Magmatic Evolution of the Western Branch of the East African Rift System Melts: Evidence by Silicate Melt Inclusions, Rock Petrography and Geochemistry of the Nyiragongo 1977 and 2002 Lavas in DRC
Auteur(s): Makutu Kumakele DouxdouxNom de la revue/Journal: Open Journal of Geology
Mois: mai
Volume: 13
Année: 2023
pages: 449–486
Résumé
<p>Nyiragongo volcanic eruptions of 1977 and 2002 emitted silica-undersaturated lavas named melilite-nephelinites with microlithic to sub-porphyritic textures, and consisted of olivine, clinopyroxene (augite), phlogopite, melilite, magnetite, and rare plagioclases. This melilite-nephelinite as an evolved rock, shows low SiO2 high FeOt (13.76 - 14.10 wt%), Al2 wt%) and Na2O + K2O (10.34 - 11.85 wt%). Unlike LA-ICP-MS on silicatemelt inclusions (SMIs) hosted in augite show a pristine melt of picrobasaltic (low Ti-picrite) rock poor in SiO2 Al2O3 (8.01 - 9.57 wt%), and Na2(31.14 - 32.26 wt%), FeOt (2.19 - 2.79 wt%), O + K2O (2.34 - 3.05 wt%), while enriched in MgO (20.27 - 28.63 wt%), and CaO (24.95 - 33.17 wt%). The sums (∑REEs) for lavas and SMIs are ranging 712 - 799 and 43 - 119 ppm respectively. REE contracted multi-element patterns showed a W-feature for most lavas except for SMIs. High Rb/Sr, and low Ba/Rb, Zr/Nb, and Sm/Hf ratios of lavas suggest a phlogopite-rich source of material.</p>