explain how partial melting and fractional crystallisation produce felsic magma from more maficparent magma
Would this help:
http://en.wikipedia.org/wiki/Fractional_crystallization_%28geology%29
Certainly! Partial melting and fractional crystallization are two processes that can lead to the formation of felsic magma from a more mafic parent magma. Let's break it down step by step:
1. Partial melting: This process occurs when certain minerals in the parent magma melt at different temperatures. Mafic minerals have a higher melting point, while felsic minerals have a lower melting point. When the parent magma undergoes partial melting, the mafic minerals start to melt, leaving behind residual solid material.
2. Composition of the melt: As the mafic minerals melt, the resulting melt becomes enriched in the elements that make up the felsic minerals. This is because the mafic minerals have a higher concentration of those elements compared to the felsic minerals.
3. Fractional crystallization: After partial melting, the melt rises to higher levels within the Earth's crust or magma chamber. As it cools, it starts to undergo fractional crystallization. This process involves the cooling and solidification of the melt, with different minerals crystallizing at different temperatures.
4. Crystal separation: The minerals that crystallize first from the melt are usually the mafic minerals, as they have a higher crystallization temperature. These newly formed mafic crystals are denser than the residual melt and tend to sink towards the bottom of the magma chamber or the crust.
5. Enrichment in felsic composition: As the mafic minerals are removed from the melt through crystal separation, the residual melt becomes progressively more enriched in the elements that make up the felsic minerals. This leads to an overall increase in the felsic composition of the magma.
6. Formation of felsic magma: Over time, as more and more mafic minerals crystallize and separate from the residual melt, the composition of the remaining melt becomes predominantly felsic. This process results in the formation of felsic magma from the more mafic parent magma.
In summary, partial melting selectively melts mafic minerals, leading to the enrichment of felsic elements in the resulting melt. Fractional crystallization then removes the newly formed mafic minerals, leaving behind a felsic-rich melt that ultimately solidifies into felsic magma.
I hope this explanation helps! If you'd like further details, you can also refer to the link you provided, which contains more comprehensive information on fractional crystallization in geology.