Bowen's reaction series

Bowen’s reaction series is named after the petrologist Norman Bowen, who summarized the cristallization sequence of typical basaltic magma undergoing fractional crystallization. The series is based on observations of natural rocks and experiments he performed in the early 1900s with powdered rock material. He heated the material until it melted and then allowed it to cool to target temperatures whereupon he observed the composition of the rocks that formed based on the types of minerals that composed them.
Minerals at the top have relatively high crystallization temperature, so they will be the first to crystallize from a magma as it cools. Minerals at the bottom have relatively low crystallization temperatures, so they will crystallize last. Bowen suggested that crystallization of minerals from high to low temperatures could be divided into a continuous reaction series and a discontinuous reaction series.
The discontinuous series, on the left, is formed by mafic minerals that usually completely react to form totally new minerals with different crystal structures as magma cools. Therefore, olivine is the first to crystallize, but may completely react with the magma as it cools further to recrystallize into pyroxene. And as the magma keeps cooling, pyroxene may react with the magma to produce hornblende, then hornblende to produce biotite. Therefore, a rock that has olivine and hornblende is not in an equilibrium state, since these are formed at different conditions. Stable pairs could be olivine and pyroxene, or hornblende and biotite, for example. On the right side, we have the continuous series, which consists of the plagioclase feldspar solid solution series. A basaltic magma would initially crystallize a Ca- rich plagioclase, with the highest melting point, and upon cooling continually react with the liquid to produce more Na-rich plagioclase. During this process, the first crystals to form may react partially with the melt, but without destroying the basic feldspar crystal structure. Very often, large plagioclase crystals in igneous rocks have cores that are more calcium rich and then outer layers rich in Na that were added to crystal structure as the system cooled.The bottom of the series contains the minerals that end up having the the higher silica content and will be the last to crystallize as silica has the lowest melting point. So as the magma cools, potassium feldspar will crystallize, then muscovite mica then quartz. Note that if we could freeze the system and retrieve the rocks with the listed minerals at any of these four stages, we would obtain rocks that would be ultramafic, mafic, andesitic or intermediate, and granitic.

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