What does the Earth's magnetic field have to do with plate tectonics?

Answer 1

Earth's magnetic field doesn't have much to do with tectonic plates. But both are caused by movement of the magma.

The magnetic field is caused by electrical currents flowing in the magma, roughly parallel with the Equator. [A few % of the field is caused by the flow of the Solar Wind past the Earth.]

Tectonic plates move around the surface of the Earth over the liquid magma. The gravity drag of the Moon causes the Earth's crust to rotate (very) slightly more slowly than the inner core.

Consider the shape of the island arc joining S America to the Antarctic. And the slow movement of the Pacific Ocean's floor with regard to a few (postulated) stationary hot spots. Such as Hawaii, and some ocean floor chains of sea-mounts East of New Zealand.

Answer 2

The Earth's magnetic field is generated by the movement of molten iron in the outer core. As the tectonic plates move around on the Earth's surface, the magnetic minerals in the rocks align themselves with the Earth's magnetic field. This creates a record of the past positions of the magnetic poles, which helps scientists study the movement of tectonic plates over time.