Bowen's reaction principle: Reaction series and its application to petrogenesis

Original Paper

Bowen's Reaction Series Norman L. Bowen, an experimental petrologist in the early 1900s, realized this from his determinations of simple 2- and 3-component phase diagrams, and proposed that if an initial basaltic magma had crystals removed before they could react with the liquid, that the common suite of rocks from basalt to rhyolite could be produced.  This is summarized as Bowen's Reaction Series.

Bowen suggested that the common minerals that crystallize from magmas could be divided into a continuous reaction series and a discontinuous reaction series. The continuous reaction series is composed of the plagioclase feldspar solid solution series.  A basaltic magma would initially crystallize a Ca- rich plagioclase and upon cooling continually react with the liquid to produce more Na-rich plagioclase.  If the early forming plagioclase were removed, then liquid compositions could eventually evolve to those that would crystallize a Na-rich plagioclase, such as a rhyolite liquid.

The discontinuous reaction series consists of minerals that upon cooling eventually react with the liquid to produce a new phase.  Thus, as we have seen, crystallization of olivine from a basaltic liquid would eventually reach a point where olivine would react with the liquid to produce orthopyroxene.  Bowen postulated that with further cooling pyroxene would react with the liquid, which by this time had become more enriched in H2O, to produce hornblende.  The hornblende would eventually react with the liquid to produce biotite.  If the earlier crystallizing phases are removed before the reaction can take place, then increasingly more siliceous liquids would be produced. This generalized idea is consistent with the temperatures observed in magmas and with the mineral assemblages we find in the various rocks.  We would expect that with increasing SiO2 oxides like MgO, and CaO should decrease with higher degrees of crystal fractionation because they enter early crystallizing phases, like olivines and pyroxenes. Oxides like H2O, K2O and Na2O should increase with increasing crystal fractionation because they do not enter early crystallizing phases.  Furthermore, we would expect incompatible trace element concentrations to increase with fractionation, and compatible trace element concentrations to decrease.  This is generally what is observed in igneous rock suites.   Because of this, and the fact that crystal fractionation is easy to envision and somewhat easy to test, crystal fraction is often implicitly assumed to be the dominant process of magmatic differentiation. ___________________________________________________________________________ Source Link: Magmatic Differentiation ___________________________________________________________________________ More Links to See: What is Bowen's Reaction Series? Bowen's Reaction Series and the Igneous Rock Forming Minerals