Bowen’s Reaction Series
• Describes the formation of igneous rocks from
different starting temperatures and magma
compositions.
• Fractional Crystallization – process by which
minerals are formed and removed from the
molten rock
Discontinuous Reaction Series
• On left
• Earlier-formed crystals react with the
remaining magma in a series of steps to form
a new mineral
• From an initial basaltic magma, the first
formed mineral is olivine (Mg2SiO4).
• removal of olivine increases the silica content
and decreases the iron and magnesium in the
parent magma
• As temperatures lower, a new chain silicate
mineral, pyroxene (CaMg(SiO3)2 is formed.
• As temperatures drop further (1100C 850C), the magma becomes even richer in
silicates.
• Amphibole begins to form
• The original basaltic magma becomes
andesitic magma
• As temperatures cool to 800C and silica
increases further, the sheet silicate biotite
forms.
• Andesitic magma now evolves into rhyolitic
magma.
• Quartz forms last at low temperatures.
• Muscovite mica and potassium feldspar also
form at this temperature
• All of these minerals are poor in mafic
components (Fe, Mg) which were removed
from the melt by minerals that formed earlier.
Continuous Reaction Series
• On right
• Earlier formed minerals slowly and steadily
change into new minerals
• Crystallization of plagioclase feldspar depletes
calcium from the parent magma and replaces
the missing element with sodium as new
minerals are formed
• Feldspar minerals form continually at the
same time as minerals shown opposite in the
Discontinuous Series
Bowens and Weathering
• Minerals that crystallize at high temperatures
generally break down more quickly on the surface
on Earth
• Minerals that crystallize at low temperatures are
more abundant on the surface because they are
more resistant to weathering