PDF《量电子探针原位分析：》

10000569 /

2019 / 035( 04)105870 Acta Petrologica Sinica 岩石学报doi:

10 18654 /

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2019 04

05 石榴子石Fe3 + 含量电子探针原位分析:Flank Method 方法的实例应用李小犁陶仁彪李清云朱建江张立飞LI XiaoLi,TAO RenBiao,LI QingYun,ZHU JianJiang and ZHANG LiFei 北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871 MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China

20180702 收稿,20190122 改回Li XL,Tao RB,Li QY,Zhu JJ and Zhang LF

2019 Microprobe analysis of ferric iron in garnet:The Flank Method and case application Acta Petrologica Sinica,35( 4):

1058 -1070,doi:

10 18654 /

10000569 /

2019 04

05 Abstract The electron microprobe ( EMP)analysis is a quick and nondestructive method for qualitative and quantitative analyses upon samples from material science and geoscience,which plays a fundamental and vital role in these subjects It is of great scientific significance in the geological research to use EMP to determine the insitu contents of Fe with different valences ( ferric and ferrous)in minerals The newly developed microprobebased Flank Method measurement to quantify the Fe3 + content in minerals is comparatively of much higher precision and greater credibility than the early experimental approaches The Flank Method measures the defined flank positions instead of the actual peaks of the iron'

s Xray characteristic L emission spectra (FeL) ;

those flank positions correspond to the maxima (FeLα )and minima (FeLβ )values of the iron'

s absorption difference spectrum Meanwhile,a spectrometer calibration procedure is designed for the peak shift error correction prior to the Flank Method measurement in order to maintain the analytical reliability and reproducibility This calibration procedure should be performed in each working session within a proper time duration In this work,we propose a modified and improved Flank Method measuring procedure after the early suggestions,to analyze the Fe3 + content in the garnet by using JEOL JXA8100 microprobe in our facility The feasibility,reliability and repeatability of this method has been well tested on several standard garnets with known Fe3 + contents in our laboratory,and then it is applied on some natural garnet samples The analyzed garnets are from the typical oceanic subduction type mediumlow temperature and (ultra)high pressure eclogites of SW Tianshan (Habutengsu) ,Lhasa terrane (Songduo area)and North Qilian (Baijingsi foliate zone) .

The results show that the Fe3 + content serves a good indicator of the oxidation state,and its (zonal)change in garnet corresponds to the metamorphic PT path,suggesting that the oxygenfugacity is probably prone to decline in the subduction process Key words Microprobe;

Garnet;

Flank Method;

Ferric iron 摘要电子探针分析技术主要应用于对物质进行快速无损的定性、定量分析,是材料科学和地质学领域最基础和重要的研究手段.而 利用电子探针对矿物中不同价态Fe 的含量进行原位定量分析,更是具有非常重要的科学意义.近 来发展起来的可进行Fe3 + 含量定量分析的电子探针Flank Method 测试方法,相比早期的实验方法具有更高的准确度和精确性.该 方法主要是通过定义Fe 的特征X射线L能级谱线峰位的峰侧位置(flank position), 对应了不同价态Fe 吸收谱线的差值线谱(difference spectrum)中强度计数最大值(FeLα )和最小值(FeLβ )的位置,从而避免了在早期实验中,一般通过直接测量Fe 的L能级峰位(FeLα 和FeLβ)可能导致的测试不确定性.同 时,该测试方法通过对电子探针谱仪系统进行实时的位移误差校正,确保其在某一个稳定的实验条件(周 期 )下 具有可重现性(精 确度).在本文中,我们根据北京大学造山带与地壳演化教育部重点实验室的JEOL JXA8100 型号电子探针的实际性能状态,在前人建立的实验步骤基础上,进行了测试流程的自适性改进和修正,建立了更符合本实验室实际情况的电子探针Flank Method 测试方法,用于分析石榴子石中的Fe3 + 含量.通 过对已知Fe3 + 含量的标准石榴子石样品进行检测验证,确定了该方法的可行性、可靠性以及可重复性.在 对天然样品的分析中,我本文受国家自然科学基金项目(