地质学报2025，Vol.99Issue(4)：1150-1168,19.DOI:10.19762/j.cnki.dizhixuebao.2023180
变质岩中磷灰石变形与元素分布特征:以青藏高原东构造结变质岩为例
Deformation and element redistribution characteristic of in-situ apatite in metamorphic rocks:A case study of metamorphic rocks in the Eastern Himalayan Syntaxis
摘要
Abstract
The structural characteristics and element distribution within accessory minerals are crucial in documenting the metamorphicand deformational processes in rocks.In particular,in-situ geochronological dating of apatite has gained significant prominence,becoming vital for dating magmatic rocks and mineral deposits.Despite its significance,unresolved issues persist regarding the deformation mechanism,behavior,and restrictive impact on element diffusion in apatite during different metamorphic-deformation processes.This study focuses on rocks from the Eastern Himalayan Syntaxis,renowned for its intense tectonic deformation and metamorphism.Using SEM and CL observations,we identified notable differences inapatite within granulite and mylonitic schist.Granulite apatite lacks an apparent compositional structure,while mylonitic schist apatite exhibits distinct light and dark compositional changes.Statistical analysis of apatite distribution in thin sections revealed that the long axis of apatite grains in both metamorphic rocks aligns approximately parallel to the main foliation.Furthermore,EBSD fabric analysis unveiled clear intra-granular deformation in granulite apatite,whereas mylonitic schist apatite displayed minimal intra-granular deformation.EPMA scanning of apatite composition demonstrated a relatively uniform distribution of major elements in granulite,while silicon(Si)elements in mylonitic schist displayed evident zoning or unevenness,consistent with CL scanning results.Based on these observations,preliminary conclusions were drawn.Firstly,despite its directional distribution and intra-granular deformation,granulite apatitemay be influenced by higher metamorphic temperatures,promoting rapid element diffusion and uniform redistribution.Late-stage fluid activity metasomatized elements along low-angle grain boundaries or fractures perpendicular to maximum tensile stress.Secondly,mylonitic schist apatite,alignedwith mylonite foliation,exhibits minimal intra-granular deformation,likely due to lower deformation temperatures or the concentration of strain in quartz and mica domains,which effectively spared the relatively tough apatite from deformation.Compositional variations observed in CL images and major element distribution maps suggest limited diffusion due to lower metamorphic/deformation temperatures.Lastly,preliminary age results indicate multiple ages in granulite apatite,reflecting inherited apatite influencing element redistribution during metamorphism and late-stage metasomatism.In contrast,felsic mylonitic schist apatite records continuous fluid activity during mylonitization,leading to continuous crystallization.These findings offer valuable insights for interpreting apatite age in metamorphic and deformational rocks.关键词
喜马拉雅造山带/麻粒岩/糜棱岩化片岩/磷灰石粒内形变/磷灰石元素分布特征Key words
Himalayan Syntaxis/granulite/mylonitic schist/intragranular deformation of apatite/element distribution characteristics of apatite引用本文复制引用
张岩岩,赵中宝,杜瑾雪,梁凤华,毛小红,田作林,马绪宣..变质岩中磷灰石变形与元素分布特征:以青藏高原东构造结变质岩为例[J].地质学报,2025,99(4):1150-1168,19.基金项目
本文为中国地质科学院自然资源部深地科学与探测技术实验室基本科研业务费(编号JB2314)、国家自然科学基金项目(编号41902211)和中国地质调查项目(编号DD20221630)联合资助的成果. （编号JB2314）
