the crust is thinned and the tectonic plates diverge.
Divergent boundaries are formed when two plates namely continental and oceanic plates diverges or separates. The oceanic plate being lighter in weight exhibit thin crust subducts at the bottom where the magma from the mantle causes the subducted plate to melt and lifted . The magma rises up forms cracks in subducted plate. The magma erupt as undersea volcanoes. The magma cools down and forms a raised ridge called a mid-ocean ridge.