High Temperature Fluid-Rock Interaction in the Oceanic Crust: A Fluid Inclusion Study, IODP Expeditions 309 & 312.

由于综合大洋钻探计划等科学方案，我们现在对大洋地壳、其过程和产物有了大量的了解。然而，由于它的不可接近性和沉积盖层对研究的限制，仍然存在许多问题。该项目旨在解决的问题是流体在流经洋壳时与岩石相互作用而产生的演化问题。勘探309和312旨在加深ODP 1256 D孔，该孔已经穿透沉积物覆盖层，并在东太平洋超快速（20厘米/年）扩展地壳中进入火山岩502米。孔应贯穿整个席状岩墙复合体，并进入上部辉长岩。洋中脊是岩浆系统，是洋壳生成的场所。海洋地壳被海水的热液循环冷却-这是本研究的重点。这些热液系统非常重要，原因有很多，包括它是地球失去热量的主要过程。此外，热液流体在流经地壳时与海洋地壳发生反应的事实意味着被呼出回海洋的流体可能与放入（海水）的流体非常不同。这意味着这些过程形成了海水成分的主要控制因素。这些系统在现代环境中的末端成员是相对公知的。然而，在这两者之间发生的事情仍然是一个争论不休的话题。过去曾对洋壳中的流体包裹体进行过研究，但由于分析技术的局限性，迄今为止制作的模型无法详细了解流体化学演化。我们将使用各种技术对IODP Expeditions 309和312的样品中的流体进行非常详细的分析，包括光学显微镜岩相学，显微测温，阴极发光和背散射电子成像技术，以及激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）。LA-ICP-MS是一种将这项研究与以前的研究区分开来的技术，它允许对单个流体包裹体中的主元素、次元素和微量元素成分进行原位分析。这将允许确定系统中流体的数量及其来源，以及能够准确地定位系统中主要流体-岩石相互作用发生的位置。事实上，309和312号探险队的目标是钻取一个完整的洋壳，这意味着应该能够研究一个连续的热液系统。因此，由此建立的大洋地壳热液演化地球化学模型应该是可靠的，并具有良好的约束性。

Due to scientific programmes such as the Integrated Ocean Drilling Program (IODP) we now know a significant amount about the oceanic crust, its processes and products. However, due its inaccessibility and the limitations imposed on research by a sedimentary cover, there remain numerous questions. The question which this project aims to address is that of the evolution of fluids by interaction with rocks as they flow through the oceanic crust. Expeditions 309 and 312 aim to deepen ODP Hole 1256D, which already penetrates through the sediment cover and 502m into volcanic rocks in superfast (20cm/year) spreading crust in the East Pacific. The Hole should penetrate the entire sheeted dyke complex and into the upper gabbros. Mid-ocean ridges are magmatic systems which are the sites of oceanic crustal generation. The ocean crust is cooled by hydrothermal circulation of seawater - this is the focus of this study. These hydrothermal systems are extremely important for a number of reasons including the fact that it is the major process by which the Earth loses heat. In addition, the fact that the hydrothermal fluids react with the oceanic crust as they flow through the crust means that the fluid that is exhaled back into the oceans can be very different from that which was put in (seawater). This means that these processes form a major controlling factor on the composition of seawater. The end members of these systems in modern environments are relatively well known. However, what occurs in between remains a topic of much debate. Studies of fluid inclusions in the oceanic crust have been conducted in the past, but models produced to date do not allow for a detailed appreciation of fluid chemical evolution owing to limitations of analytical techniques. We will be conducting extremely detailed analyses of fluids within the samples from IODP Expeditions 309 & 312 using a variety of techniques including optical microscope petrography, microthermometry, cathodolumiscence and back scattered electron imaging techniques, as well LASER Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). LA-ICP-MS is the technique which will stand this research apart from what has gone before, allowing in situ analysis for major-, minor- and trace-element compositions in individual fluid inclusions. This will allow for the determination of the number of fluids in the system and their sources, as well as being able to accurately target where in the system the major fluid-rock interactions occur. The fact that Expeditions 309 & 312 aim to drill a complete section of oceanic crust means that a continuous hydrothermal system should be able to be studied. Hence the resulting geochemical model for hydrothermal fluid evolution in the oceanic crust should be reliable and well constrained.