| 2 | Record of hydrothermal activity in the Yuhuang hydrothermal field and its implications for the Southwest Indian Ridge:evidence from sulfide chronology显示文摘The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits.However,the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained.In this study,mineralogical analyses and 230Th/U dating were performed.Hydrothermal activity may start about(35.9±2.3)ka from the southwest part of the YHF and may cease about(708±81)a ago from the northeast part of the YHF.The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR.Hydrothermal activity in the SWIR has been relatively active over the past20 ka.In contrast,between 40 ka and 100 ka,hydrothermal activity was relatively infrequently and short in duration.The maximum activity occurred at 15–11 ka,9–7 ka,6–0.2 ka.There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage.The minimum mass accumulation rate of YHF is about 278 t/a,which is higher than most HFs related to ultramafic systems.The ultraslow spreading SWIR has the greatest potential to form large-scale seafloor massive sulfides(SMS)deposits.The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges. | Weifang Yang Chunhui Tao Shili Liao Jin Liang Wei Li Teng Ding Ágata Alveirinho Dias Xuefeng Wang Lisheng Wang | 2023 | Acta Oceanologica Sinica2023，42，11： | 0 |
| 3 | Sulfide metallogenic model for the ultraslow-spreading Southwest Indian Ridge显示文摘Polymetallic sulfides present in mid-ocean ridges(MORs)have become important strategic resources for humans,and a scientific metallogenic model is necessary for the investigation and exploration of these resources.Compared to fast-and slow-spreading MORs,ultraslow-spreading MORs show substantial differences in magma supply,tectonic activity,and oceanic crust structures.However,information on hydrothermal circulation and a metallogenic model related to sulfides along the ultraslow-spreading ridges is still limited,which hinders further exploration of these resources.In this study,the distribution of hydrothermal activities,as well as the characteristics of the structures,heat sources,fluid pathways,host rock types,fluid properties,and sulfide assemblages in typical hydrothermal fields along the ultraslow-spreading Southwest Indian Ridge(SWIR),have been studied.It is concluded that the hydrothermal systems along the SWIR can be categorized into three types,including local enhanced magma-controlled,one-way detachment/high-angle large-offset fault-controlled,and flip-flop detachment-controlled types,which are further categorized into five subtypes based on their distinct geological backgrounds.Herein,we present a sulfide metallogenic model called Local Enhanced Heat Supply-Deep Faults(eHeat-dFault)for the SWIR.The overall spreading rate remains almost constant(14-18 mm/year),while the magma supply is heterogeneous in the segment scale along the SWIR.Over the past two decades,various hydrothermal systems and sulfide deposits have been identified along the SWIR.A deep magma chamber(4-9 km)is developed in the ridge segment with sufficient magma supply owing to the local enhanced magma supply,while long-lived active deep detachment faults(up to 13 km)with associated metallogenic belts are developed in ridge segments with poor magma supply.Hence,the ultraslow-spreading MORs fulfill the necessary conditions of a sustained heat source and stable hydrothermal pathway for the formation of large-scale polymetallic sulfide deposits.The number of hydrothermal fields detected in the investigation area is 2-3 times that predicted by the traditional Spreading Rate-Magma Flux model,demonstrating its significant endowment for sulfide resources.A balance between magma supply and faulting may influence the type and depth of hydrothermal circulation,the frequency of hydrothermal activity along the axis,and the scale of sulfide deposits.Spreading rate was previously believed to control heat sources,magma supply,and tectonic processes.However,for the SWIR,we suggest that local enhanced heat supply and deep detachment faults have a greater influence than the spreading rate on hydrothermal circulation and sulfide mineralization.The eHeat-dFault sulfide metallogenic model proposed herein could provide guidance for further exploration and research on polymetallic sulfides in ultraslow-spreading SWIR. | Chunhui TAO Zhikui GUO Jin LIANG Teng DING Weifang YANG Shili LIAO Ming CHEN Fei ZHOU Jie CHEN Nannan WANG Xiaohe LIU Jianping ZHOU | 2023 | Science China Earth Sciences2023，66，6： | 0 |
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