ALLOCHTHONOUS METAMORPHIC BLOCKS ON THE HEBRIDEAN PASSIVE MARGIN, SCOTLAND

Radiometric age determinations on syn-orogenic intrusive rocks coupled with evidence from field relationships, indicate that metamorphism an d ductile deformation was taking place in the Scottish metamorphic blo cks coeval with extension on the Hebridean foreland. Consequently meta morphic rocks now found east and south of the Moine Thrust are regarde d as substantially allochthonous, being located within the region wher e there was formerly a Cambrian-Early Ordovician passive margin sequen ce and its attendant oceanic crust. We regard these blocks as displace d terranes which acquired their metamorphic and structural signatures outside of the present Hebridean foreland regime. This may have occurr ed initially at the time of megacontinent splitting and later on the d estructive margin which was initiated in Laurentia.