Identification of coesite-bearing amphibolitein the North Qinling and its geological significance

The Qinling orogen lying in between the North and South China blocks is a key for understanding the tectonic framework of China continent. Tectonically, the Qinling orogen is divided into the North Qinling Tectonic Belt (NQTB) and the South Qinling Tectonic Belt (SQTB) by the Shangdan Fault Zone. With discoveries and study of the continental subduction ultrahigh pressure (UHP) metamorphic belt in the Dabie-Sulu and the North Qaidam-Altyn orogens in east and west China, respectively, a frequently-asked question is whether or not the Qinling orogen which belongs to the same orogenic system with the Dabie-Sulu orogen in central China has experienced the similar continental subduction and what timing of the subduction is. In fact, several UHP metamorphic outcrops such as the diamond-bearing eclogite and muscovite quartz schist in the Guanpo area, quartz-feldspathic UHP rocks in the Songshugou area and diamond-bering amphibolite in the Qingyouhe area have been reported lately in the Qinling group of the NQTB. However, these UHP findings have not been widely accepted with serious attention. The reason for this situation can be attributed to absence of convincing interpretation for the mineral exsolution structure and the UHP index minerals other than diamond especialy often-seen coesite in the orogens containing the UHP metamorphic bodies in the world.