Recent Advances in the Study of Granulites from the North China Craton

The North China craton is one of the most important Archean cratons in the world. Nearly all Archean rocks in this craton were subjected to high-grade granulite-upper amphibolite-facies metamorphism. Protoliths include metamorphosed supracrustal rocks, orthogneisses, and basic intrusive rocks. Most granulites are low to moderate-pressure and high-temperature metamorphic rocks. Isotopic data show that granulite-upper amphibolite-facies rocks represent Archean formations, and greenschist-low amphibolite-facies rocks are early to middle Proterozoic formations. The major granulite-facies metamorphism occurred in four metamorphic episodes of >3000 Ma, ∼2900 to 2700 Ma, ∼2600 to 2450 Ma, and ∼1750 to 1900 Ma. The 2600-2450-Ma granulite-facies recrystallization is the most important latest Archean metamorphic event in the North China craton. Geochemical data indicate that the Archean moderate to low-pressure granulite terrain possibly represents a section of the middle to lower continental crust rather than lowermost crust. Some high-pressure basic granulites and eclogites also have been reported. The Sanggan structural belt is a typical high-pressure granulite and retrograded eclogite-bearing metamorphic belt. These high-pressure metamorphic rocks have isotopic ages of ∼2600 Ma, and make it necessary for geologists to reconsider the early Precambrian plate tectonics of the North China craton. At the same time, the high-P terrain provides an important oblique cross-section of the lowermost Archean continental crust.