Subduction zones and back arc basins — A review

In the framework of plate tectonics, the basic mechanism operating in the trencharc-back arc systems is believed to be the subduction of oceanic lithosphere. This model, however, was developed more or less as a logical consequence of sea-floor spreading. The question then is whether or not the subduction model can explain all the major features of the trench-arc-back arc systems. Many features, such as thrust type inter-plate earthquakes and deep earthquakes along Wadati-Benioff zones, are readily explained. But, the occurrences of extentional spreading and high heat flow in the back arc region and arc volcanism are difficult to explain. An approach to solve these problems may be found in what may be called “comparative subductology”: there seem to exist two basically different modes of subduction; one — Chilean type — causing compressional stress regime in the arc and back arc regions, the other — Mariana type — causing tensional. World's subduction zones are classified in terms of the postulated two modes, and some tectonic implications and causes of the two modes are discussed.