Graphical estimations of magma densities and compositional expansion coefficients |
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Authors: | Takehiro Koyaguchi |
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Institution: | (1) Department of Geology, Faculty of Science, Kumamoto University, 860 Kumamoto, Japan |
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Abstract: | Assuming that the partial molar volume of each chemical component in a magma is constant, the magma density,
m
, is expressed as 1/
m
= C
i
/
fi
, whereC
i
is the weight fraction, and
fi
is the fractionation density of thei
th component. Using this linear relationship between 1/ and weight fraction, the density change due to addition or subtraction of any component can be graphically estimated on 1/ vs oxide wt% diagrams. The compositional expansion coefficient of thei
th component,
fi
, is expressed as
i
=
m
/
fi
–1. The compositional expansion coefficient of H2O has a much larger absolute value than those of any other oxide or mineral components, showing that addition of a small amount of H2O can significantly decrease magma density. These simple expressions facilitate the estimation of magma densities during fractionation. |
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Keywords: | |
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