Physical conditions & Bowen’s Reaction Series
Mafic
(An)
(Fo then Fa)
(Ens then Aug & Di)
(Ab)
Felsic
Igneous Rocks & Bowen’s Reaction Series
Mafic
Felsic
Composition of Igneous Rocks
Heat Sources
in the Earth
1. Heat from the early accretion and
differentiation of the Earth

still slowly reaching surface
2. Heat released by the radioactive
breakdown of unstable nuclides
Ionic charge
vs. radius
Preference
for melt
Plot of ionic radius vs. ionic charge for
trace elements of geological interest.
Ionic radii are quoted for eight-fold
coordination to allow for comparison
between elements. From Rollinson
(1993).
Preference for
mineral phase
Heat flow and geothermal gradients
10°C/km
16°/km
24°C/km
Heat flow and geothermal gradients
10°C/km
16°/km
24°C/km
Base of crustal root in the Sierra ~30km (=300°C),
in the Basin & Range ~20km (=480°C)
Estimating
pressure
increases
Estimate ~3.33 kbar/km
(1 GPa = 10 kbar)
Figure 1-9. Estimated ranges of oceanic and
continental steady-state geotherms to a depth
of 100 km using upper and lower limits based
on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys.
Space Sci., 18, 269-311.
~6 kb
~12 kb
To calculate
A geothermal
gradient from
heat flow:
k = q z
T
k, thermal
conductivity
constant
(mediumdependent)
k q

(q)
z
T