A fine-grained, sometimes porphyritic volcanic rock type intermediate in colour and composition between rhyolite and basalt.
Andesites typically occur as extensive lava flows associated with compression plate margins.
The layer below the lithosphere marked by low seismic wave velocities and high seismic attenuation. The asthenosphere has low strength and little rigidity compared to the lithosphere, probably because it is partially molten. The horizontal displacement or rotation of continents relative to one another after the break-up of larger land masses. Supercontinent consisting of Laurasia and Gondwanaland together. It is inferred from paleomagnetic and other data that it coalesced in the Late Paleozoic and broke up in the Mesozoic Era.