Loch Laxford: the Lewisian Gneiss Complex (3)

Loch Laxford marks the boundary in the Lewisian Gneiss Complex between a region to the south, containing Scourian high grade metamorphic rocks with undeformed Scourie dykes, and a region from here northwards of lower metamorphic grade and rocks of different appearance, deformed and metamorphosed during the Laxfordian episode. Along this boundary (known by many geologists as the "Laxford Front") there are abundant sheets of pink granite and pegmatite, intruded about 1750 million years ago. They were evidently intruded into hot country-rock, and the metamorphic minerals in the gneisses here formed at about the same time.

Another road cut on the A838 north of Loch Laxford shows alternating layers of black mafic gneiss and grey felsic gneiss cut across by steeper-dipping sheets of granite and pegmatite. Notice how the pink pegmatites "pinch and swell" into bulbous shapes. These indicate that the rocks into which they were intruded were at the time very hot and quite soft.

Rock types at this locality

D.J. Waters, Department of Earth Sciences, May 2003