Oceanic ridge
Depth of water
Mesopelagic - Abyssopelagic (200 - 5,000 m)
Circumstances
Submarine mountain ranges composed of basaltic volcanos on oceanic plates. It is considered that the oceanic ridges is the place where new oceanic plates and oceanic crusts are produced. Slits of oceanic plates are formed by tensile force from the both sides, and mantle rises adiabatically. Magma is produced by partial melting of matle in this process. This process is also recognized during formation of back-arc basin.
Sedimentary facies (Sediments)
Basaltic lavas, hyaloclastites, dykes, and gabbro. Basalt is MORB (Mid-Ocean Ridge Basalt) and tholeiitic. The melt of MORB is undifferentiated and poor in volatile and incompatible elements, and having low 87Sr/86Sr ratio. It is considered that MORB is produced from depleted mantle. The MORB of back-arc basins are rich in water.
Sedimentary facies (Structures)
Pillow lava