Low-temperature effects of the Skye Tertiary intrusions on Mesozoic sediments in the Sea of Hebrides Basin

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Abstract
Fission track analysis of samples from the Sea of Hebrides Basin and surrounding regions demonstrates two very distinct age groups around 50 Ma and 300 Ma, regardless of the stratigraphic age. Apatite fission track results from sediments within 8 km of the Tertiary igneous complex on Skye were totally reset by temperatures >110°C during intrusion of the centres, but now yield ages younger than the granites. Zircon fission track results from the granites also demonstrate ages significantly younger than their hosts. Mean track lengths in apatites of <13.5 µm, and reduced apatite and zircon ages, suggest that temperatures remained elevated throughout the 6 Ma during which intrusive activity occurred, but were hotter within the granite bodies than the surrounding sediments. Prior to intrusion of the complex, temperatures in the basin sediments presently at outcrop were unlikely to have been higher than 50°C, and beyond the effects of the Tertiary intrusions, age and track length distributions from northern Skye, the Isle of Lewis and the west coast of Scotland illustrate that the area is unlikely to have been buried beneath more than 2 km of sediment at any one time since the end of the Devonian. North of the Highland Boundary Fault, Tertiary uplift and erosion in Scotland is considered to have been between 1–1.5 km. This is consistent with a regional pattern of Tertiary erosion identified across the British Isles, but considerably less than that recognised in Northern England.