Using geophysical methods to characterize the Møre- Trøndelag Fault Complex, Mid Norway

Møre-Trøndelag Fault Complex (MTFC) is one of the most prominent fault complexes in Scandinavia. The MTFC appears to have controlled the tectonic evolution of Mid Norway and its shelf for the past 400 Myr and has experienced repeated reactivation during Paleozoic (Devonian to Permian), Mesozoic (Jurassic) and presumably Cenozoic times. Geological and geophysical observations demonstrate that the MTFC exerted a strong control in shaping the basins offshore but also in influencing the development of the landscape onshore, and continues today in modifying the regional stress pattern. Regional gravity and aeromagnetic data are used to map regional-scale faults and, in particular, to delineate the main geophysical features related to the MTFC. The advantage of potential field data is to provide an almost continuous coverage and to tie bedrock mapping onshore to seismic interpretation offshore. Potential field transformations were applied to focus on the regional and deep-seated structures in order to extract new geological information. Also the tilt derivative technique (TDR) is applied to gravity and magnetic data with the aim of enhancing linear trends. The results indicate the possible onshore-offshore links of large scale structural elements like the MTFC and late-Caledonian detachments (e.g. Kollstraumen Detachment). The locations of different segments of the MTFC are detected and possible new faults/lineaments are depicted. Correlating petrophysical data with gravity and magnetic maps explains the influence of the MTFC on the deformation and mineralization of bedrock along its strike. In addition, the structural pattern seen in the enhanced lineaments is diagnostic for the sinistral strike-slip movements that are known to have occurred in Devonian time along the MTFC. This confirms the important role of the MTFC in the tectonic setting and geological evolution of Mid Norway. Regional gravity and aeromagnetic data are used for mapping the MTFC at the regional scale, while new and multidisciplinary geophysical data sets such as 2D resistivity, gravity, magnetic and seismic profiles are utilized to characterize one of the fault zones in a much more focused area. Rock sampling and petrophysical measurements on densities, suceptibilities and seismic velocities constrain the geophysical models. 2D models are built from selected local profiles in order to provid

A new tectonic model for the Palaeoproterozoic Kautokeino Greenstone Belt, northern Norway, based on high-resolution airborne magnetic data and field structural analysis and implications for mineral potential

The Palaeoproterozoic Kautokeino Greenstone Belt (KkGB) is a highly tectonised metasupracrustal belt sandwiched between the gneissic R\ue1iseatnu Complex to the west and the metaplutonic Jergul Complex to the east. The KkGB has been interpreted as an Early Proterozoic rift basin inverted during the Svecofennian orogeny (c. 1.9-1.7 Ga). The structural framework and tectonic development of the KkGB remain poorly investigated and understood. New airborne magnetic and structural data help to unravel the belt\ub4s architecture and tectonic evolution, allowing its subdivision into two tectonic compartments. The eastern part shows NE-SW-trending, weak magnetic anomalies. The western part has pronounced NNW-SSE-trending anomalies. In the Jergul Complex, to the east of the KkGB, only relatively weak but pervasive NE-SW-trending anomalies are observed, similar to those in the eastern KkGB. These are locally deflected into NNE-SSW sets of discrete anomalies with a dextral offset. These two anomaly sets in the east are truncated by a pervasive set of NNW-SSE-trending strong anomalies in the western KkGB. The Jergul and R\ue1iseatnu Complexes display different aeromagnetic signatures suggesting that they are different terranes juxtaposed along the KkGB. Field structural analysis supports our interpretation of the geophysics. The eastern NE-SW-trending KkGB and the Jergul Complex contain flat-lying, west-dipping, NE-SW-trending shear zones accommodating dip-slip, top-to-the-east thrusting. The western NNW-SSE-trending KkGB is characterised by steeply dipping shear zones with both dip-slip and strike-slip kinematics. Strike-slip shear zones are predominantly sinistral, but coexisting sinistral and dextral kinematics are commonly observed together with steeply plunging lineations suggesting a degree of horizontal flattening. The NNW-SSE-trending shear zones, corresponding to the NNW-SSE-trending magnetic anomalies, form a mega-sinistral array truncating and sinistrally deflecting the earlier thrust structures. The KkGB is geometrically and kinematically similar to other Archaean-Palaeoproterozoic basement domains in northern Norway. Gold mineralisation at the Bidjovagge mine is genetically related to deformation along the NNW-SSE-trending ductile shear zone of the western KkGB

Geophysical characterisation of two segments of the Møre-Trøndelag Fault Complex, Mid-Norway

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

Break-up and seafloor spreading domains in the NE Atlantic

An updated magnetic anomaly grid of the NE Atlantic and an improved database of magnetic anomaly and fracture zone identifications allow the kinematic history of this region to be revisited. At break-up time, continental rupture occurred parallel to the Mesozoic rift axes in the south, but obliquely to the previous rifting trend in the north, probably due to the proximity of the Iceland plume at 57-54 Ma. The new oceanic lithosphere age grid is based on 30 isochrons (C) from C24n old (53.93 Ma) to C1n old (0.78 Ma), and documents ridge reorganizations in the SE Lofoten Basin, the Jan Mayen Fracture Zone region, in Iceland and offshore Faroe Islands. Updated continent-ocean boundaries, including the Jan Mayen microcontinent, and detailed kinematics of the Eocene- Present Greenland-Eurasia relative motions are included in this model. Variations in the subduction regime in the NE Pacific could have caused the sudden northwards motion of Greenland and subsequent Eurekan deformation. These events caused seafloor spreading changes in the neighbouring Labrador Sea and a decrease in spreading rates in the NE Atlantic. Boundaries between major oceanic crustal domains were formed when the European Plate changed its absolute motion direction, probably caused by successive adjustments along its southern boundary.</p

Palaeoproterozoic foreland fold-thrust belt structures and lateral faults in the West Troms Basement Complex, northern Norway, and their relation to inverted metasedimentary sequences

Palaeoproterozoic fold-thrust belt structures and steep, lateral shear zones characterize the foreland deformation of Neoarchaean basement tonalites in Vanna, West Troms Basement Complex, northern Norway. Low-grade par-autochthonous and allochthonous cover units (2.4–2.2. Ga) with sandstones and calcareous metapelites exist in separate areas of the foreland. They were formed as intracontinental rift- and/or deltaic shelf deposits, and subsequently intruded by a diorite sill at c. 2.2 Ga. The basement and cover units were folded and inverted along low-angle thrusts and steep reverse faults during two late/post Svecofennian (1.77–1.63 Ga) orthogonal shortening events (D1-D2). The D1 event involved NE-SW shortening, folding, ENE-directed thrusting, and dextral lateral shearing, controlled by pre-existing, N-S striking mafic dykes (c. 2.4 Ga) and basin-bounding normal faults. The D2 event involved SE vergent nappe translation, flat-ramp thrust propagation in a frontal duplex above a basement-seated detachment, and sinistral lateral reactivation in a partitioned orogen-parallel, transpressive setting. Hydrothermal fluid circulation affected all the shear zones. New aeromagnetic data show the basement-involved fold-thrust belt architecture well. The orthogonal Vanna Island fold-thrust belt styles of deformation resemble other inverted rift-basin deposits in northern Fennoscandia, deformed during the Svecofennian Orogeny (1.92–1.79 Ga), Alta-Kautokeino and Karasjok greenstone belts in northern Norway, Central Lapland, Peräpohja, Kittilä and Kuusamo belts of Finland, and in the Norrbotten province of Sweden. Westward younging of the orogenic events explain the younger age span of deformation on Vanna Islan