Timescales of South Atlantic ridge flank hydrothermal exchange; UK-IODP Moratorium Award for Thomas Belgrano - Shipboard Scientist, Expedition 393.

地球表面约三分之二由构造板块扩张和沿全球大洋中脊网络的岩浆作用产生的洋壳组成。在整个地质历史中，这种新形成的洋壳和海水之间的化学作用一直调节着海洋化学。特别是，从这种相互作用中沉淀在地壳中的矿物提供了一种手段，使二氧化碳、水、硫和钾等具有地质、生物和社会意义的重要物质在最终重新输送到地幔之前被隔离数百万年。尽管有这种理解，但洋壳吸收这种物质的速度和细节并不特别为人所知，特别是对于2000万到6000万年之间的中年地壳。在地表测量的热量与纯粹基于传导热损失的模型预测的热量之间的众所周知的逆差表明，在这段时间内，地壳发生了实质性的海水冷却。同样，在同一时间框架内测量到的穿过洋壳的地震波速度逐渐增加，表明矿物反应在这段中年时期仍在继续。确定这些次表层变化是什么，以及它们是如何随着时间的推移而发展的--无论是平稳的还是脉冲的，是快的还是慢的--是将地球系统的这个组成部分整合到全球生物地球化学循环模型中的先决条件。这项研究旨在确定在2,000万-6,000万年的地壳成熟阶段，海水-海洋结壳交换的发展速度和均匀程度。国际大洋钻探计划(IODP)的南大西洋断面考察390/393次专门计划对这一年龄段进行采样，在600-6100万年前的上层洋壳中钻6个孔。这将通过测定热液矿物中天然、弱放射性元素的衰变时间来实现。通过测定所有洞穴的年代，我们将评估热液流动是否持续了2000-6000万年的时间间隔。通过比较不同覆盖层厚度的钻孔和附近不同数量的基底露头的年龄，将进一步评估这些因素对延长热液循环的影响。最后，钻芯特征的年代参考点，如矿脉，将允许其他研究这些特征的起源和微生物殖民的探险科学家将他们的结果置于时间背景下。

About two thirds of the Earth's surface is made up oceanic crust produced by tectonic plate spreading and magmatism along the global network of mid-ocean ridges. Chemical interaction between this newly formed ocean crust and seawater has regulated ocean chemistry throughout geological history. In particular, minerals precipitated in the crust from this interaction provide a means for geologically, biologically, and societally important substances such as carbon dioxide, water, sulfur, and potassium to be sequestered for many millions of years before eventual redelivery to the mantle.Despite this understanding, the rates and specifics of such uptakes by oceanic crust are not particularly well known, especially for 'middle aged' crust between 20-60 million years old. A well-known deficit between the amount of heat measured at the surface and that predicted by models based purely on conductive heat loss indicates that substantial seawater cooling of the crust occurs over this interval. Similarly, a measured gradual increase in the speed of seismic waves through oceanic crust over the same timeframe suggests mineral reactions continue over this middle aged period. Defining what these sub-surface changes are and how they develop with time - smoothly or in pulses, quickly or slowly - is prerequisite to integrating this component of the Earth system into global models for biogeochemical cycling. This study aims to determine the rate and the uniformity with which seawater-ocean crust exchange develops over the 20-60 million year stage of crustal maturation. The International Ocean Drilling Program (IODP) South Atlantic Transect Expeditions 390/393 were specifically planned to sample this age interval, with six drill holes into upper oceanic crust of 6-61 million years age. This will be achieved by dating the decay of natural, weakly radioactive elements in hydrothermal minerals. By dating material from all of the holes, we will assess whether hydrothermal fluid flow persisted over the 20-60 million time interval. Comparison of ages from drill holes with different thicknesses of blanketing sediments and different amounts of nearby basement outcrops will further allow the influence of these factors on prolonging hydrothermal circulation to be assessed. Finally, the chronological reference points for features in the drill core such as mineral veins will allow other expedition scientists studying the origin and microbial colonisation of these features to place their results in a temporal context.