Lawsonite-bearing eclogites in the north Qilian and north Altyn Tagh:Evidence for cold subduction of oceanic crust

作     者：ZHANG Jianxin MENG Fancong 

作者机构：Institute of Geology Chinese Academy of Geological Sciences Beijing100037 China 

出 版 物：《Chinese Science Bulletin》 (中国科学通报)

年 卷 期：2006年第51卷第10期

页      面：1238-1244页

核心收录：

学科分类：08[工学] 0824[工学-船舶与海洋工程] 

基　　金：Geological Survey Project of China, (200313000058) National Natural Science Foundation of China, NSFC, (40272095, 40472102) Ministry of Land and Resources of the People's Republic of China, MLR 

主　　题：祁连山 阿尔泰山 硬柱石 榴辉岩 洋底壳 

摘      要：Lawsonite-bearing eclogites are recog-nized respectively in the north Qilian (NQL) and north Altyn Tagh (NAT), based on petrography and mineral chemistry. Lawsonite coexists with omphacite and phengite as inclusions in garnet, indicating ec-logite-facies metamorphism. Peak metamorphic con-ditions for equilibrium lawsonite-omphacite-phengite- garnet peak assemblages are estimated to be 2.1―2.4 GPa and 420―500℃, which is in the stability field of lawsonite eclogite-facies. A low geotherm of 6―8℃/km is referred, which is in consistent with a cold subduction. The occurrences of lawsonite-bearing eclogites in both NQL and NAT provide further evi-dence that the NAT HP/LT metamorphic belt is pos-sibly the northwestward extension of the NQL HP/LT metamorphic belt offset by the Altyn Tagh left-lateral slip fault. The NQL and NAT lawsonite-bearing ec-logites are formed by subduction of oceanic crust before collision of the Alashan and Qilian blocks in early Paleozoic.