Granite is an intrusive, felsic rock, which may be produced by partial melting or fractional crystillisation. Explain how these processes can produce felsic magmas from more mafic parent magmas.
any ideas please
Wouldn't the presence of magnesium and iron lower the melting point of the rock? So at the same temperature, it is now a liquid.
Certainly! The process of partial melting and fractional crystallization can indeed produce felsic magmas from more mafic parent magmas. Allow me to explain how these processes work.
1. Partial Melting: While rocks are made up of various minerals, each mineral has a different melting point. During partial melting, only certain minerals within a rock begin to melt while others remain solid. This occurs because different minerals have different chemical compositions and melting points.
In the case of mafic magmas, which are rich in magnesium and iron, the minerals that contain these elements, such as olivine and pyroxene, have relatively low melting points. Thus, when a mafic rock undergoes partial melting, the minerals rich in magnesium and iron tend to melt first, leaving behind residual solid materials. These melting minerals contribute to the formation of a more felsic magma.
2. Fractional Crystallization: Once a magma has formed through partial melting, it begins to cool and solidify. During this cooling process, minerals start to crystallize out of the magma in a specific order. Minerals that crystallize at higher temperatures tend to be more mafic, while those that crystallize at lower temperatures tend to be more felsic.
In the case of fractional crystallization, as the magma cools, the minerals with higher melting points solidify first and are removed from the remaining magma. These removed minerals are more mafic and consist of minerals rich in magnesium and iron. As a result, the remaining magma becomes enriched in silica, aluminum, potassium, and sodium, which are components of felsic minerals.
By undergoing both partial melting and fractional crystallization, a more felsic magma can be generated from a more mafic parent magma.