NSFGEO-NERC: Data Mining the Deep: Combining Geochemistry and Imaging Spectroscopy to Quantify Deep Hydrothermal Circulation at Mid-Ocean Ridges

洋壳形成于洋中脊，覆盖了地球表面的60%以上。由于板块构造旋回和俯冲作用，洋壳在地质上是年轻的，平均年龄小于7000万年，全部小于2亿年；比构成大陆的古老岩石年轻得多。加热的海水从洋脊轴线在海洋地壳内循环，直到它在俯冲带被消耗殆尽。在这种循环过程中，这些来自海水的流体与岩石反应形成新的矿物，水、二氧化碳、钾、镁等关键元素和分子在海水和海洋地壳之间交换。这些流体和岩石之间的相互作用是海水化学的主要贡献者，但尚未量化，并通过俯冲作用决定了地球内部的组成。一个关键的挑战是，海洋钻探还没有对海底以下许多公里处最深的海洋地壳进行采样。然而，在过去的几年里，国际大陆科学钻探计划的阿曼钻探项目已经在阿曼钻探了几公里的海洋地壳和最上层地幔，在那里，地壳的这一关键部分被地壳推到了大陆上。在这个项目中，加州理工学院的科学家们将与英国南安普顿大学和普利茅斯大学的同事们合作，调查这些钻芯，以计算海水和深海地壳之间的交换程度。我们将采用一种创新的方法，将详细但传统的实验室分析与一种新的技术相结合，微成像光谱，使我们能够利用红外光的反射率，以小于1毫米的空间分辨率确定整个钻芯的矿物学。这项研究将通过在以前不可能的规模和采样完整性上的客观表征，在我们对海洋地壳内流体深层循环的理解方面取得重大进展。它将有助于了解流体-岩石反应对全球地球化学循环和海水化学的贡献，以及深层流体循环在海洋地壳冷却和蚀变中的限制作用。我们将建立一个带有岩心查看器的网站，向更广泛的科学界传播钻孔岩心的矿物图，并在课堂上用于教育用途。

Ocean crust is formed at mid-ocean ridge spreading ridges and covers more than 60% of the surface of Earth. Because of the plate tectonic cycle and subduction, the ocean crust is geologically young, on average less than 70 million years old and all is less than 200 million years; much younger than the old rocks that make up the continents. Heated seawater circulates within the ocean crust from the ridge axes until it gets consumed in subduction zones. During this circulation, these seawater-derived fluids react with the rocks forming new minerals, and key elements and molecules such as water, CO2, K, Mg are exchanged between seawater and the ocean crust. These interactions between fluids and the rock are a major - but not yet quantified - contributor to seawater chemistry, and through subduction the composition of the interior of Earth. A key challenge is that ocean drilling has not sampled the deepest ocean crust many kilometers below the seafloor. However, in the past few years, the International Continental Scientific Drilling Program's Oman Drilling Project has drilled a few kilometers of oceanic crust and the uppermost mantle in Oman, where tectonics have pushed this critical portion of Earth's crust onto the continent. In this project, scientists at Caltech will work with colleagues at the Universities of Southampton and Plymouth in the UK to investigate these drill core to work out how much exchange there has been between seawater and the deep ocean crust. We will take an innovative approach that combines detailed but traditional laboratory analyses with a novel technique, micro-imaging spectroscopy, which allows us to use the reflectance of infrared light to determine the mineralogy of the entire drill core at a spatial resolution of less than one millimeter. This research will achieve major advances in our understanding of deep circulation of fluids within the ocean crust through objective characterization at a scale and sampling completeness previously impossible. It will yield insights into the contribution of fluid-rock reactions to global geochemical cycling and seawater chemistry as well as constraining the role of deep fluid circulation in cooling and alteration of the lower oceanic crust. We will build a website with a core viewer to disseminate mineral maps of the drill cores to the broader scientific community and for educational use in classes.