赣西北蒙山地区三叠纪挤压‒伸展构造体制转换及其对硅灰石矿的控矿意义  

Triassic Compressional⁃Extensional Transition in Mengshan Area,NW Jiangxi Province,and Its Ore⁃Controlling Significance for Wollastonite Deposit

作　　者：赵东安 王国灿[1] 王先广 胡正华 刘少华 申添毅[1] 朱能杰 Zhao Dongan;Wang Guocan;Wang Xianguang;Hu Zhenghua;Liu Shaohua;Shen Tianyi;Zhu Nengjie(School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;Administration of Geological Exploration of Jiangxi Province,Nanchang 330025,China;No.224 Geological Brigade,Coal Geological Bureau of Jiangxi Province,Fenyi 330002,China)

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074 [2]江西省地质勘查基金管理中心,江西南昌330025 [3]江西省煤田地质局224地质队,江西分宜330002

出　　处：《地球科学》2023年第11期4053-4071,共19页Earth Science

基　　金：江西省地质勘查基金项目(Nos.20160046,20210034).

摘　　要：蒙山位于萍乐坳陷带西段的中部,三叠纪经历了较为复杂的构造‒岩浆过程,发育石竹山超大型硅灰石矿床.为了揭示该地区硅灰石矿的构造控矿机理,本研究基于野外宏观构造变形与室内显微构造特征的构造解析结合方解石EBSD分析,对该地区不同期次岩石变形特征进行了详细梳理.研究结果表明,蒙山地区三叠纪经历了两期构造变形事件,指示由挤压到伸展的构造体制转换:第一期(D1)为向SE低角度韧性逆冲推覆,伴随强烈的糜棱岩化;第二期(D2)为与蒙山花岗岩侵入相关的向SSW的伸展滑脱变形,变形灰岩发生大理岩化并伴有硅灰石矿化.微观构造分析表明,两期构造变形的方解石的颗粒大小和形态优选方位呈现出截然不同的特点.电子背散射衍射(EBSD)结果显示:D1变形方解石晶的C轴极密发育在Z轴附近,呈单斜对称指示向SE的逆冲型剪切;D2变形方解石发育多个随机分布的C轴极密,其经历同构造变质重结晶,重置了D1的微观构造变形.晚三叠世蒙山岩体侵入D1变形带,指示D1变形时限早于蒙山岩体的侵位时间;D2韧性滑脱变形和硅灰石矿化均受蒙山岩体侵位的伸展构造‒热体制控制,伸展滑脱导致层带状富矿化.D1变形与赣西北地区普遍存在的NW-SE向强烈挤压作用有关,受控于中三叠世华南与华北板块碰撞;D2变形则是在先期挤压变形基础上,于晚三叠世发生岩石圈伸展调整的结果.Mengshan,located in the middle of the western Pingxiang-Leping depression zone,have experienced complex tectonomagmatic processes during the Triassic,forming the Shizhushan giant wollastonite deposit.In order to reveal the structural orecontrolling mechanism of wollastonite deposit,in this study it probes into the rock deformation characteristics of different periods in detail based on the structural analysis of macroscopic and microscopic structural and the electron backscatter diffraction(EBSD)analysis of calcite.The results show that Mengshan experienced two tectonic deformation events during Triassic,indicating a tectonic regime transition from compression to extension.The D1 event is characterized by low angle ductile thrust with top-to-the-SE,accompanied by intense calci-mylonitization.The D2 event is a top-to-the-SSW extensional detachment related to the intrusion of the Mengshan granite.The deformed limestone is marmarosis and wollastonite mineralization.The microstructure analysis shows that the grain size and shape preferred orientation of calcite in the two deformed stages have different characteristics.EBSD results show that the D1 deformed calcite displays a wide c-axis maximum close to Z,indicating monoclinic symmetry and a top-tothe-SE thrust shearing.The calcite of D2 event developed randomly oriented c-axis poles,and underwent syn-tectonic recrystallization which resulted in resetting the microstructures of D1 event.The Late Triassic Mengshan granite intruded into the first deformation zone as a post-kinematic product in an extensional tectonic background that provides time constraints for the deformations.The D2 ductile detachment and wollastonite mineralization were both controlled by the extensional tectonothermal system of the Mengshan granite.The extensional detachment leads to layered rich mineralization.The D1 deformation can be related to the strong NW-SE compression widely developed in the Northwest Jiangxi Province,which was controlled by the collision of the South China block and North

关 键 词：赣西北蒙山地区 三叠纪 挤压‒伸展构造体制转换 控矿构造 硅灰石矿化 地球动力学 构造地质学 

分 类 号：P54[天文地球—构造地质学]