The relative and absolute chronology of strato-tectonic events in the Gorom-Gorom granitoid terrane and Oudalan-Gorouol belt, northeast Burkina Faso

Abstract

The integration of field mapping and analytical studies of magmatic units of the northeast of Burkina Faso has provided new information on the tectonic and magmatic evolution of the Oudalan-Gorouol belt and the Gorom-Gorom granitoid terrane. Structural, geochemical and geochronological analyses have helped to clarify the geological evolution of the region during the Tangaean Event (D1) and Eburnean Orogeny (D2) through to the Wabo Tampelse Event (D3). Further to this, zircon U–Pb geochronology data have demonstrated that the Oudalan-Gorouol belt and the Gorom-Gorom granitoid terrane represents some of the oldest outcropping geology in the Palaeoproterozoic Baoulé-Mossi domain recognised to date, with the oldest age at 2253±9Ma. The geochronology and geology suggests that the basement or a pre-Birimian crust to the Birimian Supergroup may be found in the northeast of Burkina Faso.The Eburnean Orogeny in the northeastern Burkina is preceded by the two phases of deformation (D1−x and D1), and two phases of magmatism. D1−x is associated with the emplacement of the Dori Batholith at the onset of D1 (2164–2141Ma). D1 ductile–brittle deformation formed F1 folds and discrete high-strained mylonite zones that deformed the Oudalan-Gorouol belt and the Gorom-Gorom granitoid terrane during a southwest-directed palaeo-principal transport direction. The pre-Birimian to Birimian supracrustal rocks and intrusions were regionally metamorphosed during D1 to greenschist to amphibolite facies.The Eburnean Orogeny (2130–1980Ma) is characterised by northwest–southeast shortening; it was followed by north–northwest to south–southeast shortening with development of sinistral strike-slip faults and shears. D2 brittle-(ductile) deformation is manifested by refolding of F1 by northeast-trending F2, and development of a pervasive northeast-trending S2 to S2-C foliation. Metamorphic grade attained greenschist facies during D2 with development of the mineral assemblage of quartz-chlorite–muscovite±actinolite.The Wabo Tampelse (D3) deformation event is brittle in character and does not significantly affect regional geological architecture in the study area.