Please help me understand these questions and the phase diagrams for my Mineralo
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Question
Please help me understand these questions and the phase diagrams for my Mineralogy Final. Thank you in advance.
a. Suppose some olivine or pyroxene crystallizes from a mafic magma. The remaining magma then moves upward leaving the crystals behind. If this process repeats, how will the magmas composition change?
b. The Earth’s upper mantle is roughly basaltic (mafic) in composition and acts as a source region for magmas that move up into the crust. Partial crystallization alluded to in a, commonly occurs. If olivine crystals are left behind in the mantle and the magmas then crystallize in the crust, what effect does this have on the relative compositions of the crust and mantle? Assume olivine crystallized between 1700° and 1600° C. (No calculations are required)
c. Suppose magma in c after leaving the mantle crystallizes plagioclase between 1500° and 1400° C in the lower crust and the magma rises to the upper crust leaving the plagioclase behind. What effect will this have on the relative composition of the upper and lower crust.
d. Suppose olivine begins to crystallize at high temperature. It grows larger as cooling continues. If the cooling is too rapid for the olivine to remain in equilibrium, growth rings or zoning will develop. How will the composition of the center of the grain compare to the composition of the margins.
My Drive x D Blackboar x D Blackboa x D possible x D PossibleF x M Search re x Y YolNS-1 x C Chegg St x C Please E x C https://bb.uhd.edu 1577340-dt-content-rid 1/courses/20171013406/possiblefinalexamquestions.pdf /bbcswebdav/pid Possible New Essay Questions for the Mineralogy Lecture Final Use the phase diagrams below to help you answer the following questions 1800 melt 1600 liquidus plagioclase,. crystals liquid Curve melt 1400 1200 plagioclase,s Crystals solidus Curve 1000 northile albite 40 60 20 80 100 Mg2SiO4 Fe2SiO4 forsterite fayalite Ask me anything A 2:52 AM 2/13/2016Explanation / Answer
a. If the magma containing olivine or pyroxene crystallizes then this will result in crystallization of Mg rich varieties in early phases (clino pyroxenes and olivines) and results in enrichment of Fe in magma. With repeated crystallization and upward movement the last crystal to be crystallize will be only iron containing (ortho pyroxenes and olivines).
b. If the olivine crystal is left behind in the mantle and the magma moves upwards and crystallizes in the crust then this will result in mantle consisting of Mg olivine and ortho pyroxene enriched crust.
c. The movement of Magma to upper crust after leaving behind plagioclase will result in crystallization of K-felspar and quartz in the upper crust. Thus the upper crust rocks will be enriched in K-felspar and quartz.
d. The composition of the core of the mineral will be more Mg enriched and this will be surrounded by more Fe enriched zones towards the margins with the margin highly concentrated with Fe.