Which type of plate boundary is most closely associated with the formation of new ocean floor?

Divergent plate margins

Explanation:

Divergent plate margins are constructive zones on the surface of the earth. They are constructive in the sense that new materials are brought to the surface from within the crust.

An example of such is the mid-altlantic ridge. Here as two plates pull apart, new melts up-wells and finds a way to get to the surface where they cool and solidify.