^(40)Ar/^(39)Ar isochron ages of lawsonite blueschists from Jiuquan in the northern Qilian Mountain,NW China,and their tectonic implications  

作　　者：LIN YiHui ZHANG LiFei JI JianQing WANG QianJie SONG ShuGuang 

机构地区：[1]The Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education of China,School of Earth and Space Sciences,Peking University,Beijing 100871,China

出　　处：《Chinese Science Bulletin》2010年第19期2021-2027,共7页

基　　金：supported by the National Natural Science Foundation of China (40821002);the National Basic Research Pro-gram of China (2009CB825007)

摘　　要：Using laser 40Ar/39Ar dating method,we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan,northern Qilian Mountain,NW China.The high quality laser 40Ar/39Ar dating of glaucophane from lawsonite blueschist gives an isochron age of 413±5 Ma.The isochron age obtained from phengite in epidote blueschist is 415±7 Ma.These data,combining with peak metamorphic P-T conditions and regional geological setting,allow us to infer that the lower limit of the ages of the prograde subduction metamorphism from lawsonite blueschist facies to epidote blueschist facies occurred at ca.413-415 Ma,which also suggests that the formation of lawsonite blueschist in the northern Qilian Mountain maybe resulted from the corner flow in the cold subduction zone.This study shows that the final closing time of the northern Qilian remnant oceanic basin is about 413-415 Ma,which also represents the convergent age between the North China Craton and the Qaidam block.Using laser ^40Ar/^39Ar dating method, we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan, northern Qilian Mountain, NW China. The high quality laser ^40Ar/^39Ar dating of glaucophane from lawsonite blueschist gives an isochron age of 413±5 Ma. The isochron age obtained from phengite in epidote blueschist is 415±7 Ma. These data, combining with peak metamorphic P-T conditions and regional geological setting, allow us to infer that the lower limit of the ages of the prograde subduction metamorphism from lawsonite blueschist facies to epidote blueschist facies occurred at ca. 413-415 Ma, which also suggests that the formation of lawsonite blueschist in the northern Qilian Mountain maybe resulted from the corner flow in the cold subduction zone. This study shows that the final closing time of the northern Qilian remnant oceanic basin is about 413-4 15 Ma, which also represents the convergent age between the North China Craton and the Qaidam block.

关 键 词：northern Qilian Mountain lawsonite-blueschist ^(40)Ar/^(39)Ar isochron age corner flow 

分 类 号：P597.3[天文地球—地球化学]