The Tian Shan contains two late Paleozoic sutures. The older, southern suture marks the collision of a passive margin at the north of the Tarim block and an active continental margin; subduction under the latter was to the north. The late Paleozoic continent-continent collision along Tarim's northern margin created an orogenic belt along the southern part of the Tian Shan. The younger, northern suture separates a northern Carboniferous island arc from an active continental margin developed over a south-dipping subduction zone.