The oceanic crust is primarily composed of basalts. Thus we take ρc = 2900 kg m−3, hc = 6 km, and Hc = 2.6 × 10−11 W kg−1. (The radiogenic heat production rate per unit mass of basalts was calculated in Problem 4–4.) From Equation (4–23) the resultant contribution to the surface heat flow is qc = 0.45 mW m−2; this is a small fraction of the mean oceanic heat flow, which is about 100 mW m−2. The conclusion is that heat production in the oceanic crust does not make a significant contribution to the oceanic surface heat flow. Therefore, an alternative explanation must be found for the failure of the simple conduction profile to model the suboceanic mantle geotherm. In later sections we show that heat flow due to mantle convection invalidates the conduction results.
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