 Solution

ID: past-exam-of-the-year-2-of-the-earth-sciences-geology-course-of-the-university-of-oxford/2022/paper-1/7/d/solution

ϕ_{f} = 0.8

, use

f = ϕ_{f} P = 4800

bar. Retain the same ideal mineral-site activities, giving

Q = \frac{4800}{64} = 75.

Hence

T = \frac{127442.28}{170.7 - 8.3145 ln 75} = 945.40 K = 672.2 5^{\circ} C .

The lower fluid chemical fugacity stabilizes the water-bearing products of the forward dehydration relative to the ideal-gas calculation and lowers the required temperature by about

13.19

K. Here the stated fugacity coefficient is treated as a given constant for evaluating the equilibrium.

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