Chapter 29 Ans

Chapter 29 Ans - Answers for Chapter 29: Metamorphism of...

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Answers for Chapter 29: Metamorphism of Calcareous and Ultramafic Rocks 1. How does a skarn differ from other calc-silicate rocks? A calc-silicate rock is any metamorphic dominated by Ca-rich silicate minerals. A skarn is a specific type of calc-silicate rock formed by the interection between carbonates and SiO 2 - rich fluids. 2. Explain the transition from Figure 29.4a to b to c using the geometric principles of reaction-based chemographic topology changes (Section 26.9). Pick three well- distributed points on the diagrams and discuss the mineralogical changes in each. a b involves a tie-line flip indicating Dol + Qtz = Tlc + Cal. The b c transition involves Tlc + Cal + Qtz = Tr (Tr inside the Tlc-Cal-Qtz subtriangle). The red dot develops the sequence Dol + Cal + Qtz Tlc + Cal + Qtz Tr + Cal + Qtz. The blue dot develops Tlc + Dol + Qtz Tlc + Cal + Qtz Tlc + Tr + Cal. The green dot (typical dolostone) develops Dol + Cal + Qtz Dol + Cal + Tlc and does not manifest the final reaction. 3. What reaction is most likely to introduce tremolite into the majority of siliceous dolostones? Why? Tlc + Cal = Tr + Dol puts most carbonates (shaded in the above figure) in the Tr + Dol + Cal field. 1
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4. At what value of X CO2 is T max of Reaction (29.4)? Tr + Qtz + 3 Cal = 5 Di + 3 CO + H O 2 2 2 (29.4) T max occurs at X CO2 = 0.75 because of the #:1 ratio of CO 2 :H 2 O generated (see Section 26.4) How did you determine this (see Section 26.4)? CO 2 :H 2 O = 3:1 so X CO2 = 3/(3+1) = 3/4 = 0.75 Describe the closed-system evolution of fluid composition due to Reaction (29.4) with reference to Figure 26.7. What determines whether or not the fluid is buffered to T max
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Chapter 29 Ans - Answers for Chapter 29: Metamorphism of...

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