Evolution of Arc Systems in the Western Pacific

Abstract

Very shortly after their discovery arcuate island chains, with their associated volcanoes, trenches, and seismicity, were recognized as critical tectonic complexes in some way related to the development of orogenic zones (e.g. 102). However, technical inability to adequately investigate these primarily submarine features, and even worse, the often misleading conclusions drawn from the few segments above water, delayed an adequate understanding of island arc systems until after the Second World War. Since then, high precision echo-sounders, low-frequency acoustic profiling, and better bottom sampling apparatus have clarified arc system morphology and shallow structure. These observations, coupled with seismological and other geophysical studies, have now directly and indirectly indicated the role of island arc systems in the orogenic process and in global tectonics. Differences in opinion exist concerning many, or most, details of arc system character and evolution, but most workers in western Europe, Japan, and the Americas accept the underlying concept of plate tectonics. In this framework, island arc systems result from the underthrusting, or subduction, of one lithospheric plate beneath another. The following discussions assume the validity of plate tectonics and concentrate on processes by which subduction is manifested in the geologic record. Different concepts of island arc evolution, which deny the concept of subduction, are discussed by Meyerhoff, Meyerhoff & Briggs (74), Carey (13), Beloussov (7), and others. This paper reviews recent data and the resulting ideas which bear on evolution of arc systems in the western Pacific. Results and conclusions from arc systems in other regions have been introduced where pertinent. Geological and crustal geo­ physical aspects are stressed, and there is no attempt to review either data or theoretical studies from the subcrustal regions beneath the arc systems, or petrologic studies of island arc igneous activity.