Geologiske og petrografiske undersøkelser i området Tynset-Femunden.

Abstract

The present paper is a description of the geology and petrology of the map quadrangle 38 C, Tynset, in southern Norway. Within the map Tynset we find the border between the large S.E.-Norwegian sparagmite area and the Cambrian and Silurian rocks of the \"Trondhjemsfeltet\". In isolated areas, pre-Sparagmitean rocks appear. They are of igneous habit and do not throw much light upon the archean of this region, which is mostly composed of red granites. The granites can be divided into two groups: in one of them chess-board albite is very common; the other consists of regular microcline granites. However, the youngest among the pre-Sparagmitean rocks are coarse-grained dolerites, very similar to the Jotnian dolerites of Sweden and Finland, with which they are correlated by the present writer. Upon the probable Archean and Jotnian lies a thin autochthoneous series of Sparagmitean age. The oldest autochthoneous member of this series seems to be a tillite-bearing horizon, wellknown from many parts of the Caledonian range. The tillite is most strongly deformed by Caledonian movements, but it nevertheless displays easily recognisable large boulders of granite of the same type as that which is found within the pre-Sparagmitean areas of the Tynset map, as well as boulders of a quartzite unknown to any neighbouring area in southern Norway.