Bowen reaction series:
Bowen's Reaction Series describes the temperature at which minerals crystallize when cooled, or melt when heated.
The cooling and crystallization of magma is a complex chemical process in which various silicate minerals crystallize in definite order.
BOWEN REACTION SERIES
(a) DISCONTINUOUS SERIES.
(b) CONTINUOUS SERIES.
The sequence of separation of minerals from a silicate mineral is established.
If a mineral remained in the melt after it crystallised it would react with remaining melt and produce the next mineral in sequence.
While studying the crystallization of cooling silicate melts N. L Bowen discovered 2 reaction series.
1. Continuous reaction series:
Minerals of a solid solution series generally form continuous reaction series.
Plagioclase felspars with end members anorthite and albite exhibit such reaction.
In a cooling melt An-rich plagioclases crystallize before the Ab- rich members.
With falling temperature there is a continuous reaction between the melt and precipitated crystals and thus the composition of crystals is continuously being changed.
Such a solid solution series in which the variation in composition is perfectly continuous is called continuous reaction series.
2. Discontinuous reaction series:
Discontinuous reaction are those which occur at definite temperature.
Such a reaction takes place in a cooling magma at certain lower temperature.
When an early crystallized mineral reacts with magma to form a new mineral of different composition.
A series of Mg-Fe rich minerals that crystallize from a basaltic magma are found to be related to each other by discontinuous reaction.
Such minerals when arranged in proper order constitute a discontinuous reaction series.
| Olivine ↓ | Ca-rich plagioclase ↓ |
| Orthopyroxene. ↓ | Ca-Na plagioclase ↓ |
| Clinopyroxene. ↓ | Na-Ca plagioclase ↓ |
| Amphibole ↓ | ↓ |
| Biotite. | Na-rich plagioclase |
| (A) | (B) |
| K -Felspar | |
| Muscovite | |
| Muscovite | |
| Muscovite | |
| Quartz | |
Advantage of Bowen reaction series:
Bowen reaction series is able to explain why certain types of minerals tend to be found together while others are almost never associated with one another.
Limitations of Bowen reaction series:
The main limitations are the state of the liquid, the rate of cooling and the tendency of mineral crystals to settle under gravity.
If the liquid is depleted from an element needed for a particular mineral, the series containing that mineral is discontinued.
Significance of Bowen reaction rate:
The slower a magma cools the larger the crystals can grow. This series allow geologists to predict chemical composition and texture based upon the temperature of a cooling magma.
