New Data on the Genesis and Evolution of the Primitive Magmas of Mount Cameroon: Contribution of Melt Inclusions

• 作者: Legrand Joseph Tchop Pauline Wokwenmendam Nguet Benjamin Ntieche Victor Metang Jacques Dili Rake Merlin Isidore Teitchou Jacqueline Vander Auwera Georges Emmanuel Ekodeck Charles Nkoumbou
• 来源期刊: 地质研究(英文)
• 学科: 地球科学
• 关键词: Primitive magma Partial melting Fractional crystallization Alkali basalt Mount Cameroon Active volcano
• 年，卷（期）: 2020,（4）
• 页码范围: 46-61
• 页数: 16页
• 分类号: P58

摘要

Mount Cameroon is a Plio-Quaternary volcanic massif, without a centralcrater, made up of more than 140 pyroclastic cones. It is one of theactive volcanoes of the Cameroon Volcanic Line. Mount Cameroon meltinclusions are found in microdroplets trapped in the early minerals (olivines)from the pyroclastic products. The analysis of these melt inclusions allowedus to find primitive liquids compared to lavas. Major elements study ofthe magmatic inclusions, trapped in the most magnesian olivines (Mg#84-86) of Mount Cameroon revealed “primitive” liquids of basanite and alkalibasalt type with variable composition compared to the much more uniformbasalts of the magmatic series of Mount Cameroon. The study of thesetrapped liquids shows that: (1) the original primitive lavas did not undergothe process of evolution by FC, but rather underwent fundamentally (orexclusively) the process of partial melting;(2) the emitted lavas, evolvedessentially by FC;(3) the variations in the trace element contents of theprimitive liquids directly reflect a variation in the rate of partial melting ofa homogeneous mantelic source. The very high La/Yb ratios of the MountCameroon melt inclusions (> 20) characterize a garnet lherzolite source.Spectra of the melt inclusions show a negative anomaly or depletion in K,Rb and Ba as those of HIMU. The “primitive” liquids and lavas of MountCameroon represent a co-genetic sequence formed by varying degrees ofpartial melting of a source considered as homogeneous.