Geology Phase Diagram Questions.

Question 18 In the phase diagram below, which path best represents cooling of a liquid which will ultimately lead to a solid with 50% leucite and 50% K-spar? 1800 1713:59 1686:59 1600 Liquid Liquid + Cristobalite 1470 $ 109 antigrade 1400 Leucite + liquid Temperature, degrees 1200 Tridymite + liquid 1150 : 201 Leucite + potosh feldspor 0 Liquid potash feldspar 1000 1990+20° Potash feldspar + Fridymite KAISI 40 60 80 (Leucitel 20 KAIS, (Potash feldspar) Sio (Cristobolite and tridymite) Melt G Melt H O Melt O Melt D Question 19 The image below shows zoning in a plagioclase phenocryst and a phase diagram for plagioclase crystallization. Which of the following histories best represents this crystal growth? PLAGIOCLASE CRYSTAL 7 Ango • Anto •An Ango -Ango 1600 Liquid 1400 T°C 1200 Plagioclase + Liquid 1000 Plagioclase 800 0 20 40 60 NaAISI, Og Ab % An 80 100 CaAL, SIO An a) Fractional crystallization of a melt with a starting composition of 50% Anorthite Equilibrium crystallization of a melt with a starting composition of 50% Anorthite Equilibrium crystallization of a melt with a starting composition of 90% An Fractional crystallization of a melt with a starting composition of 90% An