Accurate and precise measurements of the D/H ratio and hydroxyl content in lunar apatites using NanoSIMS
Accurate and precise measurements of the D/H ratio and hydroxyl content in lunar apatites using NanoSIMS
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DOI：
10.1016/j.chemgeo.2012.11.015
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发表时间：
2013-01-28
期刊：
影响因子：
3.9
通讯作者：
Russell, S. S.
中科院分区：
文献类型：
--
作者：
Barnes, J. J.;Franchi, I. A.;Russell, S. S.
本文介绍了一种技术的发展，使用NanoSIMS进行精确和准确的氢同位素组成和磷灰石颗粒的羟基含量的测定。还进行了实验以确定在通过二次离子质谱（西姆斯）分析之前使用二次电子显微镜（SEM）和电子探针显微分析（EPMA）对磷灰石颗粒中挥发性元素（H）的迁移率的影响（如果有的话）。实验结果表明，使用相对低的束流，短的曝光时间，没有对H的迁移率的不利影响，没有明显的变化，在测量的D/H比从或在一个晶粒内。因此，根据我们的研究，我们建议，常规的SEM分析确实可以用来定位合适的磷灰石颗粒西姆斯分析，而不会危及氢同位素measurements.As的磷灰石颗粒位于研究部分使用SEM和氢同位素组成的月球磷灰石颗粒从两个阿波罗月海玄武岩使用NanoSIMS确定。分析样品的Δ D值范围为600至1000份/千份，OH含量为1200至4400 ppm。在本研究中进行的磷灰石中Δ D和OH含量的测量与10044的先前结果一致，但12064的新数据集包含的Δ D值和OH含量范围比先前记录的更大。我们使用10 x 10 μ m的光栅尺寸（从5 x 5 μ m区域收集数据）进行每次分析，并在2 σ水平下获得典型的+/- 40至80千分之一的精度。这证明了使用NanoSIMS 50 L精确测量含有超过300-400 ppm OH的磷灰石中的D/H比和OH含量的能力。耦合的羟基丰度和氢同位素组成数据允许潜在的D/H分馏，可能发生在岩浆脱气，这可能最终是负责相对较高的三角洲D签名月海玄武岩磷灰石的评估。(C)2012爱思唯尔有限公司版权所有。
This paper describes the development of a technique using NanoSIMS to make precise and accurate determination of the hydrogen isotopic composition and the hydroxyl content of apatite grains. An experiment was also performed to determine the effects, if any, of using secondary electron microscopy (SEM) and electron probe micro-analysis (EPMA) on the mobility of volatile elements (H) in apatite grains, prior to analysis by secondary ion mass spectrometry (SIMS). The results of the experiment show that using a relatively low beam current, for a short exposure time, did not have adverse effects on the mobility of H with no apparent change in the measured D/H ratio from or within a grain. Thus, based on our study, we suggest that routine SEM analysis can indeed be used to locate suitable apatite grains for SIMS analyses without jeopardising the hydrogen isotopic measurements.As such, apatite grains were located in the studied sections using SEM and the hydrogen isotopic compositions of the lunar apatite grains from two Apollo mare basalts were determined using NanoSIMS. The delta D values for the samples analysed ranges from similar to 600 to 1000 parts per thousand and OH content from 1200 to 4400 ppm. The measurements of delta D and OH contents in apatites, performed in this study, are consistent with previous results for 10044 but the new dataset for 12064 consists of a larger range in delta D values and OH contents than previously documented. We used a raster size of 10 x 10 mu m (with data collected from a 5 x 5 mu m area) for each analysis and obtained typically +/- 40 to 80 parts per thousand precision at the 2 sigma-level. This demonstrates the capability of using the NanoSIMS 50L to accurately measure D/H ratios and OH contents in apatites containing more than 300-400 ppm OH. The coupled hydroxyl abundance and hydrogen isotopic composition data permitted an assessment of the potential D/H fractionation which may have occurred during magmatic degassing, which may ultimately be responsible for the relatively high delta D signatures of apatites from mare basalts. (C) 2012 Elsevier B.V. All rights reserved.