Thursday, September 1, 2016

Laxford bridge: famous outcrop in Scottish Highlands

This outcrop is exposed along the roadcut of the A838 road in NW Scotland. It can be found at coordinates 58°23'24.43"N   5° 1'29.66"W. Google map streets view. Also called as multi-coloured rock stop, the outcrop became famous because it shows conspicuous cross-cutting relationship between the oldest rocks in Europe. The Precambrian rocks exposed here tells us a story: from oldest to youngest units can be distinguished by cross-cutting boundaries between them. The oldest rock in Scotland is Lewisian gneiss (grey). The original rock formed about 3 billion years ago and was metamorphosed multiple times (so now it's called gneiss). Then it was cut by mafic intrusions (black), or dykes (British spelling preserved), at about 2.5 billion years ago. Then all of these units were cut by granitic intrusions (pink), much later at about 1.8 billion years ago. After than, the whole assembly of rocks experienced metamorphism that shaped it's final look (sheared and stretched). Remember, the age of the Earth is 4.54 billion years, these rocks are really old!
Here's the outcrop with boundaries shown schematically.




1 comment:

  1. Hi David, I'm putting together site descriptions for a project documenting Scotland's 50 best places to see geology :) We're a bit pushed for time so I was wondering if you would consider letting us use your photo here of the multi-coloured rock stop? It will be widely publicised in October this year. If you would grant us permission we would indicate you have copyright and also credit you. Thanks for considering! - Laura

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