TEM and HRTEM Study of Microstructures in Omphacite from UHP Eclogites at Shima,Dabie Mountains,China  

作　　者：WU Xiuling HAN Yujing MENG Dawei YANG Weiran LI Douxing 

机构地区：[1]Test Center and Faculty of Earth Sciences,China University of Geosciences,Wuhan 430074,Hubei [2]Laboratory of Atomic Imaging of Solids,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110015,Liaoning

出　　处：《Acta Geologica Sinica(English Edition)》2000年第2期154-162,共9页地质学报（英文版）

基　　金：This work was supported by the Research Fund for the Doctoral Program of Higher Education of China(Project No.9349101);National Natural Science Foundation of China grants 49572146 and 49872069.

摘　　要：Transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) analyses have been performed on omphacite from ultra-high pressure (UHP) eclogites at the locality of Shima, Dabie Mountains, China. TEM reveals that the microstructures consist dominantly of dislocation substructures, including free dislocations, loops, tiltwalls, dislocation tangles and subboundaries. They were produced by high-temperature ductile deformation, of which the main mechanism was dislocation creep. Antiphase domain (APD) boundaries are common planar defects; an age of 470 ± 6 Ma for UHP eclogite formation has been obtained from the equiaxial size of APDs in ordered omphacites from Shima, coincident with ages given by single-zircon U-Pb dating (471 ± 2 Ma). HRTEM reveals C2/c and P2/n space groups in different parts of one single omphacite crystal, and no exsolution is observed in the studied samples, which is attributed to rapid cooling. It is suggested that the UHP eclogites underwent a long period of annealing at high temperatures, followed by relatively rapid cooling. These data provide valuable information for the formation and exhumation mechanism of UHP eclogites in the Dabie high-pressure (HP) and UHP metamorphic belt.Transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) analyses have been performed on omphacite from ultra-high pressure (UHP) eclogites at the locality of Shima, Dabie Mountains, China. TEM reveals that the microstructures consist dominantly of dislocation substructures, including free dislocations, loops, tiltwalls, dislocation tangles and subboundaries. They were produced by high-temperature ductile deformation, of which the main mechanism was dislocation creep. Antiphase domain (APD) boundaries are common planar defects; an age of 470 ± 6 Ma for UHP eclogite formation has been obtained from the equiaxial size of APDs in ordered omphacites from Shima, coincident with ages given by single-zircon U-Pb dating (471 ± 2 Ma). HRTEM reveals C2/c and P2/n space groups in different parts of one single omphacite crystal, and no exsolution is observed in the studied samples, which is attributed to rapid cooling. It is suggested that the UHP eclogites underwent a long period of annealing at high temperatures, followed by relatively rapid cooling. These data provide valuable information for the formation and exhumation mechanism of UHP eclogites in the Dabie high-pressure (HP) and UHP metamorphic belt.

关 键 词：UHP eclogite OMPHACITE TEM and HRTEM Dabie Mountains 

分 类 号：P588.125[天文地球—岩石学]