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In the Marrakech High-Atlas (MHA) at the southern Variscan segment of the Western Meseta crop out several granitoids, which intrude a sequence of the metavolcano-sedimentary, metapelitic, and metasedimentary with early Cambrian to Ordovician in age. Compared to previous work realized in the region, the relationship between deformation and the timing of granitic emplacement remains poorly studied. This work was realized mostly in the northern and central part of MHA and involved fields of petrostructural analysis, whole-rock geochemistry (WR), and isotopic geology. The WR geochemistry of granitic rocks is classified into three main groups S-, I-, and A-type granitoids. The WR Rb–Sr isochron dating shows a crystallization age of 268 ± 9 Ma for the granite of Azegour. The Medinat intrusion yielded an age value of 275.3 ± 5.3 Ma obtained by the 40Ar/39Ar amphibole dating. The 295.8 ± 0.8 Ma age were obtained by ID-TIMS U-Pb zircon for the Adassil intrusion. The structural analysis in the MHA shows three Variscan deformational events (D1, D2, and D3). The first one is subdivided into two stages (D1a, D1b). Three different domains have been proposed for this study: (a) the southern domain is affected by a dominant deformational event (D1a) limited by ENE-WSW trending dextral ductile shear zones. This domain consists of Tichka granitoids NNE-SSW elongated with a syn-D1a emplacement. (b) the central domain is characterized by three deformational stages: NNE-SSW trending D1a, WNW-ESE conjugate sinistral ductile shear zone (D1b), and ENE-WSW trending sinistral brittle-ductile shear zones (D3). This domain is characterized by WNW-ESE elongated-shaped Medinat and Adassil granitoids. These intrusions show a syn- to late-D1b emplacement. (c) The northern domain is distinguished by NNE-SSW trending deformational event (D1a, D2). This domain displays two groups of granitoids, a tonalitic granitoid of Bouzouga with a syn- to late-D2. The age of 268 Ma was obtained for the alkaline granite of Azegour with a post-tectonic emplacement with respect to D2. The structural evolution of the MHA is in agreement with the collisional phase of the Variscan orogeny during the Late Carboniferous time between Gondwana and Laurasia.

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Deformation Geometry and Plutonism in the Marrakech High-Atlas, Moroccan Variscan Belt: Geodynamical Implications

  • 会议论文

  • 发表日期：

    2025年

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

摘要

In the Marrakech High-Atlas (MHA) at the southern Variscan segment of the Western Meseta crop out several granitoids, which intrude a sequence of the metavolcano-sedimentary, metapelitic, and metasedimentary with early Cambrian to Ordovician in age. Compared to previous work realized in the region, the relationship between deformation and the timing of granitic emplacement remains poorly studied. This work was realized mostly in the northern and central part of MHA and involved fields of petrostructural analysis, whole-rock geochemistry (WR), and isotopic geology. The WR geochemistry of granitic rocks is classified into three main groups S-, I-, and A-type granitoids. The WR Rb–Sr isochron dating shows a crystallization age of 268 ± 9 Ma for the granite of Azegour. The Medinat intrusion yielded an age value of 275.3 ± 5.3 Ma obtained by the 40Ar/39Ar amphibole dating. The 295.8 ± 0.8 Ma age were obtained by ID-TIMS U-Pb zircon for the Adassil intrusion. The structural analysis in the MHA shows three Variscan deformational events (D1, D2, and D3). The first one is subdivided into two stages (D1a, D1b). Three different domains have been proposed for this study: (a) the southern domain is affected by a dominant deformational event (D1a) limited by ENE-WSW trending dextral ductile shear zones. This domain consists of Tichka granitoids NNE-SSW elongated with a syn-D1a emplacement. (b) the central domain is characterized by three deformational stages: NNE-SSW trending D1a, WNW-ESE conjugate sinistral ductile shear zone (D1b), and ENE-WSW trending sinistral brittle-ductile shear zones (D3). This domain is characterized by WNW-ESE elongated-shaped Medinat and Adassil granitoids. These intrusions show a syn- to late-D1b emplacement. (c) The northern domain is distinguished by NNE-SSW trending deformational event (D1a, D2). This domain displays two groups of granitoids, a tonalitic granitoid of Bouzouga with a syn- to late-D2. The age of 268 Ma was obtained for the alkaline granite of Azegour with a post-tectonic emplacement with respect to D2. The structural evolution of the MHA is in agreement with the collisional phase of the Variscan orogeny during the Late Carboniferous time between Gondwana and Laurasia.