Borrowdale Volcanic Group

Borrowdale Volcanic Group
Stratigraphic range: Caradocian (late Ordovician)
Lapilli-tuff of the Helvellyn Tuff Formation on High Crag
Type	Group
Sub-units	Birker Fell Andesite Formation, Whorneyside Tuff Formation, Airy's Bridge Tuff Formation, Lingwell Tuff Formation, Seathwaite Fell Sandstone Formation, Lincomb Tarns Tuff Formation, Esk Pike Formation, Tarn Hows Tuff Formation
Underlies	Windermere Supergroup
Overlies	Skiddaw Group
Thickness	probably up to 6000m
Lithology
Primary	volcanic rocks
Other	siltstone, sandstone
Location
Region	Cumbria
Country	England
Extent	Central Lake District & Cross Fell
Type section
Named for	Borrowdale

The Borrowdale Volcanic Group is a group of igneous rock formations named after the Borrowdale area of the Lake District, in England. They are Caradocian (late Ordovician) in age (roughly 450 million years old).^[1] It is thought that they represent the remains of a volcanic island arc, approximately similar to the island arcs of the west Pacific today. This developed as oceanic crust to the (present) north-west and was forced by crustal movement under a continental land-mass to the present south-east. Such forcing under, as two plates meet, is termed subduction. This land-mass has been named Avalonia by geologists. It is now incorporated into England and Wales and a sliver of North America.