Collaborative Research: Examining Upper Mantle Volatile History Through Isotopic Variations of Carbon, Nitrogen, Hydrogen and Noble Gases in Undegassed Mid-Ocean Ridge Basalts

对大洋中脊海底玄武岩中二氧化碳、水、氮和惰性气体等挥发性物质的测量为我们提供了对地球大气和海洋的起源以及地球表面和地球内部之间循环的地质历史的相当大的洞察。然而，几乎所有的海底玄武岩在喷发时都通过脱气失去了大部分挥发性库存，这导致了从地球地幔中识别原始化学特征所需的可靠化学数据的重大损失。因此，我们对挥发物的来源及其进出地球的通量的理解存在很大的不确定性和争议。这项研究对非常罕见的未脱气的大洋中脊玄武岩进行分析，以获得关于碳、氮、氢和惰性气体(氦、霓气和氩)的地幔同位素组成的信息。总的来说，这些气体可以协同使用，以更好地了解地球大气和海洋是如何形成和演化的。大洋中脊是地球表面的基本地质特征，而地球科学中最耐人寻味的挑战之一是了解它们的形成和演化过程。该项目产生的化学和同位素数据是这方面的基础，并将在未来几年为大洋海脊脱气模型和地球挥发物的起源和演化提供基准。这项工作的更广泛影响包括为俄克拉荷马州的一个机构提供资金，该州获得的联邦资金相对较少(即EPSCoR州)，以及与法国科学家发展新的国际合作。它还使用美国国家科学基金会资助的俄勒冈州立大学的分析设施，开发分析岩石样品中惰性气体的新方法，为科学建设基础设施。研究结果还将被纳入研究人员教授的课程，并用于为研究生开发一个新的研讨会，重点是对化学地球动力学中的储层、过程和通量进行建模。这项研究的科学目标是测试大洋中脊和大陆裂谷之下的上地幔区域在全球范围内在挥发性丰度和同位素组成方面的相似程度。对未脱气的大洋中脊玄武岩中的碳、氮、氢和惰性气体的分析将首次能够在不进行脱气校正的情况下测试二氧化碳、氮气和水中惰性气体和主要挥发性同位素的相互关系。这使得可以直接测试上地幔的区域不均一性。这项研究还具体解决了以下问题：(1)上地幔中的挥发物C、N和H2O的原始比例与再循环比例；(2)超贫化的大洋中脊玄武岩中的碳稳定同位素是否带有形成超贫化源所需的较早程度熔体的贫化记录；(3)贫化的上地幔中N的行为和浓度是什么；以及(4)在上地幔稀有气体的原始同位素比率中保存了什么早期地球过程的记录。

Measurements of volatiles such as carbon dioxide, water, nitrogen and noble gases in submarine basalts from mid-ocean ridges have provided considerable insight into the origin of Earth's atmosphere and oceans, and the geologic history of cycling between the surface of the Earth and its interior. However, almost all submarine basalts have lost much of their volatile inventory by degassing when they are erupted, which has led to a major loss of the reliable chemical data needed to identify pristine chemical signatures from Earth's mantle. As a result, there is significant uncertainty and controversy in our understanding of the origins of volatiles and their fluxes into and out of the Earth. This research carries out analyses of the very rare occurrences of undegassed mid-ocean ridge basalts to obtain information on the mantle isotopic composition of carbon, nitrogen, hydrogen and noble gases (helium, neon and argon). Collectively, these gases can be used synergistically to better understand how Earth's atmosphere and oceans formed and evolved. Mid-ocean ridges are fundamental geologic features of Earth's surface, and one of the most intriguing challenges in geosciences is understanding the processes by which they are created and evolve. The chemical and isotopic data resulting from this project are fundamental in this regard, and will provide benchmarks for years to come for models of degassing at ocean ridges and the origin and evolution of Earth's volatiles. Broader impacts of the work include funding an institution in Oklahoma, a state that receives comparatively little federal money (i.e., an EPSCoR state) and the development of new international collaborations with French scientists. It also uses NSF-funded analytical facilities at Oregon State University and develops new methods for analyzing noble gases in rock samples, building infrastructure for science. Findings will also be incorporated into classes taught by the investigators and used to develop a new seminar for graduate students centered on modeling of reservoirs, processes and fluxes in chemical geodynamics. The scientific goals of this research are to test the extent to which regions of the upper mantle beneath mid-ocean ridges and continental rifts are similar in their volatile abundances and isotopic compositions on a global scale. Analyses of carbon, nitrogen, hydrogen, and noble gases in undegassed mid-ocean ridge basalts will allow, for the first time, testing of the inter-relationships of noble gas and major volatile isotopes in CO2, N2, and H2O without employing degassing corrections. This allows a direct test for regional heterogeneity in the upper mantle. The research also specifically addresses the questions: (1) What proportions of the volatiles C, N and H2O in the upper mantle are primordial versus recycled; (2) do carbon stable isotopes in the ultra-depleted mid-ocean ridge basalts carry a record of earlier depletion in low degree melts that appears to be required in formation of the ultra-depleted source; (3) what is the behavior and concentration of N in the depleted upper mantle; and (4) what record of early Earth processes is preserved in the primordial isotope ratios of upper mantle noble gases.