Metamorphic rocks lab Part III Metamorphic mineral assemblages and reactions Due Tuesday 4/13 Problem 24-1: Given the following mineral compositions (Fe is Fe +2 unless indicated): Staurolite (St) (Fe,Mg) 2 Al 9 O 6 [(Si 3 Al)O 16 ](OH) 2 Chloritoid (Ctd) (Fe,Mg) 2 Al 4 O 2 [Si 2 O 8 ](OH) 4 Anorthite (An) CaAl 2 Si 2 O 8 Glaucophane (Gln) Na 2 Mg 3 Al 2 [Si 8 O 22 ](OH) 2 Vesuvianite (Ves) Ca 10 (Fe,Mg) 2 Al 4 [Si 2 O 7 ] 2 [SiO 4 ] 5 (OH) 4 Calcite (Cal) CaCO 3 Epidote (Ep) Ca 2 Fe +3 Al 2 O[Si 2 O 7 ][SiO 4 ](OH) Kyanite (Ky) Al 2 SiO 5 Biotite (Bt) KFeMg 2 [AlSi 3 O 10 ](OH) 2 Garnet (Grt) Fe 2.1 Mg 0.9 Al 2 [Si 3 O 12 ] Muscovite (Ms) KAl 2 [AlSi 3 O 10 ](OH) 2 Cordierite (Crd) (Fe,Mg) 2 Al 4 Si 5 O 18.H 2 O Diopside (Di) Ca(Fe,Mg)Si 2 O 6 Grossular (Grs) Ca 3 Al 2 Si 3 O 12 Andalusite (And) Al 2 SiO 5 Hypersthene (Hy) (Fe,Mg)SiO 3 Wollastonite (Wo) CaSiO 3 Show your calculations for all of the following: 1) Calculate and plot St, Ctd, Ves, Cal, An, Glc, and Ep on an ACF diagram. 2) Calculate and plot Ky, Bi, Grt, and Ms on an AKF diagram. 3) Calculate and plot Bt and Grt on an AFM diagram (projected from Mu). 4) You are studying a suite of rocks from a field area. You notice that the rocks contain the following mineral assemblages: And-An-Crd An-Di-Grs Grs-Di-Wo An-Crd-Hy An-Hy-Di Calculate and plot these assemblages on an ACF diagram (plot the minerals, and connect coexisting phases with tie-lines). What metamorphic facies is represented (see chapter 25)? Why do some rocks have cordierite and others diopside?
Find the Excel spreadsheet like the one below on the course web site. Use this spreadsheet to calculate normalized components for the ACF, AKF, and AFM diagrams. On the web site, you will also find a document that discusses using Excel spreadsheets you may find this useful if you are not familiar with Excel or want to learn more about Excel. When normalizing to get the percentage of different components, you will create formulas in Excel that look like: =100*C8/SUM(C8:E8), where C8 and E8 refer to specific cells within your spreadsheet. C8/SUM(C8:E8) gives you the ratio of whatever is in cell C8 to the sum of the values in C8, D8, and E8. Multiplying by 100 converts that ratio to a percentage. SUM(C8:E8) adds the values in cells C8, D8, and E8. E-mail me a copy of your spreadsheet when you turn in this part of the lab.
Problem 26-00: This problem tests if you understand some basic principles of reactions that we have been discussing in class. You may want to refer to your text to help answer this question, particularly the discussion of brucite-periclase and perfectly mobile components in Section 24.2 and again in the discussion of Schreinemakers bundles in Chapter 26. The above diagram contains a hypothetical reaction A + B = C. Where would a second reaction B = C + D would go? There are only two possibilities: to the left or right of the A + B = C reaction. When solving this problem, consider the information contained within the diagram that at higher temperatures, C is stable at the expense of a reaction between A and B. Draw and label a line for the reaction B = C + D and explain your answer below. Why is your answer correct and the alternative incorrect?
Problem 28-2: Read the entire question before beginning. Given the two following reactions: Ms + Qtz + St = Bt + Al 2 SiO 5 + H 2 0 (1) Ms + Qtz = Kfs + Al 2 SiO 5 + H 2 0 (2) a. Which occurs at the higher temperature? Why? Note: this can be determined from basic principles, and need not reflect the specific nature of any of the minerals involved in the reactions. This is similar to Problem 26-00. b. Remembering the common shape of dehydration reactions, sketch both reaction curves on a P-T phase diagram (qualitatively, you need assign no values to P and T). In three different field areas the following occurs with these reactions: Field area A: reaction (1) produces andalusite whereas reaction (2) produces sillimanite. Field area B: reaction (1) produces kyanite whereas reaction (2) produces sillimanite. Field area C: both reactions produce andalusite. Field area D: both reactions produce sillimanite. c. Experiment around with the two reactions and the Al 2 SiO 5 phase diagram by trial-anderror until you can explain the four sequences. Sketch the final phase diagram and list the four field areas in order of P/T metamorphic field gradients. Pressure Kyanite Sillimanite Andalusite Temperature