Essay GEOL2003 – Komatiites Are Volcanic Ultramafic Rocks – Geology Assignment Help

Assignment Task

Komatiites are volcanic ultramafic rocks that are mostly restricted to Archaean, although there is one known location (in Caribbean) where Phanerozoic komatiites are found. Komatiites are formed at very high temperature (1700-2000oC) by a high degree of mantle melting. They are extruded to the surface as a low viscosity flows and crystallise quickly as they cool down. As a result of this fast cooling many komatiites exhibit so called spinifex texture, which is formed by elongated olivine and pyroxene crystals. However, some thicker flows of komatiites can, internally, cool down slower and crystallise some minerals that settle to the bottom of the flows forming cumulates.

You are provided with the excel file that contains analyses of komatiites from three locations: Kaapvaal craton, Superiour province and Gorgona Island. The file also contains two separate sheets with (1) REE concentrations in chondrite and (2) partition coefficients

1. Plot binary diagrams for major elements 

2. What elements show similar behaviour in three groups of komatiites and which highlights some differences?

Focussing on similarities:

3. Describe trends observed in the plots.

4. Crystallisation of which minerals can explain observed trends?

5. Are there any bends? If there are, which minerals can explain it?

6. Can you determine approximate chemical composition of the solid that is crystallising from the onset of solidification?

7. Does that confirm your initial guess in (4)? Explain

8. What trace elements can be used to further confirm mineralogy of the solid? Show it with a plot (or plots?)

9. Can you provide estimate of degree of fractionation for the first stage of melt evolution? Explain.