川西马尔康地区李家沟锂辉石伟晶岩同构造侵位记录:来自白云母和锂辉石显微构造的证据  

Syntectonic emplacement of the Lijiagou spodumene pegmatite in the Markam region,western Sichuan Province:Evidence from microstructure of muscovite and spodumene

作　　者：马绪宣 郑碧海[3] 赵恒兵 赵中宝[1,2] 高建国 李海兵 黄宇航[1] 秦宇龙 MA XuXuan;ZHENG BiHai;ZHAO HengBing;ZHAO ZhongBao;GAO JianGuo;LI HaiBing;HUANG YuHang;QIN YuLong(Key Laboratory of Continental Tectonics and Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Jiangsu Donghai Continental Deep Hole Crustal Activity National Observation and Research Station,Donghai 222300,China;State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Institute of Continental Geodynamics,Nanjing University,Nanjing 210023,China;Sichuan Dexin Mining Resources Co.Ltd,Jinchuan 624100,China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China;Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province,Sichuan Institute of Comprehensive Geological Survey,Chengdu 610081,China)

机构地区：[1]自然资源部大陆动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]江苏东海大陆深孔地壳活动国家野外观测研究站,东海222300 [3]南京大学地球科学与工程学院,内生金属成矿机制研究国家重点实验室,大陆动力学研究院,南京210023 [4]四川德鑫矿业资源有限公司,金川624100 [5]成都理工大学,油气藏地质及开发工程国家重点实验室,成都610059 [6]四川省综合地质调查研究所,稀有稀土战略资源评价与利用四川省重点实验室,成都610081

出　　处：《岩石学报》2024年第12期3909-3922,共14页Acta Petrologica Sinica

基　　金：中国地质调查局项目(DD20242126、DD20221630);南京大学卓越计划《川西伟晶岩型锂矿科学钻探》项目;国家自然科学基金项目(42272267、42230312);国家重点研发计划项目(2019YFA0708601);第二次青藏科考项目(2019QZKK0802);中国地质科学院自主基金(JKYQN202309);四川省科技计划项目(2023NSFSC0267)联合资助。

摘　　要：中国西部松潘-甘孜造山带广泛分布晚三叠世-早侏罗世花岗伟晶岩型锂矿床。理清该时期锂辉石伟晶岩脉形成的构造地质背景及其侵位过程对于未来勘探找矿具有重要意义。本文以川西李家沟晚三叠世-早侏罗世锂辉石伟晶岩为例,在详细的野外观测和显微构造分析基础上,聚焦伟晶岩脉中白云母和锂辉石两种矿物的显微结构和构造特征。研究发现白云母主要有两种类型,一种是分布于锂辉石破裂处,具有自形、板条状特征;另一种白云母主要分布于相邻锂辉石晶体的边缘,并发生明显的弯折、沿解理面的滑动、晶内破裂、重结晶造成的晶内及边缘新晶粒生成,以及云母鱼等现象,为典型的韧-脆性变形特征。锂辉石呈巨晶状,表现出脆、韧性两种变形特征。脆性变形主要是晶内破裂,破裂处被晚期结晶的白云母、石英等充填;韧性变形特征包括晶体弯曲、双晶纹错动、双晶纹一端变细或尖灭等。这些显微结构、构造证据表明锂辉石伟晶岩脉完全结晶固结之前发生脆、韧性变形,是吸收了区域构造应力的结果。区域调查发现围岩地层中顺层侵位的同构造无矿伟晶岩脉与部分切层含矿伟晶岩脉为连通关系,指示二者为同源岩浆、同期侵位。此外,李家沟矿区井下工作发现大部分锂辉石伟晶岩脉都是侵位在三叠系变沉积地层褶皱的核部,靠近伟晶岩脉的围岩变形面理平行或小角度斜交二者接触面。以上证据表明李家沟锂辉石伟晶岩脉形成于造山挤压背景下,即锂辉石伟晶岩为同构造岩浆侵位的产物。The Late Triassic-Early Jurassic granitic pegmatite lithium deposits are widely spread in the Songpan-Ganze orogenic belt in western China.It is important to understand the tectonic setting and the processes involved in the formation of the spodumene-rich pegmatite for future prospecting.In our study,a detailed field investigation and observation on the microstructures of the muscovite and spodumene in the Late Triassic-Early Jurassic pegmatite in the Lijiagou region was conducted to constrain these problems.Our results revealed there are two types of muscovite:one is found in the fracture zone of spodumene,exhibiting a euhedral lath shape;while the other type is mainly located in the contact zone of two large spodumene grains,showing obvious microstructures formed by ductile-brittle deformation,such as folding,sliding along the cleavage plane,intragranular fracture,muscovite neoblasts within and along the margins due to recrystallization,and muscovite fish,etc.The spodumene generally appears as megacrysts,exhibiting brittle and ductile deformation characteristics.The brittle deformation of the spodumene is represented by intragranular fracture filled by muscovite and quartz grains;while the ductile deformation includes folding,offset of grown twin lamellae,and tapering of deformation twin lamellae.These microstructures were likely formed before the complete crystallization of the pegmatite and caused by regional deformation.Field investigation reveals that the syntectonic barren pegmatite emplaced along the deformation foliation connected with the spodumene-rich pegmatite that cuts the deformation foliation of country rocks,indicating that they were synchronously emplaced and derived from the same source.Additionally,most of the spodumene-rich pegmatites in the Lijiagou region occurred in the fold core of the Triassic metasedimentary rocks.The deformation foliation of the host rocks parallels or is at a small angle oblique to the pegmatite.These lines of evidence demonstrate that the spodumene-rich pegmatites ar

关 键 词：显微构造 白云母 锂辉石 伟晶岩 同构造侵位 李家沟 

分 类 号：P578.954[天文地球—矿物学] P578.959[天文地球—地质学] P588.131