Chapter Eight Oceans in a Context of Plate Convergence

Abstract

Publisher Summary This chapter discusses the structure, tectonics, and sedimentation of convergent oceans. The chapter also provides examples of active margin areas. Convergent ocean systems are essentially characterized by the development of active continental margins and/or active island arcs. Both continental and oceanic lithospheres are involved in active continental margins, whereas active island arcs implicate two oceanic lithospheres. The morphological elements of such active areas include oceanic trenches, accretionary wedges, volcanic arcs, and backarc systems. The accretion and relative motion of lithospheric plates generate internal stress, which is transmitted within the lithosphere to plate boundaries. Where internal stress converges, minor compression is accommodated via intraplate deformation, whereas important compression may cause the rupture of the lithospheric plate in areas of mechanical weakness and the subduction of the lithosphere of highest density. Such areas of mechanical weakness include—for example, transition zones from oceanic to continental lithosphere and transform areas where the contrast in thickness and/or physical properties of adjacent lithospheres is important, and midoceanic ridges where oceanic lithosphere is very thin. However, it is generally assumed that old oceanic lithospheres are easily separated from adjacent continental lithospheres and entrained in the asthenosphere because of high contrasts in density.