大别造山带宿松杂岩中石榴斜长角闪岩变质演化过程、原岩时限及其构造涵义  

Metamorphic evolution,protolith formation time and tectonic implications of garnet-plagioclase amphibolite in the Susong complex of the Dabie Orogenic Belt

作　　者：腊晓峰 石永红[1] 王娟[1] 周安泰 LA XiaoFeng;SHI YongHong;WANG Juan;ZHOU AnTai(College of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《岩石学报》2024年第1期140-158,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金重点项目(42330303);国家自然科学基金面上项目(41972059)联合资助.

摘　　要：大别造山带是由扬子板块向华北板块俯冲碰撞而形成的,出露了世界上规模最大的、种类最齐全的各类超高压岩石,全面深刻地记录了大陆深俯冲过程。然而,对于该造山带“浅层”(地壳层次)俯冲折返过程的研究则较少涉及,这制约了对大别造山带形成全过程的整体理解。为此,本次研究以大别造山带最南缘经历绿帘-角闪岩变质的宿松杂岩为研究靶区,针对该杂岩别河地区的石榴斜长角闪岩展开了精细的岩相学、矿物化学、温压评价和年代学研究。研究表明,该岩石记录了三个变质阶段,其中第二阶段可进一步分为a和b两个亚阶段,具体的变质温压条件分别为:①阶段Ⅰ:T=562±12℃、P=1.03±0.05GPa;②阶段Ⅱ-a:T=663±8℃、P=1.09±0.04GPa;③阶段Ⅱ-b:T=508~584℃、P_(-设定)=0.5~0.7GPa;④阶段Ⅲ:T=396~472℃、P_(-设定)=0.1~0.3GPa。其中,①→②表现为近等压增温型式,反映了一个俯冲迟滞过程,暗示了“浅层”俯冲止于莫霍面附近,并受下伏岩石地幔热源供给导致其持续增温,而②→③→④则显示降温降压样式,表现为缓慢抬升的过程。显然,大别造山带“浅”地壳层次的俯冲属于“暖”俯冲类型,并表现为一个缓慢变质演化过程,明显不同于大别造山带“冷”俯冲类型的大陆深俯冲的快速演化过程。锆石U-Pb年代学研究显示,石榴斜长角闪岩的锆石均为具振荡环带结构,测定的37个谐和年龄范围数据范围为1470±80Ma~1258±101Ma,Th/U比值均大于0.4,加权平均年龄为1381±25Ma,该年龄应为其原岩结晶年龄,代表了哥伦比亚超大陆最终裂解时限。此外,侵入于石榴斜长角闪岩中的富石英花岗岩的加权平均年龄为129±5Ma,反映了中国东部中生代伸展事件。结合前人的年龄资料,可以推测1.38~1.30Ga为哥伦比亚超大陆向罗迪尼亚超大陆转换的时间节点。同时,可以明确宿松杂岩则是由不同时代、不同岩石类型The Dabie Orogenic Belt(DOB)was formed by the subduction-collision between the Yangtze Plate and the North China Plate,which contained the largest and most complete variety of ultrahigh-pressure rocks in the world,and comprehensively recorded the process of continental deep subduction.However,few studies involve in the subduction and exhumation process of the‘shallow’level(at crust),and restricts overall understanding for the formation process of the DOB.In this study,the garnet-plagioclase amphibolite from the Susong complex in the southernmost of the DOB has been investigated by carrying out petrology,mineral chemistry,P-T estimates and chronology in detail.The result show that the garnet-plagioclase amphibolite contains three metamorphic stages ofⅠ,ⅡandⅢ,in further stageⅡcan be divided into stageⅡ-a andⅡ-b.The P-T conditions for these stages correspond to①StageⅠ:T=562±12℃,P=1.03±0.05GPa;②StageⅡ-a:T=663±8℃,P=1.09±0.04GPa;③StageⅡ-b:T=508~584℃,P_(-setting)=0.5~0.7GPa;④StageⅢ:T=396~472℃,P_(-setting)=0.1~0.3GPa,respectively,and display a clockwise P-T path.The process from①to②shows a nearly isobaric heating,and reflects a subduction stagnation.This imply that the‘shallow’subdution terminates at the Moho and is subject to a continuous heating by the supply of heat from the underlying lithospheric mantle.While the process from②to③and④exhibits a cooling and depression pattern,and reveals a slow exhumation.Obviously,the‘shallow’subduction in the DOB belongs to the‘warm’subduction and shows a slow metamorphic evolution process.On the contrary,the continental deep subduction of the DOB as a typical‘cold’subduction has undergone a rapid evolution process.In zircon U-Pb dating,all zircons from garnet-plagioclase amphibolite develop oscillatory zoning.Thirty-seven spots have been analyzed with 207 Pb/206 Pb ages ranging from 1470±80Ma to 1258±101Ma,and yield a weighted mean of 207 Pb/206 Pb age of 1381±25Ma with higher Th/U ratio>0.4,representing the a

关 键 词：宿松杂岩 石榴斜长角闪岩 中元古代 P-T轨迹 金红石Zr温度计 

分 类 号：P588.345[天文地球—岩石学] P597.3[天文地球—地质学]