Investigation of reaction porosity and permeability, IODP Expedition 399, Atlantis Massif

亚特兰蒂斯地块 IODP 399 号探险队反应孔隙度和渗透率研究

• 批准号: NE/Y001737/1
• 负责人: Andrew McCaig
• 金额: $ 10.34万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FY001737%2F1
• 关键词: Investigation; reaction; porosity; permeability; IODP

The Atlantis Massif Oceanic Core Complex (OCC) is one of the best studied locations in the ocean crust, the site of four IODP expeditions so far (304, 305, 340T and 357). It is the site of the very important Lost City Hydrothermal Field (LCHF), venting alkaline fluids rich in hydrogen and methane at 40-90 centigrade. the LCHF has been suggested as an environment where Life may first have evolved on the early Earth > 3 billion year ago. Similar alkaline vents in serpentinising rocks are thought to occur on icy worlds in the Solar System such as Enceladus. Hydrogen, methane, alkanes and organic acids have all been found in the Lost City fluids, and amino acids of probably abiotic origin in previous drill core from the Massif. Our new IODP Expedition 399, sailing in April to June 2023, will seek to understand how these "building blocks of life" can be produced abiotically by interaction of seawater with rocks in the subsurface, and also the conditions under which "extremophile" microbial communities living at high T and high pH can be established and flourish.IODP Hole U1309D, located 5km north of the LCHF, is the deepest (1415m) hole so far drilled in young (<2 Ma) ocean crust; This hole will be deepened in Exp. 399 to depths of 2050 metres below seafloor, and temperatures of around 220 C, inoodre to sample rocks that have never been below the known temperature limit for life, and to study igneous processes of crustal acretion at mid-ocean ridges. However this is not the main target of our proposal here. Instead we will collect new samples from the 100m thick detachment fault zone which caps the Atlantis Massif, which is known to contain zones of reaction permeability, where minerals have been dissolved away by high temperature reactive fluids, and then the fluid filled pore spaces that result filled in by secondary minerals at much lower temperatures, within the limits of life. Other scientists on the Expedition will study microbes that may be trapped in this porosity, and the pore fluid chemistry that may have helped them to grow. We will characterise the same porosity by state of the art techniques of Scanning Electron microscopy (SEM), Electron Probe Microanalysis (EPMA) and computerised X-ray Tomography (XCT). This last technique is the same as the CAT-scan used in medicine, but targeted at a micro scale. We will be able to quantify the porosity and also work out how large it was before it was partially filled by secondary minerals.Reaction porosity and permeability is thought to be important in the formation of some types of ore deposits, and also may be formed in geothermal energy projects, for example in Iceland. the creation and filling in porosity is also important both in petroleum engineering, and in sequestration of carbon in reservoir rocks and perhaps in reactive igneous rocks such as those in the Atlantis Massif. Hence there may be applications of our work both in the search for rare minerals, in renewable energy, and in carbon capture underground all key objectives of geoscience in the aim for net-zero. Not to mention the origin of Life on Earth!

亚特兰蒂斯地块海洋核复合体（OCC）是海洋地壳中研究得最好的地点之一，迄今为止，IODP已经在这里进行了四次探险（304、305、340T和357）。它是非常重要的失落之城热液场（LCHF）的所在地，在40-90摄氏度的温度下喷出富含氢和甲烷的碱性液体。LCHF被认为是30亿年前地球早期生命最早进化的环境。蛇纹岩中类似的碱性喷口被认为出现在太阳系的冰冷星球上，比如土卫二。在失落之城的流体中发现了氢、甲烷、烷烃和有机酸，在之前从该块岩心中发现的氨基酸可能是非生物来源的。我们新的IODP探险队399将于2023年4月至6月航行，将试图了解这些“生命的基石”是如何通过海水与地下岩石的相互作用而非生物地产生的，以及生活在高温度和高pH值下的“极端微生物”微生物群落可以建立和繁荣的条件。U1309D孔位于LCHF以北5km处，是迄今为止在年轻（<2 Ma）海洋地壳中钻出的最深（1415m）孔；在实验399中，这个洞将被加深到海底以下2050米的深度，温度约为220摄氏度，适合采集从未低于已知生命温度极限的岩石样本，并研究洋中脊地壳喷发的火成岩过程。然而，这不是我们在这里提议的主要目标。相反，我们将从覆盖亚特兰蒂斯地块的100米厚的分离断裂带中收集新的样本，已知该断裂带包含反应渗透性带，在那里矿物被高温反应流体溶解，然后流体填充孔隙空间，导致二次矿物在更低的温度下填充，在生命的限制范围内。探险队的其他科学家将研究可能被困在这个孔隙中的微生物，以及可能帮助它们生长的孔隙流体化学。我们将通过扫描电子显微镜（SEM）、电子探针显微分析（EPMA）和计算机x射线断层扫描（XCT）等最先进的技术来表征相同的孔隙度。最后一种技术与医学中使用的cat扫描相同，但目标是在微观尺度上。我们将能够量化孔隙度，并计算出它在被二次矿物部分填充之前的大小。反应孔隙度和渗透性被认为对某些类型的矿床的形成很重要，也可能在地热能源项目中形成，例如在冰岛。孔隙的形成和填充在石油工程、储集岩和反应性火成岩（如亚特兰蒂斯地块）中的碳封存中也很重要。因此，我们的工作可能会在寻找稀有矿物、可再生能源和地下碳捕获方面得到应用，所有这些都是地球科学的关键目标，旨在实现净零排放。更不用说地球上生命的起源了！