A tectonic model of the Offerdal—Olden area, Jämtland, Sweden

Abstract

The geology of a narrow traverse running NW. from Offerdal towards the Swedish—Norwegian border is described. Imbrication structures consisting of slices of basement rocks, quartzites, limestones and graywackes are found in the eastern part. Similar structures, but predominantly of graywackes, appear in the central part and can befollowed to the border of the Olden massif. The author finds no support for the Föllinge Nappe and the Olden Nappe. The Olden massif is found to be autochthonous in most parts. The massif, and large portions of the parautochthonous graywackes, are overridden by the Offerdal Nappe, a composite unit of meta-arkoses, schists and mylonites, with Offerdal Schist at the top, then a polymict conglomerate, sometimes with quartzites, dolomites and shales (the Offerdal Conglomerate) and a silty shale at the bottom (the Rönnöfors Shale). The rocks of the Offerdal Nappe are of Precambrian age and have been correlated with the Rensjönäs Group, east of the Mullfjället basement window.