Hydrothermal alteration during the aging of the ocean crust: IODP Expedition 393 South Atlantic Transect

洋壳老化过程中的热液蚀变：IODP Expedition 393 South Atlantic Transect

• 批准号: NE/X002543/1
• 负责人: Michelle Harris
• 金额: $ 3.37万
• 依托单位: Plymouth University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX002543%2F1
• 关键词: Hydrothermal; alteration; during; aging; ocean

Interactions between the atmosphere, hydrosphere, biosphere, and the solid geosphere are fundamental to how our Earth system operates. These interactions drive exchanges in heat, mass and chemical components that are essential for our habitable and active planet. The chemistry of seawater records the changing balance between these exchanges and understanding and quantifying the fluxes to and from the oceans are essential for understanding the Earth system. When and for how long these exchanges take place are also important to guide our extrapolation of these results to a global scale.The formation of new seafloor is the foundation step of the plate tectonic cycle and takes place along the chain of submarine volcanoes know as mid-ocean ridges that circuit the ocean basins . New ocean crust formed though seafloor spreading at the mid-ocean ridges is the principal mechanism for the exchange of heat and mass from Earths interior to the surface. Much of this heat transfer at mid-ocean ridges takes place by the circulation of seawater through the newly formed rocks. Seawater reacts with these hot rocks transforming seawater into heated hydrothermal fluids that are expelled at the seafloor through spectacular black-smoker vents but also as lower temperature diffuse fluids. Hydrothermal circulation continues during plate tectonics as the newly formed seafloor moves away from mid-ocean ridge and ages, and due to the vast volumes of the seafloor, even small chemical exchanges scale up to significant geochemical fluxes to the oceans. The rocks that make up the seafloor record this interaction with seawater by forming new minerals that can be identified and analysed to understand the temperatures and pathways of hydrothermal fluids and the chemical changes that result from fluid-rock reaction. How the seafloor changes as it ages, whether this is physical, chemical or biological (microbial activity), is important but chiefly unknown. This is because although scientific ocean drilling has successfully sampled the volcanic upper crust over the last 50 years, this sampling is biased towards seafloor <10Ma in age and there are only a few boreholes that sample the very oldest ocean crust (~170Ma). IODP Expeditions 390 and 393 have been specifically designed to address this sampling gap, and will drill a transect of holes in crust between 6-61 million years old. This project will target samples from these new drill holes that represent the range of hydrothermal alteration (the product of seawater-rock circulation) and analyse them for their geochemistry to understand and quantify the extent of elemental exchange during hydrothermal circulation. To help inform our understanding on when and for how long these reactions took place, samples of calcium carbonate from hydrothermal veins will be analysed for specific isotopes (U and Pb) to determine the age that they formed at. These new datasets will be combined to build up new insights into the geochemical exchanges happening during this key Earth process.

大气，水圈，生物圈和固体地质之间的相互作用对于我们的地球系统的运作方式至关重要。这些相互作用驱动热，质量和化学成分的交换，这对于我们宜居和活跃的行星至关重要。海水的化学记录了这些交流之间的不断变化与理解和量化海洋的通量对于理解地球系统至关重要。这些交流发生的时间和时间在指导我们将这些结果推断到全球尺度上也很重要。新海底的形成是板块构造循环的基础步骤，并沿着海底火山的链条沿着海洋盆地中山脊而沿着海洋流动。虽然海底散布在海脊中的海底是新的海壳，这是从地球内部到表面交换热量和质量的主要机制。海水通过新形成的岩石的循环进行了大量海水的热传递。海水与这些热岩石反应，将海水转化为加热的热液流体，这些水热流体通过壮观的黑人烟雾剂在海底排出，但温度弥漫性较低。随着新形成的海底远离海底山脊和年龄段，由于板块构造过程中的热液循环持续，并且由于海底的大量，即使是小型化学交换，也可以缩放到大量的地球化学通量到海洋。构成海底的岩石通过形成可以鉴定和分析的新矿物来记录与海水的相互作用，以了解水热液的温度和途径以及流体摇滚反应导致的化学变化。海底如何随着年龄的增长而变化，无论是物理，化学还是生物学活性）很重要，但主要未知。这是因为尽管科学海洋钻探在过去的50年中已经成功地采样了火山上皮，但这种采样的年龄偏向于海底<10mA，只有少数井眼可以采样最古老的海壳（〜170mA）。 IODP Expeditions 390和393是专门设计用于解决此抽样差距的，并将在6至6100万年历史的地壳中钻出孔的样带。该项目将针对这些新的钻孔的样品，这些样品代表了水热改变范围（海水岩石循环的乘积），并分析它们以了解和量化水热循环过程中元素交换的程度。为了帮助我们了解这些反应何时何地发生了多长时间，将分析从热液静脉中的碳酸钙样品中的特定同位素（U和PB），以确定它们形成的年龄。这些新数据集将结合起来，以建立对这个关键地球过程中发生的地球化学交流的新见解。