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Two billion years of geology in one road cutting 

OneMinuteGeology
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Just outside Laxford on the A838 is the road cutting known to geologists around the World as the Multi-Coloured Rock Stop. Here you can see fresh exposures of Lewisian Gneiss cut by successive dyke intrusions of Scourie basalt and Laxfordian granites.
The Lewisian Gneiss was metamorphosed in the roots of a mountain chain about 3 billion years ago, but it was originally a granodioritic igneous rock before that. The Sourie and Laxfordian dykes are about 2.5 and 1.7 billion years old respoectively. The cross-cutting relationships which show the relative ages of the intrusions are still clear but the whole sequence has then been deformed by later shear. This shows as semi-brittle deformation in the granite dykes which have stretched out into discrete pods resembling a string of sausages (boudinage), allowing us to estimate the sense of shear deformation quite easily here.
So we have at three periods of igneous intrusion and at least two mountain-building episodes spanning about 2 billion years of geological history here.

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18 сен 2024

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Комментарии : 4   
@jncolligan1
@jncolligan1 3 года назад
That was a wonderful explanation! It’s such a puzzle to put together the sequence and actions that made these time-humbling places look the way they look! You do a tremendous job! Do More! :) thank you!
@OneMinuteGeology
@OneMinuteGeology 3 года назад
Dear Joseph, Glad you like them. There are plenty more to come. I have a full schedule up till the end of the year at least after my most recent trip to Scotland. I will slot in English and Welsh ones as I get the chance for more trips.
@jncolligan1
@jncolligan1 3 года назад
@@OneMinuteGeology so glad your stamina is still strong. I moved to Edinburgh from the States and become utterly fascinated by it all. I work in finance so have zero background in this field, just picking up new knowledge by going on geotours and books and RU-vid, the most recent tour to Arran. I just came back from Shetland this weekend on a solo trip and was trying to explain this exact same tri-rock feature to them! You demystified it all in a minute. Next time I’ll know exactly how to explain it! If you ever open a patreon page I’ll be your first member! Thanks again!
@OneMinuteGeology
@OneMinuteGeology 3 года назад
@@jncolligan1 I'll let you know if I go down that route. I am hoping to offer some geologically themed walking and scrambling next year, which you might be interested in.
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