ABSTRACT
Convection resulting from the thermal gradients in the plastic rock of the asthenosphere is believed to be the cause of movement of the crustal plates (Kerr, 1995; Wysession, 1995; Ritter, 1999). In some locations this movement may manifest itself in a collision of plates and in other locations in plates of nearly equal density sliding past one another along transform faults. In still others, interacting plates may partially slide over one another in a process of crustal convergence called subduction where a denser oceanic plate slides below a lighter continental plate. Either of the last two processes may lead to formation of a trench-volcanic island arc system. Island arc systems result from a sedimentary wedge formed by the oceanic plate. In subduction, the resulting arc system may eventually accrete to the continental margin as a result of the movement of the subducting oceanic plate in the direction of the continental plate (Van Andel, 1992; Gurnis, 1992).
