A CALEDONIAN AGE FOR THE KILORAN BAY APPINITE INTRUSION ON COLONSAY, INNER HEBRIDES

A sample of hornblendite from the Kiloran Bay intrusion on the island of Colonsay in the Inner Hebrides, previously of uncertain age, has yi elded a U-Pb zircon SHRIMP age of 439.0 +/- 8.8 Ma (2 sigma). This age is the same, within error, as the Caledonian Appinite Suite on the Sc ottish mainland. The distinctive geochemical characteristics of the Ap pinite Suite, high Mg, K, Cr, Ni, Sr, Ba and the light REE, are faithf ully reproduced in the Kiloran Bay intrusion. There are no published S r 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 inher ited zircons indicate the involvement of old crustal material during m agma genesis. Correlation of the Kiloran Bay intrusion with the Appini te Suite supports a Colonsay Group-Dalradian Supergroup correlation Ho wever, difficulties remain in correlating the structural history of th e two successions and a stratigraphic link cannot be proven.