Eplanation of this presentation The object is to: 1.Link major element chemical variations to a measure of crystallization progress (Mg’). 2.To link major elements and crystallization progress to the crystal fractionation sequence indicated from the phenocryst assemblages. 3.To show that kinks in the major element trends indicate step changes in the fractionating mineral assemblages 4.To illustrate how trace elements can be used to estimate crystallization progress. The following presentation is based on a set of Kilauea lava analyses presented in Table 13-1 of Anthony Philpotts, 1990, Principles of igneous and metamorphic petrology, Prentice Hall. It also includes an adaptation and extension of his analysis of the data on pages 237 to 241 of that same text, and his figures 13.1 to 13.5.

Hawaii basalt data set analyses From Table 13-1 of Philpotts, 1990, Principles of igneous and metamorphic petrology, Prentice Hall.

Hawaii phenocryst compositions These are typical phenocryst compositions for Hawaii tholeiitic basalts.

Hawaii: differentiation index 1 Mg’ is the measure of magma evolution used here. It increases almost linearly with the differentiation index as mafic phases are fractionated from the liquid. Mg’ = molar Mg/(Mg+Fe 2+ )

Hawaii: differentiation index 2 Mg’ is the measure of magma evolution used here. It increases almost linearly with the differentiation index as dominantly mafic phases are fractionated from the liquid. Mg’ = molar Mg/(Mg+Fe 2+ ) Primitive Evolved Magma evolution proceeds by crystal fractionation.

Hawaii: norms 1 With fractional crystallization of olivine, the amount of olivine component in the liquid (normative olivine) decreases until there is none, after which there is normative quartz. Then, ilmenite crystallization continues the trend.

Hawaii: norms 2 Kink is an artifact of the norm calculations With fractional crystallization of olivine, the amount of olivine component in the liquid (normative olivine) decreases until there is none, after which there is normative quartz. Then, ilmenite crystallization continues the trend.

Hawaii: Mg- Al-Ca 1 Plot of three major oxides vs. Mg’, the index of magma evolution. Data do not define straight lines and so indicate changes in the crystal fractionation assemblage.

Hawaii: Mg- Al-Ca 2 Plot of three major oxides vs. Mg’, the index of magma evolution. Data do not define straight lines and so indicate changes in the crystal fractionation assemblage. Olivine Augite Olivine Augite Plagioclase Augite Plagioclase Enstatite Ilmenite

Hawaii: Ti- Na-K-P 1 Plot of four rather incompatible oxides, generally having less response to changes in the fractionating mineral assemblage modes.

Hawaii: Ti- Na-K-P 2 Plot of four rather incompatible oxides, generally having less response to changes in the fractionating mineral assemblage modes. Olivine ± Augite ± Plagioclase Enstatite + Augite + Plagioclase + Ilmenite

Hawaii: AFM diagram 1

Hawaii: AFM diagram 2 Olivine ± Augite ± Plagioclase Enstatite + Augite + Plagioclase + Ilmenite

Hawaii: incompatible elements 1 The major phases: Olivine: (Mg,Fe) 2 SiO 4 Augite Ca(Mg,Fe)Si 2 O 6 Plagioclase (Ca,Na)(Al,Si) 4 O 8 Enstatite (Mg,Fe)SiO 3 Ilmenite FeTiO 3 Which major elements are incompatible??

Hawaii: incompatible elements 2 The major phases: Olivine: (Mg,Fe) 2 SiO 4 Augite Ca(Mg,Fe)Si 2 O 6 Plagioclase (Ca,Na)(Al,Si) 4 O 8 Enstatite (Mg,Fe)SiO 3 Ilmenite FeTiO 3 Which major elements are incompatible?? Slight drop in TiO 2 because of Ti in pyroxenes? Large drop later due to ilmenite Substantial drop in Na 2 O due to Na in plagioclase. No change in P 2 O 5 -K 2 O ratio, because neither are included in major phases and so both are highly incompatible.

Hawaii: percent liquid remaining 1 The % liquid remaining can be calculated: %l = 100*I o /I n I o :Original concentration of an incompatible element in the parent magma (sample 1). I n :concentration of the same element in any derived magma.

Hawaii: percent liquid remaining 2 The % liquid remaining can be calculated: %l = 100*(I o /I n ) I o :Original concentration of an incompatible element in the parent magma (sample 1). I n :concentration of the same element in any derived magma.