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)和英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。该协定允许美国和英国提交一个单一的联合提案，并由该机构进行同行审查，该机构的调查员在预算中所占比例最大。在成功地联合确定一项裁决后，每个机构将为与其本国有关的预算和调查人员的比例提供资金。克拉通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期间，这些稳定的地壳区域分裂，最终让位于从地球深处上升的岩浆和新地壳的形成。挥发性元素如氦、氮和二氧化碳在板块构造的各个方面都起着重要的作用。在俯冲过程中，主要挥发物从地球表面输送到地球内部，并可能由于辐射产生和从下面的地幔上涌而积累在稳定的克拉通下方和内部。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)和地质上重要的气体(如二氧化碳)的储藏库。当克拉通最终分裂时，这些气体被释放到大气中，并在地质时间尺度上对气候产生潜在的重大影响。这项工作的目的是确定控制克拉通中挥发性物质产生的地质过程，它们在地壳中的迁移和在表面的释放。所调查的野外地点是坦桑尼亚克拉通周围地区，是被东非裂谷包围的稳定克拉通的典型例子，也是强烈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于研究克拉通挥发分的形成过程及其由于磁性和裂谷作用而可能释放的机制。在项目过程中，两名坦桑尼亚学生将在伍兹霍尔/麻省理工学院研究生项目和新墨西哥大学获得博士教育和经验。学生将接受野外和实验室技术、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成藏过程。该项目是对坦桑尼亚克拉通两侧气体和水渗漏释放出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被裂谷活动“破裂”，同时被烟柱引发的火山活动加热。总体目标是了解：1)在109年的时间尺度上，气体在稳定的克拉通中产生和储存的机制，以及2)在克拉通解体期间，它们是如何被释放和输送到地表的。这项研究主要集中在氦(He)和氮(N2)及其同位素特征，这是克拉通天然气聚集的主要成分，但我们将测量所有其他惰性气体(Ne、Ar、Kr、Xe)及其同位素、CO2、CH4(及其同位素)和渗漏中的H2。PIS将使用现场和实验室产生的天然气化学结果，形成沿着坦桑尼亚克拉通侧翼的天然气形成和运输的综合模型。将计算挥发通量，以了解克拉通地区被裂谷和火山活动破坏时气体释放的程度。确定克拉通气体如何被释放到地壳并最终释放到大气中，对于了解大空间和时间尺度上的挥发性运动非常重要。通过限制挥发分在稳态裂谷和岩浆条件下的积累和释放，PI将表征克拉通挥发分库存和通量。这些信息将引起更广泛的地球科学界的兴趣，并为研究气体突然从稳定的克拉通释放到大气中以及形成具有经济价值的氦和氢气藏时的潜在气候影响的研究人员提供宝贵的背景资料。两名坦桑尼亚学生将由该奖项的国际和平研究所联合监督，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气藏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优势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.