Summary: Mathematical Geology, Vol. 37, No. 8, November 2005 ( C
2005) Tetrahedral Plots of the Phase Relations for Basalts1 and
Richard N. Abbott, Jr.3 The phase relations of quaternary
systems are generally represented by projections onto ternary
compositional planes. Such projections often obscure
relationships that would only be evident in a three-dimensional
tetrahedral plot. The tetrahedral plot requires that
compositions of the minerals and melts be transformed into
Cartesian coordinates. It is shown here how this transformation
is carried out. The application is demonstrated by tetrahedral
plots of experimental melt compositions of partially molten
lherzolite. Furthermore, the plot can be used to evaluate
whether or not a particular basaltic composition represents a
primary melt. The methods are applicable to any four-component
KEY WORDS: phase diagrams, basalts, primary magmas. The
compositions of primary basaltic magmas are controlled by the
phase re- lations of lherzolite and the way melt accumulat