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

• 来源期刊: 科学通报(英文版)
• 学科: 地球科学
• 关键词: 等时线年龄 祁连山北部 蓝片岩相 中国西北 硬柱石 酒泉 构造 区域地质背景
• 年，卷（期）: 2010,（19）
• 所属期刊栏目: Geochemistry
• 页码范围: 2021-2027
• 页数: 7页
• 分类号: P597 P588.3
• 语种: 英文

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.