Uplift of southwestern Sweden ‐ implications from the orthoclase‐microcline transformation in the Hinneryd granite

Abstract

Abstract The Hinneryd granite is a strongly deformed adamellitic granitoid in the southern part of the SW Scandinavian Gneiss Complex. The area has been exposed to a late granulite‐facies metamorphic event. The X‐ray obliquity (“triclinicity”) of its potash feldspar was determined by applying precision, step‐scan X‐ray diffraction to measure the splitting of the (131)‐(131) and the (130)‐(130) doublets. Twenty‐one samples were investigated. Eleven of them reveal a well‐defined or slightly broadened, single orthoclase (131) reflex. The (130) reflex is significantly more broadened than the (131) reflex. A clearly split doublet is found only in four samples. The reflexes of these four and the remaining six samples are broad and cannot be accurately defined. This is interpreted to be due to an incomplete transformation from orthoclase to microcline. The data suggest that the strong deformation of the granite took place close to the peak temperature during the granulite‐facies event. The uplift was rapid enough to prevent a microclinization of the orthoclase except for an incomplete transformation in volatile‐rich parts of the rock. Mannerstrand, M. & Lindh, A., 1995: Uplift of southwestern Sweden ‐implications from the orthoclase‐microcline transformation in the Hinneryd granite. GFF, Vol. 117 (Pt. 3, September), pp. 139–142. Stockholm. ISSN 1103–5897.