Geochemistry of the volcanic rocks from Bioko Island（“Cameroon Hot Line”）： Evidence for plume-lithosphere interaction

• Published in: 地学前缘：英文版 2016, Vol.7 (5), p.743-757
• Main Author: Fadimatou Ngounouno Yamgouot Bernard Déruelle Isaac Bertrand Gbambié Mbowou Ismaila Ngounouno Daniel Demaiffe
• Format: Article
• Language: English
• Subjects: 单斜辉石; 喀麦隆; 地球化学特征; 壳幔相互作用; 火山岩; 热线; 碱性玄武岩; 证据
• ISSN: 1674-9871

Bioko Island（3008 m a.s.l） is located in the presently more active volcanic zone of the Cameroon Line and composed essentially of alkaline basalts and hawaiites, and lesser mugearites. The rocks show microlitic porphyritic texture with phenocrysts of olivine（83% 〈 Fo 〈 87%） and clinopyroxene in a matrix of plagioclase, clinopyroxene and oxides. Hawaiites and mugearites also include phenocrysts of plagioclase（An62-67Ab35-32Or3-1）. Major element variation diagrams show an increase in Si O2, Al2O3, Na2 O and K2 O with increasing Mg O for the studied rock groups. The rocks are characterized by low（^86Sr/^87Sr）i ratios（0.70320e0.70406）, high 3Nd（t） values（2.56e4.33） and high（^206Pb/^204Pb）i ratios（20.032e20.035） values.Basalts are enriched in LILE and LREE, and have（Hf/Sm）N= 0.57e1.16. These geochemical signatures are similar to those of the Mount Cameroon rocks, and might be attributed to low degrees of partial melting from a garnet-amphibole-bearing mantle source. The trace elements and isotopic compositions suggest that the parental magma source might have involved HIMU- and EM1-components.