Thermal state of the Norwegian lithosphere: insights from integrated heat flow and isostatic studies

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Pascal, Christophe; Elvebakk, Harald; Olesen, Odleiv; Midttّmme, Kirsti
Holding Date 08 September 2008

Modern heat flow data has been recently acquired in Norway in the framework of the Kontiki and HeatBar projects. Both projects, supported by StatoilHydro (Kontiki and HeatBar) and the Research Council of Norway (HeatBar), involved a wide range of activities from deep drilling (commonly down to 800 m) to thermal modelling, including well logging, conductivity measurements on drillcore material and systematic sampling of the Norwegian bedrock for determination of heat generation rates. This brand new dataset represents an improvement with respect to pre-existing heat flow determinations and leads to a dramatic reassessment of our views on the thermal state of the Norwegian lithosphere. The new heat flow data shows that typical heat flow values are significantly higher than previously thought.
In this paper we present an attempt to determine the thermal characteristics of the lithosphere, including its thickness, below Norway and adjacent areas. We use the new heat flow data and the new fine determinations of the thermal parameters of the Norwegian basement, together with crustal models derived from seismic profiling and modelling of potential field data (i.e. gravity and magnetic data). Possible thermal states for the lithosphere are explored using a self-consistent numerical method for which local isostasy is assumed. In agreement with previous geophysical studies, the results of the modelling suggest that the lithosphere thickens gradually from Norway towards the centre of the Baltic Shield. However, our modelling predicts significant differences in lithosphere thickness values when compared to previous estimates. One of the main reasons for such a disagreement comes from the poor quality of the heat flow data previously used.