Abstract
The effects of progressive metamorphism (Grampian orogeny) and later tectonic activity on detrital zircon in the Barrovian zones of Scotland were studied using secondary ion mass spectrometry (SIMS) and backscattered electron imaging (BSE). Fifteen samples recording progressive metamorphism from the chlorite through the sillimanite–K-feldspar zones were investigated by: (1) SIMS U-Pb depth profiling into rims of unpolished zircon grains to analyze sub-micrometer-scale features, and (2) conventional spot analysis on sectioned and polished grains. Spot analyses of zircon interiors yield pre-metamorphic detrital ages for all metamorphic grades. Most are in the range ca. 600 to ca. 2000 Ma, but some stretch back to the Archean. Younger ages are recorded in zircon rims, but zircon rim alteration at lower metamorphic grades occurs over much shorter length scales (the outer ~80 nm to ~1 μm of the grain) than in the upper amphibolite to granulite facies (rims of 10 to 30 μm). For example, Grampian (~470 Ma) metamorphism from the garnet and kyanite zones affected only the outermost rims (
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