The correct answer is - C. hot spots in the mantle.
The Hawaiian Islands are a volcanic islands. They are lying above a hot spot. The hot spot volcanoes, unlike the other ones, are far away from the boundaries of the tectonic plates and they are emerging on places were there's hot spots. These hot spots manage to penetrate through the crust and get the magma from the mantle up to the surface and create volcanic islands in meantime.
While most volcanoes are created by geological activity at tectonic plate boundaries, the Hawaii hotspot is located far from plate boundaries. ... According to this theory, the nearly 60° bend where the Emperor and Hawaiian segments of the chain meet was caused by a sudden shift in the movement of the Pacific Plate.
here is the definition of a pluton to prove my point:
<span>In geology, a pluton is a body of intrusive igneous rock, called a plutonic rock. It is crystallized from magma slowly cooling below the surface of the Earth. </span>