UPLIFT OF SOUTHWESTERN SWEDEN - IMPLICATIONS FROM THE ORTHOCLASE-MICROCLINE TRANSFORMATION IN THE HINNERYD GRANITE

The Hinneryd granite is a strongly deformed adamellitic ganitoid in th e southern part of the SW Scandinavian Gneiss Complex. The area has be en exposed to a late granulite-facies metamorphic event. The X-ray obl iquity (''triclinicity'') of its potash feldspar was determined by app lying precision, step-scan X-ray diffraction to measure the splitting of the (131)-(1 $($) over bar$$ 31) and the (130)-(1 $($) over bar$$ 3 0) doublets. Twenty-one samples were investigated. Eleven of them reve al a well-defined or slightly broadened, single orthoclase (131) refle x. The (130) reflex is significantly more broadened than the (131) ref lex. A clearly split doublet is found only in four samples. The reflex es of these four and the remaining six samples are broad and cannot be accurately defined. This is interpreted to be due to an incomplete tr ansformation from orthoclase to microcline. The data suggest that the strong deformation of the granite took place close to the peak tempera ture 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.