U-Pb zircon data from newly discovered granulite-facies rocks on Hisarøya, Gulen, Western Norway, yield a discordia line with upper and lower intercepts of 1646 ± 110 Ma and 987 ± 10 Ma, respectively. The upper intercept age overlaps with Gothian ages previously obtained from the Western Gneiss Complex and is interpreted to date a magmatic growth episode of the Baltic Shield, while the lower intercept age, anchored by a concordant rim analysis, is interpreted to date a Sveconorwegian granulite-facies event. A concordant U-Pb monazite age of 949 ± 3 Ma documents late stages in the prolonged Sveconorwegian metamorphism. We suggest that the granulite-facies rocks on Hisarøya, together with similar rocks on Bårdsholmen, Sunnfjord, form remnants of a once much larger granulite-facies terrane.
Sveconorwegian U-Pb zircon and monazite ages of granulite-facies rocks, Hisarøya, Gulen, Western Gneiss Region, Norway