Radiometric age determinations on syn-orogenic intrusive rocks coupled with evidence from field relationships, indicate that metamorphism and ductile deformation was taking place hi the Scottish metamorphic blocks coeval with extension on the Hebridean foreland. Consequently metamorphic rocks now found east and south of the Moine Thrust are regarded as substantially allochthonous, being located within the region where there was formerly a Cambrian-Early Ordovician passive margin sequence and its attendant oceanic crust. We regard these blocks as displaced terranes which acquired their metamorphic and structural signatures outside of the present Hebridean foreland regime. This may have occurred initially at the tune of megacontinent splitting and later on the destructive margin which was initiated hi Laurentia.

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