In situ Cr isotope measurements and early solar system history

项目背景该项目将开发原位激光烧蚀测量铬同位素的方法，以提高我们对太阳系早期历史的理解。大块陨石显示出“与质量无关”的54Cr的变化，这意味着富含54Cr的载流子的不均匀混合[Trinquier等，2007]。找到这个载体对于理解是什么导致了行星形成材料成分的变化是很重要的。研究发现氧化物颗粒明显携带异常的54Cr，但这些需要对54Fe干扰进行大量修正，而这些干扰无法解决，必须假设为“正常”[Dauphas等人，2010；秦等，2011]。此外，这些颗粒是陨石溶解的残留物，不是在原位发现的。最终我们希望在原始陨石基质中找到携带54Cr异常的太阳前颗粒。项目目标和方法本工作将利用我们独特的Proteus碰撞电池多集电极电感耦合等离子体质谱计的能力。该项目将寻找原位Cr同位素异常，并利用Proteus的能力，消除54Fe干扰（通过在碰撞单元中将Fe氧化为FeO）。这是一个具有挑战性的课题，需要大量的分析实验。作为建立方案的第一步，该项目将尝试一种更简单的装置来测量高度还原的辉化辉石球粒陨石中富锰硫化物（宁质辉石）的Cr同位素组成[Ehlers和El Gorsey， 1988]。利用53Mn-53Cr计时器（t1/2 = 3.7Ma），这有望提供承载硫化物的球粒的精确年龄。顽辉辉石球粒陨石中球粒的精确年龄很少，因此这将产生有价值的新信息。在任何原位研究中，重要的是对散装技术的基准标准。因此，该项目还将包括通过热电离质谱分析Cr同位素。在所有的工作将提供最前沿的培训，在广泛的分析技能，集中在局部宇宙化学问题。

Project BackgroundThe project will develop methods to make in situ, laser ablation measurements of Cr isotope to improve our understanding of the earliest history of the solar system. Bulk meteorites show variations in 'mass independent' 54Cr, implying inhomogeous mixing of a 54Cr-rich carrier [Trinquier et al., 2007]. Finding the carrier is important to understand what causes this variability in the composition of planetary forming materials. Studies have found oxide grains that apparently carry anomalous 54Cr, but these required large corrections for 54Fe interferences, which could not be resolved and had to be assumed to be 'normal' [Dauphas et al., 2010; Qin et al., 2011]. Moreover, the grains were the residues of meteorite dissolutions and not found in situ. Ultimately we wish to find in the matrices of primitive meteorites pre-solar grains carrying a 54Cr anomaly.Project Aims and MethodsThis work will exploit the capabilities of our unique, Proteus collision cell multi-collector inductively coupled plasma mass-spectrometer. This project will look for Cr isotope anomalies in situ, and using the capabilities of Proteus, remove 54Fe interferences (by oxidising Fe to FeO in the collision cell). This is a challenging topic, which will require extensive analytical experimentation. As an initial step in establishing a protocol, the project will try a simpler set up to measure the Cr isotopic composition of Mn-rich sulphides (niningerites) in highly reduced, enstatite chondrites [Ehlers and El Gorsey, 1988]. This holds the promise of providing precise ages, of the chondrules which host the sulphides, using the 53Mn-53Cr chronometer (t1/2 = 3.7Ma). There are few precise ages for chondrules in enstatite chondrites and so this would yield valuable new information. In any in situ study, it is important to benchmark standards against bulk techniques. So the project will also involve analysing Cr isotopes by thermal ionisation mass-spectrometry. In all the work will provide cutting edge training in a wide range of analytical skills, focussed on topical cosmochemical problems.