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

次导电洋壳脱水过程中流体释放的时间和速率：反应流体流动和高压条件

基本信息

批准号：
198703292
负责人：
Professor Dr. Michael Bröcker, since 10/2013
金额：
--
依托单位：
Institut für Geologische Wissenschaften
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2011
资助国家：
德国
起止时间：
2010-12-31 至 2014-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/198703292?language=en
关键词：
Timing rates fluid release during

项目摘要

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.

俯冲带是地球上最具动力学的系统之一，在全球挥发分循环和地球地球化学储集层之间的联系中起着重要作用。随着俯冲板块升温，它们的含水矿物变得越来越不稳定，分解并释放出水。最突出的脱水反应发生在俯冲带，导致俯冲洋壳的榴辉岩化。现场证据表明，释放板流体的优先流场是高度通道化的，这些流体往往与他们的围岩反应，从而作为微量元素的动员和运输代理。现在很明显，释放的流体可以到达地幔楔并导致熔融。这些熔融流体的化学运输被认为是产生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板片内外流动。重点将放在这里的流体流动结构中发现的折返高压岩石，从中国天山和新喀里多尼亚，及其演变的时间和空间。该项目旨在记录对流动结构形成的限制，相关的通量和不同的实验室内流体流动事件的持续时间。目的是1）检查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脉纹形成过程在空间和时间上的演变，以及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一个先决条件，以推导出现实的数字为率，同变质孔隙度和渗透率在流体释放。