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Iapetus Ocean and Caledonian Orogeny

Six hundred million years ago, the Northwest Highlands, the Northern Highlands and the Grampian Highlands lay at the edge of a continent called Laurentia. The Dalradian rocks of the Grampian Highlands were still only layers of sediment, accumulating in the shallows of the vast Iapetus Ocean which lay to the south of the continent of Laurentia.

The Iapetus Ocean began to open around 800 million years ago as a large, ancient continent was pulled apart by the forces of continental drift. Sometime around 500 million years ago, the forces of continental drift began to close the Iapetus Ocean again. It was in the Iapetus Ocean, as it closed, that the volcanic islands, thought to be the foundations of the Central Belt formed.

As the Iapetus Ocean closed, three land masses were effectively heading on a collision course towards Laurentia. Nearest, and heading towards the proto-Grampian Highlands was the chain of volcanic islands, which had formed in the Iapetus Ocean. Behind this, lying on the far shore of the Iapetus Ocean, was a continent called Eastern Avalonia which contained England. The final landmass was a continent known as Baltica which contained present-day Scandanavian Europe. This lay further east, also on the far shore of the Iapetus Ocean. However, it was on a collision course, not with the proto-Grampian Highlands but with the foundations of the Northern Highlands.

The series of collisions which followed formed a massive mountain range, of Alpine, or even possibly Himalayan proportions, known as the Caledonian Mountains. The Caledonian mountain-building event or Caledonian Orogeny occurred in three of stages. The first stage occurred around 480-460 million years ago when the chain of volcanic islands collided. This is called the Grampian Event. The second stage occurred around 440 million years ago when Baltica collided. This is called the Scandian Event. The third and final stage occurred when Eastern Avalonia soft docked around 425 million years ago. This completed the joining of Scotland's geological foundations and also joined Scotland and England together



Last updated on Tuesday 14th July 2015 at 09:55 AM. Click here to comment on this page