Bulletin of the Geological Society of Malaysia, Volume 20, August 1986, pp. 97 – 136
Marine Geological Institute, lndonesia
Abstract: The Indonesian Archipelago consists of accretionary development of island arcs, continental blocks, rifted and drifted microcontinents, ophiolite fragments and sedimentary cover. These through a series of complicated past to recent tectonic processes form the current configuration of the archipelago. In the geological evolution of Southeast Asia, active plate margins, resulting in island arc development and accretionary terranes have played an important role since Late Triassic time.
Prior to their development, the Proto Kalimantan and Proto Sumatera continents, both including island arc were amalgamated during Late Triassic time along the Bentong-Raub suture to form the Sunda Platform. In contrast the northwestern margin of Australia has always been a passive margin. Based on palaeontology, palaeomagnetics and stratigraphy the Indonesian Archipelago is provisionally subdivided into 13 terranes. Material accreted along active margins commonly called accretionary terrane is excluded from this terrane classsification. The terranes are Proto-Kalimantan, Sumatera basement, Southwest Sulawesi, East Sulawesi Opiolite, Sumba, Seram, Timor, Buton, Banggai-Sula, Buru and Bacan. The continental fragments Sikuleh and Natal have recently been reported to occur in the southwestern coast of Sumatera. The NE margin of Australia has continued to develop as an active margin up to the present day, producing the Banda Arc. During the Paleogene southwest Sulawesi rifted away from east Kalimantan to collide with oceanic crust to the east and in the Tertiary, west Sulawesi magmatic arc came into existence.
The Sulawesi ophiolite originates from oceanic crust that was pushed westward by the migrating Banggai-Sula terrane and blocked by the Tertiary West Sulawesi magmatic arc. The terranes Sumba, Buton, Seram and Timor result from a rift-drift event affecting northwest Australia during Jurassic time. The terranes Banggai-Sula, Bacan and Buru have been formed by the Sarong Fault slicing off the northernmost portion of lrian Jaya and moving these slices westward. The northwestern Australian continent, including Irian Jaya, has acted continuously as a passive margin moving northward behind a front of oceanic crust. It collided with the northern Irian Jaya Island Arc during Oligocene time after the oceanic crust had been consumed by subduction. The polarity of the subduction changed after the collision, becoming southward.