Thermal state of the Roer Valley Graben, part of the European Cenozoic Rift System

We performed a detailed analysis of the thermal state of the Cenozoic Roer Valley Graben, the north-western branch of the European Cenozoic Rift System, based on a new set of temperature data. We developed a numerical technique for correcting bottom hole temperatures, including an evaluation of the uncertainty of thermal parameters. Comparison with drill stem test temperatures indicated that the uncertainty in corrected bottom hole temperatures using a two-component numerical model is approximately +/- 4 degrees C, which is much more accurate than the up to 15 degrees C errors encountered in often-used line-source or Horner correction methods. The subsurface temperatures and the derived regional heat flow estimates of 53 +/- 6 to 63 +/- 6 mW m-2 show no significant difference between the central rift and the adjacent structural highs. The absence of an elevated heat flow is attributed to the low amount of lithospheric thinning during the Cenozoic rifting phase (beta=1.06-1.15). A local thermal anomaly exceeding +10 degrees C was found in five wells in the north-western part of the rift basin at depths of 1000-1500 m, and is most likely caused by the upward flow of fluids along faults, whereas lower temperatures in the upper 1500 m in the southern part of the rift basin could indicate cooling by topography-driven groundwater flow. Conflicting ideas exist on the active or passive rifting mechanisms responsible for the formation of the different rift basins of European Cenozoic Rift System. The low spatial variation in heat flow found in this study suggests that the mechanism responsible for forming the Roer Valley Graben is passive rifting.