In situ Cr isotope measurements and early solar system history

项目背景该项目将开发原位激光消融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。大块陨石在“质量无关”的54 Cr中显示出变化，这意味着富含54 Cr的载体的不均匀混合[Trinquier等人，2007年]。找到载体对于理解是什么导致行星形成材料成分的变化很重要。研究已经发现氧化物颗粒明显携带异常54 Cr，但是这些需要对54 Fe干扰进行大的校正，其不能被分辨并且必须被假设为“正常”[Daufas等人，2010; Qin等人，2011年]。此外，这些颗粒是陨石溶解的残留物，不是在原地发现的。最终，我们希望找到在矩阵的原始陨石太阳前颗粒进行54铬异常。项目的目的和MethodsThis工作将利用我们独特的，变形碰撞池多收集器电感耦合等离子体质谱仪的能力。该项目将在现场寻找Cr同位素异常，并利用Proteus的能力，消除54 Fe干扰（通过在碰撞池中将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。作为建立协议的第一步，该项目将尝试一种更简单的设置，以测量高度还原的顽火辉石中富锰硫化物（钠闪石）的铬同位素组成[Ehlers和El Gorsey，1988年]。利用53 Mn-53 Cr精密计时器（t1/2 = 3.7Ma），这有望提供硫化物所在球粒的精确年龄。顽火辉石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。在任何现场研究中，重要的是对照散装技术确定标准。因此，该项目还将涉及通过热电离质谱法分析铬同位素。在所有的工作中，将提供广泛的分析技能方面的尖端培训，重点是局部宇宙化学问题。

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.