Collision with England in the Caledonian Orogeny

The third and final stage of the Caledonian Orogeny was the collision of Eastern Avalonia with Laurentia. This is thought to have occurred around 425 million years ago. Unlike the collision that lead to the Grampian Event and the Scandian Event, this collision was relatively soft and did not cause huge amounts of rock deformation. This process of soft collision is sometimes referred to as soft docking.

As the Iapetus Ocean closed, ocean-floor was pushed down (subducted) below the southern edge of Laurentia. Sediment scraped off this ocean-floor created a huge pile or accretionary prism which now forms the Southern Uplands. The northern edge of the continent of Eastern Avalonia, marked by the Iapetus Suture, lies buried under younger sediments just south of the Scottish-English border.

Around 400 million years ago molten magma derived as a consequence of the collision and loss of the ocean, gave rise to the granites of Criffel and Cairnsmore in the Southern Uplands.