| The formation of crust by partial melting and fractional crystallization |
The role of partial melting and fractional crystallization in the formation of crust
The table below presents a simplified view of the stages in which continental crust of felsic composition is produced by distillation of mantle peridote of ultramafic composition. For a more complete view of this complex process refer to Internal Processes, Figure 7.6. Also relevant is Earth Materials, Plate 6.12.
Note that the Si02 and ferro-magnesian percentages are rounded figures, and may not be exactly the same as those given in the course units.
|
SOURCE |
ROCK TYPE |
DOMINANT MINERALS |
Overall (approx.) SiO2 content |
Overall (wt. %) ferro-magnesian content (FeO, Fe2O3, MgO) |
TECTONIC SETTING |
| continental crust | granite (rhyolite) | K-feldspar plagioclase quartz biotite | 73% | 3% | destructive margins (upper crust) |
| Partial Melting and Fractional Crystallization | |||||
| continental crust | diorite (andesite) | plagioclase amphibole biotite pyroxene quartz K-feldspar | 58% | 11% | destructive margins (lower crust) |
| Partial melting | |||||
| oceanic crust | gabbro (basalt) | pyroxene plagioclase olivine | 49% | 18% | destructive margins (descending slab) |
| Partial melting | |||||
| mantle | peridotite | olivine pyroxene plagioclase | 42% | 41% | constructive margins, hot spots |