Evidence from the U–Pb–Hf signatures of detrital zircons for a Baltican provenance for basal Old Red Sandstone successions, northern Scottish Caledonides

Abstract

The provenance of Devonian Old Red Sandstone (ORS) continental successions in the northern Scottish Caledonides is poorly known: were they derived locally or from more distal sources? The integration of U–Pb and Hf isotope analyses in detrital zircon crystals reduces potential ambiguities arising from non-unique age populations and yields information on the crustal evolution of the source terranes. Samples of basal ORS successions yield zircon U–Pb age groupings of c. 1800–1500 and c. 1200–900 Ma, with minor Neoarchean, Tonian, Ediacaran and Ordovician contributions. SW Baltica provides the best match for detrital zircon ages and Hf isotopic signatures and much of the >900 Ma zircon population was probably recycled from Neoproterozoic successions. ε Hf ( t ) values in c. 1800–1000 Ma grains reflect the assembly of Nuna, the development of a long-lived retreating subduction system along its margin and Grenville collisional orogenesis. These basal ORS successions were probably deposited within the same regional fluvial system as coeval sedimentary rocks in the Midland Valley, draining an area of positive relief in SW Baltica where continental convergence continued through the Early Devonian. Supplementary material : Isotopic data, statistical comparison of selected samples and TIMA heavy mineral data are available at https://doi.org/10.6084/m9.figshare.c.5301780

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