1. Oceanic crust: This is the thinner, denser layer found beneath the ocean floor. It's primarily made up of basalt, a dark-colored volcanic rock rich in magnesium and iron.

2. Continental crust: This is the thicker, less dense layer that forms the continents. It's primarily made up of granite, a light-colored rock rich in silica, aluminum, potassium, and sodium.

Beneath these layers lies the Earth's mantle, which is a viscous, semi-solid layer of rock. The mantle is much hotter than the crust and plays a crucial role in driving plate tectonics.

The composition of the plates themselves isn't uniform. The specific minerals and rocks present vary depending on the plate's age, location, and history of formation.

Here's a breakdown of the composition by layer:

Oceanic Crust:

* Basalt: The dominant rock type.

* Gabbro: A coarse-grained equivalent of basalt found deeper in the oceanic crust.

* Peridotite: A rock found in the upper mantle that sometimes gets incorporated into the oceanic crust.

Continental Crust:

* Granite: The dominant rock type, often found in mountainous regions.

* Sedimentary rocks: These form from the accumulation and cementation of sediments, like sandstone and limestone.

* Metamorphic rocks: These form when other rocks are transformed by heat and pressure, like gneiss and schist.

Overall, the composition of tectonic plates reflects the complex processes involved in their formation and evolution. Understanding these compositions is crucial for comprehending the driving forces behind plate tectonics and the various geological phenomena they create.