[S24-P] Poster

[S24-P-05] Geotherms of the continental crust: ambiguity from experimental P–T correction to thermal conductivity

^○Andrea Foerster, Sven Fuchs, Ben Norden, Hans-Juergen Foerster (GFZ German Research Centre for Geosciences, Potsdam, Germany)

Calculation of geotherms, reflecting steady-state heat conduction, is dependent on surface heat flow, the compositional model of the crust, and its thermo-physical properties, such as thermal conductivity (k) and radiogenic heat production (H). Available global geotherms are afflicted with uncertainties associated with the simplification of the crustal model, e.g. from dividing the crust into an upper and a lower crust. Here we address uncertainty in geotherm construction that arises from ignoring the mandatory correction of k for pressure (P) and temperature (T). For this purpose, published P-T relations derived from laboratory experiments up to T of 800 degC and performed with physical-contact methods are applied in geotherm calculation, considering different crustal models. The single P and T correction equations are used in a combined approach. The generalized conceptual geotherm model discussed here considers a surface heat flow of 60 mW/m² and a 35 km-thick crust consisting of a 16 km-thick granitic upper crust (k 3.0 W/m/K; H 1.5 microW/m³) and a granulitic lower crust (k 2.6; H 0.45), which is a scenario used in pioneering works on global geotherms in the 1980s and 1990s. P-T relations applied to k are those developed for typical upper crustal (granitic) and lower crustal (granulitic) rock types. Using those rock-specific relations, T at the Moho would amount to 570+/-15 degC. This Moho T is higher by 40 degC compared to earlier work in which some generalized P-T relation to k is applied (Chapman, 1986; Chapman & Furlong, 1992). The difference to Moho T uncorrected for k is more substantial, on the order of 80 degC. Results imply that the crust is warmer if experimental results on P-T relations to k are considered in geotherm parameterization. The difference between corrected and uncorrected geotherms become more serious for higher surface heat flow and for compositionally more diverse, i.e. closer-to-reality crust, and may well exceed 100 degC.