Microanalysis of tephra by LA-ICP-MS — Strategies, advantages and limitations assessed using the Thorsmörk ignimbrite (Southern Iceland)
Microanalysis of tephra by LA-ICP-MS — Strategies, advantages and limitations assessed using the Thorsmörk ignimbrite (Southern Iceland)
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DOI：
10.1016/j.chemgeo.2010.09.013
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发表时间：
2010-12
期刊：
影响因子：
3.9
通讯作者：
E. Tomlinson;T. Thordarson;W. Müller;M. Thirlwall;M. Menzies
中科院分区：
文献类型：
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作者：
E. Tomlinson;T. Thordarson;W. Müller;M. Thirlwall;M. Menzies
对泡状火山玻璃进行微米尺度的分析可能是有问题的，因为薄的泡状壁和连接限制了可供分析的区域，地下泡状物限制了可用的垂直厚度，表面或表面以下的微晶可能会污染玻璃分析，一些玻璃显示出成分带状。此外，远端被盖非常小(10-100μm)，物质可能稀疏。我们用激光烧蚀电感耦合等离子体质谱(LA-ICPMS)分析了来自冰岛南部Thorsmörk褐沸石的MPI-Ding参比玻璃和天然火山灰样品(浮石、Score和Fiamme)。采用了三种不同的约简策略：平均、不确定性加权和对数线性回归。然后，我们评估使用各种策略实现的数据质量。使用我们的技术，我们表明，数据质量的主要限制因素是精度，特别是对于自然的Tephra分析。在20,000 cps时，Thorsmörk tephra的相对标准偏差(%RSD)为5-10%，大约是相同条件下MPI-Ding眼镜的两倍(3-5%)。Thorsmörk褐沸石中的流纹岩浮石和Fiamme在成分上是均匀的。近端矿床中还含有次生玄武岩渣，属双峰型矿床。Thorsmörk流纹岩与海洋沉积岩芯中描述的北大西洋火山灰带2(NAAZ2)Tephra相关(Lacasse和Garbe-Schönberg，2001，JVGR 170,113-147)。
Micron-scale analysis of vesicular volcanic glass can be problematic because thin vesicle walls and junctions limit the area available for analysis, subsurface vesicles limit the vertical thickness available, microcrysts at or below the surface may contaminate glass analyses and some glasses show compositional banding. In addition, distal tephra are very small (10–100μm) and material may be sparse. We have analysed the MPI-DING reference glasses and natural tephra samples (pumice, scoria and fiamme) from the Thorsmörk ignimbrite (Southern Iceland) using laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS). Three different reduction strategies are used: averaging, uncertainty weighting and log-linear regression. We then assess the data quality achieved using the various strategies. Using our technique we show that the main limiting factor on data quality is precision, particularly for natural tephra analyses. At >20,000cps, relative standard deviations (%RSDs) in the Thorsmörk tephra are 5–10% — approximately twice those achieved in the MPI-DING glasses (3–5%) at the same conditions. Rhyolitic pumice and fiamme from the Thorsmörk ignimbrite are compositionally homogenous. The proximal deposit also contains subordinate basalt scoria, therefore the deposit is bimodal. The Thorsmörk rhyolite correlates with the North Atlantic Ash Zone 2 (NAAZ2) tephra described in a marine sediment core (Lacasse and Garbe-Schönberg, 2001, JVGR 170, 113–147).