A radiometric study of polymetamorphism in the Bamble region,Norway

Metamorphism-induced parent-daughter isotopic rearrangement yields information concerning the nature and duration of metamorphism in the Bamble Area, Southern Norway. The thermal maximum of the Bamble Sveconorwegian metamorphism was reached at 1160–1200 m.y. ago, according to zircon and sphene U-Pb, and Rb-Sr whole rock results. Dating of post-kinematic pegmatites suggests that the major kinematic episodes took place not much more than 100 m.y. and that not until more than 200 m.y. after the thermal maximum had uplift and cooling resulted in closure of the K-Ar system in micas. Petrological considerations together with radiometric data on the Levang Gneiss Dome suggest that Rb-Sr whole rock samples show open and closed system behaviour under similar temperatures but possibly different . Variable recrystallization of zircon in the Levang Gneiss Dome (when taken with accompanying radiometric U-Pb data) appears to substantiate the idea that when = P _solid, resetting of both the U-Pb systems in zircon and Rb-Sr whole rock systems is greatly facilitated.