8.8 Variation Diagrams - Fractionation Model Diagrams
Figure 8.10 and Figure 8.11 will allow you select a starting liquid composition, to select fractionating minerals, and to observe graphically the effects of removing those minerals. Figure 8.10 is a two-component variation diagram and Figure 8.11 is a ternary variation diagram. Click on either diagram to open the larger, interactive version. You may choose among olivine, orthopyroxene, augite, plagioclase, ilmenite, and magnetite as fractionating minerals. Enter the weight percent proportions of those minerals you wish to remove by fractional crystallization. You can enter any positive numbers for the weight percent proportions and the software will normalize to 100%. KD values from Morse (2015) are listed on the diagrams, but you can substitute your own KD values if you wish. Once you have made your selections, move the slider to change the percent solidified (PCS) and removed. The diagrams will show the results in 2 PCS steps until any one of the major element oxides has dropped below zero.
Take some time to explore fractional crystallization with Figure 8.10 and Figure 8.11. Change the fractionating minerals and their proportions. Try different starting compositions. See if you can predict how the magma composition will change before running each fractionation experiment. Based on what you learn from your explorations, answer the following questions.
Figure 8.10. Variation Diagram Fractionation Tool. Click on the diagram to see and use a larger version.
Figure 8.11. Ternary diagram model of fractional crystallization. Liquid path for olivine fractionation from a mafic basalt composition. Click on the diagram to see a larger, interactive version.
