The Sumba fracture: A major discontinuity between eastern and western Indonesia

Abstract

Recent tectonic interpretations of the Sunda Arcs have claimed that a continuous subduction system extends from the trench southwest of Sumatra and south of Java, through the Timor trough, south of Tanimbar then swinging in strike to continue north of Seram. This article challenges this view. It proposes instead that a major tectonic discontinuity separates eastern Indonesia, consisting of Sumba and the Banda Arcs (including eastern Sulawesi), from western Indonesia, composed of western Sulawesi and the islands west of Sumba. The evidence for this Sumba fracture is discussed and its tectonic function interpreted as initially a late Jurassic wrench fault that became a Cretaceous and Cainozoic transform. The evidence is discussed for Sumba having been detached from northern Australia, and for Timor and the other islands of the Outer Banda Arc representing the deformed margin of the Australian continent. Emphasis is placed on the need to distinguish the overthrust Asian elements present in these islands from the Permian and Mesozoic Australian facies also present. The basis for considering these Australian facies in the Banda Arcs as autochthonous is set out. The conclusion is reached that the Outer Banda Arc islands are underlain by Australian continental basement and that no subduction has taken place between these islands and Australia since the Early Permian. The plate boundary of Australia in eastern Indonesia is identified between the Inner and Outer Banda Arcs.