The simulation of the genesis of the komatiite-tholeiitic series in the Vedlozero-Segozero greenstone belt led the author to conclude that peridotite komatiites are formed at 45-55% degrees of melting of mantle lherzolite at a pressure of 30-35 KBar.
The fact that all the komatiites belong to the Yilgarn ( Al-undepleted type with the rations CaO/Al2O3<1, ( 0.25-1); Al2O3/TiO2=13-22, Ti/Y=200-290, Ti/Zr=60-100 close to average mantle rations. ) type alone and at the same time fall into different REE topological groups (1.Komatiites showing flat chondritic REE distribution -(La/Sm)n=0.8-1.1, (Gd/Yb)n=0.9-1.2, (Ce/Yb)n=0.9-1.1 -Palaselga structure; 2. Slightly LREE -depleted komatiites, (La/Sm)n=0.4-0.7, (Gd/Yb)n=0.89-1.4, Ce/Yb)n=0.6-0.8- Koykary structure, Siivikkovaara strukture- Kuhmo g.b; 3. Komatiites showing slight LREE enrichment and flat HREE distribution, (La/Sm)n=1.5, (Gd/Yb)n=1.1-1.3 , (Ce/Yb)n=0.9-1 -Sovdozero structure; 4. Komatiites LREE- enrichment, Ilomantsi g.b.) is due to their genesis and the geochemical characteristics of the mantle sources.
The mantle sources compositions of peridotite komatiites
| Ilomantsi Finland | Kuhmo Finland | Koykary C.Karelia | Palaselga C.Karelia | Sovdozero C.Karelia | Vetreny belt CE.Karelia | |
| Age (Ga) | 2750 | 2750 | 2935 | 3000 | 3000 | 2410 |
| Ti02 | 0.15 | 0.17 | 0.15 | 0.15 | 0.15 | 0.18 |
| Cr | 3000 | 2000 | 3000 | 3350 | 3000 | 1000 |
| Ni | 2000 | 1000 | 2000 | 2000 | 2000 | 650 |
| Co | 77 | - | 80 | 100 | 70 | 50 |
| Zr | 3-5 | 15-20 | 9-11 | 9-11 | 9-11 | 10-20 |
| Sr | 30 | 7 | 9-10 | 4-5 | 10-12 | 10-20 |
| Y | 2-3 | >4 | 2-4 | 2-4 | 2-4 | 3-5 |
| Nb | 5 | - | <0.5 | <0.7 | <0.7 | <0.6 |
| Ce | ~3.1 | ~1.1 | ~0.65 | ~1.45 | ~1.3 | ~4 |
| Nd | ~1.3 | ~1.3 | ~0.72 | ~0.98 | ~0.82 | ~2.8 |
| Sm | ~0.5 | ~0.5 | ~0.29 | ~0.27 | ~0.3 | ~0.7 |
| Eu | ~0.15 | ~0.15 | ~0.11 | ~0.18 | ~0.11 | ~0.3 |
| Yb | - | ~0.49 | ~0.38 | ~0.32 | ~0.35 | ~0.42 |
| eNd | - | +4 | - | +1.3 | +2 | -0.9 |
The petrogenesis of C. Karelia komatiites indicates that they were generated in a single mantle reservoir which considerably differ in some chemical characteristics such as minor and REE content from the mantle sources of peridotite komatiites in East Finland, North Karelia and the Kola Peninsula.
1. Introduction
2. Geology
3. Layered flows
4. Structures
5. Petrography
6. Geochemistry
7. Mantle sources
8. References
9. Researcher (Sergei Svetov)