Collaborative Research: Mantle Volatiles in an Emerging Ocean Basin: H2O, CO2, and He & Ar Isotopes in Basalts from the Gulf of Aden Spreading Center System

大陆裂谷和海洋伸展脊是地球内部和表面交换挥发性元素的关键场所。挥发物在裂谷/扩张的开始、火山演化和相关的地质灾害中起着核心作用。由于亚丁湾洋中脊是形成和演化早期的洋中扩张中心，本研究对亚丁湾洋中脊喷发岩浆的主要挥发性物质（H2O和CO2）和地幔源示踪物（氦和氩同位素）进行了表征。该研究还量化了该地区来自地幔的水通量。对于这项工作来说，亚丁湾是一个独特的地方，因为它是一个年轻的海洋盆地，受到非洲之角下方阿法尔地幔柱流的影响。地幔柱影响沿红海和亚丁湾西部的阿拉伯岩石圈底部；它的广泛影响被认为是由于软流圈岩浆通过裂谷从地幔柱流向扩张中心。然而，阿法尔地幔柱对亚丁湾的渗透明显较弱，这可能与扩张脊的构造分割或不连续有关。这项研究将分析从以前的海洋和采样探险中收集到的海底玄武岩玻璃，主要元素组成，挥发性浓度（CO2, H2O, Cl， F和S），以及He和Ar同位素。亚丁玄武岩玻璃的初步结果显示，一个强烈的羽流信号可能随着距离羽流轴的距离而迅速衰减。项目目标是确定部分熔融和脱气如何控制年轻海洋扩张中心的地幔挥发性特征。利用该地区约40个玄武岩玻璃的3He/4He、40Ar/36Ar、4He/40Ar*、CO2/Nb、H2O/Ce等地球化学证据进行测定。研究结果使我们能够量化来自阿法尔地幔柱和上地幔的挥发性通量在44°E和57°E之间沿这个新兴海洋盆地长度的变化。研究结果还提供了地球物理和地球动力学模型所需的基本框架，包括地幔成分、部分熔融以及与大陆裂谷到海洋扩张演化相关的热量和质量通量的区域和小尺度变化的模型输入。这项工作的广泛影响包括支持两个机构的研究生和本科生，一个在EPSCoR州（俄克拉何马州），利用先前NSF支持收集的现有样本，并利用NSF资助的俄勒冈州立大学和塔尔萨大学的分析设施。结果将在机构网页以及nsf资助的公共数据系统上进行描述。调查结果也将被纳入调查人员讲授的课程中。

Continental rifts and ocean spreading ridges are key places where volatile elements are exchanged between Earth's interior and its surface. Volatiles play a central role in the initiation of rifting/spreading, in volcanic evolution, and in associated geologic hazards. This research characterizes major volatile concentrations (H2O and CO2) and mantle source tracers (helium and argon isotopes) in magma erupted along the mid-ocean ridge in the Gulf of Aden in the Arabian Sea because this is a mid-ocean spreading center in its early stages of formation and evolution. The research also quantifies the flux of water coming from the mantle in the region. The Gulf of Aden is a unique locality for this work because it is a young ocean basin influenced by flow from the Afar mantle plume under the Horn of Africa. The plume affects the base of the Arabian lithosphere along the Red Sea and the western part of the Gulf of Aden; and its widespread influence is thought to result from the channeling of asthenospheric magma from the plume to the spreading center by rifts. However, the Afar Plume's apparent weaker penetration into the Gulf of Aden is not well understood and may be related to tectonic segmentation/discontinuities of the spreading ridge. The research will analyze submarine basalt glasses that were collected from previous oceanographic and sampling expeditions to the area for major element composition, volatile concentrations (CO2, H2O, Cl, F and S), and He and Ar isotopes. Initial results for Aden basalt glasses reveal a strong plume signal that may become rapidly attenuated with distance from the plume axis. Project goals are to determine how partial melting and degassing control mantle volatile signatures in young ocean spreading centers. Geochemical evidence (e.g., 3He/4He, 40Ar/36Ar, 4He/40Ar*, CO2/Nb, H2O/Ce) in about 40 basalt glasses from this region will be used to make this determination. Results of the study allow us to quantify variation in the volatile flux from the Afar plume and the upper mantle along the length of this emerging ocean basin between 44°E and 57°E. The results also provide a basic framework needed for geophysical and geodynamic models in terms of model input for regional and smaller scale variations in mantle composition, partial melting, and the heat and mass flux associated with the evolution from continental rifting to oceanic spreading. Broader impacts of the work include support of graduate and undergraduate students at two institutions, one in an EPSCoR state (Oklahoma), leverages existing samples collected with prior NSF support, and utilization of NSF-funded analytical facilities at Oregon State University and the University of Tulsa. Results will be described on institutional web pages as well as NSF-funded publically available data systems. Findings will also be incorporated into classes taught by the investigators.