47. Why must the liquid composition reach point with further cooling? x 48. What mineral forms when the liquid reaches and what is the variance? What is the reaction and is x it continuous or discontinuous? Why? 49. Will the liquid composition reach point y? Why or why not? 50. A liquid of Xbulk = has an interesting variation on the evolution path described above. As with d Xbulk = forsterite forms first, followed by enstatite as the liquid composition reaches and c, evolves along the peritectic curve. Note, as deduced previously, that the Xbulk always lies within the triangle with corners equal to the three coexisting phases. In other words, the whole must lie within the geometry of the parts. But at some point along the peritectic En-Xbulk-Xliq become collinear so that the Xbulk lies on the of the 3-phase triangle, not it. How much edge within forsterite can remain from the reaction you proposed in question 46? Explain. 51. What is the new assemblage and variance after that? 52. On the basis of your answers to Question 50, what is the new continuous reaction and liquid evolution path immediately after Fo disappears? Explain. 53. Outline the remainder of the liquid evolution until the system is completely solid. At what point do new minerals form, and what are they? What is the variance at each stage, and what reactions occur. Are the reactions continuous or discontinuous?
47. Why must the liquid composition reach point x with further cooling? 48. What mineral forms when the liquid reaches x and what is the variance? What is the reaction and is it continuous or discontinuous? Why? 49. Will the liquid composition reach point y? Why or why not? 50. A liquid of Xbulk = d has an interesting variation on the evolution path described above. As with Xbulk = c, forsterite forms first, followed by enstatite as the liquid composition reaches and evolves along the peritectic curve. Note, as deduced previously, that the Xbulk always lies within the triangle with corners equal to the three coexisting phases. In other words, the whole must lie within the geometry of the parts. But at some point along the peritectic En-Xbulk-Xliq become collinear so that the Xbulk lies on the edge of the 3-phase triangle, not within it. How much forsterite can remain from the reaction you proposed in question 46? Explain. 51. What is the new assemblage and variance after that? 52. On the basis of your answers to Question 50, what is the new continuous reaction and liquid evolution path immediately after Fo disappears? Explain. 53. Outline the remainder of the liquid evolution until the system is completely solid. At what point do new minerals form, and what are they? What is the variance at each stage, and what reactions occur. Are the reactions continuous or discontinuous?
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