Fluid Inclusion Evidence for Subseafloor Magmatic-Hydrothermal Processes at Brothers Volcano, Kermadec Arc, New Zealand
Fluid Inclusion Evidence for Subseafloor Magmatic-Hydrothermal Processes at Brothers Volcano, Kermadec Arc, New Zealand
复制标题
新西兰克马德克弧兄弟火山海底岩浆热液过程的流体包裹体证据
作者：
Hyun Joo Lee;Jung Hun Seo;C. D. de Ronde;C. Heinrich
兄弟火山是一个位于克马德克弧南部的海底英安质破火山口。它是NW Caldera喷口场（站点U1530和孔U1530A）的所在地，该喷口场局部排放更集中的富含金属的流体，以及上锥体热液喷口场（站点U1528和孔U1528D），主要排放扩散的酸性流体（pH 1.9）。这两个活跃的喷口地点是由国际海洋发现计划（IODP）376远征队于2018年钻探的。利用显微测温、拉曼光谱和激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）技术对取自钻孔岩芯样品的硬石膏、石英、重晶石和明矾石中的流体包裹体进行了研究，获得了详细的温度、盐度和热液成分的深度剖面。通过这些分析，可以更好地了解相分离等复杂的热液过程，并评估岩浆热液的作用，同时参考兄弟热液喷口下上升的深层热液流体的动态。
流体包裹体的均一化温度（Th）范围为149 ° C至358 ° C，上锥部位的盐度为0.7至10.0 wt % NaCl当量，NW火山口部位的Th为254 ° C至394 ° C，盐度为0.7至9.8 wt % NaCl当量。来自西北火山口的硫酸盐矿物中的流体包裹体的显微测温表明热液流体和海水之间的海底混合。流体包裹体中气相分配元素B和As的富集表明海底有相分离作用，可能伴随着岩盐的溶解和沉淀。高度分化的Cl/Br值提供了通过海底下的海水对流发生的岩盐溶解的间接证据。岩石学观察的流体包裹体，如识别组合的富液和富汽的“沸腾组合”和CO2的包裹体中的存在，表明热液流体相分离。
流体包裹体中的CO2和微量元素和金属含量明显高于兄弟喷口流体值，这反映了岩浆热液的贡献。在西北火山口现场，相对高温的热液流体与高铜（最大560 ppm）和锌（最大740 ppm）与海水混合，然后排放到海底。流体包裹体数据的深度剖面确定了一些特定深度的通道化（集中）热液流体流。我们认为，热液流体主要集中在沿着岩性接触，作为渗透通道，加强海底热液流体流动。
Brothers volcano is a submarine dacitic caldera located on the southern Kermadec arc. It is host to the NW Caldera vent field (Site U1530 and Hole U1530A) that locally discharges more focused, metal-rich fluids, and the Upper Cone hydrothermal vent field (Site U1528 and Hole U1528D) that discharges predominantly diffuse, acidic fluids (pH 1.9). These two active vent sites were drilled in 2018 by the International Ocean Discovery Program (IODP) Expedition 376. Fluid inclusions hosted in anhydrite, quartz, barite, and alunite recovered from drill core samples were studied by microthermometry, Raman spectroscopy, and laser ablation-inductively coupled plasma-mass spectrometery (LA-ICP-MS) to obtain detailed depth profiles of temperature, salinity, and composition of the hydrothermal fluids. These analyses allow for a better understanding of complex hydrothermal processes such as phase separation and an assessment of magmatic-hydrothermal contributions while making reference to the dynamics of the deep hydrothermal fluid that rises beneath the hydrothermal vents at Brothers.
The fluid inclusions have homogenization temperatures (Th) ranging from 149° to 358°C and salinities between 0.7 and 10.0 wt % NaCl equiv at the Upper Cone site and Th of 254° to 394°C and salinities between 0.7 and 9.8 wt % NaCl equiv at the NW Caldera site. Microthermometry of fluid inclusions hosted in sulfate minerals from the NW Caldera site indicates subseafloor mixing between hydrothermal fluids and seawater. The enrichment of vapor-partitioning elements B and As in the fluid inclusions suggests phase separation subseafloor, which may be accompanied by halite dissolution and precipitation. Highly diverging Cl/Br values provide indirect evidence for halite dissolution that occurred via subseafloor convection of seawater. Petrographic observations made of the fluid inclusions, such as the recognition of combined liquid-rich and vapor-rich “boiling assemblages” and the occurrence of CO2 in the inclusions, indicate phase separation of hydrothermal fluids.
The CO2 and the content of trace elements and metals in the fluid inclusions are significantly higher than that reported for Brothers vent fluid values, which reflects a magmatic-hydrothermal contribution. At the NW Caldera site, relatively high-temperature hydrothermal fluids with high Cu (max 560 ppm) and Zn (max 740 ppm) mixed with seawater before discharging at the sea floor. Depth profiles of the fluid inclusion data identify a few specific depths of channelized (focused) hydrothermal fluid flow. We suggest that the hydrothermal fluids are mainly focused along lithological contacts which act as permeable pathways, enhancing subseafloor hydrothermal fluid flow.
新西兰克马德克弧兄弟海底弧火山内的热液蚀变
影响因子：
5.8
作者：
Martin A
通讯作者：
Martin A
影响因子：
5
作者：
J. Seewald;E. Reeves;W. Bach;P. Saccocia;P. Craddock;W. Shanks;S. Sylva;T. Pichler;M. Rosner;Emily A. Walsh
通讯作者：
J. Seewald;E. Reeves;W. Bach;P. Saccocia;P. Craddock;W. Shanks;S. Sylva;T. Pichler;M. Rosner;Emily A. Walsh
影响因子：
5.8
作者：
de Ronde, Cornel E. J.;Humphris, Susan E.;Reyes, Agnes G.
通讯作者：
Reyes, Agnes G.