Editing Gneiss (section)

===Granite-greenstone belts===
[[Shield (geology)|Continental shields]] are regions of exposed ancient rock that make up the stable cores of continents. The rock exposed in the oldest regions of shields, which is of [[Archean]] age (over 2500 million years old), mostly belong to granite-greenstone belts. The [[greenstone belt]]s contain [[Metavolcanic rock|metavolcanic]] and [[metasedimentary rock]] that has undergone a relatively mild grade of metamorphism, at temperatures of {{cvt|350-500|C||}} and pressures of {{cvt|200-500|MPa|bar}}. The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over {{cvt|500|C||}}) metamorphism to the amphibolite or granulite facies. These form most of the exposed rock in Archean [[craton]]s.<ref>{{cite book |last1=Kearey |first1=P. |last2=Klepeis |first2=Keith A. |last3=Vine |first3=Frederick J. |title=Global tectonics. |date=2009 |publisher=Wiley-Blackwell |location=Oxford |isbn=9781405107778 |page=350 |edition=3rd}}</ref>