| Autor: |
Fagny Mefire, Aminatou, Bardintzeff, Jacques-Marie, Nkouandou, Oumarou Faarouk, Njankouo Ndassa, Zénab Nouraan, Adama, Haman, Magha, Alice, Wotchoko, Pierre, Ngiante, George |
| Zdroj: |
Neues Jahrbuch fuer Mineralogie - Abhandlungen; October 2024, Vol. 199 Issue: 1 p55-72, 18p |
| Abstrakt: |
Petrography and mineral chemistry of mantle xenoliths recovered from Early Miocene trachybasaltic lavas near Sabga village in northwest Cameroon reveal the complex evolution of the underlying lithospheric mantle. The xenoliths are distinguished into harzburgite and lherzolite that are ovoid and angular in shape and show protogranular and equigranular textures, respectively. Major mineral phases are olivine, orthopyroxene and clinopyroxene. Electron microprobe analyses indicate high-Mg olivine (Fo 88.5–89.7 for lherzolite and 91.1–91.2 for harzburgite). Variations in major oxide abundances, Mg#, Cr# and Ca/Al ratios of clinopyroxene are present within each xenolith type, leading to distinction of two clinopyroxene groups. Moreover, spinel is Al-rich in lherzolite (Cr/[Cr+Al] = 0.09) and Cr-rich (Cr/[Cr+Al] = 0.46–0.47) in harzburgite. Calculated equilibrium temperatures (793–1211 °C for lherzolite and 822–1067 °C for harzburgite) agree with mantle xenolith temperatures from other locations worldwide. Estimated equilibrium pressures are 1.1–3.5 GPa for lherzolite and ~1.3 GPa for harzburgite. Corresponding sampling depths are 36–115 km and ~43 km for lherzolite and harzburgite, respectively. The lithospheric mantle below Sabga volcano has experienced melt extraction that is superimposed on cryptic metasomatism involving silicate and carbonate fluid phases. Because of this metasomatism recorded in the Sabga xenoliths, it is conceivable that the lithospheric mantle beneath the western highlands of Cameroon will continue to produce CO2-rich magmas where outgassing during volcanic eruptions is particularly hazardous. |
| Databáze: |
Supplemental Index |
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