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是由构造板块沿全球大洋中脊网络沿着扩张和岩浆作用产生的洋壳组成。新形成的洋壳与海水之间的化学相互作用在整个地质历史中调节着海洋化学。特别是，由于这种相互作用而沉淀在地壳中的矿物质为地质学、生物学和社会学上重要的物质，如二氧化碳、水、硫和钾提供了一种手段，这些物质在最终重新输送到地幔之前被隔离了数百万年。尽管有这种认识，但大洋地壳吸收这些物质的速度和细节并不特别清楚，特别是对于2000 - 6000万年之间的“中年”地壳。众所周知，表面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存在差异，这表明在此期间地壳发生了大量海水冷却。同样，在同一时间段内，通过海洋地壳测量到的地震波速度逐渐增加，表明矿物反应在这一中年时期仍在继续。确定这些地下变化是什么以及它们如何随时间发展--平稳或脉冲，快速或缓慢--是将地球系统的这一组成部分纳入全球地球化学循环模型的先决条件。这项研究的目的是确定在2000万至6000万年的地壳成熟阶段，海水-海洋地壳交换发展的速率和均匀性。国际大洋钻探计划（IODP）的南大西洋断面考察390/393是专门计划对这个年龄段进行采样的，在600万至6100万年的上大洋地壳中钻了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。通过对所有洞的材料进行测年，我们将评估热液流是否持续了2000万至6000万的时间间隔。通过对覆盖沉积物厚度不同的钻孔和附近基底露头数量不同的钻孔进行年龄比较，将进一步评估这些因素对延长热液循环的影响。最后，岩芯中特征（如矿脉）的时间参考点将允许其他研究这些特征的起源和微生物定植的探险科学家将他们的结果置于时间背景中。

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.