A PETROLOGICAL AND NITROGEN ISOTOPE STUDY OF CRUSTAL RECYCLING THROUGH TIME

Peter Barry博士被授予美国国家科学基金会地球科学博士后奖学金，在田纳西大学开展一项研究和教育计划。他的研究将集中在克拉通和海洋岛屿背景下基性捕虏体的岩石学和挥发性（He-N-Ne）同位素特征。自太古宙以来，海洋地壳的俯冲不断发生，有效地将物质回收到对流的地幔中，并使表面、地幔和大陆之间的质量传递成为可能。稳定同位素（如氮）和稀有气体同位素（如氦和氖）是地幔过程的有力示踪剂，也是循环和地壳输入的敏感指标。库克群岛和西伯利亚克拉通的捕虏体样本显示了强有力的辅助证据（如氧同位素异常），表明它们来自回收的地壳原岩。我们将以捕虏体样品为目标，研究He-N-Ne同位素，这些样品之前已经使用Re-Os和Pb-Pb方法进行了年龄测定，并且跨越了很大（约30亿年）的年龄范围，以评估可能归因于再循环的时间整合地幔变化。此外，将对样品套件进行微探针（主元素）和LA-ICP-MS（微量元素和痕量元素）分析。我们使用地球化学和岩石学相结合的方法，因为同位素解释在强烈的岩石学约束下最有意义。这项研究对全面了解整个地球历史上的地幔演化和地壳循环具有广泛的影响。一个中心焦点将是氮，以及它是如何在整个地质时期在地球的水库之间运输的。氮很重要，因为它是现代地球大气中的主要气体（约78%）。然而，令人惊讶的是，人们对地幔的氮特征知之甚少——尤其是古代的循环储层。我们的目的是确定稀有捕虏岩样品的氮同位素特征，这些样品显示了地壳再循环的证据，并且跨越了很大的年龄范围。这项壮举将通过利用最近在斯克里普斯海洋学研究所建造的新开发的氮同位素提取和净化系统来完成。此外，这项研究将为学生和科学教育者提供一个绝佳的机会，通过外展计划向他们介绍实验室程序，向他们介绍当前项目的进展情况，并将前沿的地球科学研究带入课堂。此外，田纳西大学行星地球科学研究所的本科生和研究生将接受指导并参与本研究。研究结果将在国际科学会议以及田纳西大学的研讨会上发表。

Dr. Peter Barry has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at the University of Tennessee. His study will focus on petrology and volatile (He-N-Ne) isotope characteristics of mafic xenoliths from cratonic and ocean island settings. Subduction of oceanic crust has occurred continuously since the Archean, effectively recycling materials into the convecting mantle and enabling mass transfer between the surface, mantle, and continents. Stable (e.g., nitrogen) and noble gas (e.g., helium and neon) isotopes are powerful tracers of mantle processes, and sensitive indicators of recycling and crustal inputs. Selected xenolith samples from the Cook Islands and the Siberian Craton display strong ancillary evidence (e.g., oxygen isotope anomalies) suggesting they are derived from a recycled crustal protolith. We will target xenolith samples for He-N-Ne isotopes, which have previously been age dated using Re-Os and Pb-Pb methods and span a large (~3 billion years) age-range, to assess time-integrated mantle variations that are potentially attributed to recycling. In addition, microprobe (major elements) and LA-ICP-MS (minor and trace elements) analyses will be conducted on the sample suite. We use a combined geochemical and petrological approach, as isotopic interpretations are most meaningful when bracketed by strong petrological constraints.This study has broad impacts for the overall understanding of mantle evolution and crustal recycling throughout Earth history. A central focus will be on nitrogen and how it has been transported between Earth's reservoirs throughout geological time. Nitrogen is important because it is the principle gas (~78%) in Earth's modern-day atmosphere. However, surprisingly little is known about nitrogen characteristics of the Earth's mantle - particularly ancient recycled reservoirs. We aim to determine the nitrogen isotope characteristics of rare xenolith samples that show evidence of crustal recycling and span a large age-range. This feat will be accomplished by utilizing a newly developed nitrogen isotope extraction and purification system, recently constructed at Scripps Institution of Oceanography. Furthermore, this study will provide an excellent opportunity to engage both students and science educators, through outreach programs that introduce them to laboratory procedures and updating them on the progress of current projects and bringing cutting edge geoscience research into the classroom. Furthermore, undergraduate and graduate students at the University of Tennessee - Planetary Geosciences Institute, will be mentored and involved in this study. Findings will be presented at international science conferences as well as in seminars at the University of Tennessee.