Age resolution of peak metamorphism within the Caledonides of northern Scotland and Shetland

This project aims to define the timing(s) of peak metamorphism using Lu-Hf and Sm-Nd geochronology of garnets. The thesis focuses on the poly-metamorphic Northern Highland Terrane of Scotland and attempts to constrain the age of the many crustal deformation events. The project also uses Rb-Sr geochronology to date cooling. LA ICP MS and EPMA have been used to establish garnet compositions to determine if the ages yielded represent growth ages or cooling ages.
The research has shown that the currently understood model for the Caledonian orogeny in the Northern Highlands is over simplistic. Mid-Ordovician (Grampian) garnet growth ages have been recorded throughout the Moine Supergroup, including the Morar Group which indicates that the Northern Highlands shares the Grampian event recorded in the Dalradian Supergroup in Scotland and Ireland. Several samples provide evidence of a later garnet growth episode at ~450 Ma recorded within the Morar Group and part of the Glenfinnan. This study also demonstrates that the Neoproterozoic metamorphic events happened earlier than originally thought, with garnet growth recorded at ~950 Ma. This early garnet growth event recorded within the Morar Group also shows that deposition of these sediments must have ceased prior to 950 Ma. The Neoproterozoic metamorphic events can be split into several discrete episodes, with the Morar and Glenfinnan groups recording different events suggesting that they were tectonically distinct during the majority of the Neoproterozoic. This study also dated garnets within the basement inliers of the Moine Supergroup. The ages from the inliers show that there was an early Mesoproterozoic garnet growth event at ~1650 Ma which was recorded in an inlier in Sutherland and in Glenelg. Eclogite metamorphism within the Eastern Unit of the Glenelg-Attadale inlier has been dated at ~1200 Ma, which is significantly older than previous results.