New oceanic crust is created by

volcanoes
erosion
convergent faults
deposition

Oceanic crust is repeatedly being created at mid-ocean ridges. As plates diverge, or divide, magma rises into the upper mantle and the crust. And as it moves away from the ridge, the lithosphere becomes cooler and denser, and slowly, sediment builds on top of it. So, basically, your answer would be magma, or a volcano. Hope this helps! ;)