Volatiles in the Earth-Moon System: a Stable Isotope Perspective

最近对月球样品氢同位素系统学的研究表明，地月系统中的水有一个共同的起源（例如，Tartèse和Anand，2013年;萨尔等人，2013年）。另一方面，月球样本的氯同位素组成被用来证明月球是无水的（夏普等人，2010年）与需要明显更潮湿的月球内部的各种月球岩石中测量的水含量的不断增长的数据库明显矛盾（例如，Tartèse等人，2013年）。在月球样品中的氢同位素工作大部分是在磷灰石或火山玻璃上进行的。相比之下，大多数氯同位素工作集中在大块岩石测量上，很少有磷灰石分析。有趣的是，除了月球样品，Cl同位素组成的原始行星物质测量的日期，包括地球样品，显示一个非常有限的变化（平均d37 Cl = -0.3 0.3）。这一特征被用来证明内太阳星云中存在一个均匀的Cl同位素库（例如，Sharp等人，2013).月球样品的Cl同位素组成变化超过20倍（d37 Cl从-0.7到24不等），这一特征被认为是Cl同位素分馏的结果，在没有H（或水）的情况下，并声称与样品测量结果一致;根据最新的数据，这一假设目前变得站不住脚。因此，必须评估其他过程和方案，可能会导致极端的Cl同位素分馏，如月球样品中所见。目前，有一个辩论，关于一些分析协议，在批量样品氯同位素测量，因此散装岩石数据的可靠性。因此，它是可取的，应用不同的技术，可以提供一个独立的方法来评估Cl同位素系统的行星samples.Apatite和岩浆玻璃的Cl-轴承阶段，几乎所有的行星样品，因此是合适的目标，在现场Cl-同位素测量的离子探针技术。拟议的项目将建立在开放大学最近开发的使用NanoSIMS测量磷灰石和玻璃中H和Cl同位素组成的协议的基础上。这项工作将涉及对一系列月球、陆地和其他陨石材料中磷灰石和玻璃的氯同位素进行测量，以建立一个数据库，据以评价在每种情况下赋予特定氯同位素组成所涉及的过程和来源，并帮助更好地了解地月系统中挥发物的来源。

Recent work focussing on hydrogen isotope systematics of lunar samples have indicated a common origin for water in the Earth-Moon system (e.g., Tartèse and Anand, 2013; Saal et al., 2013). On the other hand, chlorine isotope composition of lunar samples have been used to argue for an anhydrous Moon (Sharp et al., 2010) in apparent contradiction to the growing database of measured water contents in a variety of lunar rocks requiring a significantly wetter lunar interior (e.g., Tartèse et al., 2013). Much of the H isotope work in lunar samples have been carried out on apatite or volcanic glasses. In contrast, most of the chlorine isotope work has focussed on bulk-rock measurements with a very few analysis on apatites. Interestingly, except for lunar samples, Cl isotopic composition of pristine planetary materials measured to date, including terrestrial samples, display a very restricted variation (average d37Cl = -0.3 0.3). This characteristics has been used to argue for a homogeneous Cl isotope reservoir in the inner solar nebula (e.g., Sharp et al., 2013).Lunar samples display more than 20 fold variation in their Cl isotopic composition (d37Cl ranging from -0.7 to 24 ), a characteristics considered to be a result of Cl isotope fractionation in absence of H (or water) and claimed to be consistent with sample measurements; a hypothesis currently becoming untenable in light of latest data. It is therefore imperative to evaluate other processes and scenarios that might give rise to extreme Cl isotopic fractionation as seen in lunar samples. Currently, there is a debate regarding some of the analytical protocols employed in bulk-sample Cl isotope measurements and hence the reliability of the bulk-rock data. Thus, it is desirable to apply a different technique for Cl isotope measurements which could provide an independent method to assess Cl isotope systematics of planetary samples.Apatite and magmatic glasses are the major Cl-bearing phases in almost all planetary samples and are therefore suitable target for in-situ Cl isotope measurements by ion-probe techniques. The proposed project will build upon recent protocols developed at the Open University for measuring H and Cl isotopic composition in apatites and glasses using a NanoSIMS. The work will involve Cl isotope measurements in apatites and glasses in a range of lunar, terrestrial and other meteoritic materials to build a database with which to evaluate the processes and sources involved in imparting a specific Cl isotope composition in each case and help in developing a better understanding of the origin of volatiles in the Earth-Moon system.