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The type of plate boundary is divergent/constructive plate boundary.
Divergent plate boundary, also known as constructive plate boundary is where the plates move apart under the rising convection current of magma.
As plates move apart, cracks are formed and the upwelling magma from mantle would fill the cracks. Once the lava cools down, new plate material is created to create new seafloor. This is also called seafloor spreading.
Therefore, the answer is divergent/constructive plate boundary.
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The block of rock is called a footwall
