Collaborative Research: NSF GEO-NERC: The Cracking of a Craton: Understanding Volatile Release during Continental Breakup

这是一个由国家科学基金会地球科学理事会（NSF/GEO）和联合王国国家环境研究理事会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协议允许美国/英国提交一份联合提案，并由研究者拥有最大预算比例的机构进行同行评审。一旦成功地共同确定了一个奖项，每个机构就为与其本国有关的预算和调查人员提供资金。南极洲是地球各大洲最古老和最稳定的部分。在大陆分裂或裂谷事件中，这些稳定的地壳区域分裂开来，最终让位于从地球内部深处上升的岩浆和新地壳的形成。氦、氮和二氧化碳等挥发性元素在板块构造的各个方面都起着重要作用。在俯冲过程中，主要的挥发物从地球表面被输送到地球内部，并可能由于放射性物质的产生和从下面的地幔上涌而在稳定的地幔子之下和之内积累。这种积累的机制和时间尺度仍然知之甚少，但意义重大，因为这些过程形成了具有经济价值的气体（如氦和氢）和地质学上重要的气体（如二氧化碳）的储层。当中子最终分裂时，这些气体被释放到大气中，并对地质时间尺度产生潜在的重大气候影响。这项工作的目的是确定控制克拉通挥发性物质产生、其通过地壳的迁移和在地表释放的地质过程。被调查的现场是坦桑尼亚克拉通周围的地区，这是一个典型的被东非裂谷包围的稳定克拉通，以及强烈的岩浆活动和伸展构造的位置。这种特殊的地质环境非常适合研究磁致伸缩挥发物的形成过程及其由于磁性和裂谷作用而可能的释放机制。在该项目的过程中，两名坦桑尼亚学生将获得博士学位。在伍兹霍尔/麻省理工学院研究生课程和新墨西哥州大学的教育和经验。学生将接受现场和实验室技术、数据解释和这些技术的应用方面的培训，以了解这些具有经济价值的气体的储层形成过程。 该项目是对坦桑尼亚克拉通两侧沿着渗透的气体和水所释放的挥发性气体的全面研究，在该地区，稳定的大陆克拉通正在因裂谷作用而活跃地“破裂”，同时又因羽流引发的火山作用而升温。总体目标是了解：1）在109年的时间尺度上，气体在稳定的质子中产生和储存的机制，以及2）在质子分裂期间，它们如何被释放和运输到表面。研究主要集中在氦（He）和氮（N2）及其同位素特征，这是氦离子气聚集的主要成分，但我们将测量所有其他稀有气体（Ne，Ar，Kr，Xe）及其同位素，CO2，CH 4（及其同位素）和H2。PI将使用现场和实验室生成的天然气化学结果，形成一个沿坦桑尼亚克拉通两侧沿着的天然气形成和运输的综合模型。将计算挥发性通量，以了解当一个火山区域被裂谷和火山活动破坏时气体释放的程度。确定电子气体是如何释放到地壳并最终释放到大气中的，对于理解大空间和时间尺度上的挥发性运动非常重要。通过限制挥发物在稳态裂谷和岩浆条件下的积累和释放，PI将表征超声波挥发物存量和通量。这些信息将引起更广泛的地球科学界的兴趣，并为研究人员研究气体突然从稳定的克拉通释放到大气中时的潜在气候影响以及形成具有经济价值的氦和氢气体储层提供有价值的背景。两名坦桑尼亚学生将由该奖项的PI共同监督，并在各自的机构接受实地和实验室技术培训。学生将有机会获得惰性气体地球化学、气体地球化学和稳定同位素方面的深入培训，以及了解这些具有经济价值的天然气储层形成过程的建模方法。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.Cratons are the oldest and most stable parts of the Earth’s continents. During continental break-up or rifting events, these stable crustal areas split apart and eventually give way to magma rising from Earth’s deep interior and the formation of new crust. Volatile elements such as helium, nitrogen and carbon dioxide play an important role during all aspects of plate tectonics. Major volatiles are transported from the Earth’s surface into Earth’s interior during subduction and may accumulate below and within the stable cratons due to radiogenic production and upwelling from the mantle below. The mechanisms and time-scales of this accumulation remain poorly understood, yet are significant because these processes form reservoirs of economically valuable gases such as helium and hydrogen, and geologically important gases such as carbon dioxide. When cratons eventually break apart, these gases are released to the atmosphere and have potentially significant climatic impacts on geological time scales. The objective of this work is to determine the geological processes that control volatile production in the craton, their migration through the crust and release at the surface. The investigated field site is the area surrounding the Tanzania Craton, a type example of a stable craton surrounded by the East African Rift, and a location of intense magmatism and extensional tectonics. This particular geologic setting is ideally suited to investigate the formation processes of cratonic volatiles and their potential release mechanism due to magnetism and rifting. During the course of the project two Tanzanian students will get their Ph.D. education and experience at the Woods Hole/MIT graduate program and the University of New Mexico. The students will be trained in field and laboratory techniques, data interpretation and application of these techniques for understanding the processes of reservoir formation of these economically valuable gases. This project is a comprehensive study of the volatile gases that are being emitted from gas and water seeps along the flanks of the Tanzanian craton - a region where the stable continental craton is actively being “cracked” by rifting and simultaneously heated by plume-induced volcanism. The overall aims are to understand: 1) the mechanisms by which gases have been produced and stored in stable cratons over 109-year timescales, and 2) how they are liberated and transported to the surface during cratonic breakup. The study primarily focuses on helium (He) and nitrogen (N2) and their isotopic characteristics, which are the main constituents of cratonic gas accumulation, but we will measure all other noble gases (Ne, Ar, Kr, Xe) and their isotopes, CO2, CH4 (as well as their isotopes) and H2 in seeps. The PIs will use field- and lab-generated gas chemistry results to form an integrated model of gas formation and transport along the flanks of the Tanzania craton. Volatile fluxes will be calculated to understand the extent of gas release when a cratonic region is disrupted by rifting and volcanism. Determining how cratonic gases are released to the crust and eventually to the atmosphere is important for understanding volatile movements on large spatial and temporal scales. By constraining how volatiles are accumulated and released during steady-state rifting and magmatic conditions, the PIs will characterize cratonic volatile inventories and fluxes. This information will be of interest to the broader Earth science community, and provide valuable context to researchers studying the potential climatic effects when gases are abruptly released from the stable craton to the atmosphere as well as the formation of economically valuable gas reservoirs of helium and hydrogen. Two Tanzanian students will be jointly supervised by the PI’s of the award and trained in field and laboratory techniques at their respective institutions. There will be opportunity for the students to obtain in depth training in noble gas geochemistry, gas geochemistry and stable isotopes, as well as modeling approaches to understand the processes of formation of these economically valuable gas reservoirs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.