Question

How do the parallel magnetic “stripes” near mid-ocean ridges form?

Answer 1

When lava erupts from mid-ocean ridges, it cools rapidly into rock. As it does, it becomes magnetised permanently in the direction of the Earth's magnetic field.

Answer 2

Answer:

When oceanic crust layer of earth pulls apart, magma erupts to the surface at the mid-ocean ridges and develops new layers of ocean floor.  

Magma contains ferromagnetic minerals. These minerals align themselves in the direction of earth’s magnetic field reversing its polarity every now and then. When this magma cools down, it freezes in this alignment. In this way first strip is developed.

Later when the earth magnetic field changes its polarity again, the next strip is formed but has opposite polarity to the first strip.