This work deals with the geochemistry of lava and pyroclastic rocks of the Lac Vert cone. We present the results of geochemicals analyzes of major and traces elements performed at the University of Naples. The results showed that these rocks are primarily nephelinite - ultrabasic very rich in iron and have calc-alkaline affinities. The geochemical compositions of lavas and pyroclastic rocks of cone of Lac Vert demonstrated a positive correlation with lavas from the 1977 and 2002 Nyiragongo eruption. The different graphs showed that these lavas and pyroclastic rocks are associated with divergent plate margins (basalt sea floor, OFB); they originated in the spreading seafloor zones specifically in alkaline basalts sclerosis on the island of the ocean. The petrogenetic model likely established through geochemical analysis shows that these rocks are from a calc-alkaline volcanism developed in an oceanic expansion and then they finally migrated to a framework of transitional continental rift before the eruption. Partial melting and fractional crystallization of mantle rich in Anorthite, olivine, clinopyroxene orthopyroxene, magnetite,... would have generated the magma. These geochemical and petrological characteristics of the lavas and pyroclastic rocks around the Lac Vert cone are the same as those of the Nyiragongo. This justifies the affiliation of the Lac Vert cone to Nyiragongo volcano.

This work aims at the understanding of the petrogenesis of Kibarian metamorphic formations in the West part of Lake Kivu. Here are presented detailed petrographic study of Miowe and Bulambika gneisses at Bunyakiri, new geochemical data of major elements and a large-scale geological map of the study area. The macroscopic petrographic study has distinguished in Miowe and Bulambika gneiss two lithological facies: the augen gneiss and the granitic gneiss. Veins and pegmatite pockets are observed in these gneisses. The geochemical study on basis of major elements revealed that these gneisses derived from a metamorphic evolution of granites and granodiorites of calc-alkaline series. They are therefore formed in a geodynamic context of subduction.