Rheological context of emplacement of the Dori, Gorom-Gorom and Touka Bayèl granitic plutons (northeast Burkina Faso, West African Craton)

Abstract

The reconstitution of the geodynamic processes of the Eburnean orogeny in the time span around 2.1 Ga in Dori area is here carried out through the examination of the internal structures and microstructures of the Dori, Gorom-Gorom and Touka Bayèl granitic plutons. The radiometric ages of these plutons vary between 2164 Ma and 2148 Ma. The internal structures have been evidenced using the Anisotropy of Magnetic Susceptibility (AMS) method and the examination of microstructures through thin sections under optical microscope.The organization of the internal fabrics strongly suggests a diapiric emplacement for the Dori and the Touka Bayèl plutons in a still soften crust. The pluton of Gorom-Gorom seems to be constituted of four small plutons. Three of them, coalescent in the southern part, are emplaced by the diapirism and the fourth in the northern part can be interpreted as emplaced in a tension gash.The overall disposition of the fabrics lets suggest a synchronous emplacement in accordance with the dextral sense of the Tiébélé-Dori-Markoye (TDM) shear zone in a regional E-W shortening context responsible of a crustal thickening.The two emplacement mechanisms (diapirism and tension gash) identified through the internal fabrics testify a rheological contrast of the crust during this early period of the Eburnean Orogeny.