How does mafic lava turn into felsic lava?

Answer 1

Mafic lava, before cooling, has a low viscosity, in comparison to felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava, so eruptions of volcanoes made of mafic lavas are less explosively violent than felsic lava eruptions. Most mafic lava volcanoes are oceanic volcanoes, like Hawaii.

Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. The term combines the words "feldspar" and "silica." Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars. The most common felsic rock is granite. On the opposite side of the rock spectrum are the iron and magnesium-rich mafic and ultramafic minerals and rocks.

There are a few means by which felsic magma can be generated from mafic magma. Felsic materials have lower melting points than mafic materials and so will tend to melt first during partial melting. This can shift composition to something more felsic. Another process is called fractional crystalization. Here, more mafic material crystallizes and settles out of a magma chamber, making the remaining molten material more felsic. Finally, as mafic magma moves though continental crust, which is generally felsic in composition, it incorporates some of the rock and becomes more felsic.

Answer 2

Mafic lava can become felsic lava through a process called fractional crystallization. As the magma cools, minerals within it crystallize at different temperatures, causing the remaining liquid to become more silica-rich and compositionally evolve to felsic lava. This process occurs deep within the Earth's crust during magma chamber cooling.