TITLE:
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
AUTHORS:
Douxdoux Kumakele Makutu
KEYWORDS:
Nyiragongo Lava, Petrography, Geochemistry, SMIs, LA-ICP-MS, Rifting, Magma Evolution
JOURNAL NAME:
Open Journal of Geology,
Vol.13 No.5,
May
31,
2023
ABSTRACT: 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 (38.40 - 39.52 wt%) and MgO (3.10 - 4.01
wt%), and relatively high FeOt (13.76 - 14.10
wt%), Al2O3 (15.01 - 16.48
wt%), CaO (11.00 - 12.29 wt%) and Na2O + K2O
(10.34 - 11.85 wt%). Unlike LA-ICP-MS on silicate melt
inclusions (SMIs) hosted in augite show a pristine melt of picrobasaltic (low
Ti-picrite) rock poor in SiO2 (31.14 - 32.26
wt%), FeOt (2.19 - 2.79 wt%), Al2O3 (8.01 - 9.57
wt%), and Na2O + 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 materials.