The X-ray obliquity of potassic feldspar in the granites of Jämtland, Northern central Sweden

Abstract

On the basis of the K-feldspar obliquity the graniroid plutonics in Jämtland can be subdivided into two principal groupings: one comprises rocks of the Svecofennian orogenic-to-early-postorogenic development and the other restricted intrusions of the Ragunda and Sörvik types. In the first group, which includes the Revsund and Rätan granites with associated migmatites, the K-feldspars are close to maximum microcline with obliquities above 0.8. Granitoids belonging to the Ragunda and Sörvik types have K-feldspars which range from mono-clinic through inhomogéneous to triclinic structural states. A large area of low obliquity in the orogenic rocks of northern Jämtland is liable to interpretation as a thermal-influence aureole around the postorogenic intrusions. The effect of rock-blasting on K-feldspar obliquity has been checked in samples obtained from road cuttings.