Programme des sessions > Recherche par auteur correspondant > Corsini M.

The Variscan Jebilet massif of the Moroccan Meseta was affected by a low-grade greenschist regional metamorphism, even absent in the Eastern and Western units of the massif, increasing near intrusions where contact metamorphism reached the pyroxene hornfels-facies conditions. However, the Sidi Bou Othmane unit (SBO), located at the boundary between Central and Eastern Jebilet, is dominated by a low‐pressure–high‐temperature (LP‐HT) metamorphism, and intruded by numerous syntectonic pegmatitic dykes. 

A microstructural and petrological study of micaschists of the SBO unit reveals the presence of a major syntectonic metamorphic event characterized by the crystallization of biotite–cordierite–andalusite–garnet with peak P/T conditions reaching the amphibolite facies. 

Using chemical zoning of garnet and calculated P–T pseudosections, the prograde metamorphic evolution is characterized by a LP-MT amphibolite assemblage composed of garnet + andalusite + biotite + muscovite + plagioclase + quartz + ilmenite. The calculated peak P-T conditions (3.6-3.9 kbar, 565-578°C) indicate a burial depth of 14-15 km and correspond to a geothermal gradient of 38-39°C/Km. Such burial results from crustal thickening related to Variscan transpression. The retrograde metamorphic evolution is characterized by the crystallization of cordierite in equilibrium with the previous metamorphic assemblage. The calculated P-T conditions (0.6-1.3 kbar, 530-550°C) indicate a hot geothermal gradient of > 100°C/km and a decompression following peak P-T conditions. The high geothermal gradient has been accompanied by crustal anatexis at depth and emplacement of a leucogranite intrusion and associated pegmatite dykes. The decompression was nearly isothermal allowing the preservation of syn-kinematic assemblages developed at the end of garnet growth. Exhumation of the SBO metapelites has taken place in the garnet-biotite-andalusite-cordierite-muscovite stability field, defining a clockwise pressure–temperature (P-T) path. The decompression was relatively rapid and was followed by isobaric cooling. 40Ar/39Ar dating on muscovite obtained on pegmatite and micaschist samples from the SBO unit shows that metamorphism, shearing deformation and pegmatite magmatism occurred almost simultaneously around 320 Ma.