Which particle cannot be accelerated by the electric or magnetic fields in a particle accelerator?

The neutrino is the particle that cannot be accelerated in a magnetic field.

To add, a neutrino is a subatomic particle that is very similar to an electron, but has no electrical charge and a very small mass, which might even be zero. 

Sometimes, the plates collide with one another or move apart. Volcanoes are most common in these geologically active boundaries. The two types of plate boundaries that are most likely to produce volcanic activity are divergent plate boundaries and convergent plate boundaries.