Using the Speel River pluton cooling history shown in Figure 6.33 (from Reiners, 2005), estimate at what depth the pluton was likely emplaced. Assume a geothermal gradient of 30°C/km. If the surface temperature is 0°C, what is the minimum exhumation rate implied by the U/Th-He date at 8 Ma?

Figure 6.33

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Temperature (°C) 1000 800 600 400 200 0 60 zircon U/Pb titanite U/Pb hornblende 40 Ar/39 Ar biotite 40 Ar/39 Ar plagioclase 40 Ar/39 Ar zircon (U-Th)/He 50 40 apatite FT 30 Age (Ma) 20 apatite (U-Th)/He 10 - 0