柴北缘锡铁山印支期热液活动:来自榴闪岩石榴子石和石英脉真空击碎^(40)Ar/^(39)Ar年代学证据  

Indosinian Hydrothermal Activities in Xitieshan Area,North Qaidam:Insight from^(40)Ar/^(39)Ar Dating by In Vacuo Crushing of Eclogitic Garnet and Quartz Vein

作　　者：胡荣国 白秀娟[2] 刘希军 杨启军 赵义来 蔡永丰 邱华宁[2] Hu Rongguo;Bai Xiujuan;Liu Xijun;Yang Qijun;Zhao Yilai;Cai Yongfeng;Qiu Huaning(College of Earth Sciences,Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541004,China;Key Laboratory of Tectonics and Petroleum Resources,Ministry of Education,School of Earth Resources,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]桂林理工大学地球科学学院,广西隐伏金属矿产勘查重点实验室,广西桂林541004 [2]中国地质大学资源学院,构造与油气资源教育部重点实验室,湖北武汉430074

出　　处：《地球科学》2023年第12期4527-4539,共13页Earth Science

基　　金：国家自然科学基金项目(Nos.42073049,41703054);广西自然科学基金项目(Nos.2020GXNSFAA297049,2017GXNSFBA198164)。

摘　　要：为了示踪锡铁山超高压变质岩折返到浅部地壳后遭受后期热液流体叠加的年代及流体来源,首次采用真空击碎提取流体包裹体和粉末阶段加热^(40)Ar/^(39)Ar测年技术,对区内强退变质榴辉岩中的石榴子石与围岩片麻岩中接触部位的石英脉进行直接定年.石榴子石和石英都形成了单调递减的阶梯状表观年龄图谱.石榴子石真空击碎19至25阶段(末阶段)数据点构成平坦的年龄坪,对应的数据点在^(36)Ar/^(40)Ar-^(39)Ar/^(40)Ar图解上形成相关性很好的反等时线,等时年龄(222.6±16.7 Ma)与坪年龄(226.3±3.9 Ma)在误差范围内一致.真空击碎后的粉末进一步进行了分步加热分析(450~950°C共6阶段),获得了相对平坦的表观年龄图谱,对应坪年龄(212.0±9.0 Ma)和反等时线年龄(212.1±8.1 Ma)非常一致.石英脉09NQ39B则由19~29阶段数据点构成年龄坪,对应的坪年龄为222.8±1.2 Ma.榴辉岩中的石榴子石和石英脉同时记录了锡铁山地区印支晚期一期重要热液流体和热液蚀变事件,推测流体来源为沿区域性韧性剪切和透入性片理带入的浅部流体.强烈的晚期流体活动可能是导致该地区榴辉岩发生强烈退化变质作用,以及超高压变质指示矿物(如柯石英、金刚石等)难以保存的原因之一.One garnet sample from an extensively retrogressed eclogite and a quartz vein located at the boundary between the host gneiss and the eclogite lens from the Xitieshan terrane,North Qaidam,western China,have been analyzed by joint^(40)Ar/^(39)Ar in vacuo crushing and stepwise heating techniques.The results provide significant information to directly constrain the origin and timing of hydrothermal fluid flow activity,as well as the age of the vein-forming.The stepwise heating result could further be used to decipher the hydrothermal alteration history of the ultrahigh pressure(UHP)metamorphic rocks.Garnet sample analyzed by in vacuo crushing forms a falling-down age spectrum and yields a relatively flat age plateaus for the last 7 steps(19 to 25)with a plateau age of 226.3±3.9 Ma(2σ).These data points constitute the plateau age yielding an excellent isochron with an isochron age of 222.6±16.7 Ma and initial^(40)Ar/^(36)Ar ratio of 297±6.The crushed powders of the garnet yields,with further stepwise heating,a flat age spectrum with plateau age of 212.0±9.0 Ma,which defined a good isochron with an age of 212.1±8.1 Ma and initial^(40)Ar/^(36)Ar ratio of 296±1.These results illustrate that the Xitieshan eclogites and their retrogressed equivalents were intensively overprinted by hydrothermal event in the Late Triassic.Quartz samples dated by^(40)Ar/^(39)Ar in vacuo crushing method yield monotonic declining release patterns:anomalously old apparent ages are obtained at the first steps and relative flat age plateaus of 222.8±1.2 Ma over the final several steps.The gases liberated in the final steps are most derived from radiogenic and trapped argon in small primary fluid inclusions and pseudo-secondary fluid inclusions and also atmospheric argon from the crusher.The plateau age is interpreted as the best estimate for the age of quartz veining formation,witnessing a significant aqueous fluid flow episode during the Late Indosinian Period.Microthermometry analyses and^(40)Ar/^(39)Ar in vacuo crushing dating suggest

关 键 词：真空击碎^(40)Ar/^(39)Ar定年 流体包裹体 石英脉 热液蚀变 锡铁山地体 矿床 

分 类 号：P597.3[天文地球—地球化学]