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  

作　　者：Douxdoux Kumakele Makutu Douxdoux Kumakele Makutu(Department of Energy Resource Engineering, College of Engineering, Inha University, Incheon, Republic of Korea;Department of Geosciences, College of Natural Sciences, Kinshasa University, Kinshasa, Republic Democratic of Congo)

机构地区：[1]Department of Energy Resource Engineering, College of Engineering, Inha University, Incheon, Republic of Korea [2]Department of Geosciences, College of Natural Sciences, Kinshasa University, Kinshasa, Republic Democratic of Congo

出　　处：《Open Journal of Geology》2023年第5期449-486,共38页地质学期刊（英文）

摘　　要：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. .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. .

关 键 词：Nyiragongo Lava PETROGRAPHY GEOCHEMISTRY SMIS LA-ICP-MS RIFTING Magma Evolution 

分 类 号：P58[天文地球—岩石学]