Microstructures, Fabrics, and Seismic Properties of Mylonitic Amphibolites: Implications for Strain Localization in a Thickening Anisotropic Middle Crust of the North China Craton

作     者：Siqi Liu Bo Zhang Jinjiang Zhang Jian Zhang Lei Guo Tao Wang Baoyou Hang Xiaorong Li Siqi Liu;Bo Zhang;Jinjiang Zhang;Jian Zhang;Lei Guo;Tao Wang;Baoyou Hang;Xiaorong Li

作者机构：Key Laboratory of Orogenic Belts and Crustal EvolutionSchool of Earth and Space SciencesPeking UniversityBeijing 100871China Department of Earth SciencesThe University of Hong KongHong KongChina Institute of GeologyChinese Academy of Geological SciencesBeijing 100037China 

出 版 物：《Journal of Earth Science》 (地球科学学刊（英文版）)

年 卷 期：2024年第35卷第3期

页      面：769-785页

核心收录：

学科分类：070904[理学-构造地质学] 070801[理学-固体地球物理学] 0709[理学-地质学] 07[理学] 0708[理学-地球物理学] 

基　　金：funded by the National Key Research and Development Program of China(No.2021YFA0716001) the National Science Foundation of China(No.42272245) 

主　　题：amphibolitic mylonite microstructures petrofabrics seismic property middle crust rheology tectonics. 

摘      要：Strain localization processes in the continental crust generate faults and ductile shear zones over a broad range of scales affecting the long-term lithosphere deformation and the mechanical response of faults during the seismic *** anisotropy originated within the continental crust can be applied to deduce the kinematics and structures within orogens and is widely attributed to regionally aligned minerals,e.g.,***,naturally deformed rocks commonly show various structural layers(e.g.,strain localization layers).It is necessary to reveal how both varying amphibole contents and fabrics in the structural layers of strain localization impact seismic property and its interpretations in terms of *** present microstructures,petrofabrics,and calculate seismic properties of deformed amphibolite with the microstructures ranging from mylonite to *** transition from mylonite to ultramylonite is accompanied by a slight decrease of amphibole grain size,a disintegration of amphibole and plagioclase aggregates,and amphibole aspect ratio increase(from 1.68 to 2.23),concomitant with the precipitation of feldspar and/or quartz between amphibole *** intensities of amphibole crystallographic preferred orientations(CPOs)show a progressively increasing trend from mylonitic layers to homogeneous ultramylonitic layers,as indicated by the JAm index increasing from 1.9–4.0 for the mylonitic layers and 4.0–4.8 for the transition layer,to 5.1–6.9 for the ultramylonitic *** CPO patterns are nearly random for plagioclase and *** amphibole aggregates in the amphibolitic mylonite deform by diffusion,mechanical rotation,and weak dislocation creep,and develop CPOs *** polymineralic matrix(such as quartz and plagioclase)of the mylonite and the ultramylonite deform dominantly by dissolution-precipitation,combined with weak dislocation *** mean P and S wave velocities are estimated to be 6.3 and 3.5 km/