Blueschist belts in Asia and possible periodicity of blueschist facies metamorphism.

Blueschist belts are widely distributed in two major geographic positions of Asia: 1) along the Pacific margins and in the Alpine-Himalayan metamorphic belt; and 2) within the intracontinental fold belts, mainly in the Ural-Mongolian orogen. The blueschist belts of the first case are mainly Mesozoic in age; only those in Japan and in NE Siberia occur as accreted fragments within Mesozoic foldbelts with blueschist metamorphic ages of about 340, 330-350, and 330-310 Ma. The intracontinental blueschist belts of the second case, on the other hand, are much older than 370 Ma and some are as old as the Riphean in age of 1100 Ma; they characteristically occur within suture zones along the boundaries of several Precambrian cratons. Compilation of available data of blueschist ages in both Pacific margins and the Ural-Mongolian foldbelts of Eurasia produces a possible periodicity of blueschist facies metamorphism with a period of 30 Ma in the Cenozoic and Mesozoic, and of 30-60 Ma in the Paleozoic. Such a periodicity may be the result of several factors such as: 1) change of relative plate motion, 2) blueschist metamorphic regime, 3) blueschist preservation, and 4) rate of continental accretion. Detail mechanisms are as yet unknown.-from Authors