Geology and structure of the Dombås-Lesja area, southern Trondheim region, south-central Norway.
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Investigations in the southernmost part of the Trondheim region have established the presence of a new tectonic unit, the Andbergshøi Complex, interposed between the Trondheim Nappe and the Western Precambrian basement. This unit is represented mainly by Precambrian orthogneisses and an Eocabrian cover sequence. The lithostratigraphy within the Trondheim Nappe is divided into three main groups, each of which is subdivided into two or more formations. Lithostratigraphical correlations between the formations and groups in the present area and those in other parts of the Trondheim region (Gula Group, Støren or Fundsjø Group, Lower Hovin or Sulåmo Group) are proposed. The small-scale structures in the various tectonic units show up to five phases of deformation. All these phases are accompanied by mineral growth, the first three of which are the most penetrative. In the Trondheim Nappe, the first deformation and metamorphic episodes (F1\/M1) is rsticted to Gula Group lithologies. The metamorphic development during the Caledonian orogeny can be regarded as a combination of two types of metamorphism, which may be indicative of two major stages in the orogenic development of the region. The basal thrust plane of the Trondheim Nappe transects the major structures of the nappe (NE-trending open to tight F3 folds), as well as the metamorphic mineral zones developed during the Barrovian metamorphism.