Microstructures,Deformation Mechanisms and Seismic Properties of Synkinematic Migmatite from Southeastern Tibet:Insights from the Migmatitic Core of the Ailao Shan-Red River Shear Zone,Western Yunnan,China  

作　　者：Weiwei Ma Bo Zhang Fulong Cai Baoyou Huang Lei Zhang 

机构地区：[1]Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing,100871,China [2]Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing,100085,China

出　　处：《Journal of Earth Science》2024年第4期1149-1169,共21页地球科学学刊（英文版）

基　　金：supported by the National Natural Science Foundation of China(No.41772207);the Second Tibetan Plateau Scientific Expedition and Research Program(No.2019QZKK0703).

摘　　要：Seismic anisotropy originating within the continental crust is commonly used to determine the deformation and kinematic flow within active orogens and is attributed to regionally oriented mica or hornblende grains.However,naturally deformed rocks usually contain compositional layers(e.g.,parallel compositional banding).It is necessary to understand how both varying mineral contents and differing intensities of compositional layering influence the seismic properties of the deep crust.In this study,we analyzed the seismic response of migmatitic amphibolite with compositional banding structures.We present the microstructures,fabrics,calculated seismic velocities,and seismic anisotropies of mylonitic amphibolite from a horizontal shear layer preserved within the Ailao Shan-Red River shear zone,southwestern Yunnan,China.The investigated sample is characterized by pronounced centimeter-scale compositional banding.The microstructures and fabrics suggest that migmatitic amphibolite rocks within deep crust may delineate regions of deformation-assisted,channelized,reactive,porous melt flow.The origin of compositional banding in the studied migmatitic amphibolite is attributed primarily to partial melting together with some horizontal shearing deformation.The microfabrics and structures investigated in this study are considered to be typical for the base of active horizontal shear layers in the deep crust of southeastern Tibet.Seismic responses are modeled by using crystal preferred orientations for minerals of the migmatitic amphibolite by applying the Voigt-Reuss-Hill homogenization method.Calculated P-wave and S-wave velocities are largely consistent in the various layers of the migmatite.However,seismic anisotropies of P-wave(AV_(p))and S-wave(AVs)are higher in the melanosomes(AV_(p)=5.6%,AV_(s)=6.83%)than those in the leucosomes and the whole rock(AV_(p)=4.2%–4.6%,AV_(s)=3.1%–3.2%).In addition,there is pronounced,S-wave splitting oblique to the foliation plane in the migmatitic amphibolite.The multiple parallel com

关 键 词：deformation-assisted melt flow seismic anisotropy microstructure compositional banding MIGMATITE deep crust southeastern Tibet 

分 类 号：P315.2[天文地球—地震学] P542[天文地球—固体地球物理学]