VOLCANIC ROCKS IN BACK-OF-THE ARC BASINS

Abstract

An analysis of the volcanic rocks of back-arc basins indicates that the compositions of the tholeiitic basalts extruded in the spreading centers of such basins is influenced by nearby island arcs. This influence may be manifested as the presence of lava flows rich in volatiles, or as an extrusion of calc-alkalic lavas in the concluding stages of the volcanism. The extent of the influence of island-arc volcanism depends on the distance between the spreading center of the back-arc basin and the Benioff zone and on the nature of the volcanism on the island arc. This result provides an important criterion for the detailed study of ophiolite complexes that developed in ancient back-arc basins.