Hydrothermal vent incidence is proportional to the spreading rate of the mid-oceanic ridges (MORs) (Baker et al., 1996). However, the ultra-slow spreading Southwest Indian Ridge (SWIR) is unique and has a relatively higher incidence of hydrothermal vent fields compared with other ultra-slow spreading ridges (German et al., 1998; Baker and German, 2004). In the present study, sediment samples from the less studied easternmost section of the ultra-slow spreading SWIR are investigated to decipher the signatures of hydrothermal activity. The sediments are mainly composed of calcium carbonate (55–85%), Fe-Mn-(oxyhydr)oxide (13–27%), and residual aluminosilicate phases (2–17%). The metalliferous nature, low Mn concentration (393–1772 ppm), negative Ce, and positive Y anomalies in the shale-normalized rare earth element (REE) pattern of the bulk sediments provide evidence for the presence of hydrothermal inputs in most of the sediments. The fractionation among lighter REEs over heavier REEs in bulk sediments indicates the high-temperature hydrothermal plume fall-out to the sediments. The leached fraction also shows similar negative Ce and positive Y anomalies, and indicates that the Fe-Mn-(oxyhydr)oxide precipitates in these sediments may be dominantly of hydrothermal origin. In addition to hydrothermal Fe-Mn-(oxyhydr)oxide phases, the residual fraction of the sediments also consists of minor quantities of hydrothermally sourced sulfate phases. Otherwise, the residual fraction is significantly dominated by mid-oceanic ridge basalt (MORB) derived components in addition to serpentinized peridotite and terrigenous material.

Among the studied sediments, sample E-3-16 from Fuji Dome (influenced by hydrothermal activity) has high zinc concentrations, which indicates the possibility of a new vent field in the vicinity. The present study also introduces a new geochemical tool (Zn/Fe vs Co/Zn proxy) for assessing the contribution of hydrothermal components in the sediments. The Zn/Fe vs Co/Zn proxy will be more useful in MOR settings hosting sulfides dominated by sphalerite.

The influence of hydrothermal activity in most of the studied sediments from the eastern SWIR indicates that the ultra-slow spreading eastern SWIR has the potential to possess a larger number of hydrothermal vent fields.

热液喷口的发生率与洋中脊（MORs）的扩散速率成正比（Baker等，1996）。然而，与其他超慢扩散脊相比，超慢扩散西南印第安海岭（SWIR）是独特的，并且热液喷口的发生率相对较高（German等，1998； Baker和German，2004）。在本研究中，对超慢扩散SWIR最东端的研究较少的沉积物样品进行了研究，以破解水热活动的特征。沉积物主要由碳酸钙（55-85％），铁锰-（羟基）氧化物（13-27％）和残留的铝硅酸盐相（2-17％）组成。金属性质，锰含量低（393–1772 ppm），铈为负，大量沉积物的页岩标准化稀土元素（REE）模式中的正Y异常，为大多数沉积物中存在热液输入提供了证据。散装沉积物中较轻的稀土元素相对较重的稀土元素的分馏表明，高温热液羽流会沉淀到沉积物中。浸出部分还显示出相似的负Ce异常和正Y异常，表明这些沉积物中的Fe-Mn-（羟基）氧化物沉淀可能主要来自水热。除水热Fe-Mn-（羟基）氧化物相外，沉积物的残余部分还由少量水热来源的硫酸盐相组成。否则，

在所研究的沉积物中，来自Fuji Dome的样品E-3-16（受水热活动影响）具有较高的锌浓度，这表明附近可能有新的通风孔。本研究还介绍了一种新的地球化学工具（Zn / Fe与Co / Zn替代物），用于评估沉积物中水热成分的贡献。Zn / Fe vs Co / Zn替代物在MOR环境中将更有用，这些环境中会容纳以闪锌矿为主的硫化物。

水热活动对来自东部SWIR的大多数研究沉积物的影响表明，超慢散布的东部SWIR有潜力拥有大量的热液喷口。