Water-rock interaction in hydrothermal systems at 'liquid-vapor' equilibrium conditions: An experimental approach

由于许多缓慢扩张海脊的部分水深超过3 000米，大西洋中脊南纬5度海底热液活动具有极端的热通量、金属和独特的稀土元素化学性质，对海洋元素收支具有普遍意义。在这些高压（P）/高温（T）热液系统中的输运-反应过程的约束很差。我们建议（1）在类似于MAR 5°S的p-T条件下进行实验，以研究海水-岩石相互作用和由此产生的元素分配，以及（2）时间分辨的岩石蚀变和次生矿物的生成，（3）随后对流体和岩石化学的时间综合变化进行建模。起始材料将是与来自IODP孔U1309 D（辉长岩：1020 m bsl，橄榄岩-辉长岩：~1050 m bsl，橄榄岩-辉长岩：~1125 m bsl;在第一个供资期仅进行了辉长岩实验）的未改变辉长岩碎片反应的天然大西洋深水。此外，对IODP U1309 D站回收的玄武岩和辉长岩样品的次生矿物组合的元素组成和稀土元素模式的系统研究将有助于更好地解释我们的实验结果和理解海洋地壳的自然蚀变过程。总之，我们的实验得出的过渡金属和稀土元素的水岩分配行为以及建模将增加我们的知识，海水-岩石相互作用过程，并将提高我们的理解，运输反应和元素通量在上升的热液系统，运行在极端温度和大水深。

Given the fact that many sections of slow-spreading ridges are at water depths greater than 3000 m, the submarine hydrothermalism at 5°S on the Mid Atlantic Ridge (MAR) with extreme fluxes of heat, metals and unique rare earth element chemistry (REE) is of general significance for oceanic element budgets. Transport-reaction processes in these high-pressure (p) / high-temperature (T) hydrothermal systems are poorly constrained. We propose (1) experiments under p-T-conditions similar to those at MAR 5°S for the study of seawater-rock interaction and resulting element partitioning as well as (2) of time-resolved rock alteration and generation of secondary minerals and (3) subsequent modelling of time-integrated changes of fluid and rock chemistry. The starting materials will be natural Atlantic Deep Water reacting with unaltered gabbroic fragments from IODP Hole U1309D (gabbro: 1020 m bsl, Olivine-gabbro: ~1050 m bsl, troctolite: ~1125 m bsl; only experiments with gabbro were performed in the first period of funding). In addition, a systematic study of elemental composition and REE pattern of secondary mineral assemblages of recovered basaltic and gabbroic samples from IODP Site U1309D will - together with other data from the literature - help to better interpret our experimental findings and understand the natural alteration processes of oceanic crust. In summary, our experimentally derived water-rock partitioning behaviour of transition metals and REE as well as the modelling will add to our knowledge of seawater-rock interaction processes and will improve our understanding of transport reactions and element fluxes during ascent in hydrothermal systems that run at extreme temperatures and great water depths.