Publications

The complex products of Neogene subduction systems in the Indonesian region are superimposed on the results of equally diverse Paleozoic, Mesozoic, and Paleogene rifting and subduction events.The outer-arc ridge between the active Java Trench and the main islands of Java and Sumatra is formed from a wedge of melange and imbricated sedimentary and crystalline rocks whose steep to moderate dips are sharply disharmonic to the gently dipping, subducting oceanic plate beneath. The wedge has grown both by scraping off of oceanic sediments and basement against and beneath its toe, and also by internal imbrication which is a gravitationally driven response to backward, subductive dragging at the base. Strata deposited on the top of the growing wedge have been imbricated down into it. The outer-arc basin behind the ridge may have originated from a Paleogene continental shelf-and-slope assemblage whose seaward side was raised by melange that was stuffed beneath it after subduction began in late Oligocene time.The Banda Arc (the east part of the Java subduction system) is now colliding with the Australian-New Guinea continent. As the frontal wedge of melange has been driven onto the continental shelf, abundant shallow-water shelf strata have been imbricated into the wedge. Eastward migration of the arc from, rotation of northwest New Guinea away from the advancing arc, and reversal of subduction direction on the south limb of the arc complicate the pattern.The Philippines are the product of a complex aggregation of segments of various island arcs. The Palawan subduction-arc system, which became extinct in late Miocene time, and the Sabah-Sulu-Zamboanga arc, active until Pleistocene time, bridge between Borneo and the Philippines. Farther east, the Sangihe and Halmahera arcs face each other and are now colliding in the south, but the collision is complete in the north, where the sutured components form central Mindanao. New subduction zones, including the Philippine Trench, have broken through on both outer sides of the arc aggregate. A small plate that includes northeastern Sulawesi is rotating clockwise over the Celebes Sea lithosphere, and is bounded by a trench on the north, a strike-slip fault in the west, and an orocline in the east.