Conversation so far:
where are all of the tectonic plates located
The tectonic plates are on the Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere.
how thick are the tectonic plates
Tectonic plates are around 100 km (62 mi) thick.

Question: what are the plates made of
Self-contained rewrite: what are the tectonic plates made of