Oceanic fissure eruptions,subvolcanic intrusions and volcanic magma Chambers

Rifting along the mid-Atlantic ridge seems to have been accompanied by fissure eruptions which flooded the ocean bottom. Locally these plateau lavas rose above sea level and erosion revealed plutonic bodies emplaced within them. There is also some evidence of shallow magma chambers feeding surface volcanism. All these facts can be conveniently interpreted by assuming fractional melting of the upper mantle, at depths below about 50 km, and a pulsation of the pressure, produced by a varying gravitation, which seems capable of squeezing the molten fraction and of fracturing the solid crust above. Magma chambers can then be formed, probably by subterranean cauldron subsidence of Scottish type, they can leed surface volcanoes and will eventually solidify as plutonic bodies. Phase changes of eclogite, possibly present in the oceanic upper mantle, could also explain the uplift of island platforms.