controlled by three Variscan deformational events (D1, D2, and D3). The first one (D1) is subdivided into two stages: NNE-SSW trending D1a and WNW-ESE conjugate sinistral ductile shear zone (D1b). D2 deformation shows N-S to NNE-SSW trending crenulation cleavage, and D3 event led to the formation of ENE-WSW trending sinistral brittle-ductile shear zones. The D1b sinistral shearing event is shown by shear sense kinematic indicators of shear or transport during a non-coaxial deformation (i.e., S-C fabric/foliation, mica fish, and syn-kinematic rotational porphyroblast, stretching lineation). These fabrics reveal sinistral syn-kinematic shearing during this transpressional stage, leading to intrusion emplacement. Regional metamorphic mineral assemblages in metapelitic rocks range from greenschist to upper amphibolite facies. The 295.8 ± 0.8 Ma U–Pb zircon age obtained by ID-TIMS in zircon fractions from one sample of the Adassil massif provides, therefore, an age for the D1 event in this region, which is in full agreement with the proposed models for the geodynamical evolution of the Moroccan Variscides. The whole-rock geochemistry, U–Pb zircon dating, and Sr–Nd data for the intrusion allow constraint the main Variscan deformation recorded in the surrounded metasedimentary rocks, the peak of regional metamorphism, and the syn-D1 emplacement of Adassil intrusion during the dextral oblique collision between Gondwana and Laurussia.