 The early geological development of the Avalonia terrane, including England, is believed to have been in volcanic arcs near a subduction zone on the margin of the Gondwana continent.Some material may have accreted from volcanic island arcs which formed further out in the ocean and later collided with Gondwana as a result of plate tectonic movements.The igneous activity had started by 730 million years ago and continued until around 570 million years ago, resulting in a region of volcanic islands within a shallow sea.