Before The Windermere: Basement Terranes
To the north west of the unit lies the Cambro-Ordovician Skiddaw Group, a sequence that formed on the Avalonian continental margin, composed mainly of turbidites. Between the two, the Borrowdale Volcanic Group consists of tuffs erupted by an underlying calc-alkaline volcanic arc, active during the subduction of the Iapetus ocean crust.
The Windermere basin was formed by flexure. Prior to its formation, the Southern Uplands accretionary prism, flanking the edge of the Laurentian continent, was advancing towards Avalonia. The load of the mountains formed during this collision weighed down the Avalonian plate, causing the development of accommodation space.
Read more about this topic: Windermere Supergroup