Interplay of proximal and distal sources in Devonian–Carboniferous sandstones of the Clair Basin, west of Shetland, revealed by detrital zircon U–Pb ages

Abstract

The Clair Basin is one of the Devonian sedimentary basins formed as a result of extensional tectonics in the aftermath of the Caledonian orogeny. The Devonian to Carboniferous Clair Group was deposited directly on Archaean basement, providing an opportunity to consider contrasting proximal and distal provenances. New secondary ion mass spectrometry detrital zircon U–Pb data and complementary heavy mineral data allow for a reinterpretation of potential source areas. Detrital zircons from the Clair Group yield ages ranging from c . 400 to 3700 Ma. All samples contain a group of Archaean ages ( c . 16–82%). However, many samples also contain a major group of Proterozoic zircons ( c . 15%–78%), allowing subdivision into two types of samples: type 1, dominated by Proterozoic zircons, and type 2, dominated by Archaean zircons. Type 2 samples are mainly derived from local basement gneisses during phases of tectonic rejuvenation of the hinterland, whereas type 1 samples are most probably sourced from NE Greenland or, less likely, SW Scandinavia. Upper Clair Group (Unit VII–IX) sandstones have type 2 zircon spectra in association with staurolite- and garnet-rich heavy mineral assemblages and were probably derived from predominantly Archaean-sourced metasedimentary rocks on the Shetland Platform. Supplementary materials: Concordia diagrams and tables reporting zircon U–Pb data are available at http://www.geolsoc.org.uk/SUP18542.