Timing and rates of fluid release during the dehydration of subconducting oceanic crust: reactive fluid flow und high-pressure conditions

俯冲带是地球上最具活力的系统，在全球挥发循环和地球地球化学储层之间的交流中起着重要作用。随着俯冲板块升温，它们的含水矿物逐渐变得不稳定，分解并释放水。在俯冲带发生的最显著的脱水反应导致俯冲洋壳的榴辉化。现场证据表明，释放的板状流体的优先流场高度渠化，这些流体容易与围岩发生反应，从而成为微量元素的动员和输送剂。现在很明显，释放出来的流体可以到达地幔楔并导致融化。这些流动流体的化学运输被认为创造了弧岩浆的独特化学特征。更好地理解俯冲带流体循环及其化学后果的关键是深入了解流体如何在下降的板块内流动和流出。重点研究中国天山和新喀里多尼亚出土高压岩石中的流体流动结构及其时空演化。该项目旨在记录流动结构形成的限制，相关的通量和不同实验室内流体流动事件的持续时间。目标是1)研究脱水板的流体释放是如何发生的；2)更好地理解流体流动和信息过程在空间和时间上的演变；3)量化不同流体流动事件的通量和持续时间。更好地了解这些方面是推断流体释放过程中速率、同变质孔隙度和渗透率的真实数字的先决条件。

Subduction zones belong to Earth’s most dynamic systems and play an important part in the global volatile cycle and the communication among Earth’s geochemical reservoirs. As subducting plates heat up, their hydrous minerals become progressively unstable, break down and release water. The most prominent dehydration reactions occurring in subduction zones lead to the eclogitisation of the subducting oceanic crust. Field evidence shows that the preferential flow field of released slab fluids is highly channelized and that these fluids tend to react with their wall rocks, thereby serving as agents for the mobilisation and transport of trace elements. It is now evident that the released fluids can reach the mantle wedge and cause melting. The chemical freight of these fluxing fluids is thought to create the distinct chemical signature of the resulting arc magmas. The key towards a better understanding of the subduction zone fluid cycle and its chemical consequences is to obtain in-depth understanding of how fluids flow within and out of the descending slab. The focus will be set here on fluid flow structures found in exhumed high-pressure rocks, from the Chinese Tianshan and New Caledonia, and their evolution in time and space. The project aims to document constraints on the formation of flow structures, the associated fluxes and the duration of distinct intraslab fluid flow events. The goal is 1) to examine how the fluid release of dehydrating slabs occurs, 2) to better understand the evolution of fluid flow and veinforming processes in space and time, and 3) to quantify fluxes and durations of distinct fluid flow events. A better knowledge of these aspects is a pre-requisite to deduce realistic numbers for rates, synmetamorphic porosity and permeability during fluid release.