Radiogenic heat production in the upper third of continental crust from KTB

The heat production rate of continental crystalline rocks was determined from cores and drill cuttings recovered from depths up to 9.1 km in boreholes drilled by the Continental Deep Drilling Program of Germany (KTB). The drilled rocks are mainly gneisses and metabasites. Based on a large amount of data, the comparison of laboratory and in situ determinations by logging shows good agreement. The loss of radioactive elements in drill cutting samples at the shaker tables was minimized by using a broad range of available fragment sizes. The data reveal a clear lithological dependence of the heat production rate of the metamorphic rocks at KTB. The lithologically caused variations of the heat production rate have a wavelength in the order of the drilled depth and therefore, they cover up any decreasing trend if there is one. Below 6 km, tectonic elements such as fault zones play also an important role in the observed vertical distribution. Despite the availability of data for the upper third of the crust, models to predict temperatures for greater depths still contain uncertainties.