(Supplement Table1) Abundances of major elements from KH93-3_DR10 at the Southwest Indian Ridge near the Rodriguez Triple Junction@en

Petrographic and geochemical analyses of basaltic rocks dredged from the first segment of the Southwest Indian Ridge near the Rodriguez Triple Junction have been completed in order to investigate water-rock interaction processes during mid-ocean ridge (MOR) hydrothermal alteration in the Indian Ocean. In the study area, we have successfully recovered a serial section of upper oceanic crust exposed along a steep rift valley wall which was uplifted and emplaced along a low angle normal fault. On the basis of microscopic observation, dredged samples are classified into three types: fresh lavas, low-temperature altered rocks, and high-temperature altered rocks. The fresh lavas have essentially the same chemical composition as typical N-MORB, although LILE and Nb are slightly enriched and depleted, respectively. Low temperature alteration brought about the enrichment of K2O, Rb, and U due to the presence of K-rich celadonite and U-adsorption onto Fe-oxyhydroxide and clay minerals. On the other hand, chloritization, albitization, and addition of base metals by high temperature hydrothermal alteration result in enrichments of MnO, MgO, Na2O, Cu, and Zn and depletions of CaO, K2O, Cr, Co, Ni, Rb, Sr, and Ba. In addition, U-enrichment is also observable in the high temperature altered rocks probably due to the decrease of uranite solubility in the reducing high-temperature hydrothermal solution. These petrological and geochemical features are comparable to those of the volcanic zone to transition zone rocks in the DSDP/ODP Hole 504B, indicating that our samples were recovered from the upper ~1000 m section of the oceanic crust. Only the alteration minerals related to off-axis alteration are absent in our samples dredged from near the spreading axis. The similarity of alteration between our samples from the Indian Ocean and the Hole 504B rocks from the Pacific Ocean suggests that MOR hydrothermal systems are probably similar across all world oceans.为探究印度洋中洋脊（mid-ocean ridge, MOR）热液蚀变过程中的水-岩相互作用机制，本研究完成了对罗德里格斯三联点附近西南印度洋海岭第一段拖网采得的玄武岩的岩石学与地球化学分析。在研究区域内，我们成功获取了沿陡坡裂谷谷壁出露的洋壳上部连续剖面，该剖面经抬升并沿低角度正断层就位。基于显微观测，本次拖网采集的样品可分为三类：新鲜熔岩、低温蚀变岩与高温蚀变岩。新鲜熔岩的化学成分与典型标准洋脊玄武岩（N-MORB）基本一致，但大离子亲石元素（Large Ion Lithophile Elements, LILE）与铌（Nb）分别呈现轻微富集与亏损特征。低温蚀变作用下，由于富钾绿鳞石的形成以及铀（U）吸附于铁的羟基氧化物与黏土矿物表面，样品中氧化钾（K₂O）、铷（Rb）与铀发生富集。与之相反，高温热液蚀变引发的绿泥石化、钠长石化以及贱金属添加作用，导致样品中氧化锰（MnO）、氧化镁（MgO）、氧化钠（Na₂O）、铜（Cu）与锌（Zn）发生富集，而氧化钙（CaO）、氧化钾（K₂O）、铬（Cr）、钴（Co）、镍（Ni）、铷（Rb）、锶（Sr）与钡（Ba）则出现亏损。此外，高温蚀变岩中也可观测到铀富集现象，这可能是由于晶质铀矿在还原性高温热液流体中的溶解度降低所致。上述岩石学与地球化学特征与深海钻探计划/大洋钻探计划（DSDP/ODP）504B钻孔中火山带至过渡带的岩石特征高度相似，表明本次采集的样品来自洋壳上部约1000米的剖面层位。本次在扩张轴附近拖网采集的样品中，仅缺失与轴外蚀变相关的蚀变矿物。印度洋采集样品与太平洋504B钻孔岩石的蚀变特征相似，这表明全球洋中脊热液系统可能具有普遍一致性。