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The origin of volatiles in the mantle

地幔挥发物的起源

基本信息

批准号：
NE/D004292/1
负责人：
Christopher Ballentine
金额：
$ 47.75万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2006
资助国家：
英国
起止时间：
2006 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FD004292%2F1
关键词：
origin volatiles mantle

项目摘要

Evidence about the early history of the Earth and how it formed has been almost completely destroyed by tectonic activity. However, volcanic gases from the Earth's mantle still preserve a relict of this information. This proposal identifies a key set of samples where we can make new observations that will constrain how the Earth got its volatiles and how the early atmosphere formed: Gases in the Earth's mantle are a mixture of gases trapped when the Earth formed, and gases recycled from the atmosphere into the mantle by subduction as the Earth has evolved. Noble gas isotopes are chemically unreactive and have different isotopic fingerprints depending on whether they come from the atmosphere, meteorites, or even the solar nebula. Identifying these fingerprints gives us unique information about the origin of volatiles in the Earth. These fingerprints are also distorted by different processes that could occur in the early earth. For example more soluble gases such as Helium would be concentrated in the melt if there was equilibrium between a molten Earth and an early atmosphere. In contrast, light gases, driven by meteorite bombardment, would be the first to be lost from the atmosphere. To be able to unravel these early processes we first need to identify what supplies the early Earth with its volatiles. We then need to compare the distortion of the different fingerprints with that predicted for different models of atmosphere/mantle interaction and evolution. For example, the noble gas isotopes now in the atmosphere are often explained by massive early atmosphere loss buffered by degassing from the planet. This would produce a predictable distortion of the gases trapped in the Earth's mantle. But what do we actually see? The main gases that could address these issues (Ar, Kr and Xe) have been, until now, impossible to resolve from the atmospheric fingerprint caused by seawater recycling into the mantle and contamination of samples on eruption. Volcanic carbon dioxide 'well-gases', for the first time allow us to see the 'primitive' Xe isotope fingerprint. If Xe primitive Xe is present, we have shown in this proposal that we should also be able to resolve primitive Ar and Kr / but only with the latest technology. We calculate that with a new instrument we can not only resolve primitive Xe, but also start to identify the type of material that carried it to the Earth. By resolving associated Ar and Kr we can start to identify the distortion and which accretionary processes was the cause. In addition, some noble gas isotopes are also formed by radioactive decay and these give us information about the timing of some of these early processes. Combining this information we can build a unique picture of from what, how and when the volatiles both in the deep Earth and present day atmosphere got there.

关于地球早期历史及其形成的证据几乎完全被构造活动破坏了。然而，来自地幔的火山气体仍然保留了这些信息的残余。该提案确定了一组关键样本，我们可以在其中进行新的观察，这些观察将限制地球如何获得挥发物以及早期大气如何形成：地球地幔中的气体是地球形成时捕获的气体和气体的混合物随着地球的进化，通过俯冲从大气层进入地幔。稀有气体的同位素在化学上是不活泼的，并且根据它们是否来自大气、陨石甚至太阳星云而具有不同的同位素指纹。识别这些指纹为我们提供了关于地球挥发物起源的独特信息。这些指纹也被早期地球可能发生的不同过程所扭曲。例如，如果熔融的地球和早期的大气层之间存在平衡，那么更易溶解的气体（如氦）将集中在熔体中。相比之下，轻气体，由陨石轰击驱动，将是第一个从大气中消失的。为了能够解开这些早期过程，我们首先需要确定是什么为早期地球提供了挥发物。然后，我们需要将不同指纹的失真与不同的大气/地幔相互作用和演化模型的预测进行比较。例如，现在大气中的稀有气体同位素通常被解释为大量的早期大气损失被行星的脱气所缓冲。这将产生一个可预测的扭曲的气体被困在地球的地幔。但我们实际上看到了什么？可以解决这些问题的主要气体（Ar，Kr和H2O）到目前为止一直无法从海水再循环进入地幔和火山爆发样品污染造成的大气指纹中解析出来。火山二氧化碳“井气”，第一次让我们看到“原始”的同位素指纹。如果存在原始的Ar和Kr，我们在这个建议中已经表明，我们也应该能够解决原始的Ar和Kr，但只有使用最新的技术。我们计算出，有了一种新的仪器，我们不仅可以解决原始的彗星，而且还可以开始识别携带它到地球的物质类型。通过解决相关的Ar和Kr，我们可以开始确定的扭曲和吸积过程的原因。此外，一些稀有气体同位素也是由放射性衰变形成的，这些同位素给了我们关于这些早期过程的时间的信息。结合这些信息，我们可以建立一个独特的图片，从什么，如何以及何时挥发物在地球深处和今天的大气到达那里。