Loch Assynt Region


After leaving the Isle of Rum the party visited the far NW of Scotland in the region of Loch Assynt. This is a classic region for geological studies dating back to the 18th century. The coastal region exposes some of the oldest rocks in Europe: the 2.8 billion year old Lewisian Gneisses, which were eroded and overlain by a thick sequence of flat-lying red sandstones, the Torridonian Group, which itself spans >300 million years of geological time. At that time these rocks were deposited by rivers on the edge of the North American continent, which broke apart at 600 million years ago (Ma) to form the Iapetus Ocean. As the margins of the continent subsided marine sediments were laid down over the Torridonian, forming the succession of sandstones and limestones now exposed along the shores of Loch Assynt (Pipe Rock, Fucoid Beds, Salterella Grits and Durness Limestones). Click here to read Rob Sohn's poetic tribute to the Durness group.

At 470 Ma the margin of North America collided with a chain of volcanic islands, similar to modern Taiwan, that caused folding and faulting, and the formation of the Appalachian Mountais in the US and Canada and the Grampian Highlands in Scotland. As the final act in this mountain building the rocks of the Assynt region were bulldozed and repeated by a thrust sheet of metamorphosed rocks riding on top of the Moine Thrust. Click here to watch a movie depicting the Moine Thrust at Knockan Crag (note that some players may not display the video - Quicktime works best). This region became a classic example of how rocks deform to compressional deformation and in particular the debate as to whether crystalline rocks were formed under the ocean, or were precipitated from magmatic liquids in the way we understand today.

Click on the slide show to see images from the Loch Assynt field excursions.