Abstract: Oceanic crust expansion is the result of the mantle voluminal variation. The factor influencing the increment of the mantle volume lies in variation of the solid substance's phase state, while the emission of the liquid substance in the interior of the earth leads to the reduction of the mantle's volume. The oceanic crust expansion can be divided into the expansion stage or the period of extensional movement of the earth crust and the uplift-emplacement stage or the period of compressional movement of it (i.e. subduction period of the oceanic crust). The rate of the oceanic crust expansion relates to the velocity of the substantial phase state variation in the inner earth; the width of the expansion relates to the temperature of the sea water; the temperature of hydrothermal fluid in oceanic crust expansion zone relates to the rate of expansion of its own; the sea ridge of the expansion zone relates to the thickness of the same density layer on the upside of the earth mantle.

Key words: oceanic crust expansion, oceanic crust uplift-emplacement, mantle substance, oceanic substance, buoyant force, expressional movement, sea water temperature