Short Paper: The depositional age of the Dalradian Supergroup: U-Pb and Sm-Nd isotopic studies of the Tayvallich Volcanics, Scotland

Zircons from a keratophyre associated with the Tayvallich Volcanics in the Dalradian rocks of the SW Scottish Highlands have been dated by U-Pb methods, yielding an age of 595 ± 4 Ma. This age indicates that most or all of the Dalradian is Precambrian in age, and that Dalradian sedimentation may have lasted for about 200 million years. The age also constrains the time interval between cessation of Dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the Grampian Orogeny. Sm-Nd isotopic data for the Tayvallich Volcanins and related metadolerite sills yield initial oNd values of +2 to +4, which are thought to reffect the effects of melting of lithospheric mantle.