Structural outline of a Tertiary Basement‐cored uplift/inversion structure in western Spitsbergen, Svalbard: Kinematics and controlling factors

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Abstract
The Tertiary fold‐and‐thrust belt of Spitsbergen can be divided into a western basement‐involved fold‐thrust stack and a central‐eastern foreland fold‐and‐thrust belt. In western Nordenskiøld Land the first‐order structure is an ENE‐verging basement‐cored fold and fault complex involving Paleozoic to Tertiary strata. The northern part reveals an upright, monocline geometry of east tilted sedimentary cover units with associated layer parallel to low‐angle thrusts and folds. These structures consist of two populations oriented both parallel to (NNW–SSE) and oblique to (WNW–ESE) the general structural trend of the fold complex. In the central and southern parts of west Nordenskiøld Land the fold complex involves tilted basement cut by steep, transverse faults and late normal faults. The east limb of the fold complex displays repeated basement and Paleozoic strata (Orustdalen formation) in its core and Mesozoic (Triassic) strata influenced by map‐scale chevron folds and two decollement levels, all located above an eastward rotated, major detachment fault, the Kleivdalen Thrust. Establishing fold‐fault relations includes a three‐stage structural history in the fold complex as follows: (1) a phase of early NNE–SSW shortening associated with WNW–ESE folds and thrusts and (2) a dominant ENE–WSW, basement‐involved shortening leading to the first‐order, NNW–SSE‐striking fold complex, followed by (3) approximately E–W extension. The resulting structures and structural variability along strike as well as across strike appear to have been controlled by basement and Carboniferous basin structures underlying the Permian‐Cretaceous platform strata. Restored stratigraphic sections based on thrust‐repetition of basement and cover (e.g., within a type section of the Carboniferous Orustdalen formation) support such an interpretation. A tentative inversion tectonic model reproduces the position(s) of local and major thrust ramps and associated folds, as a result of inheritance from Carboniferous basin structures.
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