The Caledonian orogenic belt in Gjersvik area of Central Norway is composed of a series of terranes,and the volcanic rocks in the Gjersvik terrane consisting mainly of dark and light-colored tholeiitic greenstone and quartz keratophyric pyroclastic rocks exhibit an obvious bimodal pattern.Volcanic activities can be divided into three stages which were closely asso-ciated with the evolution of rift structure. Undifferentiated tholeiite derived from the depleted mantle was formed at the early stage of rift evolution,felsic volcanic rocks from partial melting of basalt or gabbro were produced at the middle stage,and differential tholeiite derived from the deeper enriched mantle came into being at the late stage.A series of massive sulfide deposits have been found within the Gjersvik terrane,which were related to volcanic activities and are spatially in close association with felsic pyroclastic rocks.Studies show that the formation of these deposits was related to the submarine hydrothermal system accompanying the volcanic activity.