Tectonic history and mineralisation in the North Atlantic Craton: a view from Scotland

The Lewisian Gneiss Complex of North-west Scotland represents a c. 250 km x 150 km fragment of the North Atlantic Craton, comprising tonalite-trondhjemite-granodiorite (TTG) gneisses that were formed in the Archaean and successively reworked during the Palaeoproterozoic. This talk will review new work on the event history of the Lewisian, and its relationship to the wider North Atlantic Craton. A significant programme of zircon dating over the last two decades showed that the protoliths of the Lewisian Gneiss Complex TTG gneisses were formed in the Archaean (c. 3100-2800 Ma) and that different protolith ages occur in different terranes within the Lewisian Gneiss Complex (Kinny et al., 2005). Similar relationships have been recognised in the Archaean gneisses of Greenland. However, most Lewisian gneisses are characterised by a ‘smear’ of zircon ages along concordia between c. 3000 and 2500 Ma, and it is difficult to disentangle protolith and metamorphic ages. Mafic to ultramafic rocks, and some supracrustals, are locally associated with the TTG gneisses; their ages are uncertain, but they may represent the remnants of Archaean greenstone belts.