RE-OS DATING OF CU-MO MINERAL OCCURRENCES PROVIDES CHRONOLOGY OF METAMORPHISM AND DEFORMATION FOR A SUPRACRUSTAL SEQUENCE IN SOUTH NORWAY

We employ Re-Os dating of molybdenite from small abandoned mines and prospects to track the timing of regional metamorphism and deformation in south Norway. In the western allochthonous lithotectonic domain of the Sveconorwegian orogen (Rogaland-Hardangervidda), nine molybdenite samples from two small Cu-Mo mineral occurrences in the epidote-amphibolite facies Sæsvatn supracrustal sequence provide a temporal record of metamorphism and deformation from 1.05 to 1.01 Ga. Onset of metamorphism occurred at about 1047 ± 2 Ma, as recorded in small gash veinlets with incipient folding. Peak deformation occurred at about 1032 ± 2 Ma, as recorded in mineralized breccia and mineralized metagabbro in a ductile shear zone constituting the Langvatn deposit. Deformation waned significantly by about 1017 ± 2 Ma, based on mineralization hosted in a brittle fault zone within stratigraphically higher metabasalts exposed at the Kobbernuten deposit. A metamorphic origin for the Cu-Mo mineralization is supported by (1) an array of Re-Os ages that can be related to structural features and stratigraphic sequence, (2) the absence of time- and space-related plutons, (3) the confinement of ore occurrences to mafic sequences in a bimodal supracrustal package that includes rhyolites and clastic units, and (4) clear evidence for Cu mobility in metasomatized gabbro and basalt. The "main" Sveconorwegian orogenic event, probably a continent-continent collision involving imbrication, stacking, and burial of terranes, took place at about 1.05 Ga and thereafter. The results of this study indicate that comparatively low grade domains in the orogen (greenschist- to epidote-amphibolite-facies), corresponding to upper crust, were deformed in a ductile fashion at about 1.03 Ga and were affected by brittle deformation as early as 1.025-1.015 Ga. In the high-grade domains (amphibolite- to granulite-facies), corresponding to middle and lower crust, ductile deformation is younger, beginning at about 1.025 Ga and persisting until 0.97 Ga (Bingen and van Breemen 1998). With this study, we use Re-Os geochronology applied to economically insignificant mineralization to unravel regional tectonic and metamorphic history. This is an essentially unexplored application and links the field of economic geology to other major disciplines in geology.