多步浸提法在碳酸盐岩Sr同位素分析中的对比及优化  

Comparison and Optimization of Sr Isotope Analysis in Carbonate Rocks by Multiple-step Leaching Method

作　　者：潘旭 孙子威 高继苇 龚红梅[2,3] 王晓红 段梦[2,3] 肖媛媛 PAN Xu;SUN Ziwei;GAO Jiwei;GONG Hongmei;WANG Xiaohong;DUAN Meng;XIAO Yuanyuan(College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao 266590,China;Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;Laoshan Laboratory,Qingdao 266237,China)

机构地区：[1]山东科技大学地球科学与工程学院,山东青岛266590 [2]中国科学院海洋研究所,海洋地质与环境重点实验室,山东青岛266071 [3]崂山实验室,山东青岛266237

出　　处：《岩矿测试》2023年第4期691-706,共16页Rock and Mineral Analysis

基　　金：崂山实验室科技创新项目(LSKJ202204104;LSKJ202202905);泰山学者工程。

摘　　要：海相沉积碳酸盐岩是记录海水信息的重要载体,其中碳酸盐岩的Sr同位素比值(87Sr/86Sr)可以反映大陆地壳和地幔对海水组成的相对贡献,其长期变化趋势可用于反演地球历史上的全球构造事件、风化速率变化和生物地球化学循环以及确定海相沉积地层年龄等。然而,现存古老地层中的碳酸盐岩常不同程度地保留有非碳酸盐组分,并受到后期蚀变影响,从而使碳酸盐岩全岩的Sr同位素组成不等同于原生碳酸盐组分的Sr同位素组成。为了获取可以反映当时的海水组成的原生碳酸盐组分,需要建立一种有效的浸提方法。本文基于已有的两种碳酸盐岩多步浸提方法,探讨了其适用性,并简化了预浸步骤、缩短了流程时间,明确了不同种类的碳酸盐岩的浸提方法。结果表明:碳酸盐纯度≥85%的灰岩适用于采用浸提液为1%乙酸的9步浸提法,目标步骤为L7~L9;纯度≥65%的白云岩样品适用于采用浸提液为0.25%~10%乙酸的14步浸提法,目标步骤为D13~D14,采用多接收电感耦合等离子体质谱仪(MC-ICP-MS)对纯化后的目标浸提液进行Sr同位素测试。通过此方法获得中国灰岩标准物质GBW03105a原生碳酸盐组分的87Sr/86Sr比值为0.708930±0.000015(n=12,2SD),与前人研究结果(0.708879±0.000013)相吻合;并报道了欧洲钢铁标准化委员会(ECISS)白云岩标准物质ECRM-782-1原生碳酸盐组分的^(87)Sr/^(86)Sr比值为0.707868±0.000034(n=12,2SD),为后续地球化学分析提供了方法和数据支持。BACKGROUND:Marine sedimentary carbonate rock is an important carrier for recording seawater information.The Sr isotope composition(87Sr/86Sr)of carbonate rocks can reflect the relative contribution of the continental crust and mantle to the Sr isotope composition of seawater.The long-term variation trend of Sr isotope composition in geological history can be used to interpret global tectonic events,weathering rate changes,biogeochemical cycles,and determine the age of marine sedimentary strata.However,the carbonate rocks likely contain non-carbonate fractions to varying degrees,which lead to the whole rock Sr isotope composition being unequal to that of the primary carbonate fraction.In order to obtain the primary carbonate fraction that reflects the primitive seawater,an effective leaching method is required.OBJECTIVES:To identify experimental procedures and target leaching steps that can effectively extract representative primary carbonate fractions in carbonate rock samples of varying purity and variety.METHODS:Reference materials of dolostone and limestone(GBW03105a and ECRM-782-1)were selected to represent carbonate rock samples with high purity,and natural samples of limestone(C-3,purity:85%)and dolostone(E-3,purity:65%)were selected to represent samples with low purity.The leaching solution of all steps was measured for Ca and Mg contents by inductively coupled plasma-optical emission spectrometry(ICP-OES),for Sr,Mn and Al contents by inductively coupled plasma-mass spectrometry(ICP-MS).The Sr isotope was measured by multi-collector inductively coupled plasma-mass spectrometry(MC-ICP-MS)after purification of the leaching solution.Through the utilization of various indicators,such as Sr/Ca and Mn/Sr,the targeted leaching steps were ascertained.

关 键 词：碳酸盐岩 SR同位素 多步浸提法 原生碳酸盐组分 MC-ICP-MS 

分 类 号：O562.6[理学—原子与分子物理] O614.23.2[理学—物理]