Thermal structure of supra-detachment basins: a case study of the Devonian basins of western Norway

Abstract

We investigate the peak temperatures of the Devonian Hornelen, Kvamshesten and Solund basins in SW Norway to constrain their thermal history. These basins are the three largest Devonian units exposed in Norway and were formed as supra-detachment basins in the hangingwall of the Nordfjord Sogn Detachment Zone. The peak temperatures of the basins were obtained using a geothermometer based on Raman spectroscopy of carbonaceous material on detrital carbonaceous plant fossils. The data confirm an anchizone to low greenschist-facies metamorphism with temperatures (±30 °C) of 284–301 °C in the Hornelen and Solund basins and a significantly higher temperature, 345 °C in the Kvamshesten basin. The temperature increases toward the detachment fault and cannot be explained by ordinary burial alone. In the Kvamshesten basin this temperature increase is close to 100 °C. The new data demonstrate that exhumation of high-grade rocks in the footwall in the Nordfjord Sogn Detachment Zone played an important role in controlling temperatures in the hangingwall. We conclude that the dynamic evolution along large-scale detachments may introduce heat at the base of the hangingwall and thereby control the thermal state of supra-detachment basins formed during extension.