PRECISE AR-40 AR-39 AGE FOR THE INITIATION OF PALEOGENE VOLCANISM IN THE INNER HEBRIDES AND ITS REGIONAL SIGNIFICANCE/

Sanidine crystals from two tuff layers at the base of the Palaeocene E igg Lava Formation on the Isle of Muck, Inner Hebrides, yield step-wis e Ar release plateau ages of 62.8+/-0.6 (2 sigma) and 62.4+/-0.6 Ma us ing the laser Ar-40/Ar-39 dating technique. These determinations, whic h are in accord with, but significantly more precise than earlier resu lts, provide a definitive age for the inception of igneous activity in the Small Isles. From stratigraphical inferences, the Muck ages provi de precise, maximum constraints on the possible age of Skye magmatism and possibly most of the British Tertiary Volcanic Province. The new a ges significantly predate the oldest ages determined so far for Tertia ry magmatism in NE Greenland but are similar to ages obtained from W G reenland and offshore SE Greenland and support the concept that the in itiation of regional volcanism was primarily controlled by lithospheri c thin spots. The Muck sanidine age appears to precisely date the firs t manifestation of the impingement of the Iceland mantle plume on the lithosphere beneath NW Scotland.