Birimian lithological succession and structural evolution in the Goren segment of the Boromo–Goren Greenstone Belt, Burkina Faso

Abstract

Lithological and structural investigations indicate that the Goren segment of the Boromo–Goren Greenstone Belt in the Sanmatenga District is dominated by conformable successions of meta-sedimentary rocks that are interbedded with volcanic deposits. These successions are intercalated by a package of mafic-intermediate volcanic rocks, volcanic breccias and tuffs. The intercalated clastic–volcanoclastic–volcanic assemblage indicates interplay of marine-deltaic sedimentary processes and volcanic activity. Deposition is interpreted to have occurred within a marginal marine setting adjacent to an emergent volcanic centre or island arc setting. An angular unconformity between a volcanic-sedimentary package (the Lower Birimian) and a volcanic–volcanoclastic–clastic package (the Upper Birimian) does not occur within the Sanmatenga District. The supracrustal rocks were subjected to several phases of deformation and are metamorphosed to greenschist facies. Gabbro–diorite–pyroxenite bodies, and several granodiorite–tonalite and granite plutons have intruded them. Structural studies have indicated that the Goren segment underwent at least four phases of deformation, D1–D4. D1 resulted in the formation of a gently north-westerly plunging macroscopic anticline (F1), which is crosscut by D2 shear zones and D3 thrusts. D2 involved a period of north–south crustal shortening that is correlated with the Eburnean Orogeny at ∼2.1 Ga. It is characterised by the development of NE-trending shear zones (sinistral reverse) and folds (F2), and NW-trending (dextral) strike-slip faults. Deformation in D2 was concomitant with emplacement of the Baskoudré Granite, and the granodiorite–tonalite plutons (Banta, Yargo, Kob, Tantogo, Tompelse, Zitenga, Goudren and Loudo granodiorites, and Koukoundi and Soubsi tonalites). It was succeeded by emplacement of the Silmidougou Megacrystic Granite and aplite dykes. D3 involved a period of E–W crustal shortening that resulted in the formation of a series of NW to NNW-trending thrusts and northerly-plunging mesoscopic folds (F3). Deformation culminated in the repetition of stratigraphy through stacking of crustal blocks. The final deformation, D4, resulted in the formation of a series of WNW-trending thrusts (dextral reverse) collectively termed the Wabi-Tampelse Shear Zone. The zone is significant in that it marks a period of north–south crustal shortening that postdates the Eburnean Orogeny.