Petrogenesis and the evolution of garnet-pyroxene granulite from the northern Dabie Mountain, Anhui

Garnet-pyroxene granulites occur in the Northern Dabie mountain and are distributed as blocks and lens along the margin of mafic-ultrabasic rocks. They are composed mainly of garnet + diopsit + hypersthene + plagioclase. There are symplektites of Am + Pl, Cpx + Pl or Hy + Pl in different granulites, respectively. By use of geobarometers and geothermometers, the peak metamorphic P-T is about 740°C ~ 890°C, 0.8 ~ 1.52GPa; and the retrograde P-T; 700°C ~ 862°C, 0.69 ~ 0.79GPa. It is shown that the garnet-pyroxene granulites have a clockwise P-T paths by isothermal decompression process. The rock chemistry, REE and trace element geochemistry of them are research in this paper. The results indicate that their original rocks, may be a basic pyrogenic or volcanic rocks and have the trace element distribution feature of oceanic basalt. By means of distribution in figure of (La/Sm)-La for the REE data, the original rocks of the garnet-pyroxene granulites would be derived from a mantle partial melting. The garnet-pyroxene granulites in the area are located at the suture of subduction-collision orogeney between the North China and Yangtze plaleo-continents in the Northern Dabie. According to the P-T condition, the garnet-pyroxene granulites were formed under the high pressure granulite facies produced by the plate collision leaded to the compression and crustal thickening.