Abstract The Nordland area in northern Norway is the seismically most active area on mainland Fennoscandia. It exhibits patterns of coastal extension, which contrasts with the first-order regional stress pattern that reflects compression aligned with the North Atlantic ridge push. The regional stress field has been considered to emanate from the interaction of ridge push and glacial isostatic adjustment; while the local stress pattern can be additionally influenced by gravitational, topographic stresses, as well as the flexural effects of erosion and sediment deposition. We employ finite element numerical models at a crustal scale to study the 3D stress field, using existing geometric constraints from previous geophysical studies. Internal body forces, induced by variations in density, topography or Moho depth, already yield significant deviatoric stresses. In the models tested, these can strongly influence the near-surface stress regime, in particular for the continental margin setting we are investigating. In addition, redistribution of rock mass, which occurred mainly under Pleistocene glaciation, can modify the stress field significantly on a semi-regional scale. We consider this process to be the main driver for the coastal extension, in particular in areas where erosion has been high.

ABSTRACT The Seve Nappe Complex in the Scandinavian Caledonides records a range of peak metamorphic conditions and timings. To better understand pressure-temperature-deformation-time differences throughout the complex and possible tectonic scenarios, metamorphosed mafic rocks within the Tarfala Valley of the Kebnekaise Massif (Sweden) were investigated using integrated petrologic and geochronologic techniques. Thermodynamic modeling of two samples using domainal and whole-rock compositions integrated with mineral chemistry, mineral textures, and titanite and zircon U-Pb geochronology constrained a portion of the pressure-temperature ( P-T ) path. Peak metamorphic conditions of 590–660 °C and 9.7–10.5 kbar were followed by near-isothermal decompression or a subsolidus clockwise P-T path. Amphibolite units in the valley record retrograde conditions at 450–550 °C at less than 7.5 kbar, although mineral modes and textures are most consistent with pressures <4 kbar. The majority of titanite growth occurred due to the introduction of hydrous fluids during cooling and following exhumation to midcrustal levels. U-Pb ages of retrograde titanite define a spread from ca. 480 to 449 Ma, and the oldest age is interpreted to constrain the timing of retrogression following exhumation. This interpretation is supported by a U-Pb zircon crystallization age of 481 ± 7 Ma for a metamorphosed intermediate to felsic synkinematic dike hosted in one of the amphibolite units. These results indicate that the Kebnekaise region records Early Ordovician deformation and metamorphism that was of lower grade compared to other Seve Nappe Complex locations to the south. The tectonic history of these rocks includes metamorphism and exhumation during the Cambrian–Ordovician pre-Scandian event, followed by thrusting of the Seve Nappe Complex and neighboring rocks onto Baltica during the Silurian Scandian orogeny.