Strike-slip motion in the Minches, NW Scotland, deduced from the trends of the Scourie Dyke swarm

Abstract

In areas of low Laxfordian strain on the Scottish Mainland Lewisian, the strike of Scourie Dykes varies regionally; trending almost westerly in the north at Assynt and trending northwesterly in the south around Loch Torridon. These divergent trends allow an imaginary point to be constructed on the map at the intersection of these directions. In the Outer Hebrides a similarly variable arrangement of dyke trends is observed but the intersection point of the dyke trends does not coincide with that constructed for the Scottish Mainland. The non-coincidence of these intersection points is interpreted in terms of fault displacement and estimates are made of the combined slip on all faults in the Minch region (including the Minch and Outer Isles faults). Although the data are insensitive to possible dip-slip motions, they indicate a sinistral strike-slip component of between 34–145 km (90% confidence estimates) with a best estimate of 84 km. These results are in good agreement with those determined from the offset across the Minch of correlated metamorphic zones and those measured by the displacement of palaeomagnetic zones.