Mid-Ocean Ridge. A linear, narrow volcanic and tectonic region which marks the constructive boundary between two tectonic plates. It is divided into segments by transform faults and other offsets. The global ridge system cuts through every major ocean basin and comes ashore in a few places like Iceland. It forms an approximately 65,000 km long, globe-encircling, largely submarine mountain chain. Magmatism. Magmatism is the production and migration of magma, which is molten rock produced from the partial or complete melting of solid materials within a planetary body. When magma erupts on the surface, it is known as lava. Volcanism. Volcanism is the eruption of molten rock, hot gases, or solidified rock fragments from an opening (“vent”) in the Earth’s crust. Volcanism occurs on Earth and other planets and moons. Most of the volcanism on Earth occurs at mid-ocean ridges, almost always sight unseen. Mid-Ocean Ridge Magmatism. By far, the dominant type of lava resulting frommagmatic activity at mid-ocean ridges is basalt, also called mid-ocean ridge basalt (MORB). However, small amounts of other extrusive magma types (predominantly andesite, dacite, and picrite) also erupt there. Variations in the rate and style of magma production, volcanism, and faulting result from variations in upper mantle temperature, upper mantle composition, and seafloor spreading rate through the ridge system, causing differences in igneous ocean crustal thickness, structure, and composition. Mid-Ocean Ridge Volcanism. Volcanic eruptions at ocean ridges vary in style, intensity, and duration around the globe as a function of parameters such as magma chamber depth, magma supply rate, and eruption depth beneath sea level. Nevertheless, the dominant eruption styles either produce fissure-fed lava flows or point-source, single vent volcanic lava mounds. Nearly all volcanic products at ridges exhibit rapid quench textures, formed by the freezing of molten magma upon contact with cold seawater.
