The structural history of the Lewisian rocks north-west of Loch Tollie, Ross-shire, Scotland

Abstract

In the Lewisian rocks north-west of Loch Tollie corresponding deformation during three successive phases of the Laxfordian orogeny is shown in meta-sediments, hornblende-schists, amphibolites and acid gneisses. Isoclinal folds, some drag folds and open folds and associated axial planar schistosity/foliation and mineral and intersection lineations were developed during the main phase of deformation. Asymmetrical folds, of which the Tollie anticline is the most prominent, refold the isoclinal folds and the associated main phase structures. Antiforms predominate, the synforms being largely represented by shear-belts. This mid phase deformation produced the dominant N.W.-S.E. trend of the lithological layers and the main phase foliation and the pattern of alternating belts of south-easterly and north-westerly plunging main phase lineation. After the emplacement of acidic veins and sheets, late phase deformation resulted in the development of steeply-plunging brittle folds and shear-belts with pseudo-tachylite.