THE ALTUN—NORTH QAIDAM ECLOGITE BELT IN WESTERN CHINA—ANOTHER HP-UHP METAMORPHIC BELT TRUNCATED BY LARGE SCALE STRIKE-SLIP FAULT IN CHINA

THE ALTUN—NORTH QAIDAM ECLOGITE BELT IN WESTERN CHINA—ANOTHER HP-UHP METAMORPHIC BELT TRUNCATED BY LARGE SCALE STRIKE-SLIP FAULT IN CHINA

The Altun-North Qaidam Eclogite Belt in Western China-Another HP-UHP Metamorphic Belt Truncated by Large Scale Strike-Slip Fault in China

The Altun and North Qaidam Mountains at the northern margin of Qinghai|Tibet plateau are separated by the Altyn Tagh sinistral strike|slip fault, which is one of the largest strike|slip fault systems in the world and was considered as the key element in the escape tectonics model for Euraisa|India continent|continent collision.Recently,the eclogites within quratzifeldspathic gneisses or pelitic gneisses characterized by amphibolite|facies paragenesis were discovered in the Altun and the North Qaidam Mountains(Fig.1). They occur as lens or boundins within the Altun Group and Dakendaban Group respectively which previously were considered as metamorphic basement of Tarim block and Qaidam block. Our studies indicate that the eclogites outcrop in both the Altun and North Qaidam Mountains show similar occurrences, associated country rocks, rock and mineral assemblages, p|T% estimates, geochemistryand protolith feature and ages of peak metamorphism (see table) . The garnet|omphacite|phengite geothermobarometer gave equilibrium condition of %p%=2 8～3 0GPa and t =820～850℃ for the Altun eclogite and p =2 8GPa and %t%=730℃ for North Qaidam eclogite respectively(Fig..2). These p|T conditions are in the coesite stability field. Moreover, Po lycrystalline quartz pseudomorphs after coesite have been identified in the Dulan area, North Qaidam Mountains (Song et al, in review). Therefore, these features suggest that both eclogites of Altun and North Qaidam Mountains probably are a same HP|UHP metamorphic belt formed from the same of Early Paleozoic age deep subduction and collision, and subsequently displaced by the Altyn Tagh fault.The case is similar to the Dabie|Sulu HP|UHP metamorphic zone which was truncated by the Tanlu sinistral strike|slip fault and splitted it into two distincts, the Dabie region and Sulu region. These correlations support an about 350～400km displacement of the Altyn Tagh sinistral strike|slip fault (Fig.1).