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In Situ Oxygen Isotope Determination in Serpentine Minerals by SIMS: Addressing Matrix Effects and Providing New Insights on Serpentinisation at Hole BA1B (Samail ophiolite, Oman)
Geostandards and Geoanalytical Research ( IF 2.7 ) Pub Date : 2020-09-15 , DOI: 10.1111/ggr.12359
Maria Rosa Scicchitano 1 , Michael J. Spicuzza 1 , Eric T. Ellison 2 , David Tuschel 3 , Alexis S. Templeton 2 , John W. Valley 1
Affiliation  

The ability to constrain the petrogenesis of multiple serpentine generations recorded at the microscale is crucial for estimating the extent and conditions of modern versus fossil serpentinisation in ophiolites. To address matrix bias effects during oxygen isotope analysis by SIMS, we present the first investigation analysing antigorite in the compositional range Mg# = 77.5–99.5 mole %, using a CAMECA IMS‐1280 secondary ion mass spectrometer. Spot‐to‐spot homogeneity is ≤ 0.5‰ (2s) for the new antigorite reference materials. The relative bias between antigorite reference materials with different Mg/Fe ratios is described by a second‐order polynomial, and a maximum difference in bias of ~ 1.8‰ was measured for Mg# ~ 78 to 100. We observed a bias up to ~ 1.0‰ between lizardite and antigorite attributed to their different crystal structures. Orientation effects up to ~ 1‰ were observed in chrysotile. The new analytical protocol allowed the identification of oxygen isotope zoning up to ~ 7‰ in serpentine minerals from two serpentinites recovered from an area of active serpentinisation in the Samail ophiolite. Thus, in situ analysis is capable of resolving isotopic heterogeneity that may directly reflect changes in the physical and chemical conditions of multiple serpentinisation events in the Samail ophiolite.

中文翻译:

通过SIMS在蛇纹石矿物中原位氧同位素测定:解决基质效应并为BA1B洞的蛇纹石化提供新见解(阿曼Samail ophiolite)

在微观尺度上限制多个蛇纹石世代岩石形成的能力对于估算蛇绿岩中现代蛇纹石化化石蛇纹石化的程度和条件至关重要。为了解决SIMS在氧同位素分析过程中基质偏倚的影响,我们提出了使用CAMECA IMS‐1280二次离子质谱仪分析成分范围Mg#= 77.5–99.5摩尔%的反铁矿的首次研究。点对点均匀度≤0.5‰(2 s)作为新的反蛇毒参比材料。用二阶多项式描述了具有不同Mg / Fe比的抗蛇纹石参考材料之间的相对偏差,并且对Mg#〜78至100测得的偏差最大差异为〜1.8‰。我们观察到偏差最大为〜1.0蜥蜴石和蛇纹石之间的‰归因于它们的晶体结构不同。在温石棉中观察到了高达〜1‰的取向作用。新的分析规程允许从萨迈蛇绿岩蛇形岩中活跃的蛇纹岩化区域中回收的两种蛇纹岩中鉴定出蛇纹岩矿物中的氧同位素分区,最高可达〜7‰。因此,就地 分析能够解决同位素异质性问题,这种异质性可能直接反映了Samail蛇绿岩中多次蛇毒化事件的物理和化学条件的变化。
更新日期:2020-09-15
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