Petrology And Metamorphic P-T Path Of The Garnet Amphibolite In The Wenquan Group, Western North Tianshan, China

The newly discovered garnet amphibolites in the Wenquan Group, western North Tianshan, China, are of great significance for providing valuable insights into the formation and evolution of the Central Asian Orogenic Belt. The detailed petrography and phase equilibria modeling reveal that the metamorphic evolution of the garnet amphibolite can be divided into three stages : (1) the prograde metamorphic stage with heating and pressure increase, characterized by epidote wrapped by garnet, a mineral assemblage of garnet + hornblende + plagioclase + quartz + ilmenite + epidote and a peak P-T of 700 degrees C/9. 6kbar, which is suggested to be dominated by a continuous dehydration reaction : hornblende + epidote + quartz -> garnet + plagioclase + H2O ( 2 ) the metamorphic stage with isothermal decompression, featured with "white-eye socket" textures made up of " plagioclase + hornblende + quartz" , which may be controlled by the reaction garnet + quartz + H2O -> hornblende + plagioclase; (3) the retrograde stage with cooling and decompression, featured with chlorite developing along the fractures of garnet. Combined with previous results, it is speculated that the garnet amphibolite was formed during subduction and erosion of the Paleo-Asian Ocean in the Late Ordovician.