A Caledonian age for the Kiloran Bay appinite intrusion on Colonsay, Inner Hebrides

Synopsis A sample of hornbendite from the Kiloran Bay intrusion on the island of Colonsay in the Inner Hebrides, previously of uncertain age, has yielded a U-Pb zircon SHRIMP age of 439.0 ± 8.8 Ma (2σ). This age is the same, within error, as the Caledonian Appinite Suite on the Scottish mainland. The distinctive geochemical characteristics of the Appinite Suite, high Mg, K, Cr, Ni, Sr, Ba and the light REE, are faithfully reproduced in the Kiloran Bay intrusion. There are no published Sr and Nd isotopic data for the Appinite Suite, but the Rb-Sr and Sm-Nd isotope systematics of the Kiloran Bay rocks are comparable with the late Caledonian Granites. Proterozoic (1.7 Ga) Nd model ages and inherited zircons indicate the involvement of old crusta material during magma genesis. Correlation of the Kiloran Bay intrusion with the Appinite Suite supports a Colonsay Group–Dalradian Supergroup correlation. However, difficutlies remain in correlating the structural history of the two successions and a stratigraphic link cannot be proven.