Borrowdale Volcanic Group
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). 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.
| 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 |
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