Geophysical characterisation of two segments of the M re-Tr ndelag Fault Complex, Mid Norway

The M re-Tr ndelag Fault Complex (MTFC) has controlled the tectonic evolution of Mid Norway and its shelf for the past 400 Myr through repeated reactivations during Palaeozoic, Mesozoic and perhaps Cenozoic times, the very last phase of reactivation involving normal to oblique-slip faulting. Despite its pronounced signature in the landscape, its deep structure has largely remained unresolved until now. We focused on two specific segments of the MTFC (i.e. the Tjellefonna and B verdalen faults) and acquired multiple geophysical datasets (i.e. gravity, magnetic, resistivity and shallow refraction profiles). A 100–200 m-wide zone of gouge and/or brecciated bedrock steeply dipping to the south is interpreted as being the Tjellefonna fault sensu stricto. The fault appears to be flanked by two additional but minor damage zones. A secondary normal fault also steeply dipping to the south but involving indurated breccias was detected ~1 km farther north. The B verdalen fault, ~12 km farther north, is interpreted as a ~700 m-wide and highly deformed zone involving fault gouge, breccias and lenses of intact bedrock. As such, it is probably the most important fault segment in the studied area and accommodated most of the strain during presumably Late Jurassic normal faulting. Our geophysical data are indicative of a B verdalen fault dipping steeply towards the south, in agreement with the average orientation of the local tectonic grain. Our findings suggest that the influence of Mesozoic normal faulting along the MTFC on landscape development is more complex than previously thought.