Outgassing history and early atmospheric processes recorded by paleoatmospheric noble gases in Archaean rocks

太古宙岩石中古大气惰性气体记录的放气历史和早期大气过程

• 批准号: 276719708
• 负责人: Dr. Ulrich Ott
• 金额: --
• 依托单位: Max-Planck-Institut für Chemie (Otto-Hahn-Institut)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/276719708?language=en
• 关键词: Outgassing; history; early; atmospheric; processes

Origin and evolution of planetary atmospheres are key conditions that determine the habitability of a planet. Important atmosphere shaping processes are delivery of volatiles and degassing processes of the solid Earth, i.e. mantle and crust, which is largely governed by planetary geodynamics. Terrestrial noble gas systematics (e.g., 129I-129Xe) implies that a significant fraction of terrestrial volatiles were lost from the planet, and that massive mantle degassing occurred early in Earth´s history. On the other hand, mantle and crustal degassing are ongoing processes. The evolution of the 40Ar/36Ar ratio of the terrestrial atmosphere is a sensitive parameter that can constrain the modes and intensity of mantle and crustal degassing. Our proposed project aims at a) measuring paleoatmospheric argon and xenon trapped in ancient rocks b) constrain the evolution of the atmospheric 40Ar/36Ar ratio and degassing of the solid Earthc) constrain the origin of terrestrial atmospheric xenon, which is unique in composition when compared to other solar system reservoirs (except for the Martian atmosphere)Although recent studies reported interesting new results, they yielded only few values, and their significance depends on data correction for various nuclear effects. We intend to improve the present data base by measuring Archean rocks (e.g., cherts, shales, hydrothermal quartz) from the Kaapvaal craton and Australia. Samples are available from cooperations within SPP1833 and own previous studies. Samples will be measured after neutron irradiation (to correct for in situ 40K decay and 40Ar production) as well as unirradiated, and noble gases will be extracted by both stepwise heating and crushing, in order to differentiate between gases trapped in inclusions and those in mineral matrices (e.g. from radioactive decay). This enables recognition of fluid components (either high saline-high 40Ar/36Ar, or low saline-low 40Ar/36Ar) and their identification via neutron-produced 38Ar from Cl. Stepwise heating and also stepwise combustion extractions will also be possible after crushing without air exposure, and for acid resistant residues, enabling extraction of noble gases form kerogen (from shales and cherts) without mass fractionation. In promising samples, argon and xenon will be extracted simultaneously and subsequently measured by different mass spectrometers, especially for low xenon amounts we will apply a high sensitivity Noblesse mass spectrometer equipped with multi ion counting.

行星大气的起源和演化是决定行星宜居性的关键条件。重要的大气形成过程是固体地球，即地幔和地壳的挥发物的输送和脱气过程，这在很大程度上受行星地球动力学的支配。陆地惰性气体系统学(如129I-129Xe)表明，相当大一部分陆地挥发物从地球上消失，大规模地幔脱气发生在地球S历史的早期。另一方面，地幔和地壳脱气是正在进行的过程。陆地大气40Ar/36Ar比值的演化是制约地幔和地壳脱气方式和强度的敏感参数。我们拟议的项目旨在a)测量捕获在古代岩石中的古大气Ar和Xe；b)限制大气40Ar/36Ar比率的演化和固体地球的脱气c)限制陆地大气Xe的起源，与其他太阳系储集层(火星大气除外)相比，陆地大气Xe的组成是独一无二的。我们打算通过测量卡瓦尔克拉通和澳大利亚的太古宙岩石(例如，硅质岩、页岩、热液石英)来改善目前的数据库。样本可从SPP1833的合作伙伴那里获得，并拥有之前的研究。样品将在中子辐照(以校正原位40K衰变和40Ar产生)以及未辐照后进行测量，并将通过逐步加热和粉碎来提取惰性气体，以区分捕获在包裹体中的气体和矿物基质中的气体(例如来自放射性衰变)。这使得能够识别流体成分(高盐-高盐40Ar/36Ar，或低盐-低40Ar/36Ar)，并通过从氯产生的中子38Ar来识别它们。在没有空气暴露的情况下粉碎后，也可以逐步加热和逐步燃烧提取，对于耐酸残渣，可以从干酪根(从页岩和硅质岩)中提取惰性气体，而不需要进行大量分馏。在有希望的样品中，Ar和Xe将被同时提取，然后用不同的质谱仪进行测量，特别是对于低氙量的样品，我们将使用配备多离子计数的高灵敏度Noblesse质谱仪。