tectonic plates: moving geological platforms in the Earth's crust or upper mantle that are separated by belts of earthquake and volcanic activity at mountain ranges, mid-ocean ridges, and faults, and whose movements cause continental drift.
(the Earth's crust or upper mantle; are separated; by belts of earthquake and volcanic activity at mountain ranges, mid-ocean ridges, and faults)
the Earth's crust or upper mantle
are separated
by belts of earthquake and volcanic activity at mountain ranges, mid-ocean ridges, and faults