Record of hydrothermal activity in the Yuhuang hydrothermal field and its implications for the Southwest Indian Ridge: evidence from sulfide chronology

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) kyrs from the southwest part of the YHF and may cease about 708 +/- 81 years 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 past 20 kyrs. In contrast, between 40 kyrs and 100 kyrs, hydrothermal activity was relatively infrequently and short in duration. The maximum activity occurred at 15-11 kyrs, 9-7 kyrs, 6-0.2 kyrs. 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 have the greatest potential to form large-scale SMS deposits. The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.