摘要
嫩江洋闭合机制是大兴安岭地区一个争议较大的科学问题。音德尔杂岩为大兴安岭与松辽盆地盆山结合带上新发现的一套俯冲增生杂岩,岩石强烈韧性变形,其构造变形样式及时间较好的记录了嫩江洋闭合过程。该套杂岩基质由绢云片岩、绿泥石片岩及阳起石片岩等组成,岩块主要包括闪长岩、辉长岩、玄武安山岩及花岗岩。宏观变形样式观察和微观组构分析表明,音德尔杂岩发育两期构造变形:早期变形以倾向NW的片理、片麻理及糜棱面理为标志,并发育有NNW向倾伏的构造线理,线理倾伏角一般较大,指示NW-SE方向强烈挤压背景下形成的一期逆冲线理;晚期变形以NE向倾伏的低角度矿物拉伸线理为标志,石英及长石等矿物通过晶内位错滑移与膨凸式重结晶等塑性流变方式显著定向拉长,构造形迹指示一期NE-SW走向的左行走滑剪切作用,晚期线理普遍改造或置换早期线理。两期构造变形事件分别对应兴安增生地体与松嫩地块碰撞造山早期的强烈挤压阶段和造山晚期伸展走滑调整阶段。构造岩与围岩接触关系年代学研究限定音德尔杂岩构造变形发生于早石炭世末期(323Ma)之前。早石炭世早期嫩江洋开启双向俯冲模式,在兴安增生地体东缘和松嫩地块西缘形成大量增生楔。早石炭世末期嫩江洋闭合,兴安增生地体与松嫩地块碰撞拼贴并发生强烈挤压造山,两侧增生楔在NW-SE方向汇聚应力驱使下呈花状仰冲隆起,伴随斜向走滑形成早期高角度叶理与线理。造山晚期,兴安增生地体与松嫩地块之间发生显著的左行走滑剪切作用,形成了NE-SW走向的低角度矿物拉伸线理。嫩江洋闭合相关构造的解析表明其具有双向俯冲的特征。
The closure mechanism of Nenjiang Ocean(NJO)is a controversial scientific issue in the Great Xing’an Range area.The newly discovered Yinder Complex,located in the basin and mountain conjunction belt of the Great Xing’an Range and Songliao Basin,is a typical subduction-accretionary related mélange.This complex is composed of blocks of diorite,gabbro,basaltic andesite and granite within the matrix of sericite schist,chlorite schist and actinite schist,showing typical block-in-matrix texture.Field observation and microscopic fabric analysis disclosed that two deformation stages occurred in the complex:the early-stage deformation was featured by NW-dipping schistosity,gneissic schistosity and mylonite foliation,and with NNW-dipping lineation with high angle,formed by NW-SE intense compression;while the late one by NE-dipping subhorizontal stretching lineation with low angle.The quartz,K-feldspar,plagioclase,mica and other minerals were clearly elongated by intracrystalline dislocation slip and bulk recrystallization,indicating a NE-SW left strike-slip shear movement.The two deformation stages are corresponding to collisional compression and post-collisional stretching strike-slip of the Xing’an Accretionary Terrane(XAT)and Songnen Block(SNB),respectively,and the early-stage lineation were commonly replaced by the late one.The contact relationships and geochronological data of the components of the Yinder Complex limit its deformations occurred before the late Early Carboniferous(ca.323 Ma).During the Early Carboniferous,the NJO initiated a“bi-directional subduction”model beneath SNB to the southeast and XAT to the northwest,and formed plenty of accretionary prisms at each side of these units.In late Early Carboniferous,the NJO was finally closured.Meanwhile,the strongly deformed collisional and orogenic belt between the SNB and the XAT forced a NW-SE compression that leads to significant obduction and uplifting of accretionary prisms at wedges of units at both sides,forming a typical upward oriented flower shape.The early-stage high angle foliation and lineation were formed during this process.In the late orogenic stage,a clearly left strike-slip activity was occurred between SNB and XAT,forming the late-stage NE-SW low angle lineation.The structural analysis related to closure of NJO suggests bidirectional subduction model of the ocean.
作者
马永非
刘永江
秦涛
冯志强
杨晓平
MA YongFei;LIU YongJiang;QIN Tao;FENG ZhiQiang;YANG XiaoPing(Gollege of Earth Sciences,Institute of Disaster Prevention,Sanhe 065201,China;Shenyang Center of Geological Survey,China Geological Survey,Shenyang 110034,China;Frontiers Science Center for Deep Ocean Multispheres and Earth System,Key Lab of Submarine Geoscience and Prospecting Techniques,College of Marine Geosciences,Ocean University of China,Qingdao 266100,China;Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao 266237,China;Department of Earth Science and Engineering,Taiyuan University of Technology,Taiyuan 030024,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第8期2419-2441,共23页
Acta Petrologica Sinica
基金
国家自然科学基金项目(42130305、42002227、42072230与419002234)
中国地质调查局项目(DD20221632)
青岛市创新领军人才计划(19-3-2-19-zhc)
泰山学者计划(ts20190918)联合资助。
关键词
音德尔杂岩
嫩江洋
双向俯冲
构造变形
俯冲-增生-碰撞
Yinder Complex
Nenjiang Ocean
Bi-directional subduction
Structure deformation
Subduction-Accretion-Collision
