Rocks of different origins and ages occur in three fundamentally different geological provinces
Cratons or shield areas
- Are broad regions of generally low elevation and low relief, generally found near the centers of continents
- Surface topography resembles a shield; thus the name
- Rocks in cratons are usually deformed metamorphic rocks older than 1 billion years old = eroded roots of ancient mountain belts
- Cratons sometimes covered by veneers of younger sedimentary rocks, called platform deposits (many platform sequences contain rocks younger than 600 Ma)