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Localized granulite and eclogite facies metamorphism at Flatraket and Kråkeneset, Western Gneiss Region: U–Pb data and tectonic implications

Abstract The Flatraket Complex, in the ultra-high-pressure (UHP) domains of the Western Gneiss Region (WGR) of Norway, preserves granulite facies assemblages, which were locally overprinted by eclogite and amphibolite facies metamorphism. Zircon and monazite indicate magmatic crystallization of the rocks at 1680–1640 Ma and constrain the timing of the granulite facies overprint at 1100 Ma. This age is older than previously reported ages of 1000–950 Ma for regional metamorphism reaching anatexis and locally granulite facies in the WGR. The granulites at Flatraket may have developed as a consequence of local metasomatism, perhaps linked to metasomatism occurring at the same time in the nearby Sandvik peridotite. Granitic rocks from neighbouring Kråkeneset indicate magmatic emplacement at ≥1650 Ma, during the event that formed the Flatraket Complex and the bulk of the WGR. A gabbro body at Kråkeneset is dated at 1255±8 Ma by baddeleyite, which was not affected by the granulite event, implying that the rock remained impermeable to fluids, reacting instead to some degree during the Caledonian UHP event.