Pacific Ocean closed loop of the andesite line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Pacific basin. Here basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the andesite line, volcanism is of the explosive type, and the Pacific Ring of Fire is the world's foremost belt of explosive volcanism. The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones. The Pacific Ocean is the only ocean which is almost
Ring of Gullion similar structures had been described from Scotland. It was emplaced during the Paleogene opening of the Atlantic Ocean during the formation of the North Atlantic Igneous Province. The structure of the ring dyke was produced when the active volcano's caldera underwent collapse producing a concentric suite of faults providing space into which magma was able to intrude. The ring dyke is composite with both porphyritic granophyre and porphyritic felsite components. The composition of the remainder of the volcano today is dominated by gabbro and granophyre and is also the site of a noted occurrence of platinum group elements. The rocks