Retrograde mineral reactions: a heat source in the continental crust?

Chemical reactions of water with silicates are strongly exothermic. Therefeore, retrograde metamorphism is also a strongly exothermic process and thus a potentially powerful heat source. Depending on the time scale its contribution to the terrestrial heat flow can be equivalent to, or even exceed, that of radioactive decay. During hydration mafic rocks and gneisses liberate 60 J/cm³ for each weight percent H₂O they bind. It is argued that retrograde reactions constitute relatively short-lived, single or repeated episodes during crustal cooling, and that they can influence, or even strongly perturb, the geotherm during thousands to a million years. The thermal effects involved are non-trivial; they should be considered in interpretations of heat flow measurements. They could constitute the main heat source for hydrothermal mineralisations not connected with magmatic intrusions and possibly contribute to the thermal development of sedimentary basins. These effects are large enough to be one of the possible explanations for the difference between the predicted and measured heat flows at the KTB site.The authors share the work on this article equally. The order of names, therefore, is purely alphabetical.