Chapter 25 Ans

Chapter 25 Ans - Answers for Chapter 25: Metamorphic Facies...

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Answers for Chapter 25: Metamorphic Facies and Metamorphosed Mafic Rocks 1. Pentii Eskola originally defined metamorphic facies on the basis of predictable mineral assemblages that develop in metamorphosed (mafic) rocks and occur worldwide. How does a modern approach to metamorphic facies differ? We have sufficient experimental and field criteria to assign reasonable pressure and temperature ranges to the facies, so we can now add these criteria, resulting in a P-T diagram of facies (Figure 25.2). 2. Compare the concepts of facies and facies series . Facies refers to the set of predictable mineral assemblages and P-T range so represented. Facies series refers to the sequence of facies that may develop over a larger area in response to a P/T metamorphic field gradient. 3. What are the three common types of facies series, and what sequence of facies occurs along each series? Hi P/T facies series: (zeolite) – (prehnite-pumpellyite) – blueschist - eclogite Medium P/T series: (zeolite) – (prehnite-pumpellyite) – greenschist – amphibolite – (granulite) Low P/T series: (zeolite) – (prehnite-pumpellyite) – albite-epidote hornfels – hornblende hornfels – (pyroxene hornfels) – (sanidinite) 4. To what tectonic situations might you attribute each facies series? Hi P/T facies series: outer belt in subduction zones
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Chapter 25 Ans - Answers for Chapter 25: Metamorphic Facies...

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