bowens reaction series

• The ideal sequence in which minerals are expected to crystalise from a melt is known as the Bowens reaction series.|
• Discontinuous reaction series are made of a series of shorter continuous reaction series. 
• If the melt cools slowly, the olivine series should be completely assimilated into the melt, allowing pyroxenes to cool. 
• The olivine and pyroxenes are sometimes referred to as a reaction pair, as would the pyroxenes and amphiboles.  
• Olivine crystals are retained in the rock, indicating it didn’t all go back into the melt. It then provided a solid surface on which later formed pyroxene could crystalise. 
• Reaction rims are common, indicating the disrupted cooling history of magmas. Rims of both pyroxene and amphibole can be found surrounding olivine crystals. 
• The plagioclase feldspars are part of a continuous reaction series, from anorthite to albite. 
• At lower temperatures the two series join together and you produce K-feldspar, muscovite and quartz. 
• The minerals at the high temperature ends of both series have the highest melting points, and would be expected to crystallise first. 

  • High temperature = most unstable and more susceptible to weathering 
  • Low temperature minerals like quartz are more stable. 
• Series in nature:

  • If magma runs out of an element needed for a particular mineral, the reaction series with that mineral is interrupted 
  • If the magma cools quickly, early minerals can be preserved, this alters the melt composition and changes how the magma then changes after that 
  • If crystals can rise or sink they stop reacting with the melt and gather elsewhere.  
  • The composition may be mafic, intermediate or silicic in composition, so the reaction series is often partially followed