STRUCTURAL OUTLINE OF A TERTIARY BASEMENT-CORED UPLIFT INVERSION STRUCTURE IN WESTERN SPITSBERGEN, SVALBARD - KINEMATICS AND CONTROLLING FACTORS

The Tertiary fold-and-thrust belt of Spitsbergen can be divided into a western basement-involved fold-thrust stack and a central-eastern-for eland fold-and-thrust belt. In western Nordenskiold Land the first-ord er structure is an ENE-verging basement-cored fold and fault complex i nvolving Paleozoic to Tertiary strata. The northern part reveals an up right, monocline geometry of east tilted sedimentary cover units with associated layer parallel to low-angle thrusts and folds. These struct ures consist of two populations oriented both parallel to (NNW-SSE) an d oblique to (WNW-ESE) the general structural trend of the fold comple x. In the central and southern parts of west Nordenskiold Land the fol d complex involves tilted basement cut by steep, transverse faults and late normal faults. The east limb of the fold complex displays repeat ed basement and Paleozoic strata (Orustdalen formation) in its core an d 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 relat ions includes a three-stage structural history in the fold complex as follows: (1) a phase of early NNE-SSW shortening associated with WNW-E SE folds and thrusts and (2) a dominant ENE-WSW, basement-involved sho rtening leading to the first-order, NNW-SSE-striking fold complex, fol lowed by (3) approximately E-W extension. The resulting structures and structural variability along strike as well as across strike appear t o have been controlled by basement and Carboniferous basin structures underlying the Permian-Cretaceous platform strata. Restored stratigrap hic sections based on thrust- repetition of basement and cover (e.g., within a type section of the Carboniferous Orustdalen formation) suppo rt such an interpretation. A tentative inversion tectonic model reprod uces the position(s) of local and major thrust ramps and associated fo lds, as a result of inheritance from Carboniferous basin structures.