Igneous Structures, Deformation And Contact Metamorphism Associated With The Emplacement Of Boussouma Dolerite Dyke (burkina Faso, West- African Craton)

The dolerite/gabbro dyke of Boussouma area in Burkina Faso, more than one hundred km in length, cuts Birimian volcano-sedimentary series following E-W to NWW-SEE trend. Petrologic studies highlight a layered structure within the dyke due to magmatic segregation flow and accumulation processes as well as grain-size change from the margin to the core of the intrusion. Deformation of the surrounding Birimian country rocks took place and thermal metamorphism reaching near the contact to the biotite-garnet isograd occurred. The presence of Birimian rocks xenoliths in dolerite and the development of microlitic or microgranular chilled margin at the contact, indicates a post Eburnean (2200-2000Ma) probably a Mesoproterozoic emplacement of this dyke which is undeformed and unmetamorphosed. Similar characters were enhanced in numerous post-Birimian doleritic dykes of Burkina Faso and of West African countries.