The structure and regional setting of the Skei Group, Leka, north-central Norway
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- Artikler 
The unconformity between the metasedimentary Skei Group and subjacent ophiolite on Leka has important implications for the tectonostratigraphy of the region. As a distinctive marker horizon, it permits correlations within and between nappes and provides a datum level on which to establish lithostratigraphies in the several units of the Helgeland Nappe Complex. The unconformity records a major change in the pattern of events and parti- tions the tectonothermal history into two polyphase orogenies, whose indivi- dual effects can be recognised in many nappes along the whole length of the belt. Deformations predating the unconformity relate to ocean-floor tectonics and a subsequent phase of regional tectonothermal development. The Skei Group records two fold phases accompanied by low-grade regional metamorphism. The distinctive lithostratigraphy facilitates delineation of macroscopic folds, whose geometry indicates that the whole outcrop lies within the inverted limb of the major D1 Leknes Syncline. This, in turn, controlled the altitude of mesoscopic D2 folds which are themselves para- sitic to the large-scale Austra Antiform, one of a regional system of near- symmetrical late folds which affect both the Helgeland Nappe Complex and its substrate. The litho- and tectonostratigraphic relationships established on Leka and extended to the adjacent mainland reiterate a theme currently being espou- sed for the evolution of the whole Scandian belt, namely dissection and disruption by Scandian thrusts of a cratonic substrate, already structured into a Finnmarkian and in part Late Ordovician nappe pile.