Moine mylonite (folded), Moine Thrust Zone

Locality: Knockan Crag

Outcrop

Moine mylonite (folded), Moine Thrust Zone, Knockan Crag
The mylonites formed when the rocks in the Moine Thrust Zone were quite deep in the crust, and warm. As they were brought closer to the surface they deformed by bending rather than flowing, so many of the mylonites are now folded. This is what the folded banding looks like in outcrop.

Hand specimen

Moine mylonite (folded), Moine Thrust Zone, Knockan Crag
This sample has darker and lighter layers (mica-rich and quartz-rich) that have been compressed into a set of tight little folds.

Thin section

Moine mylonite (folded), Moine Thrust Zone, Knockan Crag
The thin section view shows how the bands of aligned mica crystals have been crumpled by the folding.

Plane polarized light. Field of view 4 mm across.

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