Chapter 30 Ans

Chapter 30 Ans - Answers for Chapter 30: Metamorphic...

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Answers for Chapter 30: Metamorphic Fluids, Mass Transport, and Metasomatism. 1. What direct evidence is there for fluids having been present during metamorphism of rocks? Fluid inclusions are still present in thin sections and indicate than many fluids are high T-P fluids. Volatile-bearing metamorphic minerals are stable under a range of metamorphic conditions and require fluid pressure to stabilize them. Experiments suggest mineral stabilities involving fluid pressures. Some isotopic systems, particularly δ 18 O, indicate that rocks interacted with fluids during metamorphism. 2. Are fluids in regionally metamorphosed rocks a vapor, a liquid, or neither/both? Explain. Neither. P-T conditions of metamorphism is generally above the critical point for volatile species, so they are really supercritical fluids (at conditions beyond the distinction between liquid and vapor). 3. If K SP for NaCl is 36 (in the lab), what are the activities of Na + and Cl - at saturation? According to Equation (30.2) they would have to be the square root of 36, or 6 (mol/liter if the activity coefficients are 1.0). Would you expect K SP for quartz to be higher or lower than 36? Why? Much lower because quartz is far less soluble in water than is NaCl. 1
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4. How does diffusion differ from infiltration ? In diffusion, components move through the medium containing them and in infiltration the fluid medium itself moves and carries components passively. Propose a simple demonstration of each using common household materials. Diffusion would occur if I put salt in absolutely stagnant water and let it sit. Na + and Cl - ions would dissolve and diffuse into the water, making it salty. Infiltration occurs in a coffee stain on a clean tablecloth. The water carrying dissolved coffee components moves through the fibers and the coffee is infiltrated. 5.
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Chapter 30 Ans - Answers for Chapter 30: Metamorphic...

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