Analysis of deformation in the middle Kibarian of the south-east of Kamisimbi (South Kivu; Dr Congo)

The present work aims to strengthen the understanding and updating of the geological history of the Kibarian orogeny in Kivu, in the East of the Democratic Republic of Congo through the study area, South-East of Kamisimbi (Middle Kibarian) in Walungu territory. In other words, it involves characterizing all tectonic phases, both continuous and discontinuous deformations. After a detailed macroscopic description of the lithological groups identified in the field, the structural analysis was carried out at the macroscopic and mesoscopic scale. The results obtained show that the South-East of Kamisimbi is made up of three lithological groups: sedimentary (sandstone, conglomerate), metamorphic (shale and quartzite) and volcanic (basalt, trachyte). Structurally, the South-East of Kamisimbi presents a tectonic evolution marked by three (03) phases of deformation (D1, D1’ and D2). Phases D1 and D1' (shear phase) folded, then sheared the South-East of Kamisimbi giving structures with an axis from WNW-ESE or E-W to NW-SE and sometimes N-S. The D1 deformation phase, essentially ductile, includes an F1 foliation, an S1 schistosity and P1 microfolds in shales and sandstone shales with low to medium dips (10° – 47°). The majority of P1 microfolds identified on the ground in the South-East of Kamisimbi, oriented N087°E to NW84°E are more or less parallel to the major folds (N085°E; N090°E and N100°E) constructed from S0 to which they are linked. Others, on the other hand, oriented N046°E have highly dispersed axes and would therefore have a sedimentary origin (Slump), non-tectonic. The deformation phase D2, both posterior and intersecting with the first two D1 and D1’, is the most marked in the study area. It is identified in almost all rocks and results in fractures, whether sustained or not, mainly D2 joints, J2 joints, F2 veins and veins. The orientations of the principal stresses which generated the brittle deformations were also determined from the dynamic interpretation of the fracturing fed or not on Wulff canvas. Thus, we have the major principal stress(N150°E/10°SSE), the intermediate principal stress(N170°E/10°SSE), the minor principal stress (N078°E/08°ENE) and the maximum tangential stress(N058°E/45°NE) for the joints and the major principal stress(N014°E/68SSW), the intermediate principal stress(N047°E/010°NE), the minor principal stress(N134°E/11NW) and the maximum tangential stress (N124°E/53°WNW) for the veins. On a regional scale, the first phase D1 and the second D1' defined in the South-East of Kamisimbi would correspond respectively to phases D2 and D2' of Kibarian deformation where the structures are oriented NW-SE; WNW-ESE to E-W.