​https://www.geological-digressions.com/bits-of-north-america-that-were-left-behind/

The story begins on continent of Laurasia ~1000my ago, being an amalgam of North America, Greenland and northern Scotland and northwest Ireland tucked along eastern margin.

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Groups of rock that underpin the Scottish Highlands:

1. Lewisian gneiss (from ~3000-1700my ago) beneath the Northern Highlands, forming the basement foundation of Laurentia.

2. Torridonian, a thick accumulation of sediments covering eroded land-surface of the Lewisian gneiss.  Within the sediments there is a major unconformity between the Stoer Group (below – age range ~960-1100my) and the Torridon Group (above -  range ~770-1040my).  They are thought to be spreading fans debouched over the western margin of steadily subsiding rift valleys marking the early stage in the development of the Iapetus Ocean separating Laurentia from Baltica.

3. Moine Group sediments (now metamorphic rocks) deposited along eastern margin of Laurentia from about 1000 to 870my ago.  In Scotland these became the Northern Highland Terrane.

4. Dalradian metamorphic rocks which form the Grampian Highlands (Central Highland Terrane) originated as sediment and volcanics in the Grampian arc from about 800 to 510my ago.  The metamorphism occurred much later.  The Dalradian is also seen in West Ireland.

 

Laurentia then moved south of the Equator towards a volcanic arc, the Grampian Arc.

Collision between Laurentia and the Grampian Arc initiated the first phase of Caledonian mountain building between ~475-465my ago.

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At the same time Baltica (a smaller continental block) is heading north from south-east of Laurentia.  Also Laurentia and Baltica (which later became Scandinavia and North Europe) were both rotating anticlockwise – but still south of the equator.  Also Avalonia (on which England, Wales, and southern Ireland resided) both were migrating north towards Laurentia.

 

The intervening ocean, Iapetus, was gradually shrinking as crust was devoured down at least 3 different subduction zones

Caledonian Orogen   >  400my formed from plate collisions stretching from Scandinavia to Scotland-Ireland, East Greenland and the Appalachians of eastern USA and Canada.

Iapetus eventually closed, ophiolites being incorporated into the Caledonian mountain complex.

 

Baltica and Laurentia were involved in a head-on collision around 435-425my.  The Moine Thrust (defining moment of dislocation and metamorphism) carries Laurentian Lewisian gneiss over younger Cambrian limestone and sandstone during climax of Caledonian Mountain building.  The Cambrian sequence was subsequently dismembered into several smaller thrust sheets.

 

This and Avalonia’s approach (being more oblique as it slid northeastward past Laurentia in a softer collision) produced final two phases of Caledonian Mountain building.  Avalonia’s collision stitched south England, Wales and south Ireland to Scotland and north-east Ireland.

 

The amalgamation of Laurentia, Baltica and Avalonia became part of supercontinent Pangea that included Africa, South America, Antarctica, Australia and New Zealand, and Asia, the amalgamation beingwell underway 335my ago. 

 

Pangea began to break apart 175my ago, since when the present plate configuration has been developed.  North Atlantic opened at 94my between northwest Africa and North America, but Greenland is still attached to Britain, Ireland and Scandinavia.  By 80-75my ago, the mid-Atlantic Ridge had spread north, and ancient bits of North American crust in north Scotland and west Ireland were finally severed and became part of larger Eurasian plate.