One of the most exciting geologic discoveries in the last 20 years is the finding of the presence of a major ultrahigh pressure (UHP) metamorphic belt in the Dabie-Sulu region of eastern China. In this belt, high-grade continental crustal rocks contain both diamond and coesite [Xu, 1987;Xu et al., 1992; Yang et al., 1999], clear evidence of crustal subduction to depths >150 km.
This belt formed by collision between the North China and Yangtze blocks in the Mesozoic between about 240 and 220 Ma. Recent work has identified an older, parallel belt on the north side of the Dabie-Qinling Mountains dated as Ordovician (˜500–440 Ma) [Yang et al., 2001, 2002]. This older belt extends northwestward for nearly 4000 km through the Qilian Mountains into northern Tibet, where it is offset by the left-lateral Altyn Tagh Fault (Figure l). In the Dabie-Sulu region, the rocks consist chiefly of granitic gneiss, paragneiss, eclogite, and garnet peridotite, whose protoliths are supracrustal rocks with a formation age of about 800–1800 Ma.