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基武湖(Lake Kivu)南部(扎伊尔东南部)两个火山岩带是东非裂谷西支的一部分。两个火山岩带在三个火山旋回期间形成,这三个火山旋回一个是前裂谷阶段(70—7百万年)和两个同裂谷阶段(分别为7.0—1.9百万年和1.4万年一近期),并且火山岩带从前裂谷阶段的石英拉斑玄武岩演化为裂谷阶段的碱性玄武岩。玄武质岩石数量占绝对优势,其成分接近于其它与裂谷有关的玄武岩及洋岛玄武岩。本区大多数玄武岩经历了十分有限的分离结晶(约5—10%),结晶矿物以橄榄石和单斜辉石为主。即使主要元素相近的岩石,其不相容元素也有明显变异,这暗示玄武质岩石来源于由于不同程度的熔融造成的不均匀源岩。推断的源岩成分与碱性玄武岩中交代橄榄岩捕虏体的成分十分接近。
Two volcanic belts in southern Lake Kivu (southeast of Zaire) are part of the western branch of the East African Rift. Two volcanic belts were formed during the volcanic cycle of three volcanoes, one of which was a pre-rift phase (70-7 million years) and two same-rift phases (7.0-1.9 million years and 1.4 million New Year), and the volcanic belt evolves from the quartz tholei basalts of the former rift stage to alkaline basalts in the rift stage. The amount of basaltic rocks is an absolute advantage and its composition is close to that of other basalts related to rifting and oceanic basalts. Most basalts in the area have undergone very limited fractional crystallisation (about 5-10%), with the majority of crystalline minerals being olivine and clinopyroxene. Even the rocks with similar major elements have significant variations in their incompatible elements, suggesting that basaltic rocks originate from heterogeneous source rocks due to varying degrees of melting. The deduced source rocks are closely related to the metamorphic peridot xenoliths in alkaline basalts.