supracrustal

Supracrustal rocks are rocks that lie on top of the crystalline crust, overlying the older basement or crustal foundation. The term contrasts with infracrustal or subcrustal rocks, which are formed deeper within or beneath the crust. Supracrustal sequences include rocks that formed at or near the Earth’s surface and may have been subsequently subjected to low-to-high grade metamorphism.

The composition of supracrustal rocks is diverse. They can be sedimentary, volcanic, or metavolcanic/metasedimentary in origin. Typical types include sandstones, shales, cherts, and banded iron formations, as well as volcanic and volcaniclastic rocks such as basalts, rhyolites, and tuffs. In many regions, particularly in ancient crust, these rocks form recognizable packages known as supracrustal sequences, which may be preserved as greenstone belts when metamorphosed.

Significance and occurrence: supracrustal rocks record information about the surface environment, sedimentation, volcanism, and early tectonics. They are central to the study of crustal growth and the geological history of continents, especially in Archean and Proterozoic terranes. These rocks are also important in mineral exploration, as they commonly host ore deposits associated with ancient volcanic-sedimentary sequences, including precious and base metals.