Tertiary West Spitsbergen fold and thrust belt on Brøggerhalvøya, Svalbard: Structural evolution and kinematics

The Tertiary fold and thrust belt on Brøggerhalvøya is characterized by a NE vergent pile of nine thrust sheets. The basal sole thrust of the pile is located in Precambrian phyllites and climbs up section to the NE. The lower thrust sheets consist predominantly of post‐Caledonian cover sediments. Two thrust sheets in the central part of the pile contain a syncline and anticline on a kilometer‐scale. The kilometer‐scale fold is cut by juxtaposed thrusts giving rise to the formation of four structurally higher basement‐dominated thrust sheets. A five‐stage kinematic model is proposed: (1) in‐sequence foreland propagating formation of the lower thrust sheets with ramp‐flat geometries in response to N‐S subhorizontal bedding‐parallel movements, (2) change in tectonic transport to more (east) northeasterly directions and first out‐of‐sequence thrusting, inversion, and uplift of the basement in the hinterland, formation of the kilometer‐scale fold structure, (3) truncation of the kilometer‐scale fold by a thrust fault and stacking of the highest basement‐dominated thrust sheets by hindward propagating mode of thrust generation, (4) N‐S extension due to extensional collaps of the stack, (5) W‐E extension. The strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheet reflecting a temporal change to a more transpressive regime. Ramping of some thrust faults is suggested to be in part controlled by reactivated Carboniferous normal faults. The basal sole thrust of the thrust sheet stack also follows the trend of the Kongsvegen fault which showed enhanced activity during late Mesozoic‐early Tertiary extension. The curvature of the West Spitsbergen Fold and thrust belt on Brøggerhalvøya is interpreted to be controlled mainly by oblique ramping on the Kongsvegen fault associated with pinning on the Nordfjorden Block as well as by along‐strike lithological and thickness variations of the post‐Caledonian strata in addition. This suggests that pre‐existing structures have controlled the Tertiary geometry. The temporal change in the kinematics during thrust tectonics can be linked with the plate tectonic framework in the Arctic during Tertiary times.