Abstract
Abstract. The Møre-Trøndelag 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 Bæverdalen 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 Bæverdalen 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 Bæverdalen 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.
Highlights
The Møre-Trøndelag Fault Complex (MTFC, Fig. 1), Mid Norway, is a long-lived structural zone whose tectonic history has involved repeated reactivation since Caledonian times (e.g. Grønlie et al, 1994; Watts 2001)
We present the results of the acquisition of several geophysical datasets across two of the major segments of the MTFC, the so-called Tjellefonna and Bæverdalen faults (Fig. 1), and discuss their significance in terms of the geological evolution of the area
The Tjellefonna fault sensu stricto is interpreted as a 100–200 m-wide zone of gouge and/or water-saturated, fractured bedrock dipping steeply to the south
Summary
The Møre-Trøndelag Fault Complex (MTFC, Fig. 1), Mid Norway, is a long-lived structural zone whose tectonic history has involved repeated reactivation since Caledonian times (e.g. Grønlie et al, 1994; Watts 2001). The MTFC appears to have controlled the evolution of both the oil-rich basins offshore (Brekke, 2000) and the rugged landscape onshore (Redfield et al, 2005) It strikes ENE-WSW, paralleling the coastline of Mid Norway southwest of Trondheimsfjord, and separates the northern North Sea basin system from the deep Mesozoic Møre Basin (Brekke, 2000). The fault cores themselves are, in general, not exposed and their respective traces can only be seen as topographic lineaments (Fig. 1) Their exact locations, extents, widths and dips remain, with the exception of the Hitra-Snasa and Verran faults on Fosen Peninsula (e.g. Grønlie and Roberts, 1989), in most cases speculative and have not been studied systematically by means of geophysical methods
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