Discovery of coesite in the North Qaidam early Paleozoic ultrahigh-high pressure (UHP-HP) metamorphic belt, NW China

Abstract

Coesite was discovered as inclusions in zircon separates from gneiss associated with a large eclogite body in the North Belt of the Qaidam UHP terrane. Some graphite inclusions also found. This finding confirms our previous suggestion that the North Qaidam UHP terrane was recrystallized at p below the diamond stability field based on several lines of evidence such as polycrystalline K-feldspar and quartz inclusions in eclogitic garnet, quartz lamellae in omphacite and p-t estimates for both eclogite and garnet peridotite. The occurrence of coesite inclusions in zircon suggests in-situ UHP metamorphism. This UHP terrane, along with the Altun e-clogite of 504 Ma, and those to the east of Qilian Mts, in the North Qingling, Tongbai and North Dabie regions, recorded the Early Paleozoic collision between the Sino-Korean and Yangtze plates. This UHP belt could extend to further west to the similar age Kokchetav UHP belt in Kazakastan.