Variscan orogeny rifted off the north Gondwana margin in early Ordovician. By the end of the Silurian and in Early Devonian times, Baltica and Laurentia drifted towards each other, closing the Iapetus Ocean between them. They collided in the Caledonian orogeny and formed the Caledonide mountains of North America, Greenland, the British Isles and Norway. Seafloor spreading to the south of Avalonia pushed the latter into north Laurentia and thrust up the northern Appalachian Mountains in the acadian phase of the Caledonian orogeny. Contemporaneously the Tornquist Sea between Avalonia and Baltica was entirely closed. Thus Avalonia formed the southern coast of the
Hunter-Bowen orogeny Hunter-Bowen orogeny The Hunter-Bowen Orogeny was a significant arc accretion event in the Permian and Triassic periods affecting approximately 2,500 km of the Australian continental margin. The Hunter-Bowen Orogeny occurred in two main phases, a Permian accretion of previously formed passive-marginal Devonian and Carboniferous sediments in the Hunter region and mid-west region of what is now New South Wales, separated by rifting, back-arc volcanism and a later Permian to Triassic event resulting in arc accretion and metamorphism during a subduction event. The Hunter-Bowen Orogeny has resulted in the New England Fold Belt, a tectonic accretion of metamorphic terranes and mid-crustal