Rare earth element geochemistry of upper Ordovician cherts from the Southern Uplands of Scotland

Caradoc and Ashgill radiolarian cherts and siliceous mudstones from the Sou thern Uplands preserve primary rare earth element (REE) signatures which ar e comparable to those of more recent deposits from continental margin setti ngs. This is incompatible with the widely held view of these rocks as open ocean deposits incorporated in an accretionary prism and reinforces the mod el of deposition on an extensional continental margin. The REE signatures c an be used as fingerprints to differentiate between some of the fault-bound ed formations within the area. They indicate the provenance of the mud grad e siliciclastic material in these distal hemipelagites and are comparable w ith published REE data on greywackes in the same successions. This detailed analysis of the REE patterns in Lower Palaeozoic cherts demonstrates the u sefulness of this approach in ancient orogens.