Exercise: Closure temperatures

1) Calculate the closure temperatures of biotite (a) with a thickness of 100 µm, and (b) with a thickness of 50 µm, assuming a plane sheet geometry and using the diffusion parameters of Grove and Harrison (1996) (see overhead 24). Assume a cooling rate of 5°C/Ma in both cases.

2) Repeat the calculation, but now use a cooling rate of 10°C/Ma in both cases.

Summarize your findings in a few sentences and answer the following questions: (a) How will the closure temperature change if the grain size increases? And how will the closure temperature change if the cooling rate increases?

Additional information: Gas constant: 8.314 J/mol K. Take care on the units! Temperature is in K, and the cooling rate needs to be recalculated to °C/sec! Note that r in this case is half of the thickness (r is always the maximum diffusion length).

Provide the answer as a PDF if solved using Excel or any other spreadsheet program. Not only provide the result, but also the way you did the calculation!

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