A PETROLOGICAL AND NITROGEN ISOTOPE STUDY OF CRUSTAL RECYCLING THROUGH TIME

彼得·巴里博士获得了美国国家科学基金会地球科学博士后奖学金，将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环境中镁铁质包体的岩石学和挥发性(He-N-Ne)同位素特征。自太古宙以来，洋壳不断俯冲，有效地将物质循环进入对流地幔，使表层、地幔和大陆之间的物质转移成为可能。稳定(如氮)和惰性气体(如氦和霓气)同位素是地幔过程的强有力示踪剂，也是再循环和地壳输入的敏感指标。来自库克群岛和西伯利亚克拉通的一些捕虏体样本显示出强有力的辅助证据(例如氧同位素异常)，表明它们来自于再循环的地壳原岩。我们将以捕虏体样品为目标进行He-N-Ne同位素测定，这些同位素以前已使用Re-Os和Pb-Pb方法测定年龄，并跨越了很大的(约30亿年)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，还将对样品组进行微探针(主要元素)和LA-ICPMS(次要和痕量元素)分析。我们使用了地球化学和岩石学相结合的方法，因为当受到强烈的岩石学约束时，同位素解释是最有意义的。这项研究对整个地球历史上对地幔演化和地壳再循环的整体理解具有广泛的影响。中心焦点将是氮，以及在整个地质时期，氮是如何在地球上的水库之间运输的。氮很重要，因为它是地球现代大气中的主要气体(~78%)。然而，令人惊讶的是，人们对地幔的氮特征知之甚少--特别是古老的再生水库。我们的目标是确定显示地壳再循环证据的稀有捕虏体样本的氮同位素特征，并跨越大的年龄范围。这一壮举将通过利用最近在斯克里普斯海洋研究所建造的新开发的氮同位素提取和纯化系统来实现。此外，这项研究将提供一个极好的机会，通过向学生和科学教育工作者介绍实验室程序的外展计划，向他们介绍当前项目的进展情况，并将尖端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这项研究。研究结果将在国际科学会议以及田纳西大学的研讨会上公布。

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.