= Consider a 30-km layer of granite (p=2700 kg m-?) overlying mantle with a surface heat a flow of 54 mW m2. If the heat production in the granite due to radioactive sources is distributed according to H=Hse-(z/D) where H, = 9.6x10-10 W kg-1 and D is 8 km (a) Estimate the mantle heat flow (b) What fraction of the heat flow comes from the mantle, and what fraction comes from the heat production in the crust? (c) Plot the geotherm down to 50-km depth assuming uniform thermal conductivity of 4 W m-K-1. = Consider a 30-km layer of granite (p=2700 kg m-?) overlying mantle with a surface heat a flow of 54 mW m2. If the heat production in the granite due to radioactive sources is distributed according to H=Hse-(z/D) where H, = 9.6x10-10 W kg-1 and D is 8 km (a) Estimate the mantle heat flow (b) What fraction of the heat flow comes from the mantle, and what fraction comes from the heat production in the crust? (c) Plot the geotherm down to 50-km depth assuming uniform thermal conductivity of 4 W m-K-1