Geochemical composition of dykes along the Cameroon Line (CL): Petrogenesis and similarities with the Central Atlantic Magmatic Province |
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| Authors: | Asobo Nkengmatia Elvis Asaah Tetsuya Yokoyama Hikaru Iwamori Festus Tongwa Aka Jules Tamen Takeshi Kuritani Tomohiro Usui Takeshi Hasegawa Eric Martial Fozing |
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| Institution: | 1. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2–12–1, Ookayama, Meguro–Ku, Tokyo 152–8551, Japan;2. Division of Earth and Planetary Material Sciences, Earthquake Research Institute, the University of Tokyo, 1–1–1 Yayoi, Bunkyo–ku, Tokyo 113–0032, Japan;3. Department of Physical Sciences, School of Mathematics and Science, CCBC Essex Campus, 7201 Rossville Boulevard, Baltimore, MD 21237, USA;4. Department of Earth Science, Faculty of Science, University of Dschang, P.O Box 07, Dschang, Cameroon;5. Graduate School of Science, Hokkaido University, Sapporo 060–0810, Japan;6. Department of Solar System Sciences, ISAS, JAXA, 3–1–1 Yoshinodai, Sagamihara, Kanagawa 252–5210, Japan;7. Department of Earth Sciences, College of Science, Ibaraki University, 2–1–1 Bunkyo, Mito 310–8512, Japan |
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| Abstract: | We report whole-rock geochemistry and Sr–Nd–Pb isotopic compositions of mafic dykes intruded in the Precambrian granito-gneissic basement complex, exposed at Nyos, Batibo, Dschang and Foumban on the Cameroon Line. The dykes are alkaline (Batibo), transitional (Foumban), and subalkaline (Nyos, Batibo and Dschang) with SiO2 of 45–54 wt% and MgO of 2–9 wt%, similar to dykes reported in other areas of the Cameroon Line (CL) and the Central Atlantic Magmatic Province (CAMP). The abundances of rare earth elements (REE) and the Primitive Mantle normalised patterns for the Nyos, Batibo and Dschang dykes are similar to those of MORB, indicating that the dykes formed at shallower depths by a higher degree of partial melting relative to the Foumban dykes and the alkaline lavas of the CL. The transitional basaltic dykes with steeper REE patterns have their sources at deeper levels in the lithospheric mantle, possibly the garnet-spinel transition zone and were generated by a lower degree partial melting of the lithospheric and plume components. The Nyos and Batibo subalkaline dykes show similar isotopic compositions with a spectrum extending from depleted (DMM-like) to enriched (EM1-like) mantle, indicating the similarity in their source components. The Dschang dykes show distinct isotopic characteristics with relatively unradiogenic Nd-Pb isotope compositions compared to the Batibo and Nyos dykes. The Foumban transitional dykes with characteristic wide ranges in Sr-Nd-Pb isotopic compositions reveal varying contributions from enriched mantle components (EM1 and EM2) in addition to its plume signature similar to those of CL lavas. The Nyos and Batibo dykes alongside other dykes on the CL have low TiO2 abundances (<2 wt%), negative PM-normalised Nb-anomalies, and moderately to strongly enriched REE patterns, and isotopic composition that overlaps with those of CAMP, suggesting a similar lithospheric origin. |
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| Keywords: | Cameroon Line Subalkaline dykes Cameroon Volcanic Line CAMP magmatism |
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