The Laxfordian structure of the Kenmore inlier, Loch Torridon, Ross Shire

Abstract

Detailed mapping has been carried out of an area l2sq.km in extent around Kenmore on the south side of Loch Torridon together with a reconnaissance traverse on the north side of Loch Torridon in Diabaig. The Kenmore area exhibits particularly strong Laxfordian deformation. Foliated grey and pink granodioritic gneisses form the main body of the complex giving a banded appearance. Scourie dykes are present in the form of amphiboliticbands which are mainly strongly foliated. Isolated layers and pods of early amphibolite and probably metasedimentary rocks are also present. Pre-Inverian structures are rare but Inverian foliation is quite strong and has been variably transposed in Laxfordian deformations. The first Laxfordian deformation is the main fabric-producing event in the Scourie dykes and produced a strong LS fabric with subvertical NW-SE oriented foliation and subhorizontal lineation. The second Laxfordian deformation produced abundant minor folds with subhorizontal axial surfaces and NW-SE oriented hinges. The folds have a close to similar geometry and have a good axial-planar fabric. The third Laxfordian deformation produced upright NW-SE oriented folds with a near parallel style, generally without an associated fabric. All three deformations are generally co-axial. Later deformations which were localized and mild produced cross-folds and breccia zones. Two lower amphibolite-facies metamorphic episodes M1 and M2 were syntectonic with the first and second Laxfordian deformations respectively. Localized recrystallisation of low grade minerals after M2 was probably partly syntectonic with the third Laxfordian deformation. Qualitative strain analysis using grain aggregates in Scourie dykes and fold profile shape shows a highly variable bulk strain pattern due mainly to the heterogeneous and locally very large Dl strains associated probably with a steep dextral shear zone. D2 in contrast appears to be due to a low-angle shear zone with a northwards transport direction.