Basement–cover relationships and structure within the Moine rocks of central and southeast Sutherland

Abstract

Inliers of Archaean to early Proterozoic Lewisian basement crop out within the Proterozoic Moine Succession of central and SE Sutherland. Both the Lewisian basement and the Moine cover have been affected by two major tectonic events. The earliest event probably occurred during the late Proterozoic and involved minor folding and upper greenschist to upper amphibolite facies metamorphism. Intense deformation largely obliterated the unconformable relationship between the Lewisian and Moine rocks, and imposed a planar banding on the basement lithologies. Subsequent reworking during the Caledonian orogeny (500–400 Ma) resulted in ductile thrusting and folding, and was associated with a widespread low- to mid-amphibolite facies metamorphic overprint. Within this context the Lewisian inliers of central and SE Sutherland occur in two distinct structural settings: (i) as allochthonous sheets which rest on major Caledonian ductile thrusts; (ii) in the cores of NW-verging intensely curvilinear sheath folds of Caledonian age.