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Setting the Melt Composition

Magma composition is described with the 7 component PI parameterisation of Dixon (1997), though for non-tholeiitic compositions this can be approximated by parameterisation of SiO2 content only (Dixon et al., 1997). This parameterisation is also used in the program VolatileCalc (Newman and Lowenstern, 2002), which also solves the Dixon (1997) model for COH solubilities.

Select the parameterisation style (PI or SiO2) in the drop down menu. Enter the composition in the appropriate fields.

Oxide components are entered in weight%.

Default values are characteristic values for Stromboli taken from Lesne et al. (2011).

Only oxidised conditions (NNO > 0.5) are modelled, where NNO is the difference in oxygen fugacity from the Nickel-Nickel Oxide buffer, in log units. At NNO < 0.5, significant amounts of H2S are present (Jugo et al., 2010), that are not accounted for in the partition coefficient parameterisation of Lesne et al. (in press).

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To use the PI parameterisation, either:

  1. Enter the proportions of SiO2, Al2O3, MgO, CaO, FeO, Na2O and K2O in wt%. Note that Fe2O3 is not included in the parameterisation.
  2. Or, select the "Use PI directly" option and enter a value of PI into the PI field.
  3. PI is given by -6.50 (Si4+ + Al3+) + 20.17 (Ca2+ + 0.8 K+ + 0.7 Na+ + 0.4 Mg2+ + 0.4 Fe2+), as molar proportions of cations.

See also

Setting the Volatile Composition