Refining the sedimentary pyrite proxy: Applications for understanding past ocean chemistry

该提案资助开发用于海洋化学研究的黄铁矿代理工具。我们的海洋掌握着地球生命起源和进化的关键。古海洋研究不仅可以提供有关地球上生命如何进化的线索，还可以提供如何识别也可能支持生命的系外行星。研究成果还将融入经济地质学，并在矿产勘探和采矿实践中得到应用。与传统的散装样品代理相比，使用 LA-ICPMS 对黄铁矿进行海洋化学分析具有以下几个优点：1) 原位分析仅允许检查一种矿物，从而排除了共存矿物的混合地球化学特征； 2) 该技术允许根据矿物结构选择样品，这意味着仅考虑早期黄铁矿颗粒； 3）由于黄铁矿TE含量可能保留在绿片岩相中，因此我们的调查可以包括更多的盆地，特别是在前寒武纪期间。******虽然这个黄铁矿代理工具是一个诱人的突破，但在它可以在古海洋中广泛应用之前，仍然有几个方面必须进行评估。首先，沉积盆地内和不同局部氧化还原条件下 TE 的变化程度是一个重要方面，但人们对此知之甚少。我们将系统地研究沿经过深入研究的沉积盆地的横断面黄铁矿的 TE 含量，以了解从近岸到深水环境黄铁矿的 TE 含量如何变化。我们还将对与黄铁矿分析相同的样品进行 Fe 形态、S 同位素以及全岩痕量和主要元素分析，以揭示沉积氧化还原条件如何影响黄铁矿 TE 含量。******黄铁矿通过变质作用保留其 TE 含量的能力意味着黄铁矿 TE 代理有可能允许在海洋化学研究中考虑其他（变质的）沉积盆地，这在前寒武纪尤其重要。然而，尚未彻底测试变质样品最内层核心中黄铁矿的 TE 含量是否确实与未变质沉积黄铁矿相同。利用来自经历过接触变质作用的沉积盆地的黄铁矿，我们将比较沉积黄铁矿和变质黄铁矿岩心的TE含量，以确定TE是否通过变质作用保存下来。然后该项目将扩展到检查区域变质作用。******我们将使用一系列纳米和微米分析技术（LA-ICPMS、TEM、APT、nanoSIMS 和 XANES）来详细说明 TE 如何在黄铁矿中托管。使用 APT 在原子尺度上描述 3D 空间中黄铁矿中 TE 的存在方式将为其他黄铁矿相关研究（例如冶金和矿区复垦）提供宝贵的数据。通过本研究生成的数据通过建立背景未矿化黄铁矿的 TE 范围，进一步支持开发地球化学靶向工具的矿物勘探研究。

This proposal funds the development of the pyrite proxy tool for ocean chemistry studies. Our oceans hold the key to the beginning and evolution of life on Earth. Paleo-ocean studies can provide not only clues on how life evolved on Earth, but also how to identify exoplanets that may also support life. The research outcomes will also feed into economic geology, with applications in mineral exploration and mining practices. The use of LA-ICPMS analysis of pyrite for ocean chemistry offers several benefits over traditional bulk sample proxies: 1) the in-situ analysis allow only one mineral to be examined, thus excluding the mixed geochemical signatures from coexisting minerals; 2) the technique allows sample selection by mineral texture, which means only the early stage pyrite grains are considered; and 3) since pyrite TE content may be preserved up greenschist facies, more basins can be included in our investigations, especially during the Precambrian.******While this pyrite proxy tool is an enticing breakthrough, there are still several aspects that must be assessed before it can be widely implemented in both paleo-ocean. First, the degree to which TEs vary within a sedimentary basin and under different local redox conditions is an important aspect that is poorly understood. We will systematically investigate the TE content of pyrite along transects across well studied sedimentary basins to see how TE content of pyrite varies from near shore to deep water settings. We will also conduct Fe speciation, S-isotope, and whole rock trace and major element analyses on the same samples as the pyrite analyses to unravel how depositional redox conditions affect the pyrite TE content.******The ability of pyrite to preserve its TE content through metamorphism means the pyrite TE proxy has the potential to allow additional (metamorphosed) sedimentary basins to be considered for ocean chemistry studies, especially important in the Precambrian. However, it has not been thoroughly tested whether the TE content of pyrite in the unaltered, innermost core of a metamorphosed sample is indeed the same as unmetamorphosed sedimentary pyrite. Using pyrite from sedimentary basins that have experienced contact metamorphism, we will compare the TE content of sedimentary pyrite and cores of metamorphosed pyrite to determine whether the TEs are preserved through metamorphism. The project will then be expanded to examine regional metamorphism.******We will use a series of nano- and micro-analytical techniques (LA-ICPMS, TEM, APT, nanoSIMS, and XANES) to detail how TEs are hosted in pyrite. The use of APT to characterise how TEs are held in pyrite in 3D space at the atomic scale will provide invaluable data for other pyrite-related studies, such as metallurgy and mine site reclamation. The data generated through this study with further support mineral exploration studies in developing geochemical targeting tools by establishing a TE range for background, unmineralized pyrite.