A concept, first propounded in 1928 by Norman Bowen, which explains how minerals can respond to the changing equilibrium conditions when a magma is cooled, by either a continuous, diffusion-controlled exchange of elements with the magma or discontinuous melting of the mineral. In a continuous exchange or reaction, solid-solution minerals such as feldspar adjust their composition during cooling by a continuous diffusion of elements between magma and mineral, whilst in a discontinuous reaction, minerals such as olivine undergo melting at a specific temperature during cooling (the peritectic point) at the same time as a new mineral in equilibrium with the magma begins to crystallize (in this case pyroxene). Bowen suggested a series of these reactions that might take place during the cooling of a tholeiitic basalt magma, the so-called Bowen's reaction series, but pointed out that the series was a simplification of very complex reactions and could be misleading if taken at face value. The specific reaction series for tholeiitic magmas was never intended to become a general reaction series for all magmas.
Subjects: Earth Sciences and Geography.