Nanoscale Os isotopic quantification of Wadi Tayin dunite platinum group minerals by atom probe tomography

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Stefano Tenuta , Katy A. Evans , Steven M. Reddy , David W. Saxey , Tommaso Tacchetto , Denis Fougerouse , Xiao Sun
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Abstract

Serpentinites record processes that redistribute major and trace elements between mantle and crust. Platinum Group Elements (PGEs) are trace elements in serpentinites hosted in sulphides and alloys. Alloys are challenging to find, and most analytical techniques lack the spatial resolution to analyse them. This research adopts automatic mineral mapping technique to detect PGM grains in a sample from the Wadi Tayin (Oman) peridotite and uses atom probe tomography, a nanoscale quantitative analytical technique, to analyse the grain. This work applies and assesses the applicability of atom probe tomography to measure the 187Os/188Os isotopic ratio of natural alloys and uses the ratio to constrain the source of Os. A novel algorithm is used to automatically determine the number of counts of the 187Os and 188Os peaks, to calculate the isotopic 187Os/188Os ratio and the analytical uncertainty. The 187Os/188Os ratio is 0.126 ± 0.003, consistent with the isotopic composition reported by literature in the dunite of the Main Mantle Section of the Wadi Tayin ophiolite.
The analytical uncertainty is one order of magnitude higher than conventional bulk rock techniques, such as negative-thermal ionisation mass spectrometry (N-TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). However, the precision is sufficient to conclude that the non-radiogenic 187Os/188Os ratio is compatible with a mantle origin for the alloy. Decreasing whole-rock Re with increasing LOI and the overprinting of magmatic pentlandite by magnetite demonstrate that progressive serpentinisation may have modified the Re budget. The results indicate that atom probe tomography can analyse 187Os/188Os ratio quantitatively in micron-sized natural alloys and provide insights into natural processes.
利用原子探针断层扫描技术对瓦迪塔因白云石铂族矿物进行纳米级 Os 同位素定量分析
蛇绿岩记录了主要元素和微量元素在地幔和地壳之间重新分布的过程。铂族元素(PGEs)是蛇纹岩中以硫化物和合金形式存在的微量元素。合金的发现具有挑战性,大多数分析技术缺乏分析合金的空间分辨率。本研究采用自动矿物制图技术检测瓦迪塔因(阿曼)橄榄岩样本中的 PGM 晶粒,并使用纳米级定量分析技术原子探针断层扫描来分析晶粒。这项工作应用原子探针层析技术测量天然合金的 187Os/188Os 同位素比值,并对其适用性进行了评估。研究采用了一种新颖的算法,自动确定 187Os 和 188Os 峰的计数次数,计算出同位素 187Os/188Os 比率和分析不确定性。187Os/188Os 比率为 0.126 ± 0.003,与文献报道的瓦迪塔伊因蛇绿岩主幔段云英岩的同位素组成一致。分析不确定性比传统的块岩技术(如负热电离质谱法(N-TIMS)和电感耦合等离子体质谱法(ICP-MS))高一个数量级。然而,精确度足以得出结论:非辐射成因的 187Os/188Os 比值与合金的地幔成因相符。全岩 Re 随 LOI 的增加而降低,以及磁铁矿对岩浆戊铁矿的覆盖,表明蛇绿岩化可能改变了 Re 的预算。研究结果表明,原子探针层析技术可以定量分析微米级天然合金中的 187Os/188Os 比率,并提供对天然过程的深入了解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Lithos
Lithos 地学-地球化学与地球物理
CiteScore
6.80
自引率
11.40%
发文量
286
审稿时长
3.5 months
期刊介绍: Lithos publishes original research papers on the petrology, geochemistry and petrogenesis of igneous and metamorphic rocks. Papers on mineralogy/mineral physics related to petrology and petrogenetic problems are also welcomed.
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